struts2文件上传?报错

struts2在做文件上传是，当超过限制的上传文件总大小时，直接与服务器断开连接了，后台也没有报错，怎么回事啊？tomcat7.0的服务器，6.0试了也是这样。

package com.eg.action;

import java.io.File; import java.io.IOException; import java.util.List;

import org.apache.commons.io.FileUtils; import org.apache.struts2.ServletActionContext;

import com.opensymphony.xwork2.ActionSupport;

public class FileuploadAction extends ActionSupport {

private List<File> upload;
private List<String> uploadContentType;
private List<String> uploadFileName;

public List<File> getUpload() {
	return upload;
}

public void setUpload(List<File> upload) {
	this.upload = upload;
}

public List<String> getUploadContentType() {
	return uploadContentType;
}

public void setUploadContentType(List<String> uploadContentType) {
	this.uploadContentType = uploadContentType;
}

public List<String> getUploadFileName() {
	return uploadFileName;
}

public void setUploadFileName(List<String> uploadFileName) {
	this.uploadFileName = uploadFileName;
}

@Override
public String execute()  {
	for (int i = 0; i <upload.size(); i++) {
	System.out.println("上传的文件类型：" + uploadContentType.get(i));
	System.out.println("上传的文件名：" + uploadFileName.get(i));
	 try {
		FileUtils.copyFile(upload.get(i), new File(ServletActionContext
		 .getServletContext().getRealPath("/WEB-INF/uploads"),
		 uploadFileName.get(i)));
	} catch (IOException e) {
		e.printStackTrace();
		throw new RuntimeException(e);
	}
	}
	return null;
}

}

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE struts PUBLIC
	"-//Apache Software Foundation//DTD Struts Configuration 2.3//EN"
	"http://struts.apache.org/dtds/struts-2.3.dtd">

<struts>

        <!-- 限制上传的文件总大小为200M --> <constant name="struts.multipart.maxSize" value="209715200"></constant> <constant name="struts.custom.i18n.resources" value="message"></constant> <package name="default" namespace="/" extends="struts-default"> <action name="upload" class="com.eg.action.FileuploadAction"> <result name="input">/error.jsp</result> <interceptor-ref name="defaultStack"> <param name="fileUpload.maximumSize">20971520</param> <param name="fileUpload.allowedExtensions">txt,avi,doc,xml</param> </interceptor-ref> </action> </package> </struts>