Axis2 customize class problem

[binz]

hi:

I am using Axis2 Service Archive to migrate from java class to java web service.

public String send_test(String a)
 {  
  return a;
 }

for above code, it is no problem, however, when I changed the input parameter 
to my customized class, like below:

class JContents 
{
    public String content;
}

public String send_test(JContents a)
 {
  return a.content;
 }

Then, when I call from client:

   JMobileServiceMMSStub stub=new JMobileServiceMMSStub("some web service 
endpoint");
   JMobileServiceMMSStub.Sendtest send_test=new 
JMobileServiceMMSStub.Sendtest();
   JMobileServiceMMSStub.JContents co=new JMobileServiceMMSStub.JContents();
   co.setContent("test");
   
   send_mms.setA(co);
   JMobileServiceMMSStub.Send_mmsResponse res=stub.send_test(send_test);
   System.out.println(res.get_return());

it always give me empty string, I also used php and C# to build the web service 
client side to call, however, it all return the same result => empty string. 

I don't know how it happened? what should I do for customized object as web 
service input?

Thanks.

bin.