javaWEB总结(31):禁用游览器缓存的过滤器

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本文介绍了一种通过添加自定义过滤器来禁用浏览器缓存的方法。通过在web.xml中配置Cache过滤器，并在Cache类中设置HTTP响应头，可以有效地避免浏览器缓存静态资源，确保用户看到的是最新的页面内容。

前提

项目结构

web.xml

<?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_3_0.xsd" id="WebApp_ID" version="3.0">
  <display-name>javaWeb_31</display-name>
  <welcome-file-list>
    <welcome-file>a.jsp</welcome-file>
  </welcome-file-list>
</web-app>

a.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!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>A.jsp</title>
</head>
<body>

	<a href="b.jsp">TO B.jsp</a><br><br>
	<img alt="" src="<%=request.getContextPath()%>/img/a.jpg">
</body>
</html>

b.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!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>B.jsp</title>
</head>
<body>

	<a href="a.jsp">TO A.jsp</a><br><br>
	<img alt="" src="<%=request.getContextPath()%>/img/b.jpg">
</body>
</html>

运行结果

当我们修改a.jsp后

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!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>A.jsp</title>
</head>
<body>

	<a href="b.jsp">TO B.jsp</a><br><br>
	<img alt="" src="<%=request.getContextPath()%>/img/b.jpg">
</body>
</html>

图片依旧不变。

添加过滤器

项目结构

修改的页面web.xml

<?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_3_0.xsd" id="WebApp_ID" version="3.0">
  <display-name>javaWeb_31</display-name>
  <welcome-file-list>
    <welcome-file>a.jsp</welcome-file>
  </welcome-file-list>
  
  <filter>
      <filter-name>Cache</filter-name>
      <filter-class>com.dao.chu.Cache</filter-class>
  </filter>
  
  <filter-mapping>
      <filter-name>Cache</filter-name>
      <url-pattern>/*</url-pattern>
  </filter-mapping>
  
</web-app>

添加的类

HttpFilter.java

package com.dao.chu;

import java.io.IOException;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * 
 * <p>
 * Title: HttpFilter
 * </p>
 * <p>
 * Description: http请求定制Filter
 * </p>
 */
public abstract class HttpFilter implements Filter {

	/**
	 * 用于保存init(FilterConfig filterConfig)的FilterConfig对象
	 */
	private FilterConfig filterConfig;

	/**
	 * 直接返回init(FilterConfig filterConfig)的FilterConfig对象
	 */
	public FilterConfig getFilterConfig() {
		return filterConfig;
	}

	/**
	 * 不建议子类直接覆盖，将可能会导致filterConfig成员变量初始化失败
	 */
	@Override
	public void init(FilterConfig filterConfig) throws ServletException {

		this.filterConfig = filterConfig;
		init();

	}

	/**
	 * 供子类继承的初始化方法，可以通过getFilterConfig获取FilterConfig对象
	 */
	protected void init() {}

	/**
	 * 原生的doFilter方法，在方法内部把ServletRequest和ServletResponse
	 * 转为了HttpServletRequest和HttpServletResponse并调用了 doFilter(HttpServletRequest
	 * httpRequest, HttpServletResponse httpResponse, FilterChain chain)方法
	 * 
	 * 
	 * 若编写Filter的过滤方法不建议直接继承该方法，而应该继承doFilter(ServletRequest request,
	 * ServletResponse response, FilterChain chain)
	 */
	@Override
	public void doFilter(ServletRequest request, ServletResponse response,
			FilterChain chain) throws IOException, ServletException {

		HttpServletRequest httpRequest = (HttpServletRequest) request;
		HttpServletResponse httpResponse = (HttpServletResponse) response;

		doFilter(httpRequest, httpResponse, chain);

	}

	/**
	 * 抽象方法，为http请求定制，必需实现的方法
	 * 
	 */
	public abstract void doFilter(HttpServletRequest httpRequest,
			HttpServletResponse httpResponse, FilterChain chain)
			throws IOException, ServletException;

	/**
	 * 空的destroy方法
	 */
	@Override
	public void destroy() {}

}

Cache.java

package com.dao.chu;

import java.io.IOException;

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

public class Cache extends HttpFilter {

	@Override
	public void doFilter(HttpServletRequest httpRequest,
			HttpServletResponse httpResponse, FilterChain chain)
			throws IOException, ServletException {
		
		System.out.println("cache doFilter");
		
		httpResponse.setDateHeader("Expires", -1); // for IE
		httpResponse.setHeader("Cache-Control", "no-cache"); // for 火狐 或 其他。
		httpResponse.setHeader("Pragma", "no-cache"); // for 火狐 或 其他。
		
		chain.doFilter(httpRequest, httpResponse);
	}


}

添加完此过滤器后即可禁用游览器缓存的过滤器。