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

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1. 原因分析
2. 解决方案

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.