将响应数据进行压缩处理的过滤器（CompressionFilter）

功能描述

        如果浏览器支持 gzip 压缩格式的数据，则将响应的数据使用 gzip 压缩后再输出。

使用方法

        在 java web 项目的 web.xml 文件中添加如下代码。

<!--压缩过滤器的配置  开始 -->

 <filter>

 <filter-name>CompressionFilter</filter-name>

 <filter-class>com.hmw.filter.CompressionFilter</filter-class>

 </filter>

  

 <filter-mapping>

 <filter-name>CompressionFilter</filter-name>

   <servlet-name>/LongServlet</servlet-name>

 </filter-mapping>

<!--压缩过滤器的配置  结束 -->

过滤器源码

CompressionFilter.java

package com.hmw.filter;

 

import java.io.ByteArrayOutputStream;

import java.io.IOException;

import java.io.OutputStream;

import java.io.OutputStreamWriter;

import java.util.zip.GZIPOutputStream;

 

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;

 

/**

 * 压缩过滤器 <br>

 * 如果浏览器支持 gzip 压缩格式的数据，则将响应的数据使用 gzip 压缩后再输出。

 */

public class CompressionFilter implements Filter {

 

    @Override

    public void init(FilterConfig config) throws ServletException {

    }

 

    /**

     * 如果浏览器不支持 gzip 压缩，则不做直接放行（不做压缩处理）<br>

     * 反之，将HTTP响应头的编码设置为 <code>gzip</code>，然后将响应数据使用 gzip 进行压缩处理。

     */

    @Override

    public void doFilter(ServletRequest request, ServletResponse response,

            FilterChain chain) throws ServletException, IOException {

        HttpServletRequest req = (HttpServletRequest) request;

        HttpServletResponse res = (HttpServletResponse) response;

 

        if (!isGzipSupported(req)) { // Invoke resource normally.

            chain.doFilter(req, res);

            return;

        }

 

        // 将响应头信息中的内容编码设置为 gzip

        res.setHeader("Content-Encoding", "gzip");

         

        // 调用资源，使用 CharArrayWrapper 包装输出

        CharArrayWrapper responseWrapper = new CharArrayWrapper(res);

        chain.doFilter(req, responseWrapper);

        // 取得存放输出数据的 char 型数组

        char[] responseChars = responseWrapper.toCharArray();

         

        // 将响应数据压缩后存入一个 byte 型的数组，然后输出到

        ByteArrayOutputStream byteStream = new ByteArrayOutputStream();

        GZIPOutputStream zipOut = new GZIPOutputStream(byteStream);

        OutputStreamWriter tempOut = new OutputStreamWriter(zipOut);

        // 将原来的响应数据压缩后写入二字节输出流

        tempOut.write(responseChars);

        // 关闭输出流

        tempOut.close();

 

        // 更新响应头信息中 Content-Length 的值。

        res.setContentLength(byteStream.size());

        // 将压缩后的数据发送至客户端

        OutputStream realOut = res.getOutputStream();

        byteStream.writeTo(realOut);

    }

 

    @Override

    public void destroy() {

    }

 

    /**

     * 检测浏览器是否支持 Gzip 压缩

     *

     * @param req HTTP 请求对象

     * @return 如果浏览器支持 Gzip 压缩，则返回 true，反之，则返回 false

     */

    private boolean isGzipSupported(HttpServletRequest req) {

        String browserEncodings = req.getHeader("Accept-Encoding");

        return ((browserEncodings != null) && (browserEncodings.indexOf("gzip") != -1));

    }

}

CharArrayWrapper.java

package com.hmw.filter;

 

import java.io.CharArrayWriter;

import java.io.PrintWriter;

 

import javax.servlet.http.HttpServletResponse;

import javax.servlet.http.HttpServletResponseWrapper;

 

/**

 * A response wrapper that takes everything the client would normally output and

 * saves it in one big character array.

 */

public class CharArrayWrapper extends HttpServletResponseWrapper {

    private CharArrayWriter charWriter;

 

    /**

     * Initializes wrapper.

     * <P>

     * First, this constructor calls the parent constructor. That call is

     * crucial so that the response is stored and thus setHeader, *setStatus,

     * addCookie, and so forth work normally.

     * <P>

     * Second, this constructor creates a CharArrayWriter that will be used to

     * accumulate the response.

     */

    public CharArrayWrapper(HttpServletResponse response) {

        super(response);

        charWriter = new CharArrayWriter();

    }

 

    /**

     * When servlets or JSP pages ask for the Writer, don't give them the real

     * one. Instead, give them a version that writes into the character array.

     * The filter needs to send the contents of the array to the client (perhaps

     * after modifying it).

     */

    @Override

    public PrintWriter getWriter() {

        return new PrintWriter(charWriter);

    }

 

    /**

     * Get a String representation of the entire buffer.

     * <P>

     * Be sure <B>not</B> to call this method multiple times on the same

     * wrapper. The API for CharArrayWriter does not guarantee that it

     * "remembers" the previous value, so the call is likely to make a new

     * String every time.

     */

    @Override

    public String toString() {

        return charWriter.toString();

    }

 

    /** Get the underlying character array. */

    public char[] toCharArray() {

        return charWriter.toCharArray();

    }

}