JAVA_WEB之Response

Response

一、下载文件

package com.saxon.servlet;

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

public class DownLoading extends HttpServlet {
    @Override
    protected void doGet (HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //1.确定位置和名字
        String location = "..\\1.png"      //具体的地址绝对地址;
        String filename = location.substring (location.lastIndexOf ("\\") + 1);
        //2.设置传输的头文件
        resp.setHeader ("Content-Disposition", "attachment; filename=" + filename);//下载页面的文件名，可以在下载页面手动改，默认的话就是。.txt;
        //3.建立缓冲区
        int len = 0;
        byte[] buffer = new byte[1024];
        //4.将下载文件变成输入流
        FileInputStream in = new FileInputStream (location);
        //5.获得输出流是，下载
        ServletOutputStream out = resp.getOutputStream ();
        //in.read (buffer) 将文件读取到缓存中
        while (in.read (buffer) != - 1) {
            out.write (buffer, 0, len);//将这个缓存给客户端，响应
        }
        out.close ();
        in.close ();
    }

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

二、验证码的实现

1.测试

package com.saxon.servlet;

import javax.imageio.ImageIO;
import javax.servlet.ServletException;
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;

public class CheckCode extends HttpServlet {
    @Override
    protected void doGet (HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.setHeader ("refresh", "5");//刷新时间
        //图片的大小。
        BufferedImage image = new BufferedImage (80, 20, BufferedImage.TYPE_INT_RGB);
        Graphics2D pen = (Graphics2D) image.getGraphics ();
        //对图片进行填充
        pen.setColor (Color.black);
        pen.fillRect (0,0,80,20);
        //在图片中写入文字
        pen.setColor (Color.white);
        pen.setFont (new Font (null,Font.BOLD,20));
        pen.drawString (Num (),0,20);
        //浏览器的读取形式
        resp.setContentType ("image/jpeg");
        //缓存
        resp.setDateHeader ("expires",-1);
        resp.setHeader ("Cache-Control","no-cache");
        resp.setHeader ("pragma","no-cache");
        //图片交给浏览器
        ImageIO.write (image,"jpeg",resp.getOutputStream ());

    }

    private String Num(){
        StringBuffer str=new StringBuffer ();
        for (int i = 0; i <7 ; i++) {
            int i1 = new Random ().nextInt (9);
            str.append (i1);
        }
        return str.toString ();
    }
    @Override

    protected void doPost (HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet (req, resp);
    }
}

我们可以设置上面的相关的信息；

三、实现重定向

1.概念

重定向：当你想要小美的QQ号，但你不知道如何要她的QQ号，所以你去找认识小美QQ号的小札，小札叫你自己去，于是你就自己去；

转发：当你想要小美的QQ号，但是你不知道如何要她的QQ号，所以你就去找认识小美QQ号的小札，小札帮你去要，要到了再给你；

比较：重定向和转发

相同点：都是页面的跳转；

不同点：重定向的url地址发生了变化，但是转发没有。他们的状态码也不一样。重定向的是3开头的。转发是200；

//转发
ServletContext context = this.getServletContext ();
RequestDispatcher r = context.getRequestDispatcher ("/gp");//写入要跳转的页面的url-pattern
//重定向
String contextPath = this.getServletContext ().getContextPath ();//当前项目的地址
resp.sendRedirect (contextPath+"/hello.html");

2.测试

package com.saxon.servlet;

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

public class RedirectServlet  extends HttpServlet {
    @Override
    protected void doGet (HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String contextPath = this.getServletContext ().getContextPath ();//当前项目的地址
        resp.sendRedirect (contextPath+"/hello.html");
    }

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