【Java.ThirdParty】Apache Commons —— FileUpload —— web应用上传文件

最新推荐文章于 2021-06-13 10:44:41 发布

王晓斌

最新推荐文章于 2021-06-13 10:44:41 发布

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分类专栏： Java.ThirdParty 文章标签： Java 3rd Lib

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本文介绍如何利用Apache Commons FileUpload组件实现文件上传功能。包括Maven依赖配置、通过HTML表单发起文件上传请求、在Servlet中解析并保存上传文件的示例代码，以及如何配置Servlet等内容。

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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。