效果：
1、jsp前端
<%--
Created by IntelliJ IDEA.
User: Lenovo
Date: 2020/6/19
Time: 22:53
Learn from https://www.bilibili.com/video/BV18z411i7gh?t=23&p=192
To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>文件上傳</title>
</head>
<body>
<!--文件上傳對錶單的要求-->
<!--
1、表單中的請求提交方式必須是POST
2、表單中應指定所提交的請求位multipart請求，通過在<form/>標籤中添加enctype屬性
其值爲multipart/form-data
3、 表單
-->
<form method="POST" action="http://localhost:8888/hello/UploadImageServlet" enctype="multipart/form-data">
編號<input type="text" name="BNO"></br>
名字<input type="text" name="BNAME"></br>
照片<input type="file" name="picutreUrl"></br>
<input type="submit" value="註冊">
</form>
</body>
</html>
2、servlet處理提交後臺
package Servlet.bookServlet;
import org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.FileUploadException;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;
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.*;
import java.util.List;
@WebServlet(name = "UploadImageServlet")
public class UploadImageServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
this.doPost(request,response);
}
@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//1、判斷請求是不是multipart請求
if(!ServletFileUpload.isMultipartContent(request)){
throw new RuntimeException("當前請求不支持文件上傳");
}
System.out.println("開始上傳文件");
//2、創建FileItem工廠==>文件寫入硬盤的作用
DiskFileItemFactory factory = new DiskFileItemFactory();
//3、創建文件上傳核心組件
// 調用ServletFileUpload.parseRequest方法解析request對象，得到一個保存了所有上傳內容的List對象。
ServletFileUpload upload = new ServletFileUpload(factory);
upload.setHeaderEncoding("utf-8");
String bNo="defaultBNo",bName="defaultBName";
//4、解析請求
try {
List<FileItem> items =upload.parseRequest(request);
//5、遍歷請求
for(FileItem item:items){
//普通表單項，上傳名字，編號等普通信息的上i傳
if(item.isFormField()){
String fileName = item.getFieldName();// name屬性值
String fileValue = item.getString("utf-8");// name對應的value值
System.out.println(fileName + " = " + fileValue);
if(fileName.equalsIgnoreCase("BNO")){
bNo = fileValue;
}
if(fileName.equalsIgnoreCase("BNAME")){
bName = fileValue;
}
}
else{//上傳圖片等
String fileName = item.getName();
System.out.println("上傳文件名字:"+fileName);
String suffix = fileName.substring(fileName.lastIndexOf('.'));//獲取文件類型
String newFileName = bNo+"_"+bName+suffix;
System.out.println(newFileName);
//獲取輸入流，其中有上傳文件的內容
InputStream is = item.getInputStream();
//String path = this.getServletContext().getRealPath("/net/bookImage");//獲得當前項目保存服務器地址，也就是web文件夾下
String path ="D:\\tomcat\\apache-tomcat-9.0.35-windows-x64\\apache-tomcat-9.0.35\\webapps\\librarySystem\\web\\net\\bookImage";
//創建目標文件，用來保存上傳文件
File desFile = new File(path,newFileName);
//創建文件輸出流
OutputStream os = new FileOutputStream(desFile);
//將輸入流數據寫入到輸出流中
int len=-1;
byte[]buf = new byte[1024];
while((len=is.read(buf))!=-1){
os.write(buf,0,len);
}
os.close();//輸出流
is.close();//輸入流
}
}
}
catch (FileUploadException e) {
e.printStackTrace();
}
}
}