參考轉載：
https://www.cnblogs.com/longqingyang/p/5579889.html
原理：
common-fileupload組件利用DiskFileItemFactory工廠方法生成request的表單內容解析器，將表單內容解析成List<FileItem>，然後循環獲取處理上傳文件的輸入流getInputStream()。
該組件依賴commons-io組件。
步驟：
1、檢查保存目錄以及臨時文件保存目錄
2、判斷提交上來的數據是否是上傳表單的數據，即是否是enctype="multipart/form-data"
3、創建DiskFileItemFactory工廠
4、利用工廠創建ServletFileUpload文件上傳解析器
5、使用ServletFileUpload解析器解析上傳數據，解析結果返回的是List<FileItem>集合，FileItem對應Form表單的輸入項
6、循環處理每一個FileItem
7、如果是普通表單輸入項，獲取表單字段和表單內容
8、如果是文件上傳項，獲取處理文件名，並getInputStream()，然後保存到保存目錄中
代碼：
fileupload,jsp
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>fileupload test</title>
</head>
<body>
<form action="${pageContext.request.contextPath}/servlet/uploadHandleServlet" method="post" enctype="multipart/form-data">
上傳用戶：<input type="text" name="username"><br>
上傳文件1：<input type="file" name="file1"><br>
上傳文件2：<input type="file" name="file2"><br>
<input type="submit" value="submit">
</form>
</body>
</html>
uploadHandleServlet.Java
package servlet;
import org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.FileUploadBase;
import org.apache.commons.fileupload.FileUploadException;
import org.apache.commons.fileupload.ProgressListener;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;
import sun.swing.FilePane;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.*;
import java.nio.ByteBuffer;
import java.nio.channels.Channels;
import java.nio.channels.FileChannel;
import java.nio.channels.ReadableByteChannel;
import java.nio.channels.WritableByteChannel;
import java.util.List;
import java.util.UUID;
public class uploadHandleServlet extends HttpServlet {
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
String savePath = this.getServletContext().getRealPath("/WEB-INF/upload");
File saveFile = new File(savePath);
if (!saveFile.exists() && !saveFile.isDirectory()) {
System.out.println("目錄或者文件不存在");
saveFile.mkdir();
}
String tempPath = this.getServletContext().getRealPath("/WEB-INF/temp");
File tempFile = new File(tempPath);
if (!tempFile.exists() && !tempFile.isDirectory()) {
System.out.println("目錄或者文件不存在");
tempFile.mkdir();
}
//消息提示
String message = "";
try {
//使用fileupload上傳文件
//1、判斷是否爲多媒體多部件上傳，enctype=multipart/form-data
if (!ServletFileUpload.isMultipartContent(request)) {
PrintWriter writer = response.getWriter();
writer.println("Error: 表單必須寫有:enctype=multipart/form-data");
writer.flush();
return;
}
//2、創建一個創建一個DiskFileItemFactory工廠
DiskFileItemFactory diskFileItemFactory = new DiskFileItemFactory();
diskFileItemFactory.setSizeThreshold(1024 * 10);//設置工廠的緩衝區的大小，當上傳的文件大小超過緩衝區的大小時，就會生成一個臨時文件存放到指定的臨時目錄當中。
diskFileItemFactory.setRepository(tempFile);//設置上傳時生成的臨時文件的保存目錄
//3、利用工廠創建文件上傳解析器
ServletFileUpload servletFileUpload = new ServletFileUpload(diskFileItemFactory);
servletFileUpload.setHeaderEncoding("UTF-8");//解決上傳文件名的中文亂碼
servletFileUpload.setProgressListener(new ProgressListener() {
@Override
public void update(long pBytesRead, long pContentLength, int i) {
System.out.println("文件大小爲：" + pContentLength + ",當前已處理：" + pBytesRead);
}
});
servletFileUpload.setFileSizeMax(1024 * 1024);//設置上傳單個文件的大小的最大值
servletFileUpload.setSizeMax(1024 * 1024 * 10);//設置上傳文件總量的最大值，最大值=同時上傳的多個文件的大小的最大值的和
//4、使用ServletFileUpload解析器解析上傳數據，解析結果返回的是一個List<FileItem>集合，每一個FileItem對應一個Form表單的輸入項
List<FileItem> fileItemList = servletFileUpload.parseRequest(request);
for (FileItem item : fileItemList) {
//如果fileitem中封裝的是普通輸入項的數據
if (item.isFormField()) {
String name = item.getFieldName();
String value = item.getString("UTF-8");//解決普通輸入項的數據的中文亂碼問題
System.out.println(name + " " + value);
} else {
String fileName = item.getName();//如果fileitem中封裝的是上傳文件，得到上傳的文件名稱
System.out.println("文件名稱：" + fileName);
if (fileName == null || fileName.trim().equals("")) {
continue;
}
fileName = fileName.substring(fileName.lastIndexOf(File.separatorChar) + 1);//ie瀏覽器可能帶路徑
String fileExtName = fileName.substring(fileName.lastIndexOf(".") + 1);
if ("zip".equals(fileExtName) || "rar".equals(fileExtName) || "tar".equals(fileExtName) || "jar".equals(fileExtName)) {
request.setAttribute("message", "上傳文件類型不符合");
request.getRequestDispatcher("/fileupload/message.jsp").forward(request, response);
return;
}
System.out.println("上傳文件的擴展名：" + fileExtName);
fileName = UUID.randomUUID().toString() + "_" + fileName;
System.out.println("保存路徑爲:" + savePath);
// 普通IO方式讀取
// InputStream is = item.getInputStream();
// FileOutputStream fos=new FileOutputStream(savePath+File.separator+fileName);
// byte[] buffer = new byte[1024];
// int length=0;
// while ((length = is.read(buffer)) > 0) {
// fos.write(buffer,0,length);
// }
//NIO方式讀取
InputStream is = item.getInputStream();
ReadableByteChannel readChannel = Channels.newChannel(is);
FileOutputStream fos = new FileOutputStream(savePath + File.separator + fileName);
WritableByteChannel writeChannel = Channels.newChannel(fos);
ByteBuffer buffer = ByteBuffer.allocate(1024);
int length = 0;
while ((length = readChannel.read(buffer)) > 0) {
buffer.flip();
writeChannel.write(buffer);
buffer.clear();
}
is.close();
fos.close();
item.delete();
message = "文件上傳成功";
}
}
} catch (FileUploadBase.FileSizeLimitExceededException e) {
e.printStackTrace();
request.setAttribute("message", "單個文件超出最大值");
request.getRequestDispatcher("/fileupload/message.jsp").forward(request, response);
return;
} catch (FileUploadBase.SizeLimitExceededException e) {
e.printStackTrace();
request.setAttribute("message", "上傳文件的總的大小超出限制的最大值！！！");
request.getRequestDispatcher("/fileupload/message.jsp").forward(request, response);
return;
} catch (FileUploadException e) {
e.printStackTrace();
message = "文件上傳失敗";
} catch (Exception e) {
e.printStackTrace();
message = e.getMessage();
}
request.setAttribute("message", message);
request.getRequestDispatcher("/fileupload/message.jsp").forward(request, response);
}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
}
}
message.jsp
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>Title</title>
</head>
<body>
${requestScope.message}
</body>
</html>