Servlet——使用Filter对输出数据进行压缩

分手后的思念是犯贱 2022-05-16 06:12 186阅读 0赞

应用HttpServletResponseWrapper对象，压缩响应正文内容。

思路:通过filter向目标页面传递一个自定义的response对象。

在自定义的response对象中，重写getOutputStream方法和getWriter方法，使目标资源调用此方法输出页面内容时，获得的是我们自定义的ServletOutputStream对象。

在我们自定义的ServletOuputStream对象中，重写write方法，使写出的数据写出到一个buffer中。

当页面完成输出后，在filter中就可得到页面写出的数据，从而我们可以调用GzipOuputStream对数据进行压缩后再写出给浏览器，以此完成响应正文件压缩功能。

Servlet API中提供了response对象的Decorator设计模式的默认实现类++HttpServletResponseWrapper++，以避免用户在对response对象进行增强时需要实现response接口中的所有方法。

### 压缩代码 ###

String data = "aaaaaaaa";
    
            ByteArrayOutputStream bout = new ByteArrayOutputStream();
            GZIPOutputStream gout = new GZIPOutputStream(bout);
            gout.write(data.getBytes());
            gout.close();
    
    
            byte gzip[] = bout.toByteArray();
            response.setHeader("content-encoding", "gzip");
            response.setHeader("content-length", gzip.length + "");
    
            response.getOutputStream().write(gzip);

### 增强response ###

import java.io.ByteArrayOutputStream;
    import java.io.IOException;
    import java.io.OutputStreamWriter;
    import java.io.PrintWriter;
    import java.util.zip.GZIPOutputStream;
    
    import javax.servlet.Filter;
    import javax.servlet.FilterChain;
    import javax.servlet.FilterConfig;
    import javax.servlet.ServletException;
    import javax.servlet.ServletOutputStream;
    import javax.servlet.ServletRequest;
    import javax.servlet.ServletResponse;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    import javax.servlet.http.HttpServletResponseWrapper;
    
    public class GzipFilter implements Filter {
        
    
        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.getwriter  response.getOutputStream  
    
            //取出缓冲的数据压缩后输出
            byte out[] = myresponse.getBuffer();  //得到目标资源的输出
            System.out.println("压之前：" + out.length);
    
    
            byte gzipout[] = gzip(out);
            System.out.println("压之后：" + gzipout.length);
    
    
            response.setHeader("content-encoding", "gzip");
            response.setHeader("content-length", gzipout.length + "");
            response.getOutputStream().write(gzipout);
        }
    
        public byte[] gzip(byte b[]) throws IOException{
    
            ByteArrayOutputStream bout = new ByteArrayOutputStream();
            GZIPOutputStream gout = new GZIPOutputStream(bout);
            gout.write(b);
            gout.close();
            return bout.toByteArray();
        }
    
        class MyResponse extends HttpServletResponseWrapper{
            private ByteArrayOutputStream bout = new ByteArrayOutputStream();
            private PrintWriter pw;
    
            private HttpServletResponse response;
            public MyResponse(HttpServletResponse response) {
                super(response);
                this.response = response;
            }
            @Override
            public ServletOutputStream getOutputStream() throws IOException {
                return new MyServletOutputStream(bout);    //myresponse.getOutputStream().write("hahah");
            }
    
            @Override
            public PrintWriter getWriter() throws IOException {
                pw = new PrintWriter(new OutputStreamWriter(bout,response.getCharacterEncoding()));
                return pw;  //MyResponse.getWriter().write("中国");
            }
            public byte[] getBuffer(){
                if(pw!=null){
                    pw.close();
                }
                return bout.toByteArray();
            }
        }
    
        class MyServletOutputStream extends ServletOutputStream{
    
            private ByteArrayOutputStream bout;
            public MyServletOutputStream(ByteArrayOutputStream bout){
                this.bout = bout;
            }
            @Override
            public void write(int b) throws IOException {
                bout.write(b);
            }
    
        }
    
        public void destroy() {
            // TODO Auto-generated method stub
    
        }
    
    
        public void init(FilterConfig filterConfig) throws ServletException {
            // TODO Auto-generated method stub
    
        }
    
    }