160909、Filter多方式拦截、禁用IE图片缓存、Filter设置字符编码

时间：2023-03-08 22:00:19

dispatcher多方式拦截

我们来看一个例子

我们定义一个index.jsp，里面有一个链接跳转到dispatcher.jsp页面

<body>

    <a href="dispatcher.jsp">To Test Page</a>

</body>

我们来看下dispatcher.jsp页面，转发到test.jsp页面

<body>

    <jsp:forward page="/test.jsp"></jsp:forward>

</body>

我们来看下test.jsp页面，仅仅输入一行文字而已

<body>

    Test Page

</body>

当dispatcher.jsp页面，转发到test.jsp页面，我们是做2个拦截filter，我们看下web.xml中的配置吧

<filter>

        <filter-name>HelloFilter</filter-name>

        <filter-class>com.safly.HelloFilter</filter-class>

    </filter>

    <filter-mapping>

        <filter-name>HelloFilter</filter-name>

        <url-pattern>/test.jsp</url-pattern>

    </filter-mapping>

    <filter>

        <filter-name>SecondFilter</filter-name>

        <filter-class>com.safly.SecondFilter</filter-class>

    </filter>

    <filter-mapping>

        <filter-name>SecondFilter</filter-name>

        <url-pattern>/test.jsp</url-pattern>

    </filter-mapping>

Filter过滤器对应的实例代码如下： 
HelloFilter

package com.safly;

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;

public class HelloFilter implements Filter {

    public void destroy() {

    }

    public void doFilter(ServletRequest request, ServletResponse response,

            FilterChain chain) throws IOException, ServletException {

        System.out.println("before helloFilter'chain");

        chain.doFilter(request, response);

        System.out.println("after hellofilter'chain");

    }

    public void init(FilterConfig filterConfig) throws ServletException {

    }

}

SecondFilter

package com.safly;

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;

public class SecondFilter implements Filter {

    public void destroy() {

    }

    public void doFilter(ServletRequest request, ServletResponse response,

            FilterChain chain) throws IOException, ServletException {

        System.out.println("before secondFilter'chain");

        chain.doFilter(request, response);

        System.out.println("after secondFilter'chain");

    }

    public void init(FilterConfig filterConfig) throws ServletException {

    }

}

160909、Filter多方式拦截、禁用IE图片缓存、Filter设置字符编码 
我们点击上面的连接地址 
160909、Filter多方式拦截、禁用IE图片缓存、Filter设置字符编码

咦为啥？为什么没有起到拦截作用呢？ 
160909、Filter多方式拦截、禁用IE图片缓存、Filter设置字符编码

原来默认的是Request方式，点击链接是转发的方式，那么我们怎么实现转发的方式，也通过过滤器拦截呢？我们只需要在web.xml文件中，进行修改，对SecondFilter和HelloFilter均做处理

<filter>

        <filter-name>HelloFilter</filter-name>

        <filter-class>com.safly.HelloFilter</filter-class>

    </filter>

    <filter-mapping>

        <filter-name>HelloFilter</filter-name>

        <url-pattern>/test.jsp</url-pattern>

        <dispatcher>FORWARD</dispatcher>

        <dispatcher>REQUEST</dispatcher>

        <dispatcher>INCLUDE</dispatcher>

        <dispatcher>ERROR</dispatcher>

    </filter-mapping>

    <filter>

        <filter-name>SecondFilter</filter-name>

        <filter-class>com.safly.SecondFilter</filter-class>

    </filter>

    <filter-mapping>

        <filter-name>SecondFilter</filter-name>

        <url-pattern>/test.jsp</url-pattern>

        <dispatcher>FORWARD</dispatcher>

        <dispatcher>REQUEST</dispatcher>

        <dispatcher>INCLUDE</dispatcher>

        <dispatcher>ERROR</dispatcher>

    </filter-mapping>

160909、Filter多方式拦截、禁用IE图片缓存、Filter设置字符编码

before helloFilter'chain

before secondFilter'chain

after secondFilter'chain

after hellofilter'chain

我们在进行修改，只对SecondFilter做处理

<filter>

        <filter-name>HelloFilter</filter-name>

        <filter-class>com.safly.HelloFilter</filter-class>

    </filter>

    <filter-mapping>

        <filter-name>HelloFilter</filter-name>

        <url-pattern>/test.jsp</url-pattern>

    </filter-mapping>

    <filter>

        <filter-name>SecondFilter</filter-name>

        <filter-class>com.safly.SecondFilter</filter-class>

    </filter>

    <filter-mapping>

        <filter-name>SecondFilter</filter-name>

        <url-pattern>/test.jsp</url-pattern>

        <dispatcher>FORWARD</dispatcher>

        <dispatcher>REQUEST</dispatcher>

        <dispatcher>INCLUDE</dispatcher>

        <dispatcher>ERROR</dispatcher>

    </filter-mapping>

160909、Filter多方式拦截、禁用IE图片缓存、Filter设置字符编码

before secondFilter'chain

after secondFilter'chain

解决ie浏览器图片缓存的问题 
ie模式是图片缓存的，那么我们怎么设置无缓存呢？ 
160909、Filter多方式拦截、禁用IE图片缓存、Filter设置字符编码

我们定义一个b.jsp,里面有一个超链接，跳转到a.jsp

<body>

    <a href="a.html">TO AAA PAGE</a>

</body>

我们再来看下a.jsp

<body>

    <a href="b.html">TO BBB PAGE</a>

    <img alt="" src="Desert.jpg">

</body>

默认ie是自带缓存的，我们需要定义Filter过滤器进行设置，那我们先看下web.xml中的过滤器设置吧

  <filter>

    <display-name>NoCacheFilter</display-name>

    <filter-name>NoCacheFilter</filter-name>

    <filter-class>com.safly.NoCacheFilter</filter-class>

  </filter>

  <filter-mapping>

    <filter-name>NoCacheFilter</filter-name>

    <url-pattern>/cache/*</url-pattern>

  </filter-mapping>

/cache/*代表对cache目录下的所有页面进行设置操作

HttpFilter

package com.safly;

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;

/**

 * 自定义的 HttpFilter, 实现自 Filter 接口

 */

public abstract class HttpFilter implements Filter {

    /**

     * 用于保存 FilterConfig 对象.

     */

    private FilterConfig filterConfig;

    /**

     * 不建议子类直接覆盖. 若直接覆盖, 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() {}

    /**

     * 直接返回 init(ServletConfig) 的 FilterConfig 对象

     */

    public FilterConfig getFilterConfig() {

        return filterConfig;

    }

    /**

     * 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 request, HttpServletResponse response, FilterChain filterChain)

     *

     * 若编写 Filter 的过滤方法不建议直接继承该方法. 而建议继承

     * doFilter(HttpServletRequest request, HttpServletResponse response,

     *      FilterChain filterChain) 方法

     */

    @Override

    public void doFilter(ServletRequest req, ServletResponse resp,

            FilterChain chain) throws IOException, ServletException {

        HttpServletRequest request = (HttpServletRequest) req;

        HttpServletResponse response = (HttpServletResponse) resp;

        doFilter(request, response, chain);

    }

    public abstract void doFilter(HttpServletRequest request, HttpServletResponse response,

            FilterChain filterChain) throws IOException, ServletException;

    @Override

    public void destroy() {}

}

NoCacheFilter

package com.safly;

import java.io.IOException;

import javax.servlet.FilterChain;

import javax.servlet.ServletException;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

public class NoCacheFilter extends HttpFilter {

    @Override

    public void doFilter(HttpServletRequest request,

            HttpServletResponse response, FilterChain filterChain)

            throws IOException, ServletException {

        System.out.println("cacheFilter's doFilter..");

        response.setDateHeader("Expires",-1);

        response.setHeader("Cache-Control","no-cache");

        response.setHeader("Pragma","no-cache");

        filterChain.doFilter(request, response);

    }

}

这样就实现了ie浏览器的非缓存设置

过滤器-字符编码

160909、Filter多方式拦截、禁用IE图片缓存、Filter设置字符编码

a.jsp输入name提交到b.jsp

<body>

    <form action="b.jsp" method="post">

        name: <input type="text" name="name"/>

        <input type="submit" value="Submit"/>

    </form>

</body>

b.jsp显示输入的用户名

<body>

    Hello: ${param.name }

</body>

如果输入中文字符可能出现乱码，如下的情况 
160909、Filter多方式拦截、禁用IE图片缓存、Filter设置字符编码

我们需要进行过滤器设置

    <context-param>

        <param-name>encoding</param-name>

        <param-value>UTF-8</param-value>

    </context-param>

    <filter>

        <filter-name>EncodingFilter</filter-name>

        <filter-class>com.safly.EncodingFilter</filter-class>

    </filter>

    <filter-mapping>

        <filter-name>EncodingFilter</filter-name>

        <url-pattern>/encoding/*</url-pattern>

    </filter-mapping>

EncodingFilter

package com.safly;

import java.io.IOException;

import javax.servlet.FilterChain;

import javax.servlet.ServletException;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

public class EncodingFilter extends HttpFilter{

    private String encoding;

    @Override

    protected void init() {

        encoding = getFilterConfig().getServletContext().getInitParameter("encoding");

    }

    @Override

    public void doFilter(HttpServletRequest request,

            HttpServletResponse response, FilterChain filterChain)

            throws IOException, ServletException {

        System.out.println(encoding);

        request.setCharacterEncoding(encoding);

        filterChain.doFilter(request, response);

    }

}

依然用上例进制浏览器图片缓存的HttpFilter基类 
160909、Filter多方式拦截、禁用IE图片缓存、Filter设置字符编码 
浏览器输出 
160909、Filter多方式拦截、禁用IE图片缓存、Filter设置字符编码