struts2上传文件非根对象上传报错

当遇到非根对象的时候 文件上传
struts2会给我们报一个没有ContentType 没有FileName的方法的方法
警告: Error setting expression 'person.attachment' with value '[Ljava.io.File;@15772fd'
ognl.OgnlException: target is null for setProperty(null, "attachment", [Ljava.io.File;@15772fd)
警告: Error setting expression 'person.attachmentContentType' with value '[Ljava.lang.String;@1a28b5c'
ognl.OgnlException: target is null for setProperty(null, "attachmentContentType", [Ljava.lang.String;@1a28b5c)

举例:

class Person{

private String name;

private File attachment;

get....

set.....

}

public class UserAction implements ModelDriven{

private Person person;

@Override
public Object getModel() {
if(user==null){
　　user = new User();
}

return user;
}
public String add(){

//System.out.println("添加user");

return "success";
}

}

界面

<form action="sb/user!add.do" enctype="multipart/form-data" method="post">
　　<input type="text" name="person.name"/>
　　<input type="file" name="person.attachment"/>
　　<input type="submit" value="登录"/>
</form>

对于非根对象插入数据