Java 将File转换为MultipartFile类型

　　首先转换时需要用到commons-fileupload-1.3.2.jar包，若项目中没有就先加入jar包，实现代码如下：

　　1、根据File创建FileItem

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.OutputStream;  

import org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.FileItemFactory;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.springframework.web.multipart.MultipartFile;
import org.springframework.web.multipart.commons.CommonsMultipartFile; 

/*
    创建FileItem
     */
	private FileItem createFileItem(File file, String fieldName) {
		FileItemFactory factory = new DiskFileItemFactory(16, null);
		FileItem item = factory.createItem(fieldName, "text/plain", true, file.getName());
		int bytesRead = 0;
		byte[] buffer = new byte[8192];
		try {
			FileInputStream fis = new FileInputStream(file);
			OutputStream os = item.getOutputStream();
			while ((bytesRead = fis.read(buffer, 0, 8192)) != -1) {
				os.write(buffer, 0, bytesRead);
			}
			os.close();
			fis.close();
		} catch (IOException e) {
			e.printStackTrace();
		}
		return item;
	}

　　2、通过FileItem对象可以轻松获得CommonsMultipartFile对象，转换成MultiPartFile对象即可使用。

MultipartFile mfile = new CommonsMultipartFile(fileItem);