axios response 文件下载 responseentity下载文件损坏

转载

mob6454cc6faf88 2024-07-01 22:17:33

文章标签 axios response 文件下载 3请求报401 java xml Image 文章分类 iOS 移动开发

Servlet

HttpServletResponse

web服务器接收到客户端的http请求, 针对这个请求, 分别创建一个代表请求的HttpServletRequest对象, 代表响应的一个HttpServletResponse

如果要获取客户端请求过来的参数: 找HttpServletRequest
如果要给客户端响应一些信息: 找HttpServletResponse

简单分类

负责向浏览器发送数据:

ServletOutputStream getOutputStream() throws IOException; //一般情况
PrintWriter getWriter() throws IOException; //写中文, 但是可能造成字符串损坏或丢失

负责向浏览器发送响应头的方法:

void setCharacterEncoding(String var1);
void setContentLength(int var1);
void setContentLengthLong(long var1);
void setContentType(String var1);
void setDateHeader(String var1, long var2);
void addDateHeader(String var1, long var2);
void setHeader(String var1, String var2);
void addHeader(String var1, String var2);
void setIntHeader(String var1, int var2);
void addIntHeader(String var1, int var2);

响应的状态码:

int SC_CONTINUE = 100;
int SC_SWITCHING_PROTOCOLS = 101;
int SC_OK = 200;
int SC_CREATED = 201;
int SC_ACCEPTED = 202;
int SC_NON_AUTHORITATIVE_INFORMATION = 203;
int SC_NO_CONTENT = 204;
int SC_RESET_CONTENT = 205;
int SC_PARTIAL_CONTENT = 206;
int SC_MULTIPLE_CHOICES = 300;
int SC_MOVED_PERMANENTLY = 301;
int SC_MOVED_TEMPORARILY = 302;
int SC_FOUND = 302;
int SC_SEE_OTHER = 303;
int SC_NOT_MODIFIED = 304;
int SC_USE_PROXY = 305;
int SC_TEMPORARY_REDIRECT = 307;
int SC_BAD_REQUEST = 400;
int SC_UNAUTHORIZED = 401;
int SC_PAYMENT_REQUIRED = 402;
int SC_FORBIDDEN = 403;
int SC_NOT_FOUND = 404;
int SC_METHOD_NOT_ALLOWED = 405;
int SC_NOT_ACCEPTABLE = 406;
int SC_PROXY_AUTHENTICATION_REQUIRED = 407;
int SC_REQUEST_TIMEOUT = 408;
int SC_CONFLICT = 409;
int SC_GONE = 410;
int SC_LENGTH_REQUIRED = 411;
int SC_PRECONDITION_FAILED = 412;
int SC_REQUEST_ENTITY_TOO_LARGE = 413;
int SC_REQUEST_URI_TOO_LONG = 414;
int SC_UNSUPPORTED_MEDIA_TYPE = 415;
int SC_REQUESTED_RANGE_NOT_SATISFIABLE = 416;
int SC_EXPECTATION_FAILED = 417;
int SC_INTERNAL_SERVER_ERROR = 500;
int SC_NOT_IMPLEMENTED = 501;
int SC_BAD_GATEWAY = 502;
int SC_SERVICE_UNAVAILABLE = 503;
int SC_GATEWAY_TIMEOUT = 504;
int SC_HTTP_VERSION_NOT_SUPPORTED = 505;

常见应用

1.向浏览器输出消息

2.下载文件

获取下载文件的路径
下载的文件名是什么
设置想办法让浏览器能够支持下载我们需要的东西
获取下载文件的输入流
创建缓冲区
获取OutputStream对象
将FileOutputStream流写入到buffer
使用InputStream将缓冲区中的数据输出到客户端

例子:

axios response 文件下载 responseentity下载文件损坏_Image

web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee
                      http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0"
         metadata-complete="false">
  <servlet>
    <servlet-name>filedown</servlet-name>
    <servlet-class>com.peng.servlet.FileServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>filedown</servlet-name>
    <url-pattern>/download</url-pattern>
  </servlet-mapping>
</web-app>

FileServlet.java

package com.peng.servlet;

import javax.servlet.ServletContext;
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;
import java.net.URL;
import java.net.URLEncoder;

public class FileServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //    1. 获取下载文件的路径
        ServletContext servletContext = this.getServletContext();
        //    两者皆可
        String realPath = servletContext.getClassLoader().getResource("/Cap27.JPG").getPath();
        //String realPath = "C:UsersasusIdeaProjectsjavaweb-03-sevletresponsesrcmainresourcesCap27.JPG";
        System.out.println("下载文件的路径" + realPath);
        //    2. 下载的文件名是什么
        String fileName = realPath.substring(realPath.lastIndexOf("") + 1);
        //    3. 设置想办法让浏览器能够支持下载我们需要的东西, 使用URLEncoder.encode进行编码解码, 否则可能乱码
        resp.setHeader("Content-Disposition", "attachment;filename="+ URLEncoder.encode(fileName, "UTF-8"));
        //    4. 获取下载文件的输入流
        FileInputStream fileInputStream = new FileInputStream(realPath);
        //    5. 创建缓冲区
        int len = 0;
        byte[] buffer = new byte[1024];
        //    6. 获取OutputStream对象
        ServletOutputStream out = resp.getOutputStream();
        //    7. 将FileOutputStream流写入到buffer, 使用InputStream将缓冲区中的数据输出到客户端
        while((len = fileInputStream.read(buffer)) > 0){
            out.write(buffer, 0, len);
        }
        fileInputStream.close();
        out.close();
    }

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

验证码实现

验证怎么来的?

前端实现
后端实现, 需要用到Java的图片类, 生成一个图片

例子:

web.xml

<servlet>
    <servlet-name>image</servlet-name>
    <servlet-class>com.peng.servlet.ImageServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>image</servlet-name>
    <url-pattern>/image</url-pattern>
  </servlet-mapping>

ImageServlet.java

package com.peng.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 ImageServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //如何让浏览器3s自动刷新一次;
        resp.setHeader("refresh", "3");

        //在内存中创建一个图片
        BufferedImage bufferedImage = new BufferedImage(100, 20, BufferedImage.TYPE_INT_RGB);

        //得到图片
        Graphics2D graphics = (Graphics2D)bufferedImage.getGraphics(); //笔
        //设置图片的背景颜色
        graphics.setColor(Color.white);
        graphics.fillRect(0, 0, 100, 20);
        //给图片写数据
        graphics.setColor(Color.blue);
        graphics.setFont(new Font(null, Font.BOLD, 20));
        graphics.drawString(makeNum(), 0, 18);

        //告诉浏览器这个请求用图片的方式打开
        resp.setContentType("image/png");
        //网站存在缓存, 不让浏览器缓存
        resp.setDateHeader("expires", -1);
        resp.setHeader("Cache-Control", "no-cache");
        resp.setHeader("Pragma", "no-cache");

        //把图片写给浏览器
        boolean write = ImageIO.write(bufferedImage, "jpg", resp.getOutputStream());
    }

    private String makeNum(){
        Random random = new Random();
        String num = random.nextInt(999999999) + "";
        StringBuffer stringBuffer = new StringBuffer();
        for (int i = 0; i < 9-num.length(); i++){
            stringBuffer.append("0");
        }
        num = stringBuffer.toString() + num;
        return num;
    }

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

最终效果为3s刷新一次的随机9位数字验证码

axios response 文件下载 responseentity下载文件损坏_xml_02

Response重定向

下图中下面的情况即重定向, 上面的情况为请求转发

axios response 文件下载 responseentity下载文件损坏_java_03

一个web资源(B)收到客户端(A)请求后, (B)会通知客户端(A)去访问另外一个web资源(C), 这个过程叫重定向

常见场景:

用户登录

void sendRedirect(String var1) throws IOException;

RedirectServlet.java

package com.peng.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 {
        /*
        resp.setHeader("Location", "/r/img");
        resp.setStatus(HttpServletResponse.SC_MOVED_TEMPORARILY); //302
        */
        resp.sendRedirect("/r/image"); //重定向

    }

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

web.xml

<servlet>
    <servlet-name>redirect</servlet-name>
    <servlet-class>com.peng.servlet.RedirectServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>redirect</servlet-name>
    <url-pattern>/redirect</url-pattern>
  </servlet-mapping>

面试题:

重定向与转发的区别:

相同点:

页面都会实现跳转

不同点:

请求转发的时候, url不会产生变化
重定向时候, url地址栏会发生变化

用户登录例子:

页面提交过来的HTTP请求包含了参数，放在URL里面了，tomcat自动解析封装在request对象里，再调用services方法，request可以根据键得到传过来的值

index.jsp

<html>
<body>
<h2>Hello World!</h2>

<%--这里提交的路径,需要寻找到项目的路径--%>
<%--${pageContext.request.contextPath}代表当前的项目--%>
<form action="${pageContext.request.contextPath}/login" method = "get">
    用户名: <input type = "text" name = "username"><br>
    密码: <input type = "password" name = "password"><br>
    <input type = "submit">
</form>
</body>
</html>

success.jsp

<%--
  Created by IntelliJ IDEA.
  User: asus
  Date: 2020/5/29
  Time: 2:33
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
<h1>Success!</h1>
</body>
</html>

web.xml

<servlet>
  <servlet-name>login</servlet-name>
  <servlet-class>com.peng.servlet.RequestTest</servlet-class>
</servlet>
<servlet-mapping>
  <servlet-name>login</servlet-name>
  <url-pattern>/login</url-pattern>
</servlet-mapping>

RequestTest.java

package com.peng.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 RequestTest extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //处理请求
        String username = req.getParameter("username");
        String password = req.getParameter("password");
        System.out.println(username + ":" + password);

        //重定向需要注意路径问题
        resp.sendRedirect("/r/success.jsp");
    }

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

本文章为转载内容，我们尊重原作者对文章享有的著作权。如有内容错误或侵权问题，欢迎原作者联系我们进行内容更正或删除文章。