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>文件上传</title>
</head>
<body>
<!--文件上传对表单的要求-->
<!--
1、表单中的请求提交方式必须是POST
2、表单中应指定所提交的请求位multipart请求，通过在<form/>标签中添加enctype属性
其值为multipart/form-data
3、 表单
-->
<form method="POST" action="http://localhost:8888/hello/UploadImageServlet" enctype="multipart/form-data">
编号<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="注册">
</form>
</body>
</html>
2、servlet处理提交后台
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、判断请求是不是multipart请求
if(!ServletFileUpload.isMultipartContent(request)){
throw new RuntimeException("当前请求不支持文件上传");
}
System.out.println("开始上传文件");
//2、创建FileItem工厂==>文件写入硬盘的作用
DiskFileItemFactory factory = new DiskFileItemFactory();
//3、创建文件上传核心组件
// 调用ServletFileUpload.parseRequest方法解析request对象，得到一个保存了所有上传内容的List对象。
ServletFileUpload upload = new ServletFileUpload(factory);
upload.setHeaderEncoding("utf-8");
String bNo="defaultBNo",bName="defaultBName";
//4、解析请求
try {
List<FileItem> items =upload.parseRequest(request);
//5、遍历请求
for(FileItem item:items){
//普通表单项，上传名字，编号等普通信息的上i传
if(item.isFormField()){
String fileName = item.getFieldName();// name属性值
String fileValue = item.getString("utf-8");// name对应的value值
System.out.println(fileName + " = " + fileValue);
if(fileName.equalsIgnoreCase("BNO")){
bNo = fileValue;
}
if(fileName.equalsIgnoreCase("BNAME")){
bName = fileValue;
}
}
else{//上传图片等
String fileName = item.getName();
System.out.println("上传文件名字:"+fileName);
String suffix = fileName.substring(fileName.lastIndexOf('.'));//获取文件类型
String newFileName = bNo+"_"+bName+suffix;
System.out.println(newFileName);
//获取输入流，其中有上传文件的内容
InputStream is = item.getInputStream();
//String path = this.getServletContext().getRealPath("/net/bookImage");//获得当前项目保存服务器地址，也就是web文件夹下
String path ="D:\\tomcat\\apache-tomcat-9.0.35-windows-x64\\apache-tomcat-9.0.35\\webapps\\librarySystem\\web\\net\\bookImage";
//创建目标文件，用来保存上传文件
File desFile = new File(path,newFileName);
//创建文件输出流
OutputStream os = new FileOutputStream(desFile);
//将输入流数据写入到输出流中
int len=-1;
byte[]buf = new byte[1024];
while((len=is.read(buf))!=-1){
os.write(buf,0,len);
}
os.close();//输出流
is.close();//输入流
}
}
}
catch (FileUploadException e) {
e.printStackTrace();
}
}
}