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JavaWeb(五)：MVC案例

MVC是Model-View-Controller的简称，即模型-视图-控制器。
MVC是一种设计模式，它把应用程序分成三个核心模块：模型、视图、控制器，它们各自处理自己的任务。模型是应用程序的主体部分，模型表示业务数据和业务逻辑。一个模型能为多个视图提供数据。由于应用于模型的代码只需写一次就可以被多个视图重用，所以提高了代码的可重用性。视图是用户看到并与之交互的界面，作用如下：视图向用户显示相关的数据，接受用户的输入，不进行任何实际的业务处理。控制器接受用户的输入并调用模型和视图去完成用户的需求。控制器接收请求并决定调用哪个模型组件去处理请求，然后决定调用哪个视图来显示模型处理返回的数据。

把逻辑部分、访问数据库的部分放在Servlet，显示部分放在JSP页面。
发请求到服务器，服务器调用Servlet，Servlet做一个控制器，根据请求的情况取去调用Java类，Java类完成业务逻辑和访问数据库的操作，根据POJO的返回结果转向JSP，JSP进行显示，显示的时候可以使用一些标准标签库。
POJO里包含处理逻辑、业务逻辑，并去访问数据库。
Servlet根据不同的返回结果转向不同的JSP页面，转向的方式包括重定向和转发。

model：

controller：Servlet

view：JSP

一、查询和删除

1.1 查询

需求

点击超链接后在页面显示所有学生考试信息

数据库

字段

flowId
type
idCard
examCard
studentName
location
grade

数据表截图

Bean

public class Student {

    private Integer flowId;
    private int type;
    private String idCard;
    private String examCard;
    private String studentName;
    private String location;
    private int grade;


    public Integer getFlowId() {
        return flowId;
    }

    public void setFlowId(Integer flowId) {
        this.flowId = flowId;
    }

    public int getType() {
        return type;
    }

    public void setType(int type) {
        this.type = type;
    }

    public String getIdCard() {
        return idCard;
    }

    public void setIdCard(String idCard) {
        this.idCard = idCard;
    }

    public String getExamCard() {
        return examCard;
    }

    public void setExamCard(String examCard) {
        this.examCard = examCard;
    }

    public String getStudentName() {
        return studentName;
    }

    public void setStudentName(String studentName) {
        this.studentName = studentName;
    }

    public String getLocation() {
        return location;
    }

    public void setLocation(String location) {
        this.location = location;
    }

    public int getGrade() {
        return grade;
    }

    public void setGrade(int grade) {
        this.grade = grade;
    }

    public Student(Integer flowId, int type, String idCard, String examCard, String studentName, String location, int grade) {
        this.flowId = flowId;
        this.type = type;
        this.idCard = idCard;
        this.examCard = examCard;
        this.studentName = studentName;
        this.location = location;
        this.grade = grade;
    }

    // 反射需要一个无参的构造器
    public Student(){

    }
}

流程

页面

超链接的页面 c.jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
    <a href="listAllStudent">List All Student</a>
</body>
</html>

c.jsp截图

转发的页面 students.jsp

<%@ page import="java.util.List" %>
<%@ page import="com.satguigu.mvc.Student" %><%--
  Created by IntelliJ IDEA.
  User: JieZhao
  Date: 2019/8/13
  Time: 13:38
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>

<%= request.getAttribute("students") %>
<br>
<%
    List<Student> stus = (List<Student>)request.getAttribute("students");
%>


<table>
    <tr>
        <th>FlowId</th>
        <th>Type</th>
        <th>IdCard</th>
        <th>ExamCard</th>
        <th>StudentName</th>
        <th>Location</th>
        <th>Grade</th>
    </tr>
    <%
    for (Student student: stus){
    %>
        <tr>
            <td><%= student.getFlowId() %>  </td>
            <td><%= student.getType() %>  </td>
            <td><%= student.getIdCard() %>  </td>
            <td><%= student.getExamCard() %>  </td>
            <td><%= student.getStudentName() %>  </td>
            <td><%= student.getLocation() %>  </td>
            <td><%= student.getGrade() %>  </td>
        </tr>

   <% }%>


</table>

</body>
</html>

代码

Dao

public class StudentDao {

    public List<Student> getAll(){
        List<Student> students = new ArrayList<>();
        Connection connection = null;
        PreparedStatement preparedStatement = null;
        ResultSet resultSet = null;
        try{
            String driverClass = "com.mysql.jdbc.Driver";
            String url = "jdbc:mysql:///aidata";
            String user = "root";
            String passward = "root";
            Class.forName(driverClass);
            connection = DriverManager.getConnection(url, user, passward);
            String sql = "SELECT flow_id, type, id_card, exam_card, sutdent_name, Location, Grade FROM examstudent";
            preparedStatement = connection.prepareStatement(sql);
            resultSet = preparedStatement.executeQuery();
            while (resultSet.next()){
                int flowId = resultSet.getInt(1);
                int type = resultSet.getInt(2);
                String idCard = resultSet.getString(3);
                String examCard = resultSet.getString(4);
                String studentName = resultSet.getString(5);
                String location = resultSet.getString(6);
                int grade = resultSet.getInt(7);
                Student student = new Student(flowId, type, idCard, examCard, studentName, location, grade);
                students.add(student);
            }
        }catch (Exception e){
            e.printStackTrace();
        }finally {
            try{
                if(resultSet != null){
                resultSet.close();
                }
            }catch (SQLException e){
                e.printStackTrace();
            }
            try{
                if(preparedStatement != null){
                    preparedStatement.close();
                }
            }catch (SQLException e){
                e.printStackTrace();
            }
            try{
                if(connection != null){
                    connection.close();
                }
            }catch (SQLException e){
                e.printStackTrace();
            }
        }
        return students;
    }
}

Servlet

public class ListAllStudentsServlet extends HttpServlet {

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException,  ServletException {

        StudentDao studentDao = new StudentDao();
        List<Student> students = studentDao.getAll();

        request.setAttribute("students", students); //结果添加到students属性里，存到request里
        request.getRequestDispatcher("/students.jsp").forward(request, response);
       // 将request转发到students.jsp页面
     }
}

配置web.xml

<servlet>
    <servlet-name>listAllStudent</servlet-name>
    <servlet-class>com.aidata.mvc.ListAllStudentsServlet</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>listAllStudent</servlet-name>
    <url-pattern>/listAllStudent</url-pattern>
</servlet-mapping>

1.2 删除

students.jsp里添加删除按钮

Dao里添加删除方法

public void deleteByFlowId(Integer flowId){
        List<Student> students = new ArrayList<>();
        Connection connection = null;
        PreparedStatement preparedStatement = null;

        try {
            String driverClass = "com.mysql.jdbc.Driver";
            String url = "jdbc:mysql:///aidata";
            String user = "root";
            String password = "root";
            Class.forName(driverClass);
            connection = DriverManager.getConnection(url, user, password);
            String sql = "DELETE FROM examstudent WHERE flow_id = ?";
            preparedStatement = connection.prepareStatement(sql);
            preparedStatement.setInt(1, flowId);
            preparedStatement.executeUpdate();

        }catch (Exception e){
            e.printStackTrace();
        }finally {

            try{
                if(preparedStatement != null){
                    preparedStatement.close();
                }
            }catch (SQLException e){
                e.printStackTrace();
            }
            try{
                if(connection != null){
                    connection.close();
                }
            }catch (SQLException e){
                e.printStackTrace();
            }
        }

    }

Servlet添加删除的Servlet

public class DeleteStudentServlet extends HttpServlet {

    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws IOException, ServletException {

        String flowId = request.getParameter("flowId");
        StudentDao studentDao = new StudentDao();
        studentDao.deleteByFlowId(Integer.parseInt(flowId));
        List<Student> students = studentDao.getAll();
        request.setAttribute("students", students);
        request.getRequestDispatcher("/listAllStudent").forward(request, response); // 重定向到servlet

    }
}

配置web.xml

<servlet>
    <servlet-name>deleteStudent</servlet-name>
    <servlet-class>com.aidata.mvc.DeleteStudentServlet</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>deleteStudent</servlet-name>
    <url-pattern>/deleteStudent</url-pattern>
</servlet-mapping>

二、案例

2.1 架构分析

下面开始做一个小案例：利用MVC模式对数据进行增删改查

没有业务层，直接由Servlet调用DAO，所以也没有事务操作，可以在DAO中直接获取Connection对象

采取MVC设计模式

使用到的技术：

MVC设计模式：JSP、Servlet
数据库使用MySQL
连接数据库使用C3P0数据库连接池
JDBC工具采用DBUtils
页面的提示操作采用jQuery

技术难点：

多个请求如何使用一个Servlet
模糊查询
在创建或修改的情况下，验证用户名已经被使用，并给出提示信息

2.2 DAO层

DAO 模式

DAO (DataAccessobjects 数据存取对象)是指位于业务逻辑和持久化数据之间实现对持久化数据的访问。通俗来讲，就是将数据库操作都封装起来。

对外提供相应的接口

在面向对象设计过程中，有一些"套路”用于解决特定问题称为模式。

DAO 模式提供了访问关系型数据库系统所需操作的接口，将数据访问和业务逻辑分离对上层提供面向对象的数据访问接口。

从以上 DAO 模式使用可以看出，DAO 模式的优势就在于它实现了两次隔离。

1、隔离了数据访问代码和业务逻辑代码。业务逻辑代码直接调用DAO方法即可，完全感觉不到数据库表的存在。分工明确，数据访问层代码变化不影响业务逻辑代码,这符合单一职能原则，降低了藕合性，提高了可复用性。

2、隔离了不同数据库实现。采用面向接口编程，如果底层数据库变化，如由 MySQL 变成 Oracle 只要增加 DAO 接口的新实现类即可，原有 MySQ 实现不用修改。这符合 "开-闭" 原则。该原则降低了代码的藕合性，提高了代码扩展性和系统的可移植性。

一个典型的DAO 模式主要由以下几部分组成。

1、DAO接口：把对数据库的所有操作定义成抽象方法，可以提供多种实现。

2、DAO 实现类：针对不同数据库给出DAO接口定义方法的具体实现。

3、实体类：用于存放与传输对象数据。

4、数据库连接和关闭工具类：避免了数据库连接和关闭代码的重复使用，方便修改。

数据库

建立数据表

Create table customers(
    id int primary key auto_increment,
    name varchar(30) not null unique,
    address varchar(30),
    phone varchar(30)
);
# 为 name 字段添加唯一约束
alter table customers add constraint name_uk unique(name);

数据表截图

C3P0数据源

论数据库连接池的必要性及c3p0的详解

使用eclipse

添加c3p0的jar包和mysql驱动的jar包到根目录的lib目录中

添加commons-dbutils-1.3.jar到根目录的lib目录中

添加c3p0的配置文件到src目录

c3p0-config.xml

<?xml version="1.0" encoding="UTF-8"?>
<c3p0-config>

    <named-config name="mvcapp">
        
        <!-- 指定连接数据源的基本属性 -->
        <property name="user">root</property>
        <property name="password">root</property>
        <property name="driverClass">com.mysql.jdbc.Driver</property>
        <property name="jdbcUrl">jdbc:mysql:///aidata</property>
        
        <!-- 若数据库中连接数不足时, 一次向数据库服务器申请多少个连接 -->
        <property name="acquireIncrement">5</property>
        <!-- 初始化数据库连接池时连接的数量 -->
        <property name="initialPoolSize">5</property>
        <!-- 数据库连接池中的最小的数据库连接数 -->
        <property name="minPoolSize">5</property>
        <!-- 数据库连接池中的最大的数据库连接数 -->
        <property name="maxPoolSize">10</property>

        <!-- C3P0 数据库连接池可以维护的 Statement 的个数 -->
        <property name="maxStatements">20</property>
        <!-- 每个连接同时可以使用的 Statement 对象的个数 -->
        <property name="maxStatementsPerConnection">5</property>
    
    </named-config>
        
</c3p0-config>

实体类

Customer.java

package com.aidata.mvcapp.domain;

public class Customer {

    private Integer id;
    private String name;
    private String address;
    private String phone;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    public String getPhone() {
        return phone;
    }

    public void setPhone(String phone) {
        this.phone = phone;
    }

    @Override
    public String toString() {
        return "Customer [id=" + id + ", name=" + name + ", address=" + address + ", phone=" + phone + "]";
    }

}

数据库连接和关闭工具类

JdbcUtils.java

package com.aidata.mvcapp.db;

import java.sql.Connection;
import java.sql.SQLException;

import javax.sql.DataSource;

import com.mchange.v2.c3p0.ComboPooledDataSource;

/**
 * @ClassName JdbcUtils
 * @Description JDBC操作的工具类
 * @author JZ
 * @Date
 * @version 1.0.0
 */
public class JdbcUtils {

    /**
     * @Description 释放连接
     * @param connection
     */
    public static void releaseConnection(Connection connection) {
        try {
            if (connection != null) {
                connection.close();
            }
        } catch (Exception e) {
            // TODO: handle exception
        }
    }

    private static DataSource dataSource = null;

    // 数据源只能创建一次，所以用static
    static {
        dataSource = new ComboPooledDataSource("mvcapp");
    }

    /**
     * @Description 返回数据源的一个Connection对象
     * @return
     * @throws SQLException
     */
    public static Connection getConnection() throws SQLException {
        return dataSource.getConnection();
    }
}

DAO接口

CustomerDAO.java

该接口定义了和业务相关的功能，操作customer

package com.aidata.mvcapp.dao;

import java.util.List;

import com.aidata.mvcapp.domain.Customer;

public interface CustomerDAO {
    
    public List<Customer> getAll();
    
    public void save(Customer customer);
    
    public Customer get(Integer id);
    
    public void delete(Integer id);
    
    /**
     * 
     * @Description 返回和name相等的记录数
     * @param name
     * @return
     */
    public long getCountWithName(String name);

}

DAO 实现类

DAO.java

该类不和业务相关，即和customer不相关，而是关注增删改查的功能

增删改都是update，查

package com.aidata.mvcapp.dao;

import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.sql.Connection;
import java.util.List;

import org.apache.commons.dbutils.QueryRunner;
import org.apache.commons.dbutils.handlers.BeanHandler;
import org.apache.commons.dbutils.handlers.BeanListHandler;
import org.apache.commons.dbutils.handlers.ScalarHandler;

import com.aidata.mvcapp.db.JdbcUtils;

/**
 * @ClassName DAO
 * @Description 封装了CRUD的方法，以供子类继承使用 当前DAO没有事务，直接在方法中获取数据库连接 整个DAO采取DBUtils解决方案
 * @author JZ
 * @Date
 * @version 1.0.0
 * @param <T>
 *            所处理的实体类的类型
 */
public class DAO<T> {

    private QueryRunner queryRunner = new QueryRunner();

    private Class<T> clazz;

    public DAO() {
        Type superClass = getClass().getGenericSuperclass();
        if (superClass instanceof ParameterizedType) {
            ParameterizedType parameterizedType = (ParameterizedType) superClass;
            Type[] typeArgs = parameterizedType.getActualTypeArguments();
            if (typeArgs != null && typeArgs.length > 0) {
                clazz = (Class<T>) typeArgs[0];
            }
        }
    }

    /**
     * @Description 返回某一个字段的值，例如某一天记录的customerName或 返回数据表中由多少条记录等
     * @param sql
     * @param args
     * @return
     */
    public <E> E getForValue(String sql, Object... args) {
        Connection connection = null;
        try {
            connection = JdbcUtils.getConnection();
            return (E) queryRunner.query(connection, sql, new ScalarHandler(), args);
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            JdbcUtils.releaseConnection(connection);
        }
        return null;
    }

    /**
     * @Description 返回 T 所对应的List
     * @param sql
     * @param args
     * @return
     */
    public List<T> getForList(String sql, Object... args) {
        Connection connection = null;
        try {
            connection = JdbcUtils.getConnection();
            return queryRunner.query(connection, sql, new BeanListHandler<>(clazz), args);
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            JdbcUtils.releaseConnection(connection);
        }
        return null;
    }

    /**
     * @Description 返回对应T的一个实例类对象
     * @param sql
     * @param args
     * @return
     */
    public T get(String sql, Object... args) {
        Connection connection = null;
        try {
            connection = JdbcUtils.getConnection();
            return queryRunner.query(connection, sql, new BeanHandler<>(clazz), args);
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            JdbcUtils.releaseConnection(connection);
        }
        return null;
    }

    /**
     * @Description 封装了INSERT、DELETE、UPDATE操作
     * @param sql
     *            SQL语句
     * @param args
     *            填充SQL语句的占位符
     */
    public void update(String sql, Object... args) {
        Connection connection = null;
        try {
            connection = JdbcUtils.getConnection();
            queryRunner.update(connection, sql, args);
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            JdbcUtils.releaseConnection(connection);
        }
    }

}

CustomerDAOJdbcImpl.java

将业务和功能结合起来，实现了业务操作

package com.aidata.mvcapp.dao.impl;

import java.util.List;

import com.aidata.mvcapp.dao.CustomerDAO;
import com.aidata.mvcapp.dao.DAO;
import com.aidata.mvcapp.domain.Customer;

public class CustomerDAOJdbcImpl extends DAO<Customer> implements CustomerDAO {

    @Override
    public List<Customer> getAll() {
        String sql = "SELECT id, name, address, phone From customers";
        return getForList(sql);
    }

    @Override
    public void save(Customer customer) {
        String sql = "INSERT INTO customers(name, address, phone) VALUES(?,?,?)";
        update(sql, customer.getName(), customer.getAddress(), customer.getPhone());
    }

    @Override
    public Customer get(Integer id) {
        String sql = "SELECT id, name, address, phone FROM customers WHERE id = ?";
        return get(sql, id);
    }

    @Override
    public void delete(Integer id) {
        String sql = "DELETE FROM customers WHERE id = ?";
        update(sql, id);
    }

    @Override
    public long getCountWithName(String name) {
        String sql = "SELECT count(id) FROM customers WHERE name = ?";
        return getForValue(sql, name);
    }

}

2.3 多个请求对应一个Servlet

第一种方式：url添加参数

jsp

<body>

    <a href="customerServlet?method=add">Add</a>
    <br><br>
    
    <a href="customerServlet?method=query">Query</a>
    <br><br>
    
    <a href="customerServlet?method=delete">Delete</a>
    <br><br>
    
</body>

定义Servlet

package com.aidata.mvcapp.servlet;

import java.io.IOException;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class CustomerServlet extends HttpServlet {

    private static final long serialVersionUID = 1L;

    public CustomerServlet() {

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        doPost(request, response);
    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        String method = request.getParameter("method");

        switch (method) {
        case "add":
            add(request, response);
            break;
        case "query":
            query(request, response);
            break;
        case "delete":
            delete(request, response);
            break;
        }
    }

    private void add(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("add");
    }

    private void query(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("query");
    }

    private void delete(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("delete");
    }

}

web.xml

  <servlet>
    <servlet-name>customerServlet</servlet-name>
    <servlet-class>com.aidata.mvcapp.servlet.CustomerServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>customerServlet</servlet-name>
    <url-pattern>/customerServlet</url-pattern>
  </servlet-mapping>

缺点：当添加一个请求时，需要在 Servlet 中修改两处代码：switch、添加方法；url 中使用 method=xxx 暴漏了要调用的方法，不私密，有安全隐患。

第二种方式：反射

jsp

<body>

    <a href="addCustomer.do">Add</a>
    <br><br>
    
    <a href="query.do">Query</a>
    <br><br>
    
    <a href="deleteCustomer.do">Delete</a>
    <br><br>
    
</body>

web.xml

  <servlet>
    <servlet-name>customerServlet</servlet-name>
    <servlet-class>com.aidata.mvcapp.servlet.CustomerServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>customerServlet</servlet-name>
    <url-pattern>*.do</url-pattern>
  </servlet-mapping>

Servlet

package com.aidata.mvcapp.servlet;

import java.io.IOException;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class CustomerServlet extends HttpServlet {

    private static final long serialVersionUID = 1L;

    public CustomerServlet() {

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        doPost(request, response);
    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        String servletPath = request.getServletPath();
        String methodName = servletPath.substring(1);
        methodName = methodName.substring(0, methodName.length() - 3);
        System.out.println(methodName);
        Method method;
        try {
            method = getClass().getDeclaredMethod(methodName, HttpServletRequest.class, HttpServletResponse.class);
            method.invoke(this, request, response);
        } catch (NoSuchMethodException | SecurityException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IllegalArgumentException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (InvocationTargetException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

    }

    private void addCustomer(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        System.out.println("add");
    }

    private void query(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("query");
    }

    private void deleteCustomer(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        System.out.println("delete");
    }

    private void edit(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("edit");
    }

}

流程：

2.4 模糊查询

非模糊查询

JSP

<%@page import="java.util.List"%>
<%@page import="com.aidata.mvcapp.domain.Customer"%>
<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
<form action="query.do" method="post">
    <table>
        <tr>
            <td>CustomerName:</td>
            <td><input type="text" name="name"></td>
        </tr>
        <tr>
            <td>Address:</td>
            <td><input type="text" name="address"></td>
        </tr>        
        <tr>
            <td>Phone:</td>
            <td><input type="text" name="phone"></td>
        </tr>
        <tr>
            <td><input type="submit" name="Query"></td>
            <td><a href="">Add New Customer</a></td>
        </tr>
    </table>
</form>
    <br><br>
    <%
       List<Customer> customers = (List)request.getAttribute("customers");
       if(customers != null && customers.size() > 0){
    %>
    <hr>
    <br><br>
    
        <table border="1" cellpadding="0" cellspacing="10">
          <tr>
            <th>ID</th>
            <th>CustomerName</th>
            <th>Address</th>
            <th>Phone</th>
            <th>UPDATEDELETE</th>
           </tr>
        <%
            for(Customer customer: customers){
        %>
        
        <tr>
            <td><%= customer.getId() %></td>
            <td><%= customer.getName() %></td>
            <td><%= customer.getAddress() %></td>
            <td><%= customer.getPhone() %></td>     
            <td>
                <a href="">UPDATE</a>
                <a href="">DELETE</a>
            </td>      
        </tr>
       
        <%      
       }
        %>
     </table>
    <%      
       }
    %>
    
</body>
</html>

Servlet

package com.aidata.mvcapp.servlet;

import java.io.IOException;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.List;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.aidata.mvcapp.dao.CustomerDAO;
import com.aidata.mvcapp.dao.impl.CustomerDAOJdbcImpl;
import com.aidata.mvcapp.domain.Customer;

public class CustomerServlet extends HttpServlet {

    private static final long serialVersionUID = 1L;

    private CustomerDAO customerDAO = new CustomerDAOJdbcImpl();

    public CustomerServlet() {

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        doPost(request, response);
    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        String servletPath = request.getServletPath();
        String methodName = servletPath.substring(1);
        methodName = methodName.substring(0, methodName.length() - 3);
        System.out.println(methodName);
        Method method;
        try {
            method = getClass().getDeclaredMethod(methodName, HttpServletRequest.class, HttpServletResponse.class);
            method.invoke(this, request, response);
        } catch (NoSuchMethodException | SecurityException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IllegalArgumentException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (InvocationTargetException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

    }

    private void addCustomer(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        System.out.println("add");
    }

    private void query(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // 1.调用CustomerDAO的getAll()方法，得到Customer的集合
        List<Customer> customers = customerDAO.getAll();
        // 2.把customer集合放入request中
        request.setAttribute("customers", customers);
        // 3.转发页面到index.jsp，不能用重定向
        request.getRequestDispatcher("/index.jsp").forward(request, response);
    }

    private void deleteCustomer(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        System.out.println("delete");
    }

    private void edit(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("edit");
    }

}

模糊查询

接口添加方法，定义用于查询的类

需要在 CustomerDAO 接口中定义一个 getForListWithCriteriaCustomer(CriteriaCustomer cc)。其中 CriteriaCustomer 用于封装查询条件：name, address, phone。因为查询条件很多时候和 domain 类并不相同，所以要做成一个单独的类

package com.aidata.mvcapp.dao;

import java.util.List;

import com.aidata.mvcapp.domain.Customer;

public interface CustomerDAO {

    public List<Customer> getForListWithCriteriaCustomer(CriteriaCustomer cc);

    public List<Customer> getAll();

    public void save(Customer customer);

    public Customer get(Integer id);

    public void delete(Integer id);

    /**
     * @Description 返回和name相等的记录数
     * @param name
     * @return
     */
    public long getCountWithName(String name);

}

CriteriaCustomer

package com.aidata.mvcapp.dao;

public class CriteriaCustomer {

    private String name;
    private String address;
    private String phone;

    public CriteriaCustomer(String name, String address, String phone) {
        super();
        this.name = name;
        this.address = address;
        this.phone = phone;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    public String getPhone() {
        return phone;
    }

    public void setPhone(String phone) {
        this.phone = phone;
    }

}

拼 SQL
SQL: "SELECT id, name, address, phone FROM customers WHERE " +
"name LIKE ? AND address LIKE ? ANDphone LIKE ?";

package com.aidata.mvcapp.dao.impl;

import java.util.List;

import com.aidata.mvcapp.dao.CriteriaCustomer;
import com.aidata.mvcapp.dao.CustomerDAO;
import com.aidata.mvcapp.dao.DAO;
import com.aidata.mvcapp.domain.Customer;

public class CustomerDAOJdbcImpl extends DAO<Customer> implements CustomerDAO {

    @Override
    public List<Customer> getAll() {
        String sql = "SELECT id, name, address, phone From customers";
        return getForList(sql);
    }

    @Override
    public void save(Customer customer) {
        String sql = "INSERT INTO customers(name, address, phone) VALUES(?,?,?)";
        update(sql, customer.getName(), customer.getAddress(), customer.getPhone());
    }

    @Override
    public Customer get(Integer id) {
        String sql = "SELECT id, name, address, phone FROM customers WHERE id = ?";
        return get(sql, id);
    }

    @Override
    public void delete(Integer id) {
        String sql = "DELETE FROM customers WHERE id = ?";
        update(sql, id);
    }

    @Override
    public long getCountWithName(String name) {
        String sql = "SELECT count(id) FROM customers WHERE name = ?";
        return getForValue(sql, name);
    }

    @Override
    public List<Customer> getForListWithCriteriaCustomer(CriteriaCustomer cc) {
        String sql = "SELECT id, name, address, phone FROM customers WHERE "
                + "name LIKE ? AND address LIKE ? AND phone LIKE ?";

        return getForList(sql, cc.getName(), cc.getAddress(), cc.getPhone());
    }

}

为了正确的填充占位符时，重写了 CriteriaCustomer 的 getter：

package com.aidata.mvcapp.dao;

public class CriteriaCustomer {

    private String name;
    private String address;
    private String phone;

    public CriteriaCustomer(String name, String address, String phone) {
        super();
        this.name = name;
        this.address = address;
        this.phone = phone;
    }

    public String getName() {
        if (name == null) {
            name = "%%";
        } else {
            name = "%" + name + "%";
        }
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getAddress() {
        if (address == null) {
            address = "%%";
        } else {
            address = "%" + address + "%";
        }
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    public String getPhone() {
        if (phone == null) {
            phone = "%%";
        } else {
            phone = "%" + phone + "%";
        }
        return phone;
    }

    public void setPhone(String phone) {
        this.phone = phone;
    }

}

修改 Servlet

获取请求参数，把请求参数封装为CriteriaCustomer 对象，再调用 getForListWithCriteriaCustomer(CriteriaCustomer cc) 方法

package com.aidata.mvcapp.servlet;

import java.io.IOException;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.List;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.aidata.mvcapp.dao.CriteriaCustomer;
import com.aidata.mvcapp.dao.CustomerDAO;
import com.aidata.mvcapp.dao.impl.CustomerDAOJdbcImpl;
import com.aidata.mvcapp.domain.Customer;

public class CustomerServlet extends HttpServlet {

    private static final long serialVersionUID = 1L;

    private CustomerDAO customerDAO = new CustomerDAOJdbcImpl();

    public CustomerServlet() {

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        doPost(request, response);
    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        String servletPath = request.getServletPath();
        String methodName = servletPath.substring(1);
        methodName = methodName.substring(0, methodName.length() - 3);
        System.out.println(methodName);
        Method method;
        try {
            method = getClass().getDeclaredMethod(methodName, HttpServletRequest.class, HttpServletResponse.class);
            method.invoke(this, request, response);
        } catch (NoSuchMethodException | SecurityException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IllegalArgumentException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (InvocationTargetException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

    }

    private void addCustomer(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        System.out.println("add");
    }

    private void query(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String name = request.getParameter("name");
        String phone = request.getParameter("phone");
        String address = request.getParameter("address");

        CriteriaCustomer cc = new CriteriaCustomer(name, address, phone);

        // 1.调用CustomerDAO的getAll()方法，得到Customer的集合
        List<Customer> customers = customerDAO.getForListWithCriteriaCustomer(cc);
        // 2.把customer集合放入request中
        request.setAttribute("customers", customers);
        // 3.转发页面到index.jsp，不能用重定向
        request.getRequestDispatcher("/index.jsp").forward(request, response);
    }

    private void deleteCustomer(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        System.out.println("delete");
    }

    private void edit(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("edit");
    }

}

2.5 删除操作

Servlet

超链接：delete.do?id=<%=customer.getId()%>
Servlet 的 delete 方法
获取 id
调用 DAO 执行删除
重定向到 query.do（若目标页面不需要读取当前请求的 request 属性，就可以使用重定向），将显示删除后的 Customer 的 List

package com.aidata.mvcapp.servlet;

import java.io.IOException;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.List;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.aidata.mvcapp.dao.CriteriaCustomer;
import com.aidata.mvcapp.dao.CustomerDAO;
import com.aidata.mvcapp.dao.impl.CustomerDAOJdbcImpl;
import com.aidata.mvcapp.domain.Customer;

public class CustomerServlet extends HttpServlet {

    private static final long serialVersionUID = 1L;

    private CustomerDAO customerDAO = new CustomerDAOJdbcImpl();

    public CustomerServlet() {

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        doPost(request, response);
    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        String servletPath = request.getServletPath();
        String methodName = servletPath.substring(1);
        methodName = methodName.substring(0, methodName.length() - 3);
        System.out.println(methodName);
        Method method;
        try {
            method = getClass().getDeclaredMethod(methodName, HttpServletRequest.class, HttpServletResponse.class);
            method.invoke(this, request, response);
        } catch (NoSuchMethodException | SecurityException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IllegalArgumentException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (InvocationTargetException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

    }

    private void addCustomer(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        System.out.println("add");
    }

    private void query(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String name = request.getParameter("name");
        String phone = request.getParameter("phone");
        String address = request.getParameter("address");

        CriteriaCustomer cc = new CriteriaCustomer(name, address, phone);

        // 1.调用CustomerDAO的getAll()方法，得到Customer的集合
        List<Customer> customers = customerDAO.getForListWithCriteriaCustomer(cc);
        // 2.把customer集合放入request中
        request.setAttribute("customers", customers);
        // 3.转发页面到index.jsp，不能用重定向
        request.getRequestDispatcher("/index.jsp").forward(request, response);
    }

    private void deleteCustomer(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        String idStri = request.getParameter("id");
        int id = 0;
        // try...catch... 防止idStri不能转为int类型，若不能转，id=0，不进行任何删除操作
        try {
            id = Integer.parseInt(idStri);
            customerDAO.delete(id);
        } catch (Exception e) {
        }
        response.sendRedirect("query.do");
        System.out.println("delete");
    }

    private void edit(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("edit");
    }

}

JSP

jQuery 提示：
确定要删除 xx 的信息吗？

<%@page import="java.util.List"%>
<%@page import="com.aidata.mvcapp.domain.Customer"%>
<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
<script type="text/javascript" src="scripts/jquery-1.11.3.min.js"></script>
<script type="text/javascript">
    $(function () {
        $(".delete").click(function() {
            var content = $(this).parent().parent().find("td:eq(1)").text();
            var flag = confirm("确定要删除"+content+"的信息吗？");
            return flag;
        });
    });
</script>
</head>
<body>
<form action="query.do" method="post">
    <table>
        <tr>
            <td>CustomerName:</td>
            <td><input type="text" name="name"></td>
        </tr>
        <tr>
            <td>Address:</td>
            <td><input type="text" name="address"></td>
        </tr>        
        <tr>
            <td>Phone:</td>
            <td><input type="text" name="phone"></td>
        </tr>
        <tr>
            <td><input type="submit" name="Query"></td>
            <td><a href="">Add New Customer</a></td>
        </tr>
    </table>
</form>
    <br><br>
    <%
       List<Customer> customers = (List)request.getAttribute("customers");
       if(customers != null && customers.size() > 0){
    %>
    <hr>
    <br><br>
    
        <table border="1" cellpadding="0" cellspacing="10">
          <tr>
            <th>ID</th>
            <th>CustomerName</th>
            <th>Address</th>
            <th>Phone</th>
            <th>UPDATEDELETE</th>
           </tr>
        <%
            for(Customer customer: customers){
        %>
        
        <tr>
            <td><%= customer.getId() %></td>
            <td><%= customer.getName() %></td>
            <td><%= customer.getAddress() %></td>
            <td><%= customer.getPhone() %></td>     
            <td>
                <a href="">UPDATE</a>
                <a href="deleteCustomer.do?id=<%= customer.getId() %>" class="delete">DELETE</a>
            </td>      
        </tr>
       
        <%      
       }
        %>
     </table>
    <%      
       }
    %>
    
</body>
</html>

request的getParameter(String name)方法获取表单里面的name信息

只有设置了 name 属性的表单元素才能在提交表单时传递它们的值，因为服务端获取表单提交的数据是通过表单元素的 name 属性的值而得到的，没有 name 属性就无法得到表单元素提交给服务端的值

2.6 新增

流程

效果：点击Add New Customer 超链接，连接到 newcustomer.jsp

创建newcustomer.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
<form action="addCustomer.do" method="post">
    <table>
        <tr>
            <td>CustomerName:</td>
            <td><input type="text" name="name" value="<%= request.getParameter("name") == null?"": request.getParameter("name") %>"></td>
        </tr>
        <tr>
            <td>Address:</td>
            <td><input type="text" name="address"></td>
        </tr>        
        <tr>
            <td>Phone:</td>
            <td><input type="text" name="phone"></td>
        </tr>
        <tr>
            <td colspan="2"><input type="submit" name="Submit"></td>
        </tr>
    </table>
</form>
</body>
</html>

success.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
    <h4>操作成功！</h4>
    <h4><a href="index.jsp">Return...</a></h4>
</body>
</html>

修改addCustomer 方法
CustomerServlet 的 addCustomer 方法

package com.aidata.mvcapp.servlet;

import java.io.IOException;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.List;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.aidata.mvcapp.dao.CriteriaCustomer;
import com.aidata.mvcapp.dao.CustomerDAO;
import com.aidata.mvcapp.dao.impl.CustomerDAOJdbcImpl;
import com.aidata.mvcapp.domain.Customer;

public class CustomerServlet extends HttpServlet {

    private static final long serialVersionUID = 1L;

    private CustomerDAO customerDAO = new CustomerDAOJdbcImpl();

    public CustomerServlet() {

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        doPost(request, response);
    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        String servletPath = request.getServletPath();
        String methodName = servletPath.substring(1);
        methodName = methodName.substring(0, methodName.length() - 3);
        System.out.println(methodName);
        Method method;
        try {
            method = getClass().getDeclaredMethod(methodName, HttpServletRequest.class, HttpServletResponse.class);
            method.invoke(this, request, response);
        } catch (NoSuchMethodException | SecurityException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IllegalArgumentException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (InvocationTargetException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

    }

    private void addCustomer(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        // 1. 获取表单参数：name,address,phone
        String name = request.getParameter("name");
        String address = request.getParameter("address");
        String phone = request.getParameter("phone");
        // 2. 检验name是否已经被占用

        // 2.1 调用customerDAO的getCountWithName方法获取name是否在数据库中存在
        long count = customerDAO.getCountWithName(name);
        // 2.2 若返回值大于0，则响应newcustomer.jsp页面：
        // 通过转发的方式响应newcustomer.jsp
        if (count > 0) {
            // 2.2.1 要求在newcustomer.jsp页面显示一个错误消息：用户名name已经被占用，请重新选择！
            // 在request中放入一个属性，比如message：用户名name已经被占用，请重新选择！，
            // 在页面上通过request.getAttribute("message")的方式显示
            request.setAttribute("message", "用户名" + name + "已经被占用，请重新选择！");
            // 2.2.2 newcustomer.jsp的表单值可以回显
            // jsp中，value="<%= request.getParameter("name") == null?"": request.getParameter("name") %>

            // 2.2.3 结束方法：return
            request.getRequestDispatcher("/newcustomer.jsp").forward(request, response);
            return;
        }
        // 3. 若验证通过，则把表单参数封装为一个Customer对象customer
        Customer customer = new Customer(name, address, phone);
        // 4. 调用CustomerDAO的save方法，执行保存操作
        customerDAO.save(customer);
        // 5. 重定向到success.jsp页面
        response.sendRedirect("success.jsp");
    }

    private void query(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String name = request.getParameter("name");
        String phone = request.getParameter("phone");
        String address = request.getParameter("address");

        CriteriaCustomer cc = new CriteriaCustomer(name, address, phone);

        // 1.调用CustomerDAO的getAll()方法，得到Customer的集合
        List<Customer> customers = customerDAO.getForListWithCriteriaCustomer(cc);
        // 2.把customer集合放入request中
        request.setAttribute("customers", customers);
        // 3.转发页面到index.jsp，不能用重定向
        request.getRequestDispatcher("/index.jsp").forward(request, response);
    }

    private void deleteCustomer(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        String idStri = request.getParameter("id");
        int id = 0;
        // try...catch... 防止idStri不能转为int类型，若不能转，id=0，不进行任何删除操作
        try {
            id = Integer.parseInt(idStri);
            customerDAO.delete(id);
        } catch (Exception e) {
        }
        response.sendRedirect("query.do");
    }

    private void edit(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("edit");
    }

}

执行流程图

2.7 修改

先显示（SELECT 操作）修改的页面，再进行修改（update）
显示修改页面
Update 的超链接：<a href="edit.do?id=<%= customer.getId() %>">UPDATE</a>

index.jsp

<%@page import="java.util.List"%>
<%@page import="com.aidata.mvcapp.domain.Customer"%>
<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
<script type="text/javascript" src="scripts/jquery-1.11.3.min.js"></script>
<script type="text/javascript">
    $(function () {
        $(".delete").click(function() {
            var content = $(this).parent().parent().find("td:eq(1)").text();
            var flag = confirm("确定要删除"+content+"的信息吗？");
            return flag;
        });
    });
</script>
</head>
<body>
<form action="query.do" method="post">
    <table>
        <tr>
            <td>CustomerName:</td>
            <td><input type="text" name="name"></td>
        </tr>
        <tr>
            <td>Address:</td>
            <td><input type="text" name="address"></td>
        </tr>        
        <tr>
            <td>Phone:</td>
            <td><input type="text" name="phone"></td>
        </tr>
        <tr>
            <td><input type="submit" name="Query"></td>
            <td><a href="newcustomer.jsp">Add New Customer</a></td>
        </tr>
    </table>
</form>
    <br><br>
    <%
       List<Customer> customers = (List)request.getAttribute("customers");
       if(customers != null && customers.size() > 0){
    %>
    <hr>
    <br><br>
    
        <table border="1" cellpadding="0" cellspacing="10">
          <tr>
            <th>ID</th>
            <th>CustomerName</th>
            <th>Address</th>
            <th>Phone</th>
            <th>UPDATEDELETE</th>
           </tr>
        <%
            for(Customer customer: customers){
        %>
        
        <tr>
            <td><%= customer.getId() %></td>
            <td><%= customer.getName() %></td>
            <td><%= customer.getAddress() %></td>
            <td><%= customer.getPhone() %></td>     
            <td>
                <a href="edit.do?id=<%= customer.getId() %>">UPDATE</a>
                <a href="deleteCustomer.do?id=<%= customer.getId() %>" class="delete">DELETE</a>
            </td>      
        </tr>
       
        <%      
       }
        %>
     </table>
    <%      
       }
    %>
    
</body>
</html>

edit 方法：

private void edit(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        String forwardPath = "/error.jsp";
        // 1. 获取请求参数id
        String idStr = request.getParameter("id");
        // 2.调用customerDAO的customerDAO.get(id)获取和id对应的Customer对象
        try {
            Customer customer = customerDAO.get(Integer.parseInt(idStr));
            if (customer != null) {
                forwardPath = "updatecustomer.jsp";
                // 3.将customer放入request中
                request.setAttribute("customer", customer);
            }
        } catch (Exception e) {
        }
        // 4.响应updatecustomer.jsp页面：转发
        request.getRequestDispatcher(forwardPath).forward(request, response);
    }

JSP 页面
获取请求域中的 Customer 对象，调用对应的字段的 get 方法来显示值。
使用隐藏域来保存要修改的 Customer 对象的 id：<input type="hidden" name="id" value=“<%= customer.getId() %>"/>。虽然没有修改id，当然也不能改，但依然少不了，id用来判断到底是哪个customer。

使用隐藏域来保存 oldName：<input type="hidden" name=“oldName" value=“<%= customer.getName() %>"/>，oldName保存修改前的名字，name会更新为提交的名字。

关于隐藏域：和其他的表单域一样可以被提交到服务器，只不过在页面上不显示
提交到 update.do

updatecustomer.jsp：

<%@page import="com.aidata.mvcapp.domain.Customer"%>
<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
<%
    Object msg = request.getAttribute("message");
    if(msg != null){
        
%>        
    <br>
    <font color="red"><%= msg %></font>
    <br>
    <br>
<%
}
    String id = null;
    String oldName = null;
    String name = null;
    String address = null;
    String phone = null;
    
    Customer customer = (Customer)request.getAttribute("customer");
    if(customer != null){
        // 如果没有出错，从edit方法过来的，customer不为空
        id = customer.getId() + "";
        // 这里name和oldName一样，但是后面提交的时候，name会提交，即更新，而oldName保持不变，从而可以比较
        oldName = customer.getName();
        name = customer.getName();
        address = customer.getAddress();
        phone = customer.getPhone();
    }else{
        // 如果出错，即提交了重复的名字，会出现提示信息，会停留在本页面，没有edit方法了，也就没有customer属性了
        // 只能从之前提交的request中得到id等
        id = request.getParameter("id");
        oldName = request.getParameter("oldName");
        //
        name = request.getParameter("oldname");
        address = request.getParameter("address");
        phone = request.getParameter("phone");
    }
%>
<form action="update.do" method="post">
    
    <input type="hidden" name="id" value="<%= id %>" />
    <input type="hidden" name="oldName" value="<%= oldName %>" />

    <table>
        <tr>
            <td>CustomerName:</td>
            <td><input type="text" name="name" value="<%= name %>" /></td>
        </tr>
        <tr>
            <td>Address:</td>
            <td><input type="text" name="address" value="<%= address %>" /></td>
        </tr>        
        <tr>
            <td>Phone:</td>
            <td><input type="text" name="phone"value="<%= phone %>" /></td>
        </tr>
        <tr>
            <td colspan="2"><input type="submit" name="Submit"></td>
        </tr>
    </table>
</form>

</body>
</html>

隐藏域的问题
回显的问题
Newcustomer.jsp 和 updateCustomer.jsp 能汇总到一个页面吗 ?

修改操作
Update 方法：

 private void update(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // 1. 获取表单参数：name,address,phone
        String id = request.getParameter("id");
        String name = request.getParameter("name");
        String phone = request.getParameter("phone");
        String address = request.getParameter("address");
        String oldName = request.getParameter("oldName");
        // 2. 检验name是否已经被占用
        // 2.1 比较name和oldName是否相同，若相同说明name可用
        // 2.1 若不相同，调用customerDAO的getCountWithName方法获取name是否在数据库中存在
        if (!oldName.equalsIgnoreCase(name)) {
            // 如你输入了A，以前已经有了a，java的equals会认为两者不同，于是进入该if
            // 但是mysql认为A和a相同，于是返回了1，即已经存在了，从而引发message
            // 忽略大小写，不进入if，直接进行后面的update
            long count = customerDAO.getCountWithName(name);
            // 2.2 若返回值大于0，则响应updatecustomer.jsp
            if (count > 0) {
                // 2.2.1 在updatecustomer.jsp页面显示一个错误信息：用户名name已经被占用，请重新选择！
                // 在request中放入一个属性，比如message：用户名name已经被占用，请重新选择！，
                // 在页面上通过request.getAttribute("message")的方式显示
                request.setAttribute("message", "用户名" + name + "已经被占用，请重新选择！");
                // 2.2.2 updatecustomer.jsp的表单值可以回显
                // address，phone显示提交表单的新的值，而name显示oldName，而不是新提交的name
                // 2.2.3 结束方法：return
                return;
            }
        }
        // 3. 若验证通过，则把表单参数封装为一个Customer对象customer
        Customer customer = new Customer(name, address, phone);
        customer.setId(Integer.parseInt(id));
        // 4. 调用CustomerDAO的update(Customer customer)执行更新操作
        customerDAO.update(customer);
        // 5. 重定向到query.do
        response.sendRedirect("query.do");
    }

}

完整Servlet

package com.aidata.mvcapp.servlet;

import java.io.IOException;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.List;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.aidata.mvcapp.dao.CriteriaCustomer;
import com.aidata.mvcapp.dao.CustomerDAO;
import com.aidata.mvcapp.dao.impl.CustomerDAOJdbcImpl;
import com.aidata.mvcapp.domain.Customer;

public class CustomerServlet extends HttpServlet {

    private static final long serialVersionUID = 1L;

    private CustomerDAO customerDAO = new CustomerDAOJdbcImpl();

    public CustomerServlet() {

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        doPost(request, response);
    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        String servletPath = request.getServletPath();
        String methodName = servletPath.substring(1);
        methodName = methodName.substring(0, methodName.length() - 3);
        System.out.println(methodName);
        Method method;
        try {
            method = getClass().getDeclaredMethod(methodName, HttpServletRequest.class, HttpServletResponse.class);
            method.invoke(this, request, response);
        } catch (NoSuchMethodException | SecurityException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IllegalArgumentException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (InvocationTargetException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

    }

    private void addCustomer(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        // 1. 获取表单参数：name,address,phone
        String name = request.getParameter("name");
        String address = request.getParameter("address");
        String phone = request.getParameter("phone");
        // 2. 检验name是否已经被占用

        // 2.1 调用customerDAO的getCountWithName方法获取name是否在数据库中存在
        long count = customerDAO.getCountWithName(name);
        // 2.2 若返回值大于0，则响应newcustomer.jsp页面：
        // 通过转发的方式响应newcustomer.jsp
        if (count > 0) {
            // 2.2.1 要求在newcustomer.jsp页面显示一个错误消息：用户名name已经被占用，请重新选择！
            // 在request中放入一个属性，比如message：用户名name已经被占用，请重新选择！，
            // 在页面上通过request.getAttribute("message")的方式显示
            request.setAttribute("message", "用户名" + name + "已经被占用，请重新选择！");
            // 2.2.2 newcustomer.jsp的表单值可以回显
            // jsp中，value="<%= request.getParameter("name") == null?"": request.getParameter("name") %>

            // 2.2.3 结束方法：return
            request.getRequestDispatcher("/newcustomer.jsp").forward(request, response);
            return;
        }
        // 3. 若验证通过，则把表单参数封装为一个Customer对象customer
        Customer customer = new Customer(name, address, phone);
        // 4. 调用CustomerDAO的save方法，执行保存操作
        customerDAO.save(customer);
        // 5. 重定向到success.jsp页面
        response.sendRedirect("success.jsp");
    }

    private void query(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String name = request.getParameter("name");
        String phone = request.getParameter("phone");
        String address = request.getParameter("address");

        CriteriaCustomer cc = new CriteriaCustomer(name, address, phone);

        // 1.调用CustomerDAO的getAll()方法，得到Customer的集合
        List<Customer> customers = customerDAO.getForListWithCriteriaCustomer(cc);
        // 2.把customer集合放入request中
        request.setAttribute("customers", customers);
        // 3.转发页面到index.jsp，不能用重定向
        request.getRequestDispatcher("/index.jsp").forward(request, response);
    }

    private void deleteCustomer(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        String idStri = request.getParameter("id");
        int id = 0;
        // try...catch... 防止idStri不能转为int类型，若不能转，id=0，不进行任何删除操作
        try {
            id = Integer.parseInt(idStri);
            customerDAO.delete(id);
        } catch (Exception e) {
        }
        response.sendRedirect("query.do");
    }

    private void edit(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        String forwardPath = "/error.jsp";
        // 1. 获取请求参数id
        String idStr = request.getParameter("id");
        // 2.调用customerDAO的customerDAO.get(id)获取和id对应的Customer对象
        try {
            Customer customer = customerDAO.get(Integer.parseInt(idStr));
            if (customer != null) {
                forwardPath = "updatecustomer.jsp";
                // 3.将customer放入request中
                request.setAttribute("customer", customer);
            }
        } catch (Exception e) {
        }
        // 4.响应updatecustomer.jsp页面：转发
        request.getRequestDispatcher(forwardPath).forward(request, response);
    }

    private void update(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // 1. 获取表单参数：name,address,phone
        String id = request.getParameter("id");
        String name = request.getParameter("name");
        String phone = request.getParameter("phone");
        String address = request.getParameter("address");
        String oldName = request.getParameter("oldName");
        // 2. 检验name是否已经被占用
        // 2.1 比较name和oldName是否相同，若相同说明name可用
        // 2.1 若不相同，调用customerDAO的getCountWithName方法获取name是否在数据库中存在
        if (!oldName.equalsIgnoreCase(name)) {
            // 如你输入了A，以前已经有了a，java的equals会认为两者不同，于是进入该if
            // 但是mysql认为A和a相同，于是返回了1，即已经存在了，从而引发message
            // 忽略大小写，不进入if，直接进行后面的update
            long count = customerDAO.getCountWithName(name);
            // 2.2 若返回值大于0，则响应updatecustomer.jsp
            if (count > 0) {
                // 2.2.1 在updatecustomer.jsp页面显示一个错误信息：用户名name已经被占用，请重新选择！
                // 在request中放入一个属性，比如message：用户名name已经被占用，请重新选择！，
                // 在页面上通过request.getAttribute("message")的方式显示
                request.setAttribute("message", "用户名" + name + "已经被占用，请重新选择！");
                // 2.2.2 updatecustomer.jsp的表单值可以回显
                // address，phone显示提交表单的新的值，而name显示oldName，而不是新提交的name

request.getRequestDispatcher("update.jsp").forward(request, response);
// 2.2.3 结束方法：return
return; // 重定向跳转后必须加上return，要不然页面虽然跳转了，但是还会执行跳转后面的语句


            }
        }
        // 3. 若验证通过，则把表单参数封装为一个Customer对象customer
        Customer customer = new Customer(name, address, phone);
        customer.setId(Integer.parseInt(id));
        // 4. 调用CustomerDAO的update(Customer customer)执行更新操作
        customerDAO.update(customer);
        // 5. 重定向到query.do
        response.sendRedirect("query.do");
    }

}

2.8 更换底层存储源

深入理解面向接口编程：在类中调用接口的方法，而不必关心具体的实现。这将有利于代码的解耦，使程序有更好的可移植性和可扩展性。

需要修改源码

src下新建customes.xml

<?xml version="1.0" encoding="UTF-8"?>

<customers>
    <customer id="1001">
        <name>Tom</name>
        <address>Beijing</address>
        <phone>123</phone>
    </customer>
</customers>

新建实现类，功能暂时省略

package com.aidata.mvcapp.dao.impl;

import java.util.List;

import com.aidata.mvcapp.dao.CriteriaCustomer;
import com.aidata.mvcapp.dao.CustomerDAO;
import com.aidata.mvcapp.domain.Customer;


public class CustomerDAOXMLImpl implements CustomerDAO {

    @Override
    public List<Customer> getForListWithCriteriaCustomer(CriteriaCustomer cc) {
        // TODO Auto-generated method stub
        return null;
    }

    @Override
    public List<Customer> getAll() {
        // TODO Auto-generated method stub
        return null;
    }

    @Override
    public void save(Customer customer) {
        // TODO Auto-generated method stub

    }

    @Override
    public Customer get(Integer id) {
        // TODO Auto-generated method stub
        return null;
    }

    @Override
    public void delete(Integer id) {
        // TODO Auto-generated method stub

    }

    @Override
    public void update(Customer customer) {
        // TODO Auto-generated method stub

    }

    @Override
    public long getCountWithName(String name) {
        // TODO Auto-generated method stub
        return 0;
    }

}

只需要在CustomerServlet中修改一行语句

private CustomerDAO customerDAO = new CustomerDAOXMLImpl();

使用工厂模式，不修改源码

如果一行语句也不用修改怎么做？

使用属性文件

动态修改 Customer 的存储方式：通过修改类路径下的 switch.properties 文件的方式来实现

src下创建switch.properties

#type=xml
type=jdbc

创建Servlet读取配置文件

当Web 应用在启动的时候，InitServlet 被创建，并由 Servlet 容器调用其 init() 方法：

  <servlet>
    <servlet-name>InitServlet</servlet-name>
    <servlet-class>com.aidata.mvcapp.servlet.InitServlet</servlet-class>
    <load-on-startup>1</load-on-startup>
  </servlet>

读取类路径下的 switch.properties 文件，获取 switch.properties 的 type 属性值，赋给了 CustomerDAOFactory 的 type 属性值

package com.aidata.mvcapp.servlet;

import java.io.IOException;
import java.io.InputStream;
import java.util.Properties;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.aidata.mvcapp.dao.factory.CustomerDAOFactory;

public class InitServlet extends HttpServlet {

    private static final long serialVersionUID = 1L;

    @Override
    public void init() throws ServletException {
        CustomerDAOFactory.getInstance().setType("jdbc");
        InputStream in = getServletContext().getResourceAsStream("/WEB-INF/classes/switch.properties");
        Properties properties = new Properties();
        try {
            properties.load(in);
            String type = properties.getProperty("type");
            CustomerDAOFactory.getInstance().setType(type);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

}

需要通过一个类的一个方法来获取具体的实现类的对象：

package com.aidata.mvcapp.dao.factory;

import java.util.HashMap;
import java.util.Map;

import com.aidata.mvcapp.dao.CustomerDAO;
import com.aidata.mvcapp.dao.impl.CustomerDAOJdbcImpl;
import com.aidata.mvcapp.dao.impl.CustomerDAOXMLImpl;

public class CustomerDAOFactory {

    private Map<String, CustomerDAO> daos = new HashMap<String, CustomerDAO>();

    private CustomerDAOFactory() {
        daos.put("jdbc", new CustomerDAOJdbcImpl());
        daos.put("xml", new CustomerDAOXMLImpl());
    }

    private static CustomerDAOFactory instance = new CustomerDAOFactory();

    public static CustomerDAOFactory getInstance() {
        return instance;
    }

    private static String type = null;

    public void setType(String type) {
        this.type = type;
    }

    public CustomerDAO getCustomerDAO() {
        return daos.get(type);
    }
}

创建 CustomerServlet 时，为 customerDAO 属性赋值是通过 CustomerDAOFactory 的 getCustomerDAO() 方法完成的。此时的 type 已经在 InitServlet 中被赋值了。

private CustomerDAO customerDAO = CustomerDAOFactory.getInstance().getCustomerDAO();

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原文地址：https://www.cnblogs.com/aidata/p/11986345.html