【Java.ThirdParty】Apache Commons —— FileUpload —— web应用上传文件
相关资料
参考地址：
http://commons.apache.org/proper/commons-fileupload/
Maven：
<dependency> <groupId>commons-fileupload</groupId> <artifactId>commons-fileupload</artifactId> <version>1.3.1</version> </dependency>
FileUpload 依赖于 Commons IO；
Commons FileUpload
The Commons FileUpload package makes it easy to add robust, high-performance, file upload capability to your servlets and web applications.
FileUpload parses HTTP requests which conform to RFC 1867, "Form-based File Upload in HTML". That is, if an HTTP request is submitted using the POST method, and with a content type of "multipart/form-data", then FileUpload can parse that request, and make the results available in a manner easily used by the caller.
通过web form向服务器上传文件的示例如下：通过向web服务器发送一个multipart/from-data请求
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Upload Files</title>
</head>
<body>
<form method="post" enctype="multipart/form-data" action="uploadfile">
File Upload Testing:<br/>
Upload File 1: <input type="file" name="file1" size="30"/><br/>
Upload File 2: <input type="file" name="file2" size="30"/><br/>
<input type="submit" name="submit" value="Upload"/>
<input type="reset" name="reset" value="Reset"/>
</form>
</body>
</html>
FileUpload可以解析http request成为一个item list，其中每个item不管其底层具体是什么，都实现了FileItem接口。
传统的FileUpload API假定上传的文件一定会被保存在某个地方；通常为了更多的性能考虑或者灵活性，我们可以使用Streaming API,具体参考commons fileupload在线文档。
在Servlet中使用FileUpload - Save To Disk
创建一个Servlet如下：
package com.gof.test.servlet;
import java.util.List;
import java.util.Iterator;
import java.io.IOException;
import java.io.PrintWriter;
import java.io.File;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.FileCleanerCleanup;
import org.apache.commons.fileupload.servlet.ServletFileUpload;
import org.apache.commons.fileupload.FileItem;
import org.apache.commons.io.FileCleaningTracker;
public class UploadFileServlet extends HttpServlet {
/**
*
*/
private static final long serialVersionUID = 3396770132755929933L;
private String filePath = null;
private String tempFilePath = null;
public void init(ServletConfig config) throws ServletException {
super.init(config);
// get the property in servlet configuration in web.xml
filePath = getInitParameter("filePath");
tempFilePath = getInitParameter("tempFilePath");
// get the real path is disk
filePath = getServletContext().getRealPath(filePath);
tempFilePath = getServletContext().getRealPath(tempFilePath);
}
protected void doPost(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException{
PrintWriter out = resp.getWriter();
// For Chinese File Name
req.setCharacterEncoding("utf-8");
// Begin to parse the uploaded files
try{
DiskFileItemFactory factory = new DiskFileItemFactory();
// Set the factory constraints
// Set the buffer size for file upload when write to disk
factory.setSizeThreshold(4 * 1024);
// Set the temporary path
factory.setRepository(new File(tempFilePath));
// Create a new file upload handler
ServletFileUpload upload = new ServletFileUpload(factory);
// Set overall request size constraint
upload.setFileSizeMax(4 * 1024 * 1024);
// Parse the request
List<FileItem> items = upload.parseRequest(req);
// Process the uploaded items
Iterator<FileItem> iter = items.iterator();
while (iter.hasNext()){
FileItem item = iter.next();
if (item.isFormField()){
processFormFields(item, out);
}else{
processUploadFiles(item, out);
}
}
out.close();
}catch (Exception e){
e.printStackTrace();
}
}
private void processFormFields(FileItem item, PrintWriter out){
String name = item.getFieldName();
String value = item.getString();
out.println("The file name is " + name + "; The value is " + value);
}
private void processUploadFiles(FileItem item, PrintWriter out) throws Exception{
String fieldName = item.getFieldName();
String fileName = item.getName();
String contentType = item.getContentType();
long sizeInBytes = item.getSize();
if ((fileName == null) || (sizeInBytes == 0)){
return;
}
// write the file to disk
File uploadedFile = new File(filePath + "/" + fileName);
item.write(uploadedFile);
out.println("The file " + fileName + " is saved; The size of the file is " + sizeInBytes + " bytes");
}
}
在web.xml中配置上面的Servlet:
<!-- test upload file: http://localhost:8080/base-webapp/uploadfile.html -->
<servlet>
<servlet-name>uploadfiletest</servlet-name>
<servlet-class>com.gof.test.servlet.UploadFileServlet</servlet-class>
<init-param>
<param-name>filePath</param-name>
<param-value>/upload</param-value>
</init-param>
<init-param>
<param-name>tempFilePath</param-name>
<param-value>/tempupload</param-value>
</init-param>
</servlet>
<servlet-mapping>
<servlet-name>uploadfiletest</servlet-name>
<url-pattern>/uploadfile</url-pattern>
</servlet-mapping>
当点击Upload按钮时，对应的文件将被保存到webapp下的目录/upload，同时临时文件夹/tempupload的文件会被删除；如果对传入的文件没有做相应的处理，则临时文件夹下的文件不会被删除。
资源清理（临时目录）