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

發(fā)布時間：2024/8/24 编程问答 40 如意码农

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dispatcher多方式攔截

我們來看一個例子

我們定義一個index.jsp，里面有一個鏈接跳轉(zhuǎn)到dispatcher.jsp頁面

<body>

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

</body>

我們來看下dispatcher.jsp頁面，轉(zhuǎn)發(fā)到test.jsp頁面

<body>

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

</body>

我們來看下test.jsp頁面，僅僅輸入一行文字而已

<body>

    Test Page

</body>

當(dāng)dispatcher.jsp頁面，轉(zhuǎn)發(fā)到test.jsp頁面，我們是做2個攔截filter，我們看下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過濾器對應(yīng)的實例代碼如下：
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 {

    }

}

我們點擊上面的連接地址

咦為啥？為什么沒有起到攔截作用呢？

原來默認(rèn)的是Request方式，點擊鏈接是轉(zhuǎn)發(fā)的方式，那么我們怎么實現(xiàn)轉(zhuǎn)發(fā)的方式，也通過過濾器攔截呢？我們只需要在web.xml文件中，進(jìn)行修改，對SecondFilter和HelloFilter均做處理

<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>

before helloFilter'chain

before secondFilter'chain

after secondFilter'chain

after hellofilter'chain

我們在進(jìn)行修改，只對SecondFilter做處理

<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>

before secondFilter'chain

after secondFilter'chain

解決ie瀏覽器圖片緩存的問題
ie模式是圖片緩存的，那么我們怎么設(shè)置無緩存呢？

我們定義一個b.jsp,里面有一個超鏈接，跳轉(zhuǎn)到a.jsp

<body>

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

</body>

我們再來看下a.jsp

<body>

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

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

</body>

默認(rèn)ie是自帶緩存的，我們需要定義Filter過濾器進(jìn)行設(shè)置，那我們先看下web.xml中的過濾器設(shè)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/*代表對cache目錄下的所有頁面進(jìn)行設(shè)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;

/**

 * 自定義的 HttpFilter, 實現(xiàn)自 Filter 接口

 */

public abstract class HttpFilter implements Filter {

    /**

     * 用于保存 FilterConfig 對象.

     */

    private FilterConfig filterConfig;

    /**

     * 不建議子類直接覆蓋. 若直接覆蓋, 將可能會導(dǎo)致 filterConfig 成員變量初始化失敗

     */

    @Override

    public void init(FilterConfig filterConfig) throws ServletException {

        this.filterConfig = filterConfig;

        init();

    }

    /**

     * 供子類繼承的初始化方法. 可以通過 getFilterConfig() 獲取 FilterConfig 對象.

     */

    protected void init() {}

    /**

     * 直接返回 init(ServletConfig) 的 FilterConfig 對象

     */

    public FilterConfig getFilterConfig() {

        return filterConfig;

    }

    /**

     * 原生的 doFilter 方法, 在方法內(nèi)部把 ServletRequest 和 ServletResponse

     * 轉(zhuǎn)為了 HttpServletRequest 和 HttpServletResponse, 并調(diào)用了

     * doFilter(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain)

     *

     * 若編寫 Filter 的過濾方法不建議直接繼承該方法. 而建議繼承

     * 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);

    }

}

這樣就實現(xiàn)了ie瀏覽器的非緩存設(shè)置

過濾器-字符編碼

a.jsp輸入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顯示輸入的用戶名

<body>

    Hello: ${param.name }

</body>

如果輸入中文字符可能出現(xiàn)亂碼，如下的情況

我們需要進(jìn)行過濾器設(shè)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);

    }

}

依然用上例進(jìn)制瀏覽器圖片緩存的HttpFilter基類

瀏覽器輸出

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