Filter——response增强案例—压缩响应=学习笔记

最新推荐文章于 2022-10-17 16:25:49 发布

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最新推荐文章于 2022-10-17 16:25:49 发布

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文章标签：测试 java 数据库

原文链接：http://blog.51cto.com/357712148/2105519

本文介绍了一种使用自定义HttpServletResponseWrapper实现HTTP响应内容压缩的方法。通过重写getOutputStream和getWriter方法，将输出内容先缓存再进行GZIP压缩，最终发送给客户端，有效减少传输数据量。

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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

ShowServlet

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class ShowServlet extends HttpServlet {
    public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {

        ServletOutputStream sout = response.getOutputStream();
        sout.write(data.getBytes("UTF-8"));
        MyServletOutputStream mySout = myResponse.getOutputStream();
        sout.write("AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA".getBytes());
        //mySout.write("AAAAAA".getBytes[]);
    }
}

GzipFilter


import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.util.zip.GZIPOutputStream;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import cn.itcast.web.decorator.MyResponse;

public class GzipFilter implements Filter {
    public void destroy() {
    }
    public void doFilter(ServletRequest req, ServletResponse res,FilterChain chain) throws IOException, ServletException {

        HttpServletRequest request = (HttpServletRequest) req;
        HttpServletResponse response = (HttpServletResponse) res;

        MyResponse myResponse = new MyResponse(response);

        chain.doFilter(request,myResponse);

        //取得缓存中的内容
        byte[] data = myResponse.getBuffer();
        System.out.println("压缩前：" + data.length);

        //进行压缩
        ByteArrayOutputStream bout = new ByteArrayOutputStream();
        GZIPOutputStream gout = new GZIPOutputStream(bout);
        gout.write(data);
        gout.flush();
        gout.close();
        data = bout.toByteArray();
        System.out.println("压缩后：" + data.length);

        //通知浏览器接收是的一个压缩型数据库和长度
        response.setHeader("content-encoding","gzip");
        response.setHeader("content-length",data.length+"");

        //以字节方式真正输出到浏览器
        response.getOutputStream().write(data);

        //无限压缩，无出口，类似环无限循环
        //myResponse.getOutputStream().write(data);
    }
    public void init(FilterConfig filterConfig) throws ServletException {
    }
}

MyResponse


import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;

import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpServletResponseWrapper;

//对response对象的装饰/包装
public class MyResponse extends HttpServletResponseWrapper{
    private HttpServletResponse response;
    //缓存
    private ByteArrayOutputStream bout = new ByteArrayOutputStream();
    private PrintWriter pw;
    public MyResponse(HttpServletResponse response) {
        super(response);
        this.response = response;
    }
    //重写父类方法,目的是将字节输出到缓存中去[字节]
    public ServletOutputStream getOutputStream() throws IOException {
        return new MyServletOutputStream(bout);
    }
    //重写父类方法,目的是将字符输出到缓存中去[字符]
    public PrintWriter getWriter() throws IOException {
        pw = new PrintWriter(new OutputStreamWriter(bout,"UTF-8"));
        return pw;
    }
    //取得缓存中的数据
    public byte[] getBuffer(){
        if(pw!=null){
            pw.flush();
        }
        return bout.toByteArray();
    }
}
//带有缓存功能ServletOutputStream
class MyServletOutputStream extends ServletOutputStream{
    private ByteArrayOutputStream bout;
    public MyServletOutputStream(ByteArrayOutputStream bout) {
        this.bout = bout;
    }
    public void write(int b) throws IOException {
    }
    public void write(byte[] bytes) throws IOException {
        //将字节数组的内容写入缓存
        bout.write(bytes);
        //确保所有字节数组内容进入缓存
        bout.flush();
    }
}

转载于:https://blog.51cto.com/357712148/2105519