GZIP压缩代码

Question

public class GzipFilter implements Filter {

    public void init(FilterConfig filterConfig) throws ServletException {

    }

    public void doFilter(ServletRequest req, ServletResponse res,
                         FilterChain chain) throws IOException, ServletException {
        HttpServletRequest request;
        HttpServletResponse response;

        try {
            request = (HttpServletRequest) req;
            response = (HttpServletResponse) res;
        } catch (ClassCastException e) {
            throw new ServletException("non-HTTP request or response");
        }

        MyHttpServletResponse mresponse = new MyHttpServletResponse(response);
        chain.doFilter(request, mresponse);

        byte b[] = mresponse.getBytes();//原始数据:关键
        System.out.println("原始大小："+b.length);
        //判断客户端支持gzip吗
        if(request.getHeader("Accept-Encoding").contains("gzip")){
            //压缩输出
            ByteArrayOutputStream out = new ByteArrayOutputStream();
            GZIPOutputStream gout = new GZIPOutputStream(out);
            gout.write(b);
            gout.close();

            b = out.toByteArray();//压缩后的数据
            System.out.println("压缩后大小："+b.length);
            //告知客户端压缩方式
            response.setHeader("Content-Encoding", "gzip");
            response.setContentLength(b.length);
        }
        ServletOutputStream sos = response.getOutputStream();
        sos.write(b);
    }

    public void destroy() {

    }

}
class MyHttpServletResponse extends HttpServletResponseWrapper{
    private ByteArrayOutputStream baos = new ByteArrayOutputStream();//临时仓库：存放原始数据的
    private PrintWriter pw;
    public MyHttpServletResponse(HttpServletResponse response) {
        super(response);
    }
    //字节流
    public ServletOutputStream getOutputStream() throws IOException {
        return new MyServletOutputStream(baos);
    }
    //字符流
    public PrintWriter getWriter() throws IOException {
        pw = new PrintWriter(new OutputStreamWriter(baos, super.getCharacterEncoding()));
        return pw;
    }
    public byte[] getBytes(){
        try {
            if(pw!=null){
                pw.close();
            }
            baos.flush();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return baos.toByteArray();
    }
}
class MyServletOutputStream extends ServletOutputStream{
    private ByteArrayOutputStream baos;
    public MyServletOutputStream(ByteArrayOutputStream baos){
        this.baos = baos;
    }
    public void write(int b) throws IOException {
        baos.write(b);
    }

}

我刚学到过滤器，这GZIP压缩的代码我看着好晕，我知道有装饰设计模式，但是里面的好多流晕着我了，怎么办啊？另外，在class MyServletOutputStream中既然继承了ServletOutputStream这个抽象类，但是没有将之实现全部的方法，IDEA报错，但是我看视频里可以运行啊。

Answer 1

流学习记住几个规则
out开头的必是写
input开头的必是读
xxxstream一般是字节流
xxxreader xxxwriter是字符流读写

字节流字符流转化工具命名一般是xxxstreamreader