Servlet——使用Filter对缓存过滤

本是古典何须时尚 2022-05-16 06:12 199阅读 0赞

import java.io.ByteArrayOutputStream;
    import java.io.IOException;
    import java.io.OutputStreamWriter;
    import java.io.PrintWriter;
    import java.util.HashMap;
    import java.util.Map;
    
    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;
    
    import cn.itcast.web.filter.example.GzipFilter.MyServletOutputStream;
    
    public class WebCacheFilter implements Filter {
        
    
        private Map<String,byte[]> map = new HashMap();
    
        public void doFilter(ServletRequest req, ServletResponse resp,
                FilterChain chain) throws IOException, ServletException {
    
            HttpServletRequest request = (HttpServletRequest) req;
            HttpServletResponse response = (HttpServletResponse) resp;
    
            //1.得到用户想访问的资源（uri）
            String uri = request.getRequestURI();
    
            //2.看map集合中是否保存了该资源的数据
            byte b[] = map.get(uri);
    
            //3.如果保存了，则直接取数据打给浏览器
            if(b!=null){
                response.getOutputStream().write(b);
                return;
            }
    
            //4.如果没有保存数据，则放行让目标资源执行，这时还需写一个response的包装类，捕获目标资源的输出
            MyResponse my = new MyResponse(response);
            chain.doFilter(request, my);
            byte data[] = my.getBuffer();
    
            //5.以资源uri为关键字，打资源的数据保存map集合中，以备于下次访问
            map.put(uri, data);
    
            //6.输出数据给浏览器
            response.getOutputStream().write(data);
    
    
    
        }
    
        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 init(FilterConfig filterConfig) throws ServletException {
            // TODO Auto-generated method stub
    
        }
    
        public void destroy() {
            // TODO Auto-generated method stub
    
        }
    
    }