Controller中servletFileUpload.parseRequest(request)解析为空

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 +"\t" + arg1 +"\t" + 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.