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Unit03：容器对路径的处理、 Servlet特性

案例一：查询，增加员工：

　　重定向
　　处理请求资源路径

目录结构：

案例代码：

package dao;

import java.io.Serializable;
import java.util.ArrayList;
import java.util.List;

import entity.Emp;

public class EmpDao implements Serializable {

    public List<Emp> findAll() {
        List<Emp> list = new ArrayList<Emp>();
        
        Emp e1 = new Emp();
        e1.setEmpno(1);
        e1.setEname("唐僧");
        e1.setJob("师父");
        e1.setSal(9000.0);
        list.add(e1);
        
        Emp e2 = new Emp();
        e2.setEmpno(2);
        e2.setEname("悟空");
        e2.setJob("徒弟");
        e2.setSal(5000.0);
        list.add(e2);
        
        Emp e3 = new Emp();
        e3.setEmpno(3);
        e3.setEname("八戒");
        e3.setJob("徒弟");
        e3.setSal(6000.0);
        list.add(e3);
        
        return list;
    }

    public void save(Emp e) {
        System.out.println(
            "增加员工:" + e.getEname());
    }
    
}

EmpDao.java

package entity;

import java.io.Serializable;

public class Emp implements Serializable {

    private Integer empno;
    private String ename;
    private String job;
    private Double sal;
    
    public Integer getEmpno() {
        return empno;
    }
    public void setEmpno(Integer empno) {
        this.empno = empno;
    }
    public String getEname() {
        return ename;
    }
    public void setEname(String ename) {
        this.ename = ename;
    }
    public String getJob() {
        return job;
    }
    public void setJob(String job) {
        this.job = job;
    }
    public Double getSal() {
        return sal;
    }
    public void setSal(Double sal) {
        this.sal = sal;
    }
    
}

Emp.java

package web;

import java.io.IOException;

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

import dao.EmpDao;
import entity.Emp;

public class AddEmpServlet extends HttpServlet {

    @Override
    protected void service(
        HttpServletRequest req, 
        HttpServletResponse res) throws ServletException, IOException {
        req.setCharacterEncoding("utf-8");
        //接收浏览器传入的数据
        String ename = req.getParameter("ename");
        String job = req.getParameter("job");
        String sal = req.getParameter("sal");
        //增加保存这些数据
        Emp e = new Emp();
        e.setEname(ename);
        e.setJob(job);
        if(sal != null && !sal.equals("")) {
            e.setSal(new Double(sal));
        }
        new EmpDao().save(e);
        //重定向到查询页面:
        //建议浏览器自己去访问查询页面
        //当前:/EmpManager/addEmp
        //目标:/EmpManager/findEmp
        res.sendRedirect("findEmp");
    }

}

AddEmpServlet.java

package web;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.List;

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

import dao.EmpDao;
import entity.Emp;

public class FindEmpServlet extends HttpServlet {

    @Override
    protected void service(
        HttpServletRequest req, 
        HttpServletResponse res) throws ServletException, IOException {
        //查询所有的员工
        EmpDao dao = new EmpDao();
        List<Emp> list = dao.findAll();
        //向浏览器输出响应信息
        res.setContentType(
            "text/html;charset=utf-8");
        PrintWriter out = res.getWriter();
        //当前:/EmpManager/findEmp
        //目标:/EmpManager/add_emp.html
        out.println("<a href='add_emp.html'>增加</a>");
        out.println("<table border='1' cellspacing='0' width='30%'>");
        out.println("    <tr>");
        out.println("        <td>编号</td>");
        out.println("        <td>姓名</td>");
        out.println("        <td>职位</td>");
        out.println("        <td>薪资</td>");
        out.println("    </tr>");
        if(list != null) {
            for(Emp e : list) {
                out.println("<tr>");
                out.println("    <td>"+e.getEmpno()+"</td>");
                out.println("    <td>"+e.getEname()+"</td>");
                out.println("    <td>"+e.getJob()+"</td>");
                out.println("    <td>"+e.getSal()+"</td>");
                out.println("</tr>");
            }
        }
        out.println("</table>");
        out.close();
    }

}

FindEmpServlet.java

这个代码把上面两个方法合并到这里了，并用 *.do 来访问；

package web;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.List;

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

import dao.EmpDao;
import entity.Emp;

/**
 * 路径规范:
 * 查询员工: /findEmp.do
 * 增加员工: /addEmp.do
 */
public class MainServlet extends HttpServlet {

    @Override
    protected void service(
        HttpServletRequest req,
        HttpServletResponse res)
        throws IOException, ServletException{
        //获取请求路径
        String p = req.getServletPath();
        //根据规范处理路径
        if("/findEmp.do".equals(p)) {
            findEmp(req,res);
        } else if("/addEmp.do".equals(p)) {
            addEmp(req,res);
        } else {
            throw new RuntimeException("查无此页");
        }
    }
    
    protected void findEmp(
        HttpServletRequest req, 
        HttpServletResponse res) throws ServletException, IOException {
        //查询所有的员工
        EmpDao dao = new EmpDao();
        List<Emp> list = dao.findAll();
        //向浏览器输出响应信息
        res.setContentType(
            "text/html;charset=utf-8");
        PrintWriter out = res.getWriter();
        //当前:/EmpManager/findEmp
        //目标:/EmpManager/add_emp.html
        out.println("<a href='add_emp.html'>增加</a>");
        out.println("<table border='1' cellspacing='0' width='30%'>");
        out.println("    <tr>");
        out.println("        <td>编号</td>");
        out.println("        <td>姓名</td>");
        out.println("        <td>职位</td>");
        out.println("        <td>薪资</td>");
        out.println("    </tr>");
        if(list != null) {
            for(Emp e : list) {
                out.println("<tr>");
                out.println("    <td>"+e.getEmpno()+"</td>");
                out.println("    <td>"+e.getEname()+"</td>");
                out.println("    <td>"+e.getJob()+"</td>");
                out.println("    <td>"+e.getSal()+"</td>");
                out.println("</tr>");
            }
        }
        out.println("</table>");
        out.close();
    }    
    
    protected void addEmp(
        HttpServletRequest req, 
        HttpServletResponse res) throws ServletException, IOException {
        req.setCharacterEncoding("utf-8");
        //接收浏览器传入的数据
        String ename = req.getParameter("ename");
        String job = req.getParameter("job");
        String sal = req.getParameter("sal");
        //增加保存这些数据
        Emp e = new Emp();
        e.setEname(ename);
        e.setJob(job);
        if(sal != null && !sal.equals("")) {
            e.setSal(new Double(sal));
        }
        new EmpDao().save(e);
        //重定向到查询页面:
        //建议浏览器自己去访问查询页面
        //当前:/EmpManager/addEmp.do
        //目标:/EmpManager/findEmp.do
        res.sendRedirect("findEmp.do");
    }    
    
}

MainServlet.java

package web;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.List;

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

import dao.EmpDao;
import entity.Emp;

/**
 * 路径规范:
 * 查询员工: /findEmp.do
 * 增加员工: /addEmp.do
 */
public class MainServlet extends HttpServlet {

    @Override
    protected void service(
        HttpServletRequest req,
        HttpServletResponse res)
        throws IOException, ServletException{
        //获取请求路径
        String p = req.getServletPath();
        //根据规范处理路径
        if("/findEmp.do".equals(p)) {
            findEmp(req,res);
        } else if("/addEmp.do".equals(p)) {
            addEmp(req,res);
        } else {
            throw new RuntimeException("查无此页");
        }
    }
    
    protected void findEmp(
        HttpServletRequest req, 
        HttpServletResponse res) throws ServletException, IOException {
        //查询所有的员工
        EmpDao dao = new EmpDao();
        List<Emp> list = dao.findAll();
        //向浏览器输出响应信息
        res.setContentType(
            "text/html;charset=utf-8");
        PrintWriter out = res.getWriter();
        //当前:/EmpManager/findEmp
        //目标:/EmpManager/add_emp.html
        out.println("<a href='add_emp.html'>增加</a>");
        out.println("<table border='1' cellspacing='0' width='30%'>");
        out.println("    <tr>");
        out.println("        <td>编号</td>");
        out.println("        <td>姓名</td>");
        out.println("        <td>职位</td>");
        out.println("        <td>薪资</td>");
        out.println("    </tr>");
        if(list != null) {
            for(Emp e : list) {
                out.println("<tr>");
                out.println("    <td>"+e.getEmpno()+"</td>");
                out.println("    <td>"+e.getEname()+"</td>");
                out.println("    <td>"+e.getJob()+"</td>");
                out.println("    <td>"+e.getSal()+"</td>");
                out.println("</tr>");
            }
        }
        out.println("</table>");
        out.close();
    }    
    
    protected void addEmp(
        HttpServletRequest req, 
        HttpServletResponse res) throws ServletException, IOException {
        req.setCharacterEncoding("utf-8");
        //接收浏览器传入的数据
        String ename = req.getParameter("ename");
        String job = req.getParameter("job");
        String sal = req.getParameter("sal");
        //增加保存这些数据
        Emp e = new Emp();
        e.setEname(ename);
        e.setJob(job);
        if(sal != null && !sal.equals("")) {
            e.setSal(new Double(sal));
        }
        new EmpDao().save(e);
        //重定向到查询页面:
        //建议浏览器自己去访问查询页面
        //当前:/EmpManager/addEmp.do
        //目标:/EmpManager/findEmp.do
        res.sendRedirect("findEmp.do");
    }    
    
}

web.xml

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>增加员工</title>
</head>
<body>
    <!-- 
        当前:/EmpManager/add_emp.html
        目标:/EmpManager/addEmp.do
     -->
    <form action="addEmp.do" method="post">
        <p>
            姓名:<input type="text" name="ename"/>
        </p>
        <p>
            职位:<input type="text" name="job"/>
        </p>
        <p>
            薪资:<input type="text" name="sal"/>
        </p>
        <p><input type="submit" value="保存"/></p>
    </form>
</body>
</html>

add_emp.html

案例二：演示路径输出，访问项目的三种方式：

package web;

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 AbcServlet extends HttpServlet {

    @Override
    protected void service(
        HttpServletRequest req, 
        HttpServletResponse res) throws ServletException, IOException {
        //获取访问路径
        System.out.println(
            req.getContextPath());
        System.out.println(
            req.getServletPath());
        System.out.println(
            req.getRequestURI());
        System.out.println(
            req.getRequestURL());
        //若没有设置响应信息的话,服务器
        //依然会向浏览器做出默认的响应,
        //但响应的内容为空.
    }
    
}

PathServlet.java

<?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" version="2.5">
  <display-name>servlet3</display-name>
  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.htm</welcome-file>
    <welcome-file>index.jsp</welcome-file>
    <welcome-file>default.html</welcome-file>
    <welcome-file>default.htm</welcome-file>
    <welcome-file>default.jsp</welcome-file>
  </welcome-file-list>
  
  <servlet>
      <servlet-name>abc</servlet-name>
      <servlet-class>web.AbcServlet</servlet-class>
  </servlet>
  <servlet-mapping>
      <servlet-name>abc</servlet-name>
      <!-- 1.精确匹配 -->
      <!-- <url-pattern>/abc</url-pattern> -->
      <!-- 2.通配符 -->
      <!-- <url-pattern>/*</url-pattern> -->
      <!-- 3.后缀(不要写/) -->
      <url-pattern>*.duang</url-pattern>
  </servlet-mapping>
  
</web-app>

web.xml

案例三：演示Servlet程序调度规则：

package web;

import java.io.IOException;

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

public class DemoServlet extends HttpServlet {
    
    //DemoServlet，实例化 == new  调用一次
    public DemoServlet() {
        System.out.println("实例化DemoServlet");
    }

    //init，初始化  爷爷的方法  调用一次
    @Override
    public void init(ServletConfig config) throws ServletException {
        super.init(config);
        System.out.println("初始化DemoServlet");
    }

    //service,执行程序逻辑  访问多少次，调用多少次
    @Override
    protected void service(
        HttpServletRequest arg0, 
        HttpServletResponse arg1) throws ServletException, IOException {
        System.out.println("调用DemoServlet");
    }

    //destroy，关闭Servlet  调用一次
    @Override
    public void destroy() {
        super.destroy();
        System.out.println("销毁DemoServlet");
    }

}

SysServlet.java

<?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" version="2.5">
  <display-name>servlet4</display-name>
  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.htm</welcome-file>
    <welcome-file>index.jsp</welcome-file>
    <welcome-file>default.html</welcome-file>
    <welcome-file>default.htm</welcome-file>
    <welcome-file>default.jsp</welcome-file>
  </welcome-file-list>
  
  <servlet>
      <servlet-name>demo</servlet-name>
      <servlet-class>web.DemoServlet</servlet-class>
      <!-- 这里可以控制，启动时第1个加载此Servlet -->
      <load-on-startup>1</load-on-startup>
  </servlet>
  <servlet-mapping>
      <servlet-name>demo</servlet-name>
      <url-pattern>/demo</url-pattern>
  </servlet-mapping>
  
</web-app>

web.xml

后一天讲的内容：

<?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" version="2.5">
  <display-name>servlet4</display-name>
  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.htm</welcome-file>
    <welcome-file>index.jsp</welcome-file>
    <welcome-file>default.html</welcome-file>
    <welcome-file>default.htm</welcome-file>
    <welcome-file>default.jsp</welcome-file>
  </welcome-file-list>
  
  <servlet>
      <servlet-name>demo</servlet-name>
      <servlet-class>web.DemoServlet</servlet-class>
      <!-- 启动时第2个加载此Servlet -->
      <load-on-startup>2</load-on-startup>
  </servlet>
  <servlet-mapping>
      <servlet-name>demo</servlet-name>
      <url-pattern>/demo</url-pattern>
  </servlet-mapping>
  
  <servlet>
      <servlet-name>login</servlet-name>
      <servlet-class>web.LoginServlet</servlet-class>
      <init-param>
          <param-name>maxonline</param-name>
          <param-value>3000</param-value>
      </init-param>
  </servlet>
  <servlet-mapping>
      <servlet-name>login</servlet-name>
      <url-pattern>/login</url-pattern>
  </servlet-mapping>
  
  <servlet>
      <servlet-name>findDept</servlet-name>
      <servlet-class>web.FindDeptServlet</servlet-class>
  </servlet>
  <servlet-mapping>
      <servlet-name>findDept</servlet-name>
      <url-pattern>/findDept</url-pattern>
  </servlet-mapping>
  
  <servlet>
      <servlet-name>findEmp</servlet-name>
      <servlet-class>web.FindEmpServlet</servlet-class>
  </servlet>
  <servlet-mapping>
      <servlet-name>findEmp</servlet-name>
      <url-pattern>/findEmp</url-pattern>
  </servlet-mapping>

  <!-- 
          给所有的Servlet预置参数,该参数由context
          对象自动读取.
          Tomcat启动时首先就会创建context对象,它会
          给每个项目创建唯一的一个context.
          context内部有静态块,首次调用时就执行,
          此块内加载了web.xml中的参数.
   -->  
  <context-param>
      <param-name>size</param-name>
      <param-value>10</param-value>
  </context-param>
  
  <servlet>
      <servlet-name>init</servlet-name>
      <servlet-class>web.InitServlet</servlet-class>
      <load-on-startup>1</load-on-startup>
  </servlet>
  
  <servlet>
      <servlet-name>up</servlet-name>
      <servlet-class>web.UpServlet</servlet-class>
  </servlet>
  <servlet-mapping>
      <servlet-name>up</servlet-name>
      <url-pattern>/up</url-pattern>
  </servlet-mapping>
  
</web-app>

web.xml

ServletConfig，一对一和 init 调用时机讲解：

package web;

import java.io.IOException;

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

public class LoginServlet extends HttpServlet {

    /**
     * 1.config对象由tomcat创建及传入
     * 
     * LoginServlet servlet = new LoginServlet();
     * //Tomcat每创建一个Servlet后,就会立刻给它
     * //创建一个config对象.
     * //config内有静态块,调用时加载参数(首次访问)
     * ServletConfig cfg = new ServletConfig();
     * //通过init方法传入此config对象
     * servlet.init(cfg);
     * //父类的init(cfg)方法内部调用了init()
     * 
     * 2.使用config不是必须要重写init(),
     *   若在service()中调用config,通过父类
     *   提供的getServletCofig()就可以获取它.
     *   该方法返回的config就是init()所传入
     *   的那个config.
     * 
     * */
    
    @Override
    public void init(ServletConfig config) throws ServletException {
        System.out.println("调用有参的init()");
        super.init(config);
    }
    
    @Override
    public void init() throws ServletException {
        System.out.println("调用无参的init()");
        super.init();
    }

    @Override
    protected void service(
        HttpServletRequest req, 
        HttpServletResponse res) throws ServletException, IOException {
        //获取在线人数最大值
        ServletConfig cfg = getServletConfig();
        String maxonline = 
            cfg.getInitParameter("maxonline");
        System.out.println(maxonline);
    }

}

LoginServlet.java

ServletContext,一对多：

package web;

import java.io.IOException;

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

public class FindDeptServlet extends HttpServlet {

    @Override
    protected void service(
        HttpServletRequest req, 
        HttpServletResponse res) throws ServletException, IOException {
        //获取每页显示的行数
        ServletContext ctx = getServletContext();
        String size = ctx.getInitParameter("size");
        System.out.println(size);
        //统计流量
        Integer count = (Integer) 
            ctx.getAttribute("count");
        ctx.setAttribute("count", ++count);
        System.out.println("流量:"+count);
    }

}

FindDeptServlet.java

package web;

import java.io.IOException;

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

public class FindEmpServlet extends HttpServlet {

    @Override
    protected void service(
        HttpServletRequest req, 
        HttpServletResponse res) throws ServletException, IOException {
        //获取每页显示的行数
        ServletContext ctx = getServletContext();
        String size = ctx.getInitParameter("size");
        System.out.println(size);
        //统计流量
        Integer count = (Integer) 
            ctx.getAttribute("count");
        ctx.setAttribute("count", ++count);
        System.out.println("流量:"+count);        
    }

}

FindEmpServlet.java

这个文件只是初始化变量，还是访问上面这两个文件，进行测试程序，

package web;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;

/**
 * 该Servlet不用来处理任何请求,只是用来
 * 在Tomcat启动时初始化一些数据而已.
 * 在你工作时会发现很多项目中都有1个/多个
 * 这样的Servlet.
 */
public class InitServlet extends HttpServlet {

    @Override
    public void init() throws ServletException {
        super.init();
        //将流量初始化为0
        ServletContext ctx = getServletContext();
        ctx.setAttribute("count", 0);
    }

}

InitServlet.java

演示线程安全，增加 synchronized(this) 保证线程安全：

package web;

import java.io.IOException;
import java.io.PrintWriter;

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

public class UpServlet extends HttpServlet {
    
    private Double salary = 3000.0;

    @Override
    protected void service(
        HttpServletRequest req, 
        HttpServletResponse res) throws ServletException, IOException {
        synchronized(this) {
            //模拟涨工资
            salary += 100;
            //模拟网络延迟
            try {
                Thread.sleep(8000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            res.setContentType(
                    "text/html;charset=utf-8");
            PrintWriter out = res.getWriter();
            out.println(salary);
            out.close();
        }
    }
}

UpServlet.java

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原文地址：https://www.cnblogs.com/tangshengwei/p/6422233.html

Unit03： 容器对路径的处理 、 Servlet特性

Unit03： 容器对路径的处理 、 Servlet特性

案例一：查询，增加员工：

目录结构：

案例代码：

案例二：演示路径输出，访问项目的三种方式：

案例三：演示Servlet程序调度规则：

后一天讲的内容：

ServletConfig，一对一 和 init 调用时机讲解：

ServletContext,一对多：

演示线程安全，增加 synchronized(this) 保证线程安全：

Unit03：容器对路径的处理、 Servlet特性

　　　　　　Unit03：容器对路径的处理、 Servlet特性　　　　　　

ServletConfig，一对一和 init 调用时机讲解：