但是启用了gzip压缩过滤器的话（也是本书中的例子）异步处理结果不显示，Java代码  ：

@WebServlet(name="AsyncServlet", urlPatterns={"/async.do"},  
    asyncSupported=true  
)  
public class AsyncServlet extends HttpServlet {  
      
    private ExecutorService executorService = Executors.newFixedThreadPool(10);  
      
    @Override  
    protected void doGet(HttpServletRequest request, HttpServletResponse response)  
                throws ServletException, IOException{  
        response.setContentType("text/html;charset=UTF-8");  
        AsyncContext actx = request.startAsync();  
        executorService.submit(new AsyncRequest(actx));  
    }  
      
    @Override  
    public void destroy(){  
        executorService.shutdown();  
    }  
}  

AsyncRequest代码如下：

public class AsyncRequest implements Runnable {  
  
    private AsyncContext actx;  
      
    public AsyncRequest(AsyncContext actx){  
        this.actx = actx;  
    }  
      
    @Override  
    public void run() {  
        try {  
            Thread.sleep(5000);  
            PrintWriter out = actx.getResponse().getWriter();  
            out.println("久等了。。。。这是异步执行的结果");  
            out.close();  
            actx.complete();  
        } catch (Exception e) {  
             e.printStackTrace();      
        }  
    }  
  
}  

CompressionFilter如下：

/*@WebFilter(filterName="CompressionFilter", urlPatterns={"/*"}, 
    asyncSupported=true 
)*/  
public class CompressionFilter implements Filter {  
    public void init(FilterConfig filterConfig) {}  
  
    public void doFilter(ServletRequest request,  
                              ServletResponse response,  
                            FilterChain chain)  
            throws IOException, ServletException {  
        HttpServletRequest req = (HttpServletRequest) request;  
        HttpServletResponse res = (HttpServletResponse) response;  
  
        String encodings = req.getHeader("accept-encoding");  
        if ((encodings != null) && (encodings.indexOf("gzip") > -1)) {  
            CompressionWrapper responseWrapper =  
                    new CompressionWrapper(res);  
            responseWrapper.setHeader("content-encoding", "gzip");  
  
            chain.doFilter(request, responseWrapper);  
  
            GZIPOutputStream gzipOutputStream =  
                    responseWrapper.getGZIPOutputStream();  
            if (gzipOutputStream != null) {  
                gzipOutputStream.finish();  
            }  
        }  
        else {  
            chain.doFilter(request, response);  
        }  
    }  
  
    public void destroy() {}  
}  

wrapper代码如下：

public class CompressionWrapper  
                            extends HttpServletResponseWrapper {  
    private GZipServletOutputStream gzServletOutputStream;  
    private PrintWriter printWriter;  
  
    public CompressionWrapper(HttpServletResponse resp) {  
        super(resp);  
    }  
  
    @Override  
    public ServletOutputStream getOutputStream() throws IOException {  
        if(printWriter != null) {  
            throw new IllegalStateException();  
        }  
        if (gzServletOutputStream == null) {  
            gzServletOutputStream = new GZipServletOutputStream(  
                    getResponse().getOutputStream());  
        }  
        return gzServletOutputStream;  
    }  
  
    @Override  
    public PrintWriter getWriter() throws IOException {  
        if(gzServletOutputStream != null) {  
            throw new IllegalStateException();  
        }  
  
        if (printWriter == null) {  
            gzServletOutputStream = new GZipServletOutputStream(  
                     getResponse().getOutputStream());  
            OutputStreamWriter osw = new OutputStreamWriter(  
                      gzServletOutputStream,  
                      getResponse().getCharacterEncoding());  
            printWriter = new PrintWriter(osw);  
        }  
        return printWriter;  
    }  
  
    @Override  
    public void setContentLength(int len) {}  
  
    public GZIPOutputStream getGZIPOutputStream() {  
        if (this.gzServletOutputStream == null) {  
            return null;  
        }  
        return this.gzServletOutputStream.getGzipOutputStream();  
    }  
}  

我还启用了其他几个filter，asyncSupported都设置为true，其他的过滤器都没问题，只有加上这个gzip过滤器(去掉@webfilter注解的注释)，请求async.do不能正确响应，后台也不报错 ，不知道什么原因，待究。