java:详解http模块response对象

文章目录

    • 背景
    • HTTP协议相关知识
    • response对象
    • 案例:重定向
    • 重定向(redirect)与转发(forward)的区别
    • 案例:服务器输出字符数据到浏览器
    • 案例:服务器输出字节数据到浏览器
    • 案例:简单的验证码
    • ServletContext对象
    • 案例:文件下载

背景

上一篇 我们详细解释了 java 中 http模块request对象,这次我们来看看 response 对象,也就是服务器要回复客户端的对象

HTTP协议相关知识

  1. 请求消息:客户端发送给服务器端的数据
    • 数据格式:
      1. 请求行
      2. 请求头
      3. 请求空行
      4. 请求体
  2. 响应消息:服务器端发送给客户端的数据
    • 数据格式:

      1. 响应行

        1. 组成:协议/版本 响应状态码 状态码描述
        2. 响应状态码:服务器告诉客户端浏览器本次请求和响应的一个状态。
          1. 状态码都是3位数字
          2. 分类:
            1. 1xx:服务器就收客户端消息,但没有接受完成,等待一段时间后,发送1xx多状态码
            2. 2xx:成功。代表:200
            3. 3xx:重定向。代表:302(重定向),304(访问缓存)
            4. 4xx:客户端错误。
              • 代表:
                • 404(请求路径没有对应的资源)
                • 405:请求方式没有对应的doXxx方法
            5. 5xx:服务器端错误。代表:500(服务器内部出现异常)
      2. 响应头:

        1. 格式:头名称: 值
        2. 常见的响应头:
          1. Content-Type:服务器告诉客户端本次响应体数据格式以及编码格式
          2. Content-disposition:服务器告诉客户端以什么格式打开响应体数据
            • 值:
              • in-line:默认值,在当前页面内打开
              • attachment;filename=xxx:以附件形式打开响应体。文件下载
      3. 响应空行

      4. 响应体:传输的数据

    • 响应字符串格式
      HTTP/1.1 200 OK
      Content-Type: text/html;charset=UTF-8
      Content-Length: 101
      Date: Wed, 06 Jun 2018 07:08:42 GMT

response对象

response 对象包含有关服务器响应的信息,例如响应状态码、响应头、响应体等:

  1. 设置响应行
    1. 格式:HTTP/1.1 200 ok
    2. 设置状态码:setStatus(int) :例如 200、404、500 等。
  2. 设置响应头:setHeader(String name, String value) ,例如 Content-Type(内容类型)和 Cache-Control(缓存控制)。
  3. 设置响应体:
    • 使用步骤:
      1. 获取输出流

        • 字符输出流:PrintWriter getWriter()
        • 字节输出流:ServletOutputStream getOutputStream()
      2. 使用输出流,将数据输出到客户端浏览器

案例:重定向

代码实现:

//1. 设置状态码为302
response.setStatus(302);
//2.设置响应头location
response.setHeader("location","/day15/responseDemo2");

或者

//简单的重定向方法
response.sendRedirect("/day15/responseDemo2");

responseDemo1 重定向到 responseDemo2

package cn.xxx.web.servlet;

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;

/**
 * 重定向
 */

@WebServlet("/responseDemo1")
public class ResponseDemo1 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        System.out.println("demo1........");



        //访问/responseDemo1,会自动跳转到/responseDemo2资源
       /* //1. 设置状态码为302
        response.setStatus(302);
        //2.设置响应头location
        response.setHeader("location","/day15/responseDemo2");*/

        request.setAttribute("msg","response");

        //动态获取虚拟目录
        String contextPath = request.getContextPath();

        //简单的重定向方法
        response.sendRedirect(contextPath+"/responseDemo2");
        //response.sendRedirect("http://www.itcast.cn");

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request,response);
    }
}

package cn.itcast.web.servlet;

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;

@WebServlet("/responseDemo2")
public class ResponseDemo2 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("demo2222222........");

        Object msg = request.getAttribute("msg");
        System.out.println(msg);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request,response);
    }
}

转发

package cn.itcast.web.servlet;

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;

@WebServlet("/responseDemo3")
public class ResponseDemo3 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {


        //转发
        request.getRequestDispatcher("/responseDemo2").forward(request,response);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request,response);
    }
}

绝对路径与相对路径使用场景:

重定向(redirect)与转发(forward)的区别

  • 重定向的特点:redirect
    1. 地址栏发生变化
    2. 重定向可以访问其他站点(服务器)的资源
    3. 重定向是两次请求。不能使用request对象来共享数据
  • 转发的特点:forward
    1. 转发地址栏路径不变
    2. 转发只能访问当前服务器下的资源
    3. 转发是一次请求,可以使用request对象来共享数据

案例:服务器输出字符数据到浏览器

  • 步骤:

    1. 获取字符输出流
    2. 输出数据
  • 注意:

    • 乱码问题:

      1. PrintWriter pw = response.getWriter();获取的流的默认编码是ISO-8859-1
      2. 设置该流的默认编码
      3. 告诉浏览器响应体使用的编码

      //简单的形式,设置编码,是在获取流之前设置
      response.setContentType(“text/html;charset=utf-8”);

package cn.itcast.web.servlet;

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;

@WebServlet("/responseDemo4")
public class ResponseDemo4 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        //获取流对象之前,设置流的默认编码:ISO-8859-1 设置为:GBK
       // response.setCharacterEncoding("utf-8");

        //告诉浏览器,服务器发送的消息体数据的编码。建议浏览器使用该编码解码
        //response.setHeader("content-type","text/html;charset=utf-8");

        //简单的形式,设置编码
        response.setContentType("text/html;charset=utf-8");

        //1.获取字符输出流
        PrintWriter pw = response.getWriter();
        //2.输出数据
        //pw.write("

hello response

");
pw.write("你好啊啊啊 response"); } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { this.doPost(request,response); } }

案例:服务器输出字节数据到浏览器

  1. 获取字节输出流
  2. 输出数据
package cn.itcast.web.servlet;

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.IOException;

@WebServlet("/responseDemo5")
public class ResponseDemo5 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html;charset=utf-8");

        //1.获取字节输出流
        ServletOutputStream sos = response.getOutputStream();
        //2.输出数据
        sos.write("你好".getBytes("utf-8"));
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request,response);
    }
}

案例:简单的验证码

本质:图片
目的:防止恶意表单注册

package cn.itcast.web.servlet;

import javax.imageio.ImageIO;
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.awt.*;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Random;

@WebServlet("/checkCodeServlet")
public class CheckCodeServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {


        int width = 100;
        int height = 50;

        //1.创建一对象,在内存中图片(验证码图片对象)
        BufferedImage image = new BufferedImage(width,height,BufferedImage.TYPE_INT_RGB);


        //2.美化图片
        //2.1 填充背景色
        Graphics g = image.getGraphics();//画笔对象
        g.setColor(Color.PINK);//设置画笔颜色
        g.fillRect(0,0,width,height);

        //2.2画边框
        g.setColor(Color.BLUE);
        g.drawRect(0,0,width - 1,height - 1);

        String str = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghigklmnopqrstuvwxyz0123456789";
        //生成随机角标
        Random ran = new Random();

        for (int i = 1; i <= 4; i++) {
            int index = ran.nextInt(str.length());
            //获取字符
            char ch = str.charAt(index);//随机字符
            //2.3写验证码
            g.drawString(ch+"",width/5*i,height/2);
        }


        //2.4画干扰线
        g.setColor(Color.GREEN);

        //随机生成坐标点

        for (int i = 0; i < 10; i++) {
            int x1 = ran.nextInt(width);
            int x2 = ran.nextInt(width);

            int y1 = ran.nextInt(height);
            int y2 = ran.nextInt(height);
            g.drawLine(x1,y1,x2,y2);
        }


        //3.将图片输出到页面展示
        ImageIO.write(image,"jpg",response.getOutputStream());


    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request,response);
    }
}

ServletContext对象

  1. 概念:代表整个web应用,可以和程序的容器(服务器)来通信
  2. 获取:
    1. 通过request对象获取
      request.getServletContext();
    2. 通过HttpServlet获取
      this.getServletContext();
  3. 功能:
    1. 获取MIME类型:

      • MIME类型:在互联网通信过程中定义的一种文件数据类型

        • 格式: 大类型/小类型 text/html image/jpeg
      • 获取:String getMimeType(String file)

    2. 域对象:共享数据

      1. setAttribute(String name,Object value)
      2. getAttribute(String name)
      3. removeAttribute(String name)
      • ServletContext对象范围:所有用户所有请求的数据
    3. 获取文件的真实(服务器)路径

      1. 方法:String getRealPath(String path)
        String b = context.getRealPath(“/b.txt”);//web目录下资源访问
        System.out.println(b);

        String c = context.getRealPath(“/WEB-INF/c.txt”);//WEB-INF目录下的资源访问
        System.out.println©;

        String a = context.getRealPath(“/WEB-INF/classes/a.txt”);//src目录下的资源访问
        System.out.println(a);

package cn.itcast.web.servletcontext;

import javax.servlet.ServletContext;
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;

@WebServlet("/servletContextDemo1")
public class ServletContextDemo1 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        /*

            ServletContext对象获取:
                1. 通过request对象获取
			        request.getServletContext();
                2. 通过HttpServlet获取
                    this.getServletContext();
         */
        
        //1. 通过request对象获取
        ServletContext context1 = request.getServletContext();
        //2. 通过HttpServlet获取
        ServletContext context2 = this.getServletContext();

        System.out.println(context1);
        System.out.println(context2);

        System.out.println(context1 == context2);//true


    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request,response);
    }
}

package cn.itcast.web.servletcontext;

import javax.servlet.ServletContext;
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;

@WebServlet("/servletContextDemo2")
public class ServletContextDemo2 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        /*

            ServletContext功能:
               1. 获取MIME类型:
                * MIME类型:在互联网通信过程中定义的一种文件数据类型
                    * 格式: 大类型/小类型   text/html		image/jpeg

                * 获取:String getMimeType(String file)
                2. 域对象:共享数据
                3. 获取文件的真实(服务器)路径
         */
        
        //2. 通过HttpServlet获取
        ServletContext context = this.getServletContext();

        //3. 定义文件名称
        String filename = "a.jpg";//image/jpeg


        //4.获取MIME类型
        String mimeType = context.getMimeType(filename);
        System.out.println(mimeType);


    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request,response);
    }
}

package cn.itcast.web.servletcontext;

import javax.servlet.ServletContext;
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;

@WebServlet("/servletContextDemo3")
public class ServletContextDemo3 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        /*

            ServletContext功能:
               1. 获取MIME类型:

                2. 域对象:共享数据
                3. 获取文件的真实(服务器)路径
         */
        
        //2. 通过HttpServlet获取
        ServletContext context = this.getServletContext();

        //设置数据
        context.setAttribute("msg","haha");


    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request,response);
    }
}

package cn.itcast.web.servletcontext;

import javax.servlet.ServletContext;
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;

@WebServlet("/servletContextDemo4")
public class ServletContextDemo4 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        /*

            ServletContext功能:
               1. 获取MIME类型:

                2. 域对象:共享数据
                3. 获取文件的真实(服务器)路径
         */
        
        //2. 通过HttpServlet获取
        ServletContext context = this.getServletContext();

        //获取数据
        Object msg = context.getAttribute("msg");
        System.out.println(msg);

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request,response);
    }
}

package cn.itcast.web.servletcontext;

import javax.servlet.ServletContext;
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.File;
import java.io.IOException;

@WebServlet("/servletContextDemo5")
public class ServletContextDemo5 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        /*

            ServletContext功能:
               1. 获取MIME类型:

                2. 域对象:共享数据
                3. 获取文件的真实(服务器)路径
         */
        
        // 通过HttpServlet获取
        ServletContext context = this.getServletContext();


        // 获取文件的服务器路径
        String b = context.getRealPath("/b.txt");//web目录下资源访问
        System.out.println(b);
       // File file = new File(realPath);

        String c = context.getRealPath("/WEB-INF/c.txt");//WEB-INF目录下的资源访问
        System.out.println(c);

        String a = context.getRealPath("/WEB-INF/classes/a.txt");//src目录下的资源访问
        System.out.println(a);


    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request,response);
    }
}

案例:文件下载

  • 文件下载需求:

    1. 页面显示超链接
    2. 点击超链接后弹出下载提示框
    3. 完成图片文件下载
  • 分析:

    1. 超链接指向的资源如果能够被浏览器解析,则在浏览器中展示,如果不能解析,则弹出下载提示框。不满足需求
    2. 任何资源都必须弹出下载提示框
    3. 使用响应头设置资源的打开方式:
      • content-disposition:attachment;filename=xxx
  • 步骤:

    1. 定义页面,编辑超链接href属性,指向Servlet,传递资源名称filename
    2. 定义Servlet
      1. 获取文件名称
      2. 使用字节输入流加载文件进内存
      3. 指定response的响应头: content-disposition:attachment;filename=xxx
      4. 将数据写出到response输出流
  • 问题:

    • 中文文件问题
      • 解决思路:
        1. 获取客户端使用的浏览器版本信息
        2. 根据不同的版本信息,设置filename的编码方式不同
package cn.itcast.web.utils;

import sun.misc.BASE64Encoder;
import java.io.UnsupportedEncodingException;
import java.net.URLEncoder;


public class DownLoadUtils {

    public static String getFileName(String agent, String filename) throws UnsupportedEncodingException {
        if (agent.contains("MSIE")) {
            // IE浏览器
            filename = URLEncoder.encode(filename, "utf-8");
            filename = filename.replace("+", " ");
        } else if (agent.contains("Firefox")) {
            // 火狐浏览器
            BASE64Encoder base64Encoder = new BASE64Encoder();
            filename = "=?utf-8?B?" + base64Encoder.encode(filename.getBytes("utf-8")) + "?=";
        } else {
            // 其它浏览器
            filename = URLEncoder.encode(filename, "utf-8");
        }
        return filename;
    }
}

package cn.itcast.web.download;

import cn.itcast.web.utils.DownLoadUtils;

import javax.servlet.ServletContext;
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;

@WebServlet("/downloadServlet")
public class DownloadServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //1.获取请求参数,文件名称
        String filename = request.getParameter("filename");
        //2.使用字节输入流加载文件进内存
        //2.1找到文件服务器路径
        ServletContext servletContext = this.getServletContext();
        String realPath = servletContext.getRealPath("/img/" + filename);
        //2.2用字节流关联
        FileInputStream fis = new FileInputStream(realPath);

        //3.设置response的响应头
        //3.1设置响应头类型:content-type
        String mimeType = servletContext.getMimeType(filename);//获取文件的mime类型
        response.setHeader("content-type",mimeType);
        //3.2设置响应头打开方式:content-disposition

        //解决中文文件名问题
        //1.获取user-agent请求头、
        String agent = request.getHeader("user-agent");
        //2.使用工具类方法编码文件名即可
        filename = DownLoadUtils.getFileName(agent, filename);

        response.setHeader("content-disposition","attachment;filename="+filename);
        //4.将输入流的数据写出到输出流中
        ServletOutputStream sos = response.getOutputStream();
        byte[] buff = new byte[1024 * 8];
        int len = 0;
        while((len = fis.read(buff)) != -1){
            sos.write(buff,0,len);
        }

        fis.close();


    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request,response);
    }
}

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