代码来之哪里,不记得了

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GzipFilter

public class GzipFilter implements Filter {

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("过滤器被执行了");
    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response,
            FilterChain chain) throws IOException, ServletException {

        //1.对response进行改进
        MyResponse resp = new MyResponse((HttpServletResponse) response);       

        //2.放行，让后台做response做输出操作
        chain.doFilter(request, resp);

        //3.从我们定义的“字节数组输出流”中取出数据进行压缩
        ByteArrayOutputStream baout = resp.getBaout();
        byte bs[] = baout.toByteArray();// 源字节数据
        System.out.println("压缩前大小:" + bs.length);
        
        ByteArrayOutputStream zipBaout = new ByteArrayOutputStream();
        GZIPOutputStream gout = new GZIPOutputStream(zipBaout);
        gout.write(bs);// 把数据压缩到baout中
        gout.close();
        
        bs = zipBaout.toByteArray();//得到压缩后的字节
        System.out.println("压缩后大小:" + bs.length);
        
        //4.再用原生的reponse输出压缩后的内容
        HttpServletResponse httpResp = (HttpServletResponse) response;
        // 输出之前告诉客户端:我们的数据是gzip格式，然后输出
        httpResp.setHeader("Content-Encoding", "gzip");
        httpResp.setContentLength(bs.length);
        OutputStream out = httpResp.getOutputStream();
        out.write(bs);
        
    }

    @Override
    public void destroy() {
        
    }

}

class MyResponse extends HttpServletResponseWrapper { //HttpServletResponse实现类
    private PrintWriter pw;
    private ByteArrayOutputStream baout = new ByteArrayOutputStream();
    /*
     * 字节数组输了流(带缓存功能)：所有发送到输出流的数据保存在该字节数组缓冲区中,可以转成字节数组
     * 在此的作用：为了将response输出的内容先存到字节数组缓冲区中,以便后续的压缩处理*/
    
    public MyResponse(HttpServletResponse response) {
        super(response);
    }

    //重新实现response的该方法
    public ServletOutputStream getOutputStream() throws IOException {
        return new MyOutputStream(baout);
    }

    public ByteArrayOutputStream getBaout() {
        if(pw!=null){
            pw.flush();
            //这里很重要，如果不flush或close，不把字符流刷出去，baout中是不会有数据的.
        }
        return baout;
    }
    
    //重新实现response的该方法
    public PrintWriter getWriter() throws IOException {
        //字节流转字符流
        pw = new PrintWriter(new OutputStreamWriter(baout, "utf-8"),true);
        return pw;
    }

}

/**
 * 自定义ServletOutputStream子类
 * 目的：保证response获取到的outputStream是我们定义的“字节数组输入流”
 * ,且调用write方法时,是往“字节数组输入流”的缓存区中写入*/
class MyOutputStream extends ServletOutputStream {
    private ByteArrayOutputStream baout = null;

    public MyOutputStream(ByteArrayOutputStream baout) {
        this.baout = baout;
    }

    @Override
    public void write(int b) throws IOException {
        baout.write(b);//把指定内容写入到 字节数组输入流
    }
}

测试servlet

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

//      String str = "go go go let's go";
//      //1\获取字节数组
//      byte[] bytes = str.getBytes() ;
//      
//      System.out.println("压缩前的长度：" + bytes.length); 
//      //2\
//      ByteArrayOutputStream baos = new ByteArrayOutputStream() ; 
//      GZIPOutputStream  gzip = new GZIPOutputStream(baos) ;
//      
//      gzip.write(bytes) ; 
//      gzip.close() ;
//      //3\
//      bytes = baos.toByteArray() ;
//      System.out.println("压缩后的长度：" + bytes.length);
        

    
        response.setContentType("text/html;charset=utf-8");
        String str = "And I memorize each word我记住的每个字眼";
        
        OutputStream out = response.getOutputStream();
        out.write(str.getBytes("utf-8"));
        
        //response.getWriter().write(str);
    }