SpringMVC中servletFileUpload.parseRequest(request)解析为空获取不到数据问题

原因分析

首先我们来看下Spring mvc 中文件上传的配置

<bean id="multipartResolver"
		class="org.springframework.web.multipart.commons.CommonsMultipartResolver">
		<property name="defaultEncoding" value="UTF-8" />

		<property name="maxUploadSize" value="2000000000" />
	</bean>

再来看看Controller中使用

public void upload2(HttpServletRequest request) {
		// 转型为MultipartHttpRequest
		try {
			MultipartHttpServletRequest multipartRequest = (MultipartHttpServletRequest) request;
			List<MultipartFile> fileList = multipartRequest.getFiles("file");
			for (MultipartFile mf : fileList) {
				if(!mf.isEmpty()){
					
				}
			}
		} catch (Exception e) {
			e.printStackTrace();
		}
		
	}

方式二

public String upload(HttpServletRequest request,
			@RequestParam(value = "file") MultipartFile[] files) {
		try {
			for (MultipartFile mf : files) {
				if(!mf.isEmpty()){
					
				}
			}

		} catch (Exception e) {
			e.printStackTrace();
		}
		return "upload";
	}

这里springMVC 都为我们封装好成自己的文件对象了,转换的过程就在我们所配置的CommonsMultipartResolver这个转换器里面下面再来看看它的源码

他的转换器里面就是调用common-fileupload的方式解析,然后再使用parseFileItems()方法封装成自己的文件对象 . 

List<FileItem> fileItems = ((ServletFileUpload) fileUpload).parseRequest(request);

大家应该发现了上面的这句代码,已经使用过fileUpload解析过request了,你在Controller里面接收到的request都已经是解析过的,你再次使用upload进行解析获取到的肯定是空,这个就是问题的所在(大家可以在servlet里面实验,看看第二次解析后能不能获取到数据,当然是不能的)

解决方案

1)删除Spring MVC文件上传配置

<!-- 
	<bean id="multipartResolver"
		class="org.springframework.web.multipart.commons.CommonsMultipartResolver">
		<property name="defaultEncoding" value="UTF-8" />

		<property name="maxUploadSize" value="2000000000" />
	</bean>
	 -->

在控制器里面自己完成request的解析(当然上面spring MVC提供的两种方法是不能用的,所有上传的地方都需要自己做处理)

public void upload3(HttpServletRequest request) {
		DiskFileItemFactory factory = new DiskFileItemFactory();
		ServletFileUpload upload = new ServletFileUpload(factory);
		try {
			List<FileItem> list = upload.parseRequest(request);
			for(FileItem item : list){
				if(item.isFormField()){
					
				}else{
					//item.write(new File(""));
				}
			}
		} catch (FileUploadException e) {
			e.printStackTrace();
		}
		
	}

2)如果是需要使用的ProgressListener监听器我们可以重写 CommonsMultipartResolver的parseRequest方法

package com.lwp.spring.ext;

import java.util.List;
import javax.servlet.http.HttpServletRequest;
import org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.FileUpload;
import org.apache.commons.fileupload.FileUploadBase;
import org.apache.commons.fileupload.FileUploadException;
import org.apache.commons.fileupload.servlet.ServletFileUpload;
import org.springframework.web.multipart.MaxUploadSizeExceededException;
import org.springframework.web.multipart.MultipartException;
import org.springframework.web.multipart.commons.CommonsMultipartResolver;
import com.lwp.listener.FileUploadListener;
public class CommonsMultipartResolverExt extends CommonsMultipartResolver {
	@Override
	protected MultipartParsingResult parseRequest(HttpServletRequest request)
			throws MultipartException {
		FileUploadListener listener = new FileUploadListener();
		String encoding = determineEncoding(request);
		FileUpload fileUpload = prepareFileUpload(encoding);
		fileUpload.setProgressListener(listener);
		try {
			List<FileItem> fileItems = ((ServletFileUpload) fileUpload).parseRequest(request);
			return parseFileItems(fileItems, encoding);
		}
		catch (FileUploadBase.SizeLimitExceededException ex) {
			throw new MaxUploadSizeExceededException(fileUpload.getSizeMax(), ex);
		}
		catch (FileUploadException ex) {
			throw new MultipartException("Could not parse multipart servlet request", ex);
		}
	}
}

监听器方法

import org.apache.commons.fileupload.ProgressListener;

public class FileUploadListener implements ProgressListener {

	@Override
	public void update(long arg0, long arg1, int arg2) {
		//arg0 已经上传多少字节
		//arg1 一共多少字节
		//arg2 正在上传第几个文件
		System.out.println(arg0 +"	" + arg1 +"	" + arg2);
	}
	
}

配置文件改为我们自己的(这种方式的缺陷是,所有文件上传都需要使用到Listener)

<bean id="multipartResolver"
		class="com.lwp.spring.ext.CommonsMultipartResolverExt">
		<property name="defaultEncoding" value="UTF-8" />
		<property name="maxUploadSize" value="2000000000" />
	</bean>

注: 综上所述,如果只是普通的文件上传spring MVC 完全可以完成,如果需要使用进度条的listener前段可以使用假的进度条或者是上面的两种方式.