将Apache的commons-fileupload.jar放在应用程序的WEB-INF\lib下，即可使用。下面举例介绍如何使用它的文件上传功能。
所使用的fileUpload版本为1.2，环境为Eclipse3.3+MyEclipse6.0。FileUpload 是基于 Commons IO的，所以在进入项目前先确定Commons IO的jar包（本文使用
commons-io-1.3.2.jar）在WEB-INF\lib下。
此文作示例工程可在文章最后的附件中下载。
示例1
最简单的例子，通过ServletFileUpload静态类来解析Request，工厂类FileItemFactory会对mulipart类的表单中的所有字段进行处理，不只是file字段。getName（）得到文件名，getString（）得到表单数据内容，isFormField（）可判断是否为普通的表单项。
demo1.html
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=GB18030">
<title>File upload</title>
</head>
<body>
//必须是multipart的表单数据。
<form name="myform" action="demo1.jsp" method="post"
enctype="multipart/form-data">
Your name: <br>
<input type="text" name="name" size="15"><br>
File:<br>
<input type="file" name="myfile"><br>
<br>
<input type="submit" name="submit" value="Commit">
</form>
</body>
</html>
demo1.jsp
<%@ page language="java" contentType="text/html; charset=GB18030"
pageEncoding="GB18030"%>
<%@ page import="org.apache.commons.fileupload.*"%>
<%@ page import="org.apache.commons.fileupload.servlet.*"%>
<%@ page import="org.apache.commons.fileupload.disk.*"%>
<%@ page import="java.util.*"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<%
boolean isMultipart = ServletFileUpload.isMultipartContent(request);//检查输入请求是否为multipart表单数据。
if (isMultipart == true) {
FileItemFactory factory = new DiskFileItemFactory();//为该请求创建一个DiskFileItemFactory对象，通过它来解析请求。执行解析后，所有的表单项目都保存在一个List中。
ServletFileUpload upload = new ServletFileUpload(factory);
List<FileItem> items = upload.parseRequest(request);
Iterator<FileItem> itr = items.iterator();
while (itr.hasNext()) {
FileItem item = (FileItem) itr.next();
//检查当前项目是普通表单项目还是上传文件。
if (item.isFormField()) {//如果是普通表单项目，显示表单内容。
String fieldName = item.getFieldName();
if (fieldName.equals("name")) //对应demo1.html中type="text" name="name"
out.print("the field name is" + item.getString());//显示表单内容。
out.print("<br>");
} else {//如果是上传文件，显示文件名。
out.print("the upload file name is" + item.getName());
out.print("<br>");
}
}
} else {
out.print("the enctype must be multipart/form-data");
}
%>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=GB18030">
<title>File upload</title>
</head>
<body>
</body>
</html>
结果：
the field name isjeff
the upload file name isD:\C语言考试样题\作业题.rar
示例2
上传两个文件到指定的目录。
demo2.html
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=GB18030">
<title>File upload</title>
</head>
<body>
<form name="myform" action="demo2.jsp" method="post"
enctype="multipart/form-data">
File1:<br>
<input type="file" name="myfile"><br>
File2:<br>
<input type="file" name="myfile"><br>
<br>
<input type="submit" name="submit" value="Commit">
</form>
</body>
</html>
demo2.jsp
<%@ page language="java" contentType="text/html; charset=GB18030"
pageEncoding="GB18030"%>
<%@ page import="org.apache.commons.fileupload.*"%>
<%@ page import="org.apache.commons.fileupload.servlet.*"%>
<%@ page import="org.apache.commons.fileupload.disk.*"%>
<%@ page import="java.util.*"%>
<%@ page import="java.io.*"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<%String uploadPath="D:\\temp";
boolean isMultipart = ServletFileUpload.isMultipartContent(request);
if(isMultipart==true){
try{
FileItemFactory factory = new DiskFileItemFactory();
ServletFileUpload upload = new ServletFileUpload(factory);
List<FileItem> items = upload.parseRequest(request);//得到所有的文件
Iterator<FileItem> itr = items.iterator();
while(itr.hasNext()){//依次处理每个文件
FileItem item=(FileItem)itr.next();
String fileName=item.getName();//获得文件名，包括路径
if(fileName!=null){
File fullFile=new File(item.getName());
File savedFile=new File(uploadPath,fullFile.getName());
item.write(savedFile);
}
}
out.print("upload succeed");
}
catch(Exception e){
e.printStackTrace();
}
}
else{
out.println("the enctype must be multipart/form-data");
}
%>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=GB18030">
<title>File upload</title>
</head>
<body>
</body>
</html>
结果：
upload succeed
此时，在"D:\temp"下可以看到你上传的两个文件。
示例3
上传一个文件到指定的目录，并限定文件大小。
demo3.html
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=GB18030">
<title>File upload</title>
</head>
<body>
<form name="myform" action="demo3.jsp" method="post"
enctype="multipart/form-data">
File:<br>
<input type="file" name="myfile"><br>
<br>
<input type="submit" name="submit" value="Commit">
</form>
</body>
</html>
demo3.jsp
<%@ page language="java" contentType="text/html; charset=GB18030"
pageEncoding="GB18030"%>
<%@ page import="org.apache.commons.fileupload.*"%>
<%@ page import="org.apache.commons.fileupload.servlet.*"%>
<%@ page import="org.apache.commons.fileupload.disk.*"%>
<%@ page import="java.util.*"%>
<%@ page import="java.io.*"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<%
File uploadPath = new File("D:\\temp");//上传文件目录
if (!uploadPath.exists()) {
uploadPath.mkdirs();
}
// 临时文件目录
File tempPathFile = new File("d:\\temp\\buffer\\");
if (!tempPathFile.exists()) {
tempPathFile.mkdirs();
}
try {
// Create a factory for disk-based file items
DiskFileItemFactory factory = new DiskFileItemFactory();
// Set factory constraints
factory.setSizeThreshold(4096); // 设置缓冲区大小，这里是4kb
factory.setRepository(tempPathFile);//设置缓冲区目录
// Create a new file upload handler
ServletFileUpload upload = new ServletFileUpload(factory);
// Set overall request size constraint
upload.setSizeMax(4194304); // 设置最大文件尺寸，这里是4MB
List<FileItem> items = upload.parseRequest(request);//得到所有的文件
Iterator<FileItem> i = items.iterator();
while (i.hasNext()) {
FileItem fi = (FileItem) i.next();
String fileName = fi.getName();
if (fileName != null) {
File fullFile = new File(fi.getName());
File savedFile = new File(uploadPath, fullFile
.getName());
fi.write(savedFile);
}
}
out.print("upload succeed");
} catch (Exception e) {
e.printStackTrace();
}
%>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=GB18030">
<title>File upload</title>
</head>
<body>
</body>
</html>
示例4
利用Servlet来实现文件上传。
Upload.java
package com.zj.sample;
import java.io.File;
import java.io.IOException;
import java.util.Iterator;
import java.util.List;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;
@SuppressWarnings("serial")
public class Upload extends HttpServlet {
private String uploadPath = "D:\\temp"; // 上传文件的目录
private String tempPath = "d:\\temp\\buffer\\"; // 临时文件目录
File tempPathFile;
@SuppressWarnings("unchecked")
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws IOException, ServletException {
try {
// Create a factory for disk-based file items
DiskFileItemFactory factory = new DiskFileItemFactory();
// Set factory constraints
factory.setSizeThreshold(4096); // 设置缓冲区大小，这里是4kb
factory.setRepository(tempPathFile);// 设置缓冲区目录
// Create a new file upload handler
ServletFileUpload upload = new ServletFileUpload(factory);
// Set overall request size constraint
upload.setSizeMax(4194304); // 设置最大文件尺寸，这里是4MB
List<FileItem> items = upload.parseRequest(request);// 得到所有的文件
Iterator<FileItem> i = items.iterator();
while (i.hasNext()) {
FileItem fi = (FileItem) i.next();
String fileName = fi.getName();
if (fileName != null) {
File fullFile = new File(fi.getName());
File savedFile = new File(uploadPath, fullFile.getName());
fi.write(savedFile);
}
}
System.out.print("upload succeed");
} catch (Exception e) {
// 可以跳转出错页面
e.printStackTrace();
}
}
public void init() throws ServletException {
File uploadFile = new File(uploadPath);
if (!uploadFile.exists()) {
uploadFile.mkdirs();
}
File tempPathFile = new File(tempPath);
if (!tempPathFile.exists()) {
tempPathFile.mkdirs();
}
}
}
demo4.html
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=GB18030">
<title>File upload</title>
</head>
<body>
// action="fileupload"对应web.xml中<servlet-mapping>中<url-pattern>的设置.
<form name="myform" action="fileupload" method="post"
enctype="multipart/form-data">
File:<br>
<input type="file" name="myfile"><br>
<br>
<input type="submit" name="submit" value="Commit">
</form>
</body>
</html>
web.xml
<servlet>
<servlet-name>Upload</servlet-name>
<servlet-class>com.zj.sample.Upload</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>Upload</servlet-name>
<url-pattern>/fileupload</url-pattern>
</servlet-mapping>
