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Java-Response对象设置响应消息

功能：设置响应消息

1.设置响应行

格式：HTTP/1.1 200 OK
设置状态码：setStatus(int sc)

2.设置响应头：setHeader(String name,String value)

3.设置响应体:

使用步骤：
1. 获取输出流
  - 字符输入流：PrintWirter 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（核心）

案例

1.完成重定向

重定向：资源跳转的方式
代码实现：
//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", "/07_Response_war_exploded/ResponseDemo2");
// 简单的重定向
response.sendRedirect("/07_Response_war_exploded/ResponseDemo2");
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，不可以使用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
forward和redirect区别
路径写法
1. 相对路径：通过相对路径不确定唯一资源
  - 规则：找到当前资源与目标资源之间的相对位置关系
    - ./：当前目录
    - ../：后退一级目录
2. 绝对路径
  - 规则：判断定义的路径是给谁用的？判断请求将来从哪发出
    - 给客户端浏览器使用：需要加虚拟目录
      - 建议虚拟目录动态获取：request.getContextPath()
      - ,
        ,重定向....

代码如下

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("/ResponseDemo1")
public class ResponseDemo1 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("demo1111................");
        //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", "/07_Response_war_exploded/ResponseDemo2");
        //    简单的重定向
        response.sendRedirect("/07_Response_war_exploded/ResponseDemo2");
    }

    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("demo2222................");
    }

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

2.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
乱码问题：
- 简单形式//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");

代码如下

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");
        //1.获取字符输出流
        PrintWriter pw = response.getWriter();
        //2.输出数据
        // pw.write("<h1>hello response</h1>");
        pw.write("<h1>你好 response</h1>");
        System.out.println("demo444................");
    }

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

3.服务器输出字节数据到浏览器

步骤获取字节输出流，输出数据

代码如下

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.setHeader("content-type", "text/html;charset=utf-8");
        //1.获取字节输出流
        ServletOutputStream sos = response.getOutputStream();
        //2.输出数据
        // sos.write("hello".getBytes());
        sos.write("你好".getBytes("utf-8"));
    }

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

4.验证码

本质：图片
目的：防止恶意表单注册

代码如下

package cn.itcast.web.servlet;

import javax.imageio.ImageIO;
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.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;
        //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);
        //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 = "ABCDEFGHIJKLMNOPQRSTOVWXYZabcdefghijklmnopqrstovwxyz";
        //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
            g.drawString(ch + "", width / 5 * i, height / 2);
            //2.3.写验证码
        }
        //2.4画干扰线
        g.setColor(Color.GREEN);
        for (int i = 0; i <= 4; i++) {
            int x1 = ran.nextInt(width);
            int x2 = ran.nextInt(width);
            int y1 = ran.nextInt(height);
            int y2 = ran.nextInt(height);
            g.drawLine(x1, x1, x2, y2);
        }

        //将图片输出到页面显示
        ImageIO.write(image, "jpg", response.getOutputStream());
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}
--------------------------------------------------------------------------
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script>
        window.onload = function () {
            var img = document.getElementById("checkCode");
            img.onclick = function () {
                //加时间戳
                var date = new Date().getTime();
                img.src = "/07_Response_war_exploded/CheckCodeServlet?" + date;
            }
        }
    </script>
</head>
<body>
<img src="/07_Response_war_exploded/CheckCodeServlet"/>
<a id="checkCode" href="">看不清换一张</a>
</body>
</html>

5.获取ServletContext

ServletContext getServletContext()

5.1 代码如下

package cn.itcast.web.request;

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("/RequestDemo10")
public class RequestDemo10 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //    获取数据
        ServletContext servletContext = request.getServletContext();
        System.out.println(servletContext);
        System.out.println("demo1010被访问了.....");

    }


    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //    get 获取请求参数
        // String username = request.getParameter("username");
        // System.out.println("get");
        // System.out.println(username);
        this.doPost(request, response);
    }
}

5.2 概念：代表整个web应用，可以和程序的容器（服务器）来通信

5.3 获取MINE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/jepg
    * 获取：String getMimeType(String file)

代码如下

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 {
/*
1.获取MINE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/jepg
* 获取：String getMimeType(String file)
*/

        // 2.通过HttpServlet获取
        ServletContext context2 = this.getServletContext();
        //定义文件名称
        String filename = "a.jpg";//image/jpeg
        //获取MIME类型1
        String mimeType = context2.getMimeType(filename);
        System.out.println(mimeType);
    }

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

5.4 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

代码如下

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 {
        // 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 {
        // 2.通过HttpServlet获取
        ServletContext context = this.getServletContext();
        //设置数据
        Object msg = context.getAttribute("msg");
        System.out.println(msg);
    }

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

5.5 获取文件的真实（服务器）路径

    1. 方法：String getRealPath(String path)

代码如下

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 {
        // 2.通过HttpServlet获取
        ServletContext context = this.getServletContext();
        //获取文件的服务器路径
        String realPath = context.getRealPath("/b.txt");
        System.out.println(realPath);
        File file = new File(realPath);
        String c = context.getRealPath("/WEB-INF/c.txt");
        System.out.println(c);
        String a = context.getRealPath("/WEB-INF/classes/a.txt");
        System.out.println(a);
    }

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

5.4 获取：

1. 通过request对象获取
    request.getServletContext()
2. 通过HttpServlet获取
    this.getServletContext();

代码如下

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);
    }

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

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原文地址：https://www.cnblogs.com/dongxuelove/p/13042255.html