Ajax案例：三级联动查询员工的信息(三张表进行内连接)

　　需求分析：

　　通过数据库连接池，可以查询到数据库中员工的各种信息，通过点击下拉框的方式实现三级联动，即：没有点击city下拉框，后面两个下拉框中没有值，这样，点击city下拉框，department下拉框中才有值，点击department下拉框后employee下拉框中才有值，才可以进行选择，不可以跨级点击；点击最后一个下拉框可以将员工的id，last_name，email，salary，显示在下面的表格中；　　

　　实现上述功能的方法：

　　1.c3p0数据库连接池，实现数据库的链接；JdbcUtils类，连接数据库，代码更加简洁；

　　2.Jackson架包，简化JSON代码，使用其类，方法；ObjectMapper mapper=new ObjectMapper();String result=mapper.writeValueAsString(employee);其可以获取类中get方法名，并且获取其值；

　　3.使用了jstl标准标签库，jQuery，不用在jsp中插入代码

　　4.使用到了Ajax：不需要刷新页面，就可实现局部页面更新的技术；其方法：$.getJSON(url,args,function(data){}向指定的jsp页面中插入标签；

　　5.使用blockUI，使用时要插入jQuery插件jquery.blockUI.js，每次点击下拉框都出现正在刷新的假象，其实就是一张静态的图片

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先将一些架包导进去：

连接c3p0数据连接池的架包：c3p0-0.9.1.2.jar；

实现oracle数据库和Eclipse软件跨平台连接的包：ojdbc6.jar

实现数据库连接池方法的包：commons-dbutils-1.3.jar

Jackson架包，简化JSON代码：jackson-core-asl-1.9.11.jar，jackson-mapper-asl-1.9.11.jar

jstl标准标签库相关的包：jstl.jar，standard.jar

jQuery架包，放在WebContent/scripts：jquery-1.7.2.js，jQuery插件：jquery.blockUI.js

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　　连接c3p0数据库连接池，成功后，获取oracle数据中的三张表：分别是：employees，departments，locations；两两之间有相同的列，可以实现内连接；

三个封装表中部分信息的类：employee，department，location；

package com.lanqiao.javaweb.jdbc;

public class Employee {
    
    private Integer employeeId;
    private String lastName;
    private String email;
    private double salary;
    public Employee() {
        super();
        // TODO Auto-generated constructor stub
    }
    public Employee(Integer employeeId, String lastName, String email, double salary) {
        super();
        this.employeeId = employeeId;
        this.lastName = lastName;
        this.email = email;
        this.salary = salary;
    }
    public Integer getEmployeeId() {
        return employeeId;
    }
    public void setEmployeeId(Integer employeeId) {
        this.employeeId = employeeId;
    }
    public String getLastName() {
        return lastName;
    }
    public void setLastName(String lastName) {
        this.lastName = lastName;
    }
    public String getEmail() {
        return email;
    }
    public void setEmail(String email) {
        this.email = email;
    }
    public double getSalary() {
        return salary;
    }
    public void setSalary(double salary) {
        this.salary = salary;
    }
    @Override
    public String toString() {
        return "Employee [employeeId=" + employeeId + ", lastName=" + lastName + ", email=" + email + ", salary="
                + salary + "]";
    } 
    
    
    
}

package com.lanqiao.javaweb.jdbc;

public class Department {
    private Integer departmentId;
    private String departmentName;
    
    public Department() {
        super();
        // TODO Auto-generated constructor stub
    }

    public Department(Integer departmentId, String departmentName) {
        super();
        this.departmentId = departmentId;
        this.departmentName = departmentName;
    }

    public Integer getDepartmentId() {
        return departmentId;
    }

    public void setDepartmentId(Integer departmentId) {
        this.departmentId = departmentId;
    }

    public String getDepartmentName() {
        return departmentName;
    }

    public void setDepartmentName(String departmentName) {
        this.departmentName = departmentName;
    }

    @Override
    public String toString() {
        return "Department [departmentId=" + departmentId + ", departmentName=" + departmentName + "]";
    }
    
    
}

package com.lanqiao.javaweb.jdbc;

public class Location {
    private Integer locationId;
    private String city;
    
    public Location() {
        super();
        // TODO Auto-generated constructor stub
    }

    public Location(Integer locationId, String city) {
        super();
        this.locationId = locationId;
        this.city = city;
    }

    public Integer getLocationId() {
        return locationId;
    }

    public void setLocationId(Integer locationId) {
        this.locationId = locationId;
    }

    public String getCity() {
        return city;
    }

    public void setCity(String city) {
        this.city = city;
    }

    @Override
    public String toString() {
        return "Location [locationId=" + locationId + ", city=" + city + "]";
    }
    
    
}

在src目录下建立c3p0-config.xml文件，配置和映射连接数据库的属性；

<?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">oraclejava</property>
　　　　<property name="password">lxn123</property>
　　　　<property name="driverClass">oracle.jdbc.driver.OracleDriver</property>
　　　　<property name="jdbcUrl">jdbc:oracle:thin:@localhost:1521:orcl1</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">10</property>
　　　　<!-- 数据库连接池中的最小的数据库连接数 -->
　　　　<property name="minPoolSize">10</property>
　　　　<!-- 数据库连接池中的最大的数据库连接数 -->
　　　　<property name="maxPoolSize">50</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>

建立JdbcUtils类：利用JdbcUtils包中的方法，简便的实现数据库连接池的连接

package com.lanqiao.javaweb.jdbc;

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

import org.junit.Test;

import com.mchange.v2.c3p0.ComboPooledDataSource;

//c3p0数据库连接池的方法类
public class JdbcUtils {
    //释放数据库连接的方法
    public static void releaseConnection(Connection connection){
        try {
            if(connection!=null){
                connection.close();
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    
    //连接数据库的方法
    public static ComboPooledDataSource dataSource=null;
    static{
        dataSource=new ComboPooledDataSource("mvcapp");
    }
    
    //获取数据库的链接，返回connection对象
    public static Connection getConnection() throws Exception{
        return dataSource.getConnection();
    }
    @Test
    //测试数据库连接池是否连接成功
    public void testTT() throws Exception{
        System.out.println(getConnection());
    }
    
    //类的私有构造方法
    private JdbcUtils() {}
    
    //此方法，是本类的调用方法，可以调用本类的各个方法
    private static JdbcUtils instance=new JdbcUtils();
    public static JdbcUtils getInstanece(){
        return instance;
    }
}

建立BaseDAO类，其中有查询数据库中数据的方法；

package com.lanqiao.javaweb.jdbc;

import java.sql.Connection;
import java.util.List;

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

public class BaseDAO {
    //此类是 对数据库的增伤改查的一些方法，调用的是QueryRunner类中的一些方法，实现对数据库中数据的增伤改查
    
    private static final QueryRunner runner=new QueryRunner();
    
    //返回所对应的list集合,获得的是数据库中所有数据的集合
    public <T> List<T> getForList(String sql,Class<T> clazz,Object...args) throws Exception{
        //Object...args,为可变参数
        //Class<T> clazz,反射参数
        
        List<T> list=null;
        Connection conn=null;
        try {
            conn=JdbcUtils.getConnection();
            list=runner.query(conn, sql, new BeanListHandler<T>(clazz),args);
        } catch (Exception e) {
            e.printStackTrace();
            
        }finally {
            //DbUtils是，架包commons-dbutils-1.3.jar里面的类，
            //方法closeQuietly为该类的方法，实现了关闭数据库连接池
            DbUtils.closeQuietly(conn);
        }
        
        return list;
    }
    
    //此方法是传入一个sql语句进入，返回某一个对象
    public <T> T get(String sql,Class<T> clazz,Object...args){
        T result=null;
        Connection conn=null;
        try {
            conn=JdbcUtils.getConnection();
            result=runner.query(conn, sql, new BeanHandler<T>(clazz),args);
        } catch (Exception e) {
            
        }finally {
            DbUtils.closeQuietly(conn);
        }
        return result;
    }
    
}

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数据库连接池，连接的方法，查询方法等前期准备工作完成了；然后是servlet类的建立和jsp页面的处理工作；

建立一个点击触发的jsp页面：employee.jsp(比较简单)；

<%response.sendRedirect("employeeServlet?method=listLocation");%>

web.xml文件中的配置和映射；是servlet类：EmployeeServlet与两个jsp页面实现连接；

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" id="WebApp_ID" version="2.5">
  <display-name>Ajax-1</display-name>
  <servlet>
    <description></description>
    <display-name>EmployeeServlet</display-name>
    <servlet-name>EmployeeServlet</servlet-name>
    <servlet-class>com.lanqiao.javaweb.jdbc.EmployeeServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>EmployeeServlet</servlet-name>
    <url-pattern>/employeeServlet</url-pattern>
  </servlet-mapping>
</web-app>

建立servlet类：EmployeeServlet，及employees.jsp页面，实现三级联动的功能；

package com.lanqiao.javaweb.jdbc;

import java.io.IOException;
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 org.codehaus.jackson.map.ObjectMapper;


public class EmployeeServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;

    protected void doGet(HttpServletRequest request, HttpServletResponse response) 
            throws ServletException, IOException {
        
        //获取method的值
        String methodName=request.getParameter("method");
        
        try {
            //利用反射获取本类中method=?，的方法名，
            Method method=
                getClass().getDeclaredMethod(methodName, HttpServletRequest.class,HttpServletResponse.class);
            method.invoke(this, request, response);
        } catch (Exception e) {
            
            e.printStackTrace();
        }
    }
    
    //调用 BaseDAO类，其中有查询员工信息的方法
    private static BaseDAO baseDao=new BaseDAO();
    
    //通过locations查询员工id,所在城市
    protected void listLocation
        (HttpServletRequest request, HttpServletResponse response) throws Exception{
        
        String sql="select location_id locationId,city from locations";
        
        //调用BaseDAO的getForList方法，查询所有的值
        List<Location> locations=baseDao.getForList(sql, Location.class);
        
        request.setAttribute("locations", locations);
        request.getRequestDispatcher("/employees.jsp").forward(request, response);
     }
    
    protected void listDepartments(HttpServletRequest request, HttpServletResponse response) 
        throws Exception{
        String locationId=request.getParameter("locationId");
        
        String sql="select department_id departmentId,department_name departmentName "
                + "from departments d where d.location_id=?";
        
        List<Department> departments=
                baseDao.getForList(sql, Department.class, Integer.parseInt(locationId));
        
        //Jackson架包，简化JSON代码，使用其类，方法；ObjectMapper mapper=new ObjectMapper();
        //String result=mapper.writeValueAsString(employee);其可以获取类中get方法名，并且获取其值；
        ObjectMapper mapper=new ObjectMapper();
        String result=mapper.writeValueAsString(departments);
        
        //System.out.println(result);
        //text/javascript重定向到jsp页面的类型
        response.setContentType("text/javascript");
        response.getWriter().print(result);
        
    }
    
    //
    protected void listEmployees(HttpServletRequest request, HttpServletResponse response) 
            throws Exception{
            String departmentId=request.getParameter("departmentId");
            
            String sql="select employee_id employeeId,last_name lastName "
                    + "from employees e where e.department_id=?";
            
            List<Employee> employees=
                    baseDao.getForList(sql, Employee.class, Integer.parseInt(departmentId));
            
            ObjectMapper mapper=new ObjectMapper();
            String result=mapper.writeValueAsString(employees);
            
            response.setContentType("text/javascript");
            response.getWriter().print(result);
            
        }
        //通过employeeId 查看某个员工的信息
        protected void listMessage(HttpServletRequest request, HttpServletResponse response) 
            throws Exception{
            String employeeId=request.getParameter("employeeId");
            
            String sql="select employee_id employeeId,last_name lastName,email,salary "
                    + "from employees where employee_id=?";
                    
            List<Employee> employee=
                    baseDao.getForList(sql, Employee.class, Integer.parseInt(employeeId));
            
            ObjectMapper mapper=new ObjectMapper();
            String result=mapper.writeValueAsString(employee);
            
            //System.out.println(result);
            response.setContentType("text/javascript");
            response.getWriter().print(result);
                    
        }
}

employees.jsp页面

<%@page import="com.lanqiao.javaweb.jdbc.Location"%>
<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
    
<%@taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
    
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
<script type="text/javascript" src="${pageContext.request.contextPath }/scripts/jquery-1.7.2.js"></script>
<script type="text/javascript" src="${pageContext.request.contextPath }/scripts/jquery.blockUI.js"></script>
<script type="text/javascript">
    $(function(){
        //刚开始隐藏查询的table
        $("#emp").hide();
        
        //使用blockUI，使用时要插入jQuery插件jquery.blockUI.js
        //每次点击下拉框都出现正在刷新的假象，其实就是一张静态的图片
        $(document).ajaxStart(function(){
            $.blockUI({
                message: $('#loading'),
                css:{
                    top:($(window).height()-400)/2+'px',
                    lift:($(window).width()-400)/2+'px',
                    '400px',
                    border:'none'
                },
                overlayCSS:{backgroundColor:'#fff'}
            })
        }).ajaxStop($.unblockUI);
        //第一个下拉框，
        $("#city").change(function(){
            $("#department option:not(:first)").remove();
            var city=$(this).val();
            
            if(city != ""){
                var url="employeeServlet?method=listDepartments";
                var args={"locationId":city,"time":new Date()};
            
                $.getJSON(url,args,function(data){
                    if(data.length==0){
                        alert("当前城市没有部门！！！");
                    }
                    else{
                        for(var i=0;i<data.length;i++){
                            var deptId=data[i].departmentId;
                            var deptName=data[i].departmentName;
                            
                            $("#department").append("<option value='"+deptId+"'>"+deptName+"</option>");
                        }
                    }
                });
            }
        });
        //第二个下拉框
        $("#department").change(function(){
            $("#employee option:not(:first)").remove();
            var departmentName=$(this).val();
            
            if(departmentName !=""){
                
                var url="employeeServlet?method=listEmployees";
                var args={"departmentId":departmentName,"time":new Date()};
                
                $.getJSON(url,args,function(data){
                    if(data.length==0){
                        alert("当前部门没有员工！！！");
                    }
                    else{
                        
                        for(var i=0;i<data.length;i++){
                            var employeeId=data[i].employeeId;
                            var employeeName=data[i].lastName;
                            //alert("dd");
                            $("#employee").append("<option value='"+employeeId+"'>"+employeeName+"</option>");
                        }
                    }
                });
            }
        });
        //第三个下拉框
        $("#employee").change(function(){
            $("#emp").show();
            
            var employeeName=$(this).val();
            if(employeeName!=""){
                var url="employeeServlet?method=listMessage";
                var args={"employeeId":employeeName,"time":new Date()};
                
                $.getJSON(url,args,function(data){
                    if(data.length==0){
                        alert("此员工无信息无信息！！！");
                    }
                    else{
                        for(var i=0;i<data.length;i++){
                            var employeeId=data[i].employeeId;
                            var lastName=data[i].lastName;
                            var email=data[i].email;
                            var salary=data[i].salary;
                            //alert(email);
                            $("#id").append("<td>"+employeeId+"</td>");
                            $("#name").append("<td>"+lastName+"</td>");
                            $("#email").append("<td>"+email+"</td>");
                            $("#salary").append("<td>"+salary+"</td>");
                        }
                    }
                });
            }
            
        });
    });
    
</script>
</head>
<body>
    
    <img alt="" id="loading" src="images/1.jpg" style="display:none">
    
    <center>
        <br><br>
        City:
        <select id="city">
            <option value="">请选择...</option>
            <c:forEach items="${locations }" var="location">
                <option value="${location.locationId }">${location.city }</option>
            </c:forEach>
        </select>
        
        &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
        
        Department:
        <select id="department">
            <option value="">请选择...</option>
            
        </select>
        
        &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
        
        Employee:
        <select id="employee">
            <option value="">请选择...</option>
            
        </select>
        <br><br>
        <br><br>
        
        <table id="emp" width="350" border="1" cellpadding="5" cellspacing="0" >
            <tr>
                 <th>Id</th>
                 <th>Name</th>
                <th>Email</th>
                <th>Salary</th>
            </tr>
                <td id="id"></td>
                <td id="name"></td>
                <td id="email"></td>
                <td id="salary"></td>
        </table>
    </center>
    
    
</body>
</html>