Spring MultipartResolver 或者 ServletFileUpload 冲突导致获取不到http数据/Multipart数据为空

Posted on Edited on Word count in article: 2.5k Reading time ≈ 2 mins.

如果不知道MultipartResolver 或者ServletFileUpload 的，请 JAVA Server上传文件 Spring MultipartResolver 或者 ServletFileUpload

如果同时使用了MultipartResolver和ServletFileUpload，就会在iter.hasNext()返回false.然后整个循环就跳出去了。

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if (isMultipart) {
            DiskFileItemFactory factory = new DiskFileItemFactory(1024 * 1024 * 20, null);
            ServletFileUpload upload = new ServletFileUpload(factory);
            upload.setHeaderEncoding("UTF-8");
            upload.setSizeMax(1024 * 1024 * 20);

            List<FileItem> fileItems = upload.parseRequest(req);
            Iterator<FileItem> iter = fileItems.iterator();
            // 这里获取不到任何FileItem
            while (iter.hasNext()) {
                FileItem item = (FileItem) iter.next();
                if (item.isFormField()) {
                    String name = item.getFieldName();
                    String value = item.getString("UTF-8");
                    request.put(name, value);
                } else {
                    byte[] filebytes = item.get();
                    if (StringUtils.isBlank(item.getName())) {
                        continue;
                    }
                    
                    request.put(item.getFieldName(), new String(filebyte, "utf-8"));
                }
            }
        }
}

整个问题产生的原因是Spring框架先调用了MultipartResolver 来处理http multi-part的请求。这里http multipart的请求已经消耗掉。后面又交给ServletFileUpload ，那么ServletFileUpload 就获取不到相应的multi-part请求。

如果帐前 卒想快速解决这个问题。解决方法是加入帐前卒的 multipartResolver, 来单独处理某些请求。这些请求需要特判。例如下面的代码：

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package example;

import javax.servlet.http.HttpServletRequest;

import org.springframework.web.multipart.commons.CommonsMultipartResolver;

/**
 * @author 帐前卒
 */
public class MyMultipartResolver extends CommonsMultipartResolver {
    private String excludeUrls;   
    private String[] excludeUrlArray;
    
    public String getExcludeUrls() {
        return excludeUrls;
    }
    public void setExcludeUrls(String excludeUrls) {
        this.excludeUrls = excludeUrls;
        this.excludeUrlArray = excludeUrls.split(",");
    }
    /**
     * 这里是处理Multipart http的方法。如果这个返回值为true,那么Multipart http body就会MyMultipartResolver 消耗掉.如果这里返回false
     * 那么就会交给后面的自己写的处理函数处理例如刚才ServletFileUpload 所在的函数
     * @see org.springframework.web.multipart.commons.CommonsMultipartResolver#isMultipart(javax.servlet.http.HttpServletRequest)
     */
    @Override
    public boolean isMultipart(HttpServletRequest request) {
        for (String url: excludeUrlArray) {
            // 这里可以自己换判断
            if (request.getRequestURI().contains(url)) {
                return false;
            }
        }
        
        return super.isMultipart(request);
    }
     
}

然后在web.xml中这样写：

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<bean id="multipartResolver" class="example.MyMultipartResolver">
<property name="excludeUrls" value="example"/>
<!-- url中带有example的http请求就不会被multipartResolver先解析-->
</bean>