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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。

      
      
     
      CompressionFilter
       
     
      com.hmw.filter.CompressionFilter
       
        
      
     
      CompressionFilter
       	
     
      /LongServlet
       
     
    

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  * 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。 *  * @author  */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）      * 反之，将HTTP响应头的编码设置为 gzip，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.	 * 
	 * 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.	 * 
	 * 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.	 * 
	 * Be sure not 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();	}}