一、预览

介绍完Servlet-Resquest的相关内容后，接下来就是Servlet- Response的内容。读者阅读完本篇文章后将可以自如地解析请求、设置响应，完成对客户端的响应。

二、Response体系结构

Response的体系结构与Request完全一样，其中ServletResponse与HttpServletResponse都是Java官方定义的接口，ResponseFacade是Web服务器（Tomcat）的实现类。

三、常用API

Response响应分为响应字符数据与响应字节数据。

（1）字符响应

package com.byhuang.response;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;

/**
 * 响应字符数据：设置字符数据的响应体
 */
@WebServlet("/res2")
public class ResponseDemo2 extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("res2...");
        System.out.println(resp.getContentType());
        // 数据格式 以及 编码格式
        resp.setContentType("text/html;charset=utf-8");
        // 1 获取字符输出流
        PrintWriter writer = resp.getWriter();
        writer.write("<h1>aaa</h1>");

        // 流不需要关闭
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

    }
}

（2）字节响应

package com.byhuang.response;

import org.apache.commons.io.IOUtils;

import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.FileInputStream;
import java.io.IOException;

/**
 * 响应字节数据：设置字节数据的响应体
 */
@WebServlet("/res3")
public class ResponseDemo3 extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("res3...");

        FileInputStream fileInputStream = new FileInputStream("/Users/huangbingyi/Desktop/pic.png");

        ServletOutputStream outputStream = resp.getOutputStream();

        IOUtils.copy(fileInputStream, outputStream);

        fileInputStream.close();
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

    }
}