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Servlet 学习（二）

Servlet 体系结构

Servlet的实现方式

1、实现 javax.servlet.Servlet 接口 ( 最底层，最原始 )

测试案例：

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Servlet Life Cycle</title>
</head>
<body>

    <h3>Servlet的实现方式:</h3>
    
    <h5>1、实现 javax.servlet.Servlet 接口 ( 最底层，最原始 ) </h5>
    <form action="/Servlet/first" method="post">
        <input type="text" name="username" placeholder="用户名">
        <input type="password" name="password" placeholder="密码">
        <input type="submit" value="提交" >
    </form>
    
    <h5>2、继承 javax.servlet.GenericServlet 类，实现 service 方法</h5>
    <form action="/Servlet/second" method="post">
        <input type="text" name="username" placeholder="用户名">
        <input type="password" name="password" placeholder="密码">
        <input type="submit" value="提交" >
    </form>
    
    <form action="/Servlet/second/abc" method="post">
        <input type="text" name="username" placeholder="用户名">
        <input type="password" name="password" placeholder="密码">
        <input type="submit" value="提交" >
    </form>
    
    <form action="/Servlet/second/xyz/abc" method="post">
        <input type="text" name="username" placeholder="用户名">
        <input type="password" name="password" placeholder="密码">
        <input type="submit" value="提交" >
    </form>
    
    <h5>3、继承 javax.servlet.http.HttpServlet 类 ，重写 doGet 和 doPost 方法</h5>
    <form action="/Servlet/third" method="get">
        GET: 
        <input type="text" name="username" placeholder="用户名">
        <input type="password" name="password" placeholder="密码">
        <input type="submit" value="提交" >
    </form>
    <form action="/Servlet/third" method="post">
        POST: 
        <input type="text" name="username" placeholder="用户名">
        <input type="password" name="password" placeholder="密码">
        <input type="submit" value="提交" >
    </form>
    
    <h5>4、继承 javax.servlet.http.HttpServlet 类 ，重写 service( HttpServletRequest , HttpServletResponse ) 方法</h5>
    <form action="/Servlet/forth" method="get">
        GET: 
        <input type="text" name="username" placeholder="用户名">
        <input type="password" name="password" placeholder="密码">
        <input type="submit" value="提交" >
    </form>
    <form action="/Servlet/forth" method="post">
        POST: 
        <input type="text" name="username" placeholder="用户名">
        <input type="password" name="password" placeholder="密码">
        <input type="submit" value="提交" >
    </form>

</body>
</html>

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

<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns="http://xmlns.jcp.org/xml/ns/javaee"
    xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
    id="WebApp_ID" version="3.1">

    <!-- 注册 -->
    <servlet>
        <servlet-name>FirstServlet</servlet-name>
        <servlet-class>ecut.lifecycle.FirstServlet</servlet-class>
    </servlet>

    <!-- 映射(发布) -->
    <servlet-mapping>
        <servlet-name>FirstServlet</servlet-name>
        <url-pattern>/first</url-pattern>
    </servlet-mapping>

    <!-- 注册 -->
    <servlet>
        <servlet-name>SecondServlet</servlet-name>
        <servlet-class>ecut.lifecycle.SecondServlet</servlet-class>
    </servlet>

    <!-- 映射(发布) -->
    <servlet-mapping>
        <servlet-name>SecondServlet</servlet-name>
        <url-pattern>/second</url-pattern>
        <url-pattern>/second/*</url-pattern>
    </servlet-mapping>

    <!-- 注册 -->
    <servlet>
        <servlet-name>ThirdServlet</servlet-name>
        <servlet-class>ecut.lifecycle.ThirdServlet</servlet-class>
    </servlet>

    <!-- 映射(发布) -->
    <servlet-mapping>
        <servlet-name>ThirdServlet</servlet-name>
        <url-pattern>/third</url-pattern>
    </servlet-mapping>

    <!-- 注册 -->
    <servlet>
        <servlet-name>ForthServlet</servlet-name>
        <servlet-class>ecut.lifecycle.ForthServlet</servlet-class>
    </servlet>

    <!-- 映射(发布) -->
    <servlet-mapping>
        <servlet-name>ForthServlet</servlet-name>
        <url-pattern>/forth</url-pattern>
    </servlet-mapping>

    <!-- 注册 -->
    <servlet>
        <servlet-name>LifeCycleServlet</servlet-name>
        <servlet-class>ecut.lifecycle.LifeCycleServlet</servlet-class>
        <!-- 当容器 加载当前的WEB应用时就完成对 该 Servlet 的类加载、实例化、初始化操作 -->
        <!-- 数字代表加载优先级，默认值-1访问再加载 -->
        <load-on-startup>0</load-on-startup>
    </servlet>

    <!-- 映射(发布) -->
    <servlet-mapping>
        <servlet-name>LifeCycleServlet</servlet-name>
        <url-pattern>/cycle</url-pattern>
    </servlet-mapping>

    <!-- 注册 -->
    <servlet>
        <servlet-name>ConfigurationServlet</servlet-name>
        <servlet-class>ecut.lifecycle.ConfigurationServlet</servlet-class>
        <!-- 指定初始化参数 -->
        <init-param>
            <param-name>encoding</param-name>
            <param-value>UTF-8</param-value>
        </init-param>
        <init-param>
            <param-name>content-type</param-name>
            <param-value>text/html</param-value>
        </init-param>
    </servlet>

    <!-- 映射(发布) -->
    <servlet-mapping>
        <servlet-name>ConfigurationServlet</servlet-name>
        <url-pattern>/config</url-pattern>
    </servlet-mapping>
    
</web-app>

package ecut.lifecycle;

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

import javax.servlet.Servlet;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;

public class FirstServlet implements Servlet {

    @Override
    public void init(ServletConfig config) throws ServletException {
        System.out.println( "初始化" );
    }

    @Override
    public void service(ServletRequest req , ServletResponse resp ) throws ServletException, IOException {
        System.out.println( "服务" );
        
        req.setCharacterEncoding( "UTF-8" );
        resp.setCharacterEncoding( "UTF-8" );
        
        // 接受来自客户端的数据
        String username = req.getParameter( "username" );
        System.out.println( "username : " + username );
        String password = req.getParameter( "password" );
        System.out.println( "password : " + password );
        
        // 向客户端生成响应数据
        resp.setContentType( "text/html;charset=UTF-8" );
        PrintWriter w = resp.getWriter();
        w.println( "<h1 style='text-align:center;color:blue;'>你好 , " + username + " !</h1>" );        
    }
    
    @Override
    public void destroy() {
        System.out.println( "销毁" );
    }

    @Override
    public ServletConfig getServletConfig() {
        return null;
    }

    @Override
    public String getServletInfo() {
        return null;
    }

}

运行结果如下：

信息: Server startup in 350 ms
初始化
服务
username : AmyZheng
password : 123456

2、继承 javax.servlet.GenericServlet 类，实现 service 方法

测试案例：

package ecut.lifecycle;

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

import javax.servlet.GenericServlet;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;

public class SecondServlet extends GenericServlet{

    private static final long serialVersionUID = -2575698410270033395L;

    @Override
    public void service(ServletRequest req , ServletResponse resp) throws ServletException, IOException {
        
        req.setCharacterEncoding( "UTF-8" );
        resp.setCharacterEncoding( "UTF-8" );
        
        // 接受来自客户端的数据
        String username = req.getParameter( "username" );
        System.out.println( "username : " + username );
        String password = req.getParameter( "password" );
        System.out.println( "password : " + password );
        
        // 向客户端生成响应数据
        resp.setContentType( "text/html;charset=UTF-8" );
        PrintWriter w = resp.getWriter();
        w.println( "<h1 style='text-align:center;color:blue;'>你好 , " + username + " !</h1>" );
        
    }

}

运行结果如下：

username : AmyZheng
password : AmyZheng

username : AmyZheng
password : 125678

username : AmyZheng
password : 14789

3、继承 javax.servlet.http.HttpServlet 类，重写 doGet 和 doPost 方法

测试案例：

package ecut.lifecycle;

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 ThirdServlet extends HttpServlet{

    private static final long serialVersionUID = -1117957788110702968L;

    @Override
    protected void doGet( HttpServletRequest request, HttpServletResponse response ) throws ServletException, IOException {
        System.out.println( "GET" );
        
        request.setCharacterEncoding( "UTF-8" );
        response.setCharacterEncoding( "UTF-8" );
        
        // 接受来自客户端的数据
        String username = request.getParameter( "username" );
        System.out.println( "username : " + username );
        String password = request.getParameter( "password" );
        System.out.println( "password : " + password );
        
        // 向客户端生成响应数据
        response.setContentType( "text/html;charset=UTF-8" );
        PrintWriter w = response.getWriter();
        w.println( "<h1 style='text-align:center;color:blue;'>你好 , " + username + " !</h1>" );
    }

    @Override
    protected void doPost( HttpServletRequest request , HttpServletResponse response ) throws ServletException, IOException {
        System.out.println( "POST" );
        
        request.setCharacterEncoding( "UTF-8" );
        response.setCharacterEncoding( "UTF-8" );
        
        // 接受来自客户端的数据
        String username = request.getParameter( "username" );
        System.out.println( "username : " + username );
        String password = request.getParameter( "password" );
        System.out.println( "password : " + password );
        
        // 向客户端生成响应数据
        response.setContentType( "text/html;charset=UTF-8" );
        PrintWriter w = response.getWriter();
        w.println( "<h1 style='text-align:center;color:blue;'>你好 , " + username + " !</h1>" );
    }
    
    

}

运行结果如下：

GET
username : AmyZheng
password : 12589

POST
username : AmyZheng
password : AmyZhengf

4、继承 javax.servlet.http.HttpServlet 类，重写 service( HttpServletRequest , HttpServletResponse ) 方法

测试案例：

package ecut.lifecycle;

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 ForthServlet extends HttpServlet {

    private static final long serialVersionUID = -1403874146599150561L;

    @Override
    protected void service( HttpServletRequest request, HttpServletResponse response ) 
            throws ServletException, IOException {
        
        request.setCharacterEncoding( "UTF-8" );
        response.setCharacterEncoding( "UTF-8" );
        
        // 接受来自客户端的数据
        String username = request.getParameter( "username" );
        System.out.println( "username : " + username );
        String password = request.getParameter( "password" );
        System.out.println( "password : " + password );
        
        // 向客户端生成响应数据
        response.setContentType( "text/html;charset=UTF-8" );
        PrintWriter w = response.getWriter();
        w.println( "<h1 style='text-align:center;color:blue;'>你好 , " + username + " !</h1>" );
        
    }

    
}

运行结果如下：

username : AmyZheng
password : AmyZheng1

username : AmyZheng
password : AmyZheng2

Servlet的生命周期

1、加载和实例化

容器通过反射加载相应的Servlet 类并实例化该类的一个实例。
对Servlet类的加载可能发生在引擎启动时，也可能是用户第一次访问相应的Servlet 时。
容器只为相应的Servlet初始化一个实例（容器里servlet对象只创建一个）。

2、初始化：调用init() 方法

Servlet 第一次被调用时，调用init() 方法一次。
以后除非被reload 或者destory 后重新访问，才会重新调用该方法。
之所以重新调用是因为原有的Servlet 生命周期已结束，一个新的Servlet 生命周期开始。

3、处理请求：调用service() 方法

业务逻辑一般在该方法中完成，该方法可以被多次调用。
只要有一个用户访问当前Servlet，就会调用该方法(请求一次就服务，一个连接一个线程)。

4、服务结束：调用destory() 方法

有三种情况会调用destory 方法(只调用一次)

　　　　tomcat将重启
　　　　reload 该webapp
　　　　关闭或重启计算机(Servlet容器也随之关闭)

测试案例：

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

<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns="http://xmlns.jcp.org/xml/ns/javaee"
    xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
    id="WebApp_ID" version="3.1">

    <!-- 注册 -->
    <servlet>
        <servlet-name>LifeCycleServlet</servlet-name>
        <servlet-class>ecut.lifecycle.LifeCycleServlet</servlet-class>
    </servlet>

    <!-- 映射(发布) -->
    <servlet-mapping>
        <servlet-name>LifeCycleServlet</servlet-name>
        <url-pattern>/cycle</url-pattern>
    </servlet-mapping>
    
</web-app>

package ecut.lifecycle;

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

import javax.servlet.Servlet;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;

public class LifeCycleServlet  implements Servlet {
    
    static { 
        System.out.println( "加载并初始化LifeCycleServlet类" );
    }
    
    public LifeCycleServlet(){
        System.out.println( "创建 LifeCycleServlet 类的实例" );
    }

    @Override
    public void init( ServletConfig config ) throws ServletException {
        System.out.println( "对 LifeCycleServlet 实例进行初始化" );
    }

    @Override
    public void service( ServletRequest req , ServletResponse resp ) throws ServletException, IOException {
        System.out.println( "LifeCycleServlet 的实例对外提供服务" );
        
        resp.setCharacterEncoding( "UTF-8" );
        resp.setContentType( "text/html;charset=UTF-8" );
        
        // 向客户端生成响应数据
        PrintWriter w = resp.getWriter();
        w.println( "<h1 style='text-align:center;color:blue;'>Hello !</h1>" );
        
    } 
    
    @Override
    public void destroy() {
        System.out.println( "准备销毁 LifeCycleServlet 的实例" );
    }

    @Override
    public ServletConfig getServletConfig() {
        return null;
    }

    @Override
    public String getServletInfo() {
        return null;
    }

}

运行结果如下：

信息: Server startup in 337 ms
加载并初始化LifeCycleServlet类
创建 LifeCycleServlet 类的实例
对 LifeCycleServlet 实例进行初始化
LifeCycleServlet 的实例对外提供服务
LifeCycleServlet 的实例对外提供服务

如下修改xml：

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

<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns="http://xmlns.jcp.org/xml/ns/javaee"
    xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
    id="WebApp_ID" version="3.1">

    <!-- 注册 -->
    <servlet>
        <servlet-name>LifeCycleServlet</servlet-name>
        <servlet-class>ecut.lifecycle.LifeCycleServlet</servlet-class>
        <!-- 当容器 加载当前的WEB应用时就完成对 该 Servlet 的类加载、实例化、初始化操作 -->
        <!-- 数字代表加载优先级，默认值-1访问再加载 -->
        <load-on-startup>0</load-on-startup>
    </servlet>

    <!-- 映射(发布) -->
    <servlet-mapping>
        <servlet-name>LifeCycleServlet</servlet-name>
        <url-pattern>/cycle</url-pattern>
    </servlet-mapping>
    
</web-app>

指定当web 应用启动时，装载Servlet 的次序

在servlet 标签中使用<load-on-startup> 子标签设置
其中的数字含义如下:

　　　　如果这个数字是正数或0，则容器先加载数值较小的servlet，再加载数值稍大的
　　　　如果是负数或者没有设置，容器将在web 客户端首次访问该servlet 时才加载

运行结果如下：

加载并初始化LifeCycleServlet类
创建 LifeCycleServlet 类的实例
对 LifeCycleServlet 实例进行初始化
四月 08, 2018 7:07:00 下午 org.apache.coyote.AbstractProtocol start
信息: Starting ProtocolHandler ["http-nio-8080"]
四月 08, 2018 7:07:00 下午 org.apache.coyote.AbstractProtocol start
信息: Starting ProtocolHandler ["ajp-nio-8009"]
四月 08, 2018 7:07:00 下午 org.apache.catalina.startup.Catalina start
信息: Server startup in 346 ms
LifeCycleServlet 的实例对外提供服务
LifeCycleServlet 的实例对外提供服务

ServletConfig

1、ServletConfig接口：servlet容器在初始化期间将信息传递给servlet的servlet配置对象（用于描述一个Servlet 的配置信息）。

2、常用方法

获得当前Servlet 实例的名称

　　　　String getServletName()

获得当前Servlet 实例的初始化参数

　　　　String getInitParameter(String name)根据name 获取指定的初始化参数的值，如果name 对应的初始化参数不存在，返回null
　　　　Enumeration getInitParameterNames()返回当前Servlet 实例的所有的初始化参数的名称，注意返回类型是java.util.Enumeration

获得当前Servlet 实例所依赖的应用

　　　　ServletContext getServletContext()

测试案例：

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

<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns="http://xmlns.jcp.org/xml/ns/javaee"
    xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
    id="WebApp_ID" version="3.1">

    <!-- 注册 -->
    <servlet>
        <servlet-name>ConfigurationServlet</servlet-name>
        <servlet-class>ecut.lifecycle.ConfigurationServlet</servlet-class>
        <!-- 指定初始化参数 -->
        <init-param>
            <param-name>encoding</param-name>
            <param-value>UTF-8</param-value>
        </init-param>
        <init-param>
            <param-name>content-type</param-name>
            <param-value>text/html</param-value>
        </init-param>
    </servlet>

    <!-- 映射(发布) -->
    <servlet-mapping>
        <servlet-name>ConfigurationServlet</servlet-name>
        <url-pattern>/config</url-pattern>
    </servlet-mapping>
    
</web-app>

package ecut.lifecycle;

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

import javax.servlet.Servlet;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;

public class ConfigurationServlet implements Servlet {
    
    @Override
    public String getServletInfo() {
        return this.config.getServletName() ;
    }
    
    @Override
    public ServletConfig getServletConfig() {
        return this.config ;
    }
    
    private ServletConfig config ;
    
    @Override
    public void init( ServletConfig config ) throws ServletException {
        this.config = config ;
        System.out.println( "初始化" );
        System.out.println( config ); 
        System.out.println( "ServletName : " + config.getServletName() );//web.xm配置文件中的servlet名称
        /*
        String encoding = config.getInitParameter( "encoding" );
        System.out.println( "encoding : " + encoding );
        */
        Enumeration<String> initParamNames = config.getInitParameterNames();
        while( initParamNames.hasMoreElements() ){
            String name = initParamNames.nextElement() ;
            String value = config.getInitParameter( name );
            System.out.println( name + " : " + value );
        } 
    }

    @Override
    public void service( ServletRequest req , ServletResponse resp ) throws ServletException, IOException {
        System.out.println( "对外提供服务" );
        
        String ct = config.getInitParameter( "content-type" ) ;
        String en = config.getInitParameter( "encoding" ) ;
        String contentType = ct + ";charset=" + en  ; //  "text/html;charset=UTF-8"
        resp.setContentType( contentType );
        PrintWriter w = resp.getWriter();
        w.println( "<h1 style='text-align:center;color:blue;'>欢迎 !</h1>" );
    } 
    
    @Override
    public void destroy() {
        System.out.println( "销毁" );
    }

}

配置Servlet 的初始化参数

在servlet 标签中使用init-param 子标签配置

　　　　其中<param-name> 子标签用于设置初始化参数的名称
　　　　<param-value> 子标签用于设置指定参数的值

同一个servlet 中可以使用多个init-param 标签配置多个初始化参数

　　　　使用config.getInitParameter( name ) 可以获取指定名称的参数对应的值
　　　　使用config.getInitParameterNames() 可以获取所有的参数的名称

运行结果如下：

初始化
org.apache.catalina.core.StandardWrapperFacade@4c12c6a
ServletName : ConfigurationServlet
content-type : text/html
encoding : UTF-8
对外提供服务

转载请于明显处标明出处

http://www.cnblogs.com/AmyZheng/p/8742900.html

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原文地址：https://www.cnblogs.com/AmyZheng/p/8742900.html