filter拦截（Response输出压缩）此案例基础知识面广

Response两种输出方式：1.getOutputStream().writer();2.getWriter().writer();但不能同时存在

1.配置文件
<filter>

    <filter-name>GzipFilter</filter-name>

    <filter-class>cn.itcast.web.filter.GzipFilter</filter-class>

</filter>

<filter-mapping>

    <filter-name>GzipFilter</filter-name>

    <url-pattern>*.jsp</url-pattern><!-- 注意一般不要做全栈压缩，只压缩html,jsp,js -->

    <dispatcher>FORWARD</dispatcher>

    <dispatcher>REQUEST</dispatcher>

</filter-mapping>

<filter-mapping>

    <filter-name>GzipFilter</filter-name>

    <url-pattern>*.html</url-pattern>

</filter-mapping>

<filter-mapping>

    <filter-name>GzipFilter</filter-name>

    <url-pattern>*.js</url-pattern>

</filter-mapping>

2.定义GzipFilter类并 implements Filter

 public class GzipFilter implements Filter {

@Override

    public void doFilter(ServletRequest req, ServletResponse resp,FilterChain chain) throws IOException, ServletException {

        HttpServletRequest request=(HttpServletRequest) req;

        HttpServletResponse response=(HttpServletResponse) resp;

          MyResponse myresponse=new MyResponse(response);

        chain.doFilter(request,myresponse);    //response.getWriterresponse.getOutputStream

            //取出缓冲数据压缩后输出

            byte out[]=myresponse.getBuffer();

            System.out.println("压缩前："+out.length);

            byte gzipout[]=gzip(out);

            System.out.println("压缩后："+gzipout.length);
            //设置头信息，以压缩方式打开  

            response.setHeader("content-encoding", "gzip");

            response.setHeader("content-length", gzipout.length+"");
 

            response.getOutputStream().write(gzipout);    //分别对应下面橙色A/B/C处

    }

public byte[] gzip(byte b[]) throws IOException{    //压缩

    ByteArrayOutputStream bout=new ByteArrayOutputStream();

    GZIPOutputStream gout=new GZIPOutputStream(bout);

gout.write(b);

gout.close();

return bout.toByteArray();

}
 
class MyResponse extends HttpServletResponseWrapper{    //A处对应上面response

    private ByteArrayOutputStream bout=new ByteArrayOutputStream();    //定义缓冲区数组字节流

        private PrintWriter pw;

        private HttpServletResponse response;

    public MyResponse(HttpServletResponse response) {

        super(response);

        this.response=response;

    }

//response输出数据方式一：response.getOutputStream().write("xxxx");

@Override

public ServletOutputStream getOutputStream() throws IOException {    //B处对应上面getOutputStream

    return new MyServletOutputStream(bout); //response.getOutputStream.write(); 因ServletOutputStream是abstract类，不能直接 new

    }

//response输出数据方式二：response.getWriter().write("xxxx");

@Override

public PrintWriter getWriter() throws IOException{

    //pw=new PrintWriter(bout);//字符流向字节流写数据，会查编码，默认GB2312,所以要注意乱码问题

    pw=new PrintWriter(new OutputStreamWriter(bout,response.getCharacterEncoding()));    //用于解决PrintWriter().writer()的乱码问题

    return pw;    //MyResponse.getWriter.write("xxx");

}

//将缓冲区中的数据返回

public byte[] getBuffer(){

    if(pw!=null){    

    pw.close();    //保证数据会写入缓冲区，当用PrintWrier输出时，此判断有效

    }

        return bout.toByteArray();  

    }

}

class MyServletOutputStream extends ServletOutputStream{    //B处对应上面getOutputStream，

    private ByteArrayOutputStream bout;

     public MyServletOutputStream(ByteArrayOutputStream bout){

           this.bout=bout;

   }

@Override

         public void write(int b) throws IOException {  //覆写write方法//c处对应上面write

             bout.write(b);

    }

}

@Override

public void init(FilterConfig filterConfig) throws ServletException {

// TODO Auto-generated method stub

}

@Override

public void destroy() {

// TODO Auto-generated method stub

}

}

3.Servlet代码编写

public void doGet(HttpServletRequest request, HttpServletResponse response)

throws ServletException, IOException {

String data="中国";

//response.getOutputStream().write(data.getBytes("UTF-8"));//一定要指编码，用于解决getOutputStream().write输出乱码

response.getWriter().write(data); //getWriter().writer输出的乱码问题在拦截代码中处理。

}