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Javaweb崔希凡---Day9---servlet

分类: 文章 • 2025-03-05 22:01:17

Servlet概述

Javaweb崔希凡---Day9---servlet

1　什么是Servlet

Javaweb崔希凡---Day9---servlet

2　实现Servlet的方式（由我们自己来写！）

Javaweb崔希凡---Day9---servlet
Servlet.java ：

public interface Servlet{
    public void init(ServletConfig config) throws ServletException;
    public ServletConfig getServletConfig();
    public void service(ServletRequest req, ServletResponse res)
            throws ServletException, IOException;
    public String getServletInfo();
    public void destroy();
}

Servlet中的方法大多数不由我们来调用，而是由Tomcat来调用。并且Servlet的对象也不由我们来创建，由Tomcat来创建！

3　创建helloservlet应用

Javaweb崔希凡---Day9---servlet
HelloServlet.java ：

public class HelloServlet implements Servlet {
	public void init(ServletConfig config) throws ServletException {}
	public ServletConfig getServletConfig() {return null;}
	public void destroy() {}
	public String getServletInfo() {return null;}

	public void service(ServletRequest req, ServletResponse res)
			throws ServletException, IOException {
		System.out.println("hello servlet!");
	}
}

我们暂时忽略Servlet中其他四个方法，只关心service()方法，因为它是用来处理请求的方法。我们在该方法内给出一条输出语句！

web.xml（下面内容需要背下来）：

	<servlet>
		<servlet-name>hello</servlet-name>
		<servlet-class>cn.itcast.servlet.HelloServlet</servlet-class>
	</servlet>
	<servlet-mapping>
		<servlet-name>hello</servlet-name>
		<url-pattern>/helloworld</url-pattern>
	</servlet-mapping>

Javaweb崔希凡---Day9---servlet
Javaweb崔希凡---Day9---servlet

Servlet接口

1. Servlet的生命周期

Javaweb崔希凡---Day9---servlet
Javaweb崔希凡---Day9---servlet
Javaweb崔希凡---Day9---servlet
Javaweb崔希凡---Day9---servlet
Javaweb崔希凡---Day9---servlet

public class HelloServlet implements Servlet {
	public void init(ServletConfig config) throws ServletException {
		System.out.println("Servlet被创建了！");
	}
	public ServletConfig getServletConfig() {return null;}
	public void destroy() {
		System.out.println("Servlet要离去了！");
	}
	public String getServletInfo() {return null;}

	public void service(ServletRequest req, ServletResponse res)
			throws ServletException, IOException {
		System.out.println("hello servlet!");
	}
}

Javaweb崔希凡---Day9---servlet

2　Servlet接口相关类型

Javaweb崔希凡---Day9---servlet
Javaweb崔希凡---Day9---servlet
Javaweb崔希凡---Day9---servlet
Javaweb崔希凡---Day9---servlet
Javaweb崔希凡---Day9---servlet
Javaweb崔希凡---Day9---servlet
Javaweb崔希凡---Day9---servlet
Javaweb崔希凡---Day9---servlet
在< servlet>元素中还可以配置初始化参数：(配置了两个初始化参数)

  <servlet>
    <servlet-name>One</servlet-name>
    <servlet-class>cn.itcast.servlet.OneServlet</servlet-class>
    <init-param>
      	<param-name>paramName1</param-name>
    	    <param-value>paramValue1</param-value>
    </init-param>
    <init-param>
    	    <param-name>paramName2</param-name>
    	    <param-value>paramValue2</param-value>
    </init-param>
  </servlet>

Javaweb崔希凡---Day9---servlet
web.xml :

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5" 
	xmlns="http://java.sun.com/xml/ns/javaee" 
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
	xsi:schemaLocation="http://java.sun.com/xml/ns/javaee 
	http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
	
	<servlet>
		<servlet-name>xxx</servlet-name>
		<servlet-class>cn.itcast.web.servlet.AServlet</servlet-class>
		<init-param>
			<param-name>p1</param-name>
			<param-value>v1</param-value>
		</init-param>
		<init-param>
			<param-name>p2</param-name>
			<param-value>v2</param-value>
		</init-param>
	</servlet>
	
	<servlet-mapping>
		<servlet-name>xxx</servlet-name>
		<url-pattern>/AServlet</url-pattern>
	</servlet-mapping>
	
	
  	<servlet>
		<servlet-name>yyy</servlet-name>
		<servlet-class>cn.itcast.web.servlet.EServlet</servlet-class>
	</servlet>
  <servlet>
    <servlet-name>FServlet</servlet-name>
    <servlet-class>cn.itcast.web.servlet.FServlet</servlet-class>
    <load-on-startup>0</load-on-startup>
  </servlet>

	
	<servlet-mapping>
		<servlet-name>yyy</servlet-name>
		<url-pattern>/EServlet</url-pattern>
	</servlet-mapping>
  <servlet-mapping>
    <servlet-name>FServlet</servlet-name>
    <url-pattern>/FServlet</url-pattern>
  </servlet-mapping>
</web-app>

AServlet.java

package cn.itcast.web.servlet;

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

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

/*
 * 查看Servlet接口中的方法
 */
public class AServlet implements Servlet {
	/*
	 * 它也是生命周期方法
	 * 它会在Servlet被销毁之前调用，并且它只会被调用一次！
	 */
	@Override
	public void destroy() {
		System.out.println("destory()...");
	}

	/*
	 * 可以用来获取Servlet的配置信息
	 */
	@Override
	public ServletConfig getServletConfig() {
		System.out.println("getServletConfig()...");
		return null;
	}

	/*
	 * 获取Servlet的信息
	 */
	@Override
	public String getServletInfo() {
		System.out.println("getServletInfo()...");
		return "我是一个快乐的Servlet";
	}

	/*
	 * 它是生命周期方法
	 * 它会在Servlet对象创建之后马上执行，并只执行一次！（出生之后）
	 * 
	 */
	@Override
	public void init(ServletConfig servletConfig) throws ServletException {
		System.out.println("init()...");
		
		/*
		 * 获取初始化参数
		 */
		System.out.println(servletConfig.getInitParameter("p1"));
		System.out.println(servletConfig.getInitParameter("p2"));
		
		/*
		 * 获取所有初始化参数的名称
		 */
		Enumeration e = servletConfig.getInitParameterNames();
		while(e.hasMoreElements()) {
			System.out.println(e.nextElement());
		}
	}

	/*
	 * 它是生命周期方法
	 * 它会被调用多次！！！
	 * 每次处理请求都是在调用这个方法！
	 */
	@Override
	public void service(ServletRequest request, ServletResponse response)
			throws ServletException, IOException {
		System.out.println("service()...");
	}
}

Javaweb崔希凡---Day9---servlet

GenericServlet

1　GenericServlet概述

Javaweb崔希凡---Day9---servlet
GenericServlet.java :

public abstract class GenericServlet implements Servlet, ServletConfig,
        java.io.Serializable {
    private static final long serialVersionUID = 1L;
    private transient ServletConfig config;
    public GenericServlet() {}
    @Override
    public void destroy() {}
    @Override
    public String getInitParameter(String name) {
        return getServletConfig().getInitParameter(name);
    }
    @Override
    public Enumeration<String> getInitParameterNames() {
        return getServletConfig().getInitParameterNames();
    }
    @Override
    public ServletConfig getServletConfig() {
        return config;
    }
    @Override
    public ServletContext getServletContext() {
        return getServletConfig().getServletContext();
    }
    @Override
    public String getServletInfo() {
        return "";
    }
    @Override
    public void init(ServletConfig config) throws ServletException {   //实现了Servlet的init(ServletConfig)方法，
    //把参数config赋给了本类的成员config，然后再调用本类自己的无参的init()方法。
        this.config = config;
        this.init();
    }
    public void init() throws ServletException {}       //这个方法是GenericServlet自己的方法，
    //而不是从Servlet继承下来的。当我们自定义Servlet时，如果想完成初始化作用就不要再
    //重复init(ServletConfig)方法了，而是应该去重写init()方法。因为在GenericServlet中的
    //init(ServletConfig)方法中保存了ServletConfig对象，如果覆盖了保存ServletConfig的代
    //码，那么就不能再使用ServletConfig了。
    
    public void log(String msg) {
        getServletContext().log(getServletName() + ": " + msg);
    }
    public void log(String message, Throwable t) {
        getServletContext().log(getServletName() + ": " + message, t);
    }
    @Override
    public abstract void service(ServletRequest req, ServletResponse res)
            throws ServletException, IOException;
    @Override
    public String getServletName() {
        return config.getServletName();
    }
}

2　GenericServlet的init()方法

Javaweb崔希凡---Day9---servlet

3　实现了ServletConfig接口

Javaweb崔希凡---Day9---servlet
BServlet.java :

package cn.itcast.web.servlet;

import java.io.IOException;

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

/**
 * 模拟GenericServlet
 * @author cxf
 *
 */
public class BServlet implements Servlet {
	private ServletConfig config;
	
	
	/*
	 * 需要就写，不需要就不写
	 */
	@Override
	public void destroy() {
		System.out.println("啊~我要死了！");
	}

	/*
	 * 请放心，这个方法一定会在init()方法之后被调用！
	 * init()被调用后，本类的成员this.config已经有值了！
	 */
	@Override
	public ServletConfig getServletConfig() {
		return this.config;
	}

	/*
	 * 没有用的东西，爱实现不实现
	 */
	@Override
	public String getServletInfo() {
		return "我是一个快乐的Servlet";
	}

	/*
	 * 由Tomcat来调用，并且只调用一次
	 * 它是这些方法中第一个被调用的，它会在构造器之后马上被调用！
	 */
	@Override
	public void init(ServletConfig config) throws ServletException {
		// 把tomcat传递的Servletconfig赋值给本类的一个成员，其实就是把它保存起来，方便在其他方法中使用！
		this.config = config;
		init();
	}
	
	/*
	 * 这个方法是本类自己定义的！不是Servlet接口中的方法
	 */
	public void init() {
	}

	@Override
	public void service(ServletRequest arg0, ServletResponse arg1)
			throws ServletException, IOException {
		/*
		 * 这里是否可以使用ServletConfig的成员呢？
		 */
		System.out.println("每次处理请求都会被调用！");
	}
	
	public ServletContext getServletContext() {
		return config.getServletContext();
	}
	
	public String getServletName() {
		return config.getServletName();
	}
	
	public String getInitParameter(String name) {
		return config.getInitParameter(name);
	}

}

CServlet extends BServlet :

package cn.itcast.web.servlet;

import java.io.IOException;

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

public class CServlet extends BServlet {
	@Override
	public void init() {
		System.out.println("哇～～～～，很高兴啊～～～");  
	}
	
	@Override
	public void service(ServletRequest arg0, ServletResponse arg1)
			throws ServletException, IOException {
		String value = getInitParameter("p1");
	}
}

DServlet extends GenericServlet :

package cn.itcast.web.servlet;

import java.io.IOException;

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

public class DServlet extends GenericServlet {
	@Override
	public void init() throws ServletException {
		System.out.println("哈哈哈～我来也！");
	}

	@Override
	public void service(ServletRequest arg0, ServletResponse arg1)
			throws ServletException, IOException {
		System.out.println("hello world");
	}

	@Override
	public void destroy() {
		System.out.println("destory()");
	}
}

HttpServlet

1　HttpServlet概述

Javaweb崔希凡---Day9---servlet

2　HttpServlet覆盖了service()方法

Javaweb崔希凡---Day9---servlet
Javaweb崔希凡---Day9---servlet
Javaweb崔希凡---Day9---servlet
首先配置web.xml文件 ：

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5" 
	xmlns="http://java.sun.com/xml/ns/javaee" 
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
	xsi:schemaLocation="http://java.sun.com/xml/ns/javaee 
	http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
	
	<servlet>
		<servlet-name>xxx</servlet-name>
		<servlet-class>cn.itcast.web.servlet.AServlet</servlet-class>
		<init-param>
			<param-name>p1</param-name>
			<param-value>v1</param-value>
		</init-param>
		<init-param>
			<param-name>p2</param-name>
			<param-value>v2</param-value>
		</init-param>
	</servlet>
	
	<servlet-mapping>
		<servlet-name>xxx</servlet-name>
		<url-pattern>/AServlet</url-pattern>
	</servlet-mapping>
	
	
  	<servlet>
		<servlet-name>yyy</servlet-name>
		<servlet-class>cn.itcast.web.servlet.EServlet</servlet-class>
	</servlet>
  <servlet>
    <servlet-name>FServlet</servlet-name>
    <servlet-class>cn.itcast.web.servlet.FServlet</servlet-class>
    <load-on-startup>0</load-on-startup>
  </servlet>

	
	<servlet-mapping>
		<servlet-name>yyy</servlet-name>
		<url-pattern>/EServlet</url-pattern>
	</servlet-mapping>
  <servlet-mapping>
    <servlet-name>FServlet</servlet-name>
    <url-pattern>/FServlet</url-pattern>
  </servlet-mapping>
</web-app>

EServlet extends HttpServlet ：

package cn.itcast.web.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 EServlet extends HttpServlet {
	@Override
	public void doPost(HttpServletRequest req, HttpServletResponse resp)
			throws ServletException, IOException {
		System.out.println("doPost()...");
	}
}

发送get请求：
Javaweb崔希凡---Day9---servlet

改为POST请求：
login.html :

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <title>login.html</title>
	
    <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
    <meta http-equiv="description" content="this is my page">
    <meta http-equiv="content-type" content="text/html; charset=UTF-8">
    
    <!--<link rel="stylesheet" type="text/css" href="./styles.css">-->

  </head>
  
  <body>
    This is my HTML page. <br>
    <form action="/day09_1/EServlet" method="post">
     <input type="submit" value="提交"/>
    </form>
  </body>
</html>

Javaweb崔希凡---Day9---servlet
Javaweb崔希凡---Day9---servlet
直接创建servlet
Javaweb崔希凡---Day9---servlet
Javaweb崔希凡---Day9---servlet
Javaweb崔希凡---Day9---servlet
HttpServlet.java :

public abstract class HttpServlet extends GenericServlet {
    protected void service(HttpServletRequest req, HttpServletResponse resp)
        throws ServletException, IOException {
        ……
}
    @Override
    public void service(ServletRequest req, ServletResponse res)
        throws ServletException, IOException {

        HttpServletRequest  request;
        HttpServletResponse response;

        try {
            request = (HttpServletRequest) req;    //强转
            response = (HttpServletResponse) res;
        } catch (ClassCastException e) {
            throw new ServletException("non-HTTP request or response");
        }
        service(request, response);    //调用上面service()方法
}
……
}

3　doGet()和doPost()

Javaweb崔希凡---Day9---servlet

public class AServlet extends HttpServlet {
	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		System.out.println("hello doGet()...");
	}
}

public class BServlet extends HttpServlet {
	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		System.out.println("hello doPost()...");
	}
}

Servlet细节

Javaweb崔希凡---Day9---servlet

1　Servlet与线程安全

Javaweb崔希凡---Day9---servlet

2　让服务器在启动时就创建Servlet

Javaweb崔希凡---Day9---servlet

	<servlet>
		<servlet-name>hello1</servlet-name>
		<servlet-class>cn.itcast.servlet.Hello1Servlet</servlet-class>
		<load-on-startup>0</load-on-startup>         //在<servlet>中配置<load-on-startup>，其中给出一个非负整数！
	</servlet>
	<servlet-mapping>
		<servlet-name>hello1</servlet-name>
		<url-pattern>/hello1</url-pattern>
	</servlet-mapping>
	<servlet>
		<servlet-name>hello2</servlet-name>
		<servlet-class>cn.itcast.servlet.Hello2Servlet</servlet-class>
		<load-on-startup>1</load-on-startup>
	</servlet>
	<servlet-mapping>
		<servlet-name>hello2</servlet-name>
		<url-pattern>/hello2</url-pattern>
	</servlet-mapping>
	<servlet>
		<servlet-name>hello3</servlet-name>
		<servlet-class>cn.itcast.servlet.Hello3Servlet</servlet-class>
		<load-on-startup>2</load-on-startup>
	</servlet>
	<servlet-mapping>
		<servlet-name>hello3</servlet-name>
		<url-pattern>/hello3</url-pattern>
	</servlet-mapping>

Javaweb崔希凡---Day9---servlet

3　< url-pattern>

Javaweb崔希凡---Day9---servlet

  <servlet-mapping>
    <servlet-name>AServlet</servlet-name>
    <url-pattern>/AServlet</url-pattern>
    <url-pattern>/BServlet</url-pattern>
  </servlet-mapping>

那么这说明一个Servlet绑定了两个URL，无论访问/AServlet还是/BServlet，访问的都是AServlet。
Javaweb崔希凡---Day9---servlet
Javaweb崔希凡---Day9---servlet
Javaweb崔希凡---Day9---servlet

	<servlet>
		<servlet-name>hello1</servlet-name>
		<servlet-class>cn.itcast.servlet.Hello1Servlet</servlet-class>
	</servlet>
	<servlet-mapping>
		<servlet-name>hello1</servlet-name>
		<url-pattern>/servlet/hello1</url-pattern>
	</servlet-mapping>
	<servlet>
		<servlet-name>hello2</servlet-name>
		<servlet-class>cn.itcast.servlet.Hello2Servlet</servlet-class>
	</servlet>
	<servlet-mapping>
		<servlet-name>hello2</servlet-name>
		<url-pattern>/servlet/*</url-pattern>
	</servlet-mapping>

Javaweb崔希凡---Day9---servlet

4　web.xml文件的继承（了解）

Javaweb崔希凡---Day9---servlet
conf/web.xml :

<?xml version="1.0" encoding="ISO-8859-1"?>

<web-app xmlns="http://java.sun.com/xml/ns/javaee"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
                      http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
  version="3.0">
     <servlet>
     <!-- 它的优先级最低，如果一个请求没有人处理，那么它来处理！它显示404。 -->
        <servlet-name>default</servlet-name>
        <!-- 当访问路径不存在时，会执行该Servlet！其实我们在访问index.html时也是在执行这个Servlet。  -->
        <servlet-class>org.apache.catalina.servlets.DefaultServlet</servlet-class>
        <init-param>
            <param-name>debug</param-name>
            <param-value>0</param-value>
        </init-param>
        <init-param>
            <param-name>listings</param-name>
            <param-value>false</param-value>
        </init-param>
        <load-on-startup>1</load-on-startup>
</servlet>

    <servlet>
        <servlet-name>jsp</servlet-name>
        <servlet-class>org.apache.jasper.servlet.JspServlet</servlet-class>
        <init-param>
            <param-name>fork</param-name>
            <param-value>false</param-value>
        </init-param>
        <init-param>
            <param-name>xpoweredBy</param-name>
            <param-value>false</param-value>
        </init-param>
        <load-on-startup>3</load-on-startup>
    </servlet>

    <servlet-mapping>
        <servlet-name>default</servlet-name>
        <!-- 匹配所有URL，也就是说用户访问的URL路径没有匹配的页面时，那么执行的就是名为default的Servlet，即org.apache.catalina.servlets.DefaultServlet -->
        <url-pattern>/</url-pattern>
    </servlet-mapping>

    <servlet-mapping>
        <servlet-name>jsp</servlet-name>
        <!-- 任何URL后缀为jsp的访问，都会执行名为jsp的Servlet，即org.apache.jasper.servlet.JspServlet -->
        <url-pattern>*.jsp</url-pattern>
        <url-pattern>*.jspx</url-pattern>
    </servlet-mapping>

    <session-config>
    <!-- session的默认超时时间为30分钟，后面讲session时再深入。 -->
        <session-timeout>30</session-timeout>
    </session-config>

	<!-- 这里省略了大概4000多行的MIME类型的定义,这里只给出两种MIME类型的定义 -->
	<!-- MIME类型用来标识网络上资源的媒体类型，这里举例为bmp和html两种MIME类型。 -->
    <mime-mapping>
        <extension>bmp</extension>
        <mime-type>image/bmp</mime-type>
    </mime-mapping>
    <mime-mapping>
        <extension>htm</extension>
        <mime-type>text/html</mime-type>
    </mime-mapping>
<!-- 在应用的web.xml中如果没有对<welcome-file-list>进行覆盖，那么默认主页为index.html、index.html、index.jsp -->
    <welcome-file-list>
        <welcome-file>index.html</welcome-file>
        <welcome-file>index.htm</welcome-file>
        <welcome-file>index.jsp</welcome-file>
    </welcome-file-list>
</web-app>

ServletContext（重要）

Javaweb崔希凡---Day9---servlet

1　ServletContext概述

Javaweb崔希凡---Day9---servlet

2　获取ServletContext

Javaweb崔希凡---Day9---servlet
Javaweb崔希凡---Day9---servlet

public class MyServlet implements Servlet {
	public void init(ServletConfig config) {
	    ServletContext context = config.getServletContext();
	}
…
}


public class MyServlet extends HttpServlet {
	public void doGet(HttpServletRequest request, HttpServletResponse response) {
	    ServletContext context = this.getServletContext();
	}
}

3　域对象的功能

域对象就是用来在多个Servlet中传递数据！！！
——域对象必须有要存数据功能
——域对象必须要有取数据功能
域对象内部其实有一个Map

Javaweb崔希凡---Day9---servlet
Javaweb崔希凡---Day9---servlet
web.xml :

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5" 
	xmlns="http://java.sun.com/xml/ns/javaee" 
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
	xsi:schemaLocation="http://java.sun.com/xml/ns/javaee 
	http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
  <display-name></display-name>
  <servlet>
    <servlet-name>AServlet</servlet-name>
    <servlet-class>cn.itcast.servlet.AServlet</servlet-class>
  </servlet>
  <servlet>
    <servlet-name>BServlet</servlet-name>
    <servlet-class>cn.itcast.servlet.BServlet</servlet-class>
  </servlet>
  <servlet>
    <servlet-name>CServlet</servlet-name>
    <servlet-class>cn.itcast.servlet.CServlet</servlet-class>
  </servlet>
  <servlet>
    <servlet-name>DServlet</servlet-name>
    <servlet-class>cn.itcast.servlet.DServlet</servlet-class>
  </servlet>




  <servlet-mapping>
    <servlet-name>AServlet</servlet-name>
    <url-pattern>/AServlet</url-pattern>
  </servlet-mapping>
  <servlet-mapping>
    <servlet-name>BServlet</servlet-name>
    <url-pattern>/BServlet</url-pattern>
  </servlet-mapping>
  <servlet-mapping>
    <servlet-name>CServlet</servlet-name>
    <url-pattern>/CServlet</url-pattern>
  </servlet-mapping>
  <servlet-mapping>
    <servlet-name>DServlet</servlet-name>
    <url-pattern>/DServlet</url-pattern>
  </servlet-mapping>	
  <welcome-file-list>
    <welcome-file>index.jsp</welcome-file>
  </welcome-file-list>
  
  
  
  <context-param>
  	<param-name>context-param</param-name>
  	<param-value>context-value</param-value>
  </context-param>
</web-app>

AServlet.java :

package cn.itcast.servlet;

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;

/**
 * 演示向Servletcontext中保存数据
 * @author cxf
 *
 */
public class AServlet extends HttpServlet {

	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		/*
		 * 1. 获取ServletContext对象
		 * 2. 调用其setAttribute()方法完成保存数据
		 */
		ServletContext application = this.getServletContext();
		application.setAttribute("name", "张三");
	}
}

BServlet.java :

package cn.itcast.servlet;

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;

/**
 * 演示从ServletContext中获取数据
 */
public class BServlet extends HttpServlet {

	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		/*
		 * 1. 获取ServletContext对象
		 * 2. 调用其getAttribute()方法完成获取数据
		 */
		ServletContext application = this.getServletContext();
		String name = (String)application.getAttribute("name");
		System.out.println(name);
	}
}

4　获取应用初始化参数

Javaweb崔希凡---Day9---servlet
还可以使用ServletContext来获取在web.xml文件中配置的应用初始化参数！注意，应用初始化参数与Servlet初始化参数不同：

web.xml :

<web-app ...>
  ...
  <context-param>
	<param-name>paramName1</param-name>
	<param-value>paramValue1</param-value>  	
  </context-param>
  <context-param>
	<param-name>paramName2</param-name>
	<param-value>paramValue2</param-value>  	
  </context-param>
</web-app>




		ServletContext context = this.getServletContext();
		String value1 = context.getInitParameter("paramName1");
		String value2 = context.getInitParameter("paramName2");
		System.out.println(value1 + ", " + value2);
		
		Enumeration names = context.getInitParameterNames();
		while(names.hasMoreElements()) {
			System.out.println(names.nextElement());
		}

5　获取资源相关方法

Javaweb崔希凡---Day9---servlet
Javaweb崔希凡---Day9---servlet
Javaweb崔希凡---Day9---servlet
Javaweb崔希凡---Day9---servlet

package cn.itcast.servlet;

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

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

/**
 * 使用ServletContext获取资源路径
 * @author cxf
 *
 */
public class DServlet extends HttpServlet {

	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		/*
		 * 它得到的是有盘符的路径：F:/xxx/xxx/xx/
		 * F:\JavaEE20140508\apache-tomcat-7.0.42\webapps\day09_2\index.jsp
		 */
		String path = this.getServletContext().getRealPath("/index.jsp");
		System.out.println(path);
		
		/*
		 * 获取资源的路径后，再创建出输入流对象！
		 */
		InputStream input = this.getServletContext().getResourceAsStream("/index.jsp");
		
		/*
		 * 获取当前路径下所有资源的路径！
		 */
		Set<String> paths = this.getServletContext().getResourcePaths("/WEB-INF");
		System.out.println(paths);
	}
}

6　练习：访问量统计

Javaweb崔希凡---Day9---servlet
Javaweb崔希凡---Day9---servlet
相信各位一定见过很多访问量统计的网站，即“本页面被访问过XXX次”。

因为无论是哪个用户访问指定页面，都会累计访问量，所以这个访问量统计应该是整个项目共享的！

很明显，这需要使用ServletContext来保存访问量。

package cn.itcast.servlet;

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

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

/**
 * 统计访问量
 * @author cxf
 *
 */
public class AServlet extends HttpServlet {

	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		/*
		 * 1. 获取ServletContext对象
		 * 2. 从ServletContext对象中获取名为count的属性
		 *   3. 如果存在：给访问量加1，然后再保存回去；
		 *   4. 如果不存在：说明是第一次访问，向Servletcontext中保存名为count的属性，值为1
		 */
		ServletContext app = this.getServletContext();
		Integer count = (Integer)app.getAttribute("count");
		if(count == null) {
			app.setAttribute("count", 1);
		} else {
			app.setAttribute("count", count+1);
		}
		
		/*
		 * 向浏览器输出
		 *   需要使用响应对象！
		 */
		response.setContentType("text/html;charset=utf-8");
		response.getWriter().print("<h1>本页面一共被访问" + count + "次！</h1>");
		app.setAttribute("count", count);
	}
}

获取类路径下资源

Javaweb崔希凡---Day9---servlet
　这里要讲的是获取类路径下的资源，对于JavaWeb应用而言，就是获取classes目录下的资源。
　Javaweb崔希凡---Day9---servlet

		InputStream in = this.getClass().getResourceAsStream("/xxx.txt");
		System.out.println(IOUtils.toString(in));


		InputStream in = this.getClass().getClassLoader().getResourceAsStream("xxx.txt");
		System.out.println(IOUtils.toString(in));

Javaweb崔希凡---Day9---servlet

package cn.itcast.servlet;

import java.io.IOException;
import java.io.InputStream;

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

import org.apache.commons.io.IOUtils;

/**
 * 演示获取类路径下的资源
 * @author cxf
 *
 */
public class AServlet extends HttpServlet {

	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		/*
		 * 1. 得到ClassLoader
		 *   > 先得到Class，再得到ClassLoader
		 * 2. 调用其getResourceAsStream()，得到一个InputStream
		 */
//		ClassLoader cl = this.getClass().getClassLoader();
		// 相对/classes
//		InputStream input = cl.getResourceAsStream("cn/itcast/servlet/a.txt");
		
		Class c = this.getClass();
		// 相对当前.class文件所在目录！
//		InputStream input = c.getResourceAsStream("a.txt");
		
		// 相对classes下！
//		InputStream input = c.getResourceAsStream("/a.txt");
		
		InputStream input = c.getResourceAsStream("/../../index.jsp");
		
		String s = IOUtils.toString(input);//读取输入流内容，转换成字符串返回
		System.out.println(s);
	}

}

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