文件上传
1.要有一个form标签,method=post请求
2.form标签的encType属性的值必须为multipart/form-data值
3.在from标签中使用input type=file添加上传的文件
4.编写服务器代码接收上传的数据
Content-Type:表示提交的数据类型
enctype="multipart/form-data":表示提交的数据,以多段(每一个表单一个数据段)的形式进行拼接,然后以二进制流的形式发送给服务器
boundary:表示每段数据的分隔符
----WebKitFormBoundaryOZ1BoZwqflbGWUBH是由浏览器每次都随机生成,他就是每段数据的分界符
package com.pero.file.file_upload;
import jakarta.servlet.*;
import jakarta.servlet.http.*;
import java.io.IOException;
public class UploadServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
}
@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
System.out.println("文件上传");
}
}
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="https://jakarta.ee/xml/ns/jakartaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="https://jakarta.ee/xml/ns/jakartaee https://jakarta.ee/xml/ns/jakartaee/web-app_5_0.xsd"
version="5.0">
<servlet>
<servlet-name>UploadServlet</servlet-name>
<servlet-class>com.pero.file.file_upload.UploadServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>UploadServlet</servlet-name>
<url-pattern>/uploadServlet</url-pattern>
</servlet-mapping>
</web-app>
<%--
Created by IntelliJ IDEA.
User: Administrator
Date: 2023/3/15
Time: 23:08
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>
<form action="http://localhost:8080/file_Upload/uploadServlet" method="post" enctype="multipart/form-data">
用户名:<input type="text" name="username"/><br>
头像:<input type="file" name="photo"/><br>
<input type="submit" value="上传">
</form>
</body>
</html>
常用API
导入commons-fileupload-1.3.3.jar和commons-io-2.6.jar包到项目lib目录下
常用类:
ServletFileUpload类:用于解析上传的数据
FileItem类:表示每一个表单项
boolean ServletFileUpload.isMultipartContent(HttpServletRequest request):判断当前上传的数据格式是否为多段的格式
public List<FileItem> parseRequest(HttpServletRequest request):解析上传数据
boolean isFormField():判断当前表单项是普通表单项还是上传的文件类型,true表示表单项,false表示上传的文件类型
String getFieldName():获取表单项的name属性值
String getString():获取当前表单项的值
String getName():获取上传的文件名
void write(File var1) throws Exception:将上传的文件写到参数file所指向的硬盘位置
文件上传测试
package com.pero.servlet;
import org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.FileItemFactory;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.File;
import java.io.IOException;
import java.util.List;
public class UploadServlet extends HttpServlet {
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
req.setCharacterEncoding("UTF-8");
//先判断上传数据是否为多段数据(只有多段数据才是文件上传的)
if (ServletFileUpload.isMultipartContent(req)) {
//创建FileItemFactory工厂实现类
FileItemFactory fileItemFactory = new DiskFileItemFactory();
//创建用于解析上传数据的工具类
ServletFileUpload servletFileUpload = new ServletFileUpload(fileItemFactory);
//解析上传的数据得到每一个表单项Item
try {
List<FileItem> list = servletFileUpload.parseRequest(req);
//循环判断每一个表单项是普通类型还是上传文件
for (FileItem fileItem : list) {
if (fileItem.isFormField()) {
//普通表单项
System.out.println("表单项的name属性值:" + fileItem.getFieldName());
//参数UTF-8解决中文乱码
System.out.println("表单项的value值:" + fileItem.getString("UTF-8"));
} else {
//上传文件
System.out.println("表单项的name属性值:" + fileItem.getFieldName());
System.out.println("上传文件名:" + fileItem.getName());
fileItem.write(new File("G:\\test" + fileItem.getName()));
}
}
} catch (Exception e) {
throw new RuntimeException(e);
}
}
}
}
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="https://jakarta.ee/xml/ns/jakartaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="https://jakarta.ee/xml/ns/jakartaee https://jakarta.ee/xml/ns/jakartaee/web-app_6_0.xsd"
version="6.0">
<servlet>
<servlet-name>UploadServlet</servlet-name>
<servlet-class>com.pero.servlet.UploadServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>UploadServlet</servlet-name>
<url-pattern>/uploadServlet</url-pattern>
</servlet-mapping>
</web-app>
<%--
Created by IntelliJ IDEA.
User: Administrator
Date: 2023/3/15
Time: 23:08
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>
<form action="http://192.168.42.31:8080/Upload_Web/uploadServlet" method="post" enctype="multipart/form-data">
用户名:<input type="text" name="username"/><br>
头像:<input type="file" name="photo"/><br>
<input type="submit" value="上传">
</form>
</body>
</html>
文件的下载
客户端发送请求告诉服务器需要下载什么文件,服务器过去要下载的文件名,读取要下载的文件内容,把下载的文件内容回传给客户端,再回传前,通过响应头告诉客户端返回的数据类型,还要通过响应头告诉客户端收到的数据是用于下载使用
常用API说明:
response.getOutputStream():获取响应输出流
servletContext.getResourceAsStream():用于读取要下载的内容(返回对象为输入流)
servletCOntext.getMimeType():获取要下载的文件类型
response.setContentType():在回传之前通过响应头告诉客户端返回的数据类型
response.setHeader("Content-Disposition", "attachment;fileName=" + URLEncoder.encode("你好.png","UTF-8"));该响应头是告诉浏览器,这个文件是要下载的文件。attachment表示附件,也就是下载的文件,fileName=后面的表示下载的文件名
package com.pero.servlet.download_web;
import jakarta.servlet.*;
import jakarta.servlet.http.*;
import org.apache.commons.io.IOUtils;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.URLEncoder;
public class Download extends HttpServlet {
@Override
public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//1.获取要下载的文件名
String downloadFileName = "1.png";
//2.读取要下载的文件内容(通过ServletContext对象读取)
ServletContext servletContext = getServletContext();
//获取要下载的文件类型
String mimeType = servletContext.getMimeType("/file/" + downloadFileName);
System.out.println("下载的文件类型:" + mimeType);
//再回传之前通过响应头告诉客户端返回的数据类型
response.setContentType(mimeType);
//还要告诉客户端收到的数据是用于下载使用(还是使用响应头)
//Content-Disposition响应头表示收到的数据怎么处理
//attachment表示指定下载的文件名
//url编码是把汉字转换成%xx%xx的格式
response.setHeader("Content-Disposition", "attachment;fileName=" + URLEncoder.encode("你好.png","UTF-8"));
InputStream resourceAsStream = servletContext.getResourceAsStream("/file/" + downloadFileName);
//获取响应输出流
OutputStream outputStream = response.getOutputStream();
//把要下载的文件内容回传给客户端
//读取输入流中全部的数据赋值给输出流,输出给客户端
IOUtils.copy(resourceAsStream, outputStream);
}
@Override
public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
}
}
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="https://jakarta.ee/xml/ns/jakartaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="https://jakarta.ee/xml/ns/jakartaee https://jakarta.ee/xml/ns/jakartaee/web-app_5_0.xsd"
version="5.0">
<servlet>
<servlet-name>Download</servlet-name>
<servlet-class>com.pero.servlet.download_web.Download</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>Download</servlet-name>
<url-pattern>/download</url-pattern>
</servlet-mapping>
</web-app>
参考文章:http://blog.ncmem.com/wordpress/2023/11/25/javaweb-%e6%96%87%e4%bb%b6%e7%9a%84%e4%b8%8a%e4%bc%a0%e5%92%8c%e4%b8%8b%e8%bd%bd/
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标签:文件,JavaWeb,上传,jakarta,import,servlet,下载 From: https://www.cnblogs.com/songsu/p/17855503.html