Passing complex types to/from an Axis-based Web service?

[andreas.baus]

Hello.

I'm trying to exchange data between a webservice based on Apache Axis
and a client written in C#, and so far it has been working with few
problems (none that I couldn't solve myself with a bit of web
research). However, now I've tried passing complex data types between
the two, and could not get that to work.

What I did was to declare my data type on the Axis/Java side as an
Object implementing java.io.Serializable, and when I use that as a
parameter/return type in one of my web service methods, Axis includes
an appropriate type declaration in the WSDL (I'm using the code-first
approach, writing the service code as needed, and letting Axis generate
the WSDL) and when I add the web reference to the .NET project, the
Object is recreated perfectly from that. Looking good - so far...
*However* when I actually try to pass such an object to or from a
method, .NET and/or Java (depending on which way I try to pass it)
throws an exception claiming that there's no suitable (de)serializer
for the object.

Now, this may seem naive, but I thought that the default serialization
would be enough to handle a simple object containing nothing but a
handful of fields of primitive data types... So, am I missing anything?
Doing something fundamentally wrong? Or do I seriously have to
explicitly create (de)serialization code for every non-primitive data
type I'd like to pass?

Thanks in advance for any suggestions.

[John Saunders]

<an**********@meta-level.dewrote in message
news:11**********************@m73g2000cwd.googlegr oups.com...

Hello.

I'm trying to exchange data between a webservice based on Apache Axis
and a client written in C#, and so far it has been working with few
problems (none that I couldn't solve myself with a bit of web
research). However, now I've tried passing complex data types between
the two, and could not get that to work.

What I did was to declare my data type on the Axis/Java side as an
Object implementing java.io.Serializable, and when I use that as a
parameter/return type in one of my web service methods, Axis includes
an appropriate type declaration in the WSDL (I'm using the code-first
approach, writing the service code as needed, and letting Axis generate
the WSDL) and when I add the web reference to the .NET project, the
Object is recreated perfectly from that. Looking good - so far...
*However* when I actually try to pass such an object to or from a
method, .NET and/or Java (depending on which way I try to pass it)
throws an exception claiming that there's no suitable (de)serializer
for the object.

Now, this may seem naive, but I thought that the default serialization
would be enough to handle a simple object containing nothing but a
handful of fields of primitive data types... So, am I missing anything?
Doing something fundamentally wrong? Or do I seriously have to
explicitly create (de)serialization code for every non-primitive data
type I'd like to pass?

Thanks in advance for any suggestions.

Check carefully and make sure the XML namespaces are the same on both sides.

Also, for the future, be aware that there are some XML Schema constructs
that Axis (or JAXB, I guess) doesn't seem to like. Even something like a
maxOccurs on an xsd:sequence element cause it to choke.

John

[andreas.baus]

John Saunders schrieb:

Check carefully and make sure the XML namespaces are the same on both sides.

Also, for the future, be aware that there are some XML Schema constructs
that Axis (or JAXB, I guess) doesn't seem to like. Even something like a
maxOccurs on an xsd:sequence element cause it to choke.

First of all, thanks for your reply, but I'm not exactly sure what to
make of it (have patience with me, please, this whole web service
business is all new for me). There are so many different namespaces
involved, I have no idea which have to match which others...

Now, I *think* I made some progress. Realizing that maybe it was a bit
much to ask for to expect Axis to be able to serialize arbitrary
objects, I turned the object in question into a java bean, and added a
<beanMappingentry to the deployment descriptor. Now, at least, the
service itself actually manages to respond to my request instead of
throwing an exception; however, .NET still fails to convert the
response result back into a usable object in the generated stub code
for the web reference:

public ComplexDataObject ComplexOut() {
object[] results = this.Invoke("ComplexOut", new object[0]);
return ((ComplexDataObject)(results[0]));
}

Apparently, results[0] is not a single object ready for type conversion
into ComplexDataObject, it is rather an array containing the XML
attributes and elements of the response (the latter being the
individual fields of the passed object).

Obviously, I am still doing something wrong. If anyone has any idea as
to what that might be, I'd love to hear it. If more info is required,
I'd gladly post some snippets from the code/wsdd/wsdl files involved, I
just didn't want to spam this group with it without knowing if that
would even be helpful...

[John Saunders]

<an**********@meta-level.dewrote in message
news:11*********************@e3g2000cwe.googlegrou ps.com...

John Saunders schrieb:

>Check carefully and make sure the XML namespaces are the same on both
sides.

Also, for the future, be aware that there are some XML Schema constructs
that Axis (or JAXB, I guess) doesn't seem to like. Even something like a
maxOccurs on an xsd:sequence element cause it to choke.

First of all, thanks for your reply, but I'm not exactly sure what to
make of it (have patience with me, please, this whole web service
business is all new for me). There are so many different namespaces
involved, I have no idea which have to match which others...

Now, I *think* I made some progress. Realizing that maybe it was a bit
much to ask for to expect Axis to be able to serialize arbitrary
objects

....

You actually have hit the nail on the head.

Web Services isn't about communicating objects. It's about communicating
XML. We send and receive XML, which matches an XML schema, referenced by a
WSDL file which is also XML. Think XML.

We like to program to objects, of course, and we can often do so without
ever thinking about the XML in the middle. But you really have no reason to
believe that the Java object type system on one side can translate arbitrary
Java objects to XML, send them to the .NET CLR object type system on the
other side and have it deserialize into an "equivalent" arbitrary .NET CLR
type. Similarly, there will be XML structures that translate into objects in
one type system but will not translate into objects in the other type
system.

So, what to do? Take the data you want to send, and create an XML schema
which describes it at a semantic level. Leave out any high-level OO or
relational concepts and just describe the data. For instance, in
transmitting a DataSet, just describe the rows and columns and ignore
anything having to do with indexes, keys or relations. For OO classes,
ignore any of the methods and concentrate on the data. Simplify the data
types. For instance, you don't need to transmit a Java Map object or .NET
Hashtable; you need to transmit an array of key/value pairs.

Given that XSD schema, run it through XSD.EXE on .Net and the equivalent on
Java. Keep playing with the schema until you can generate correct classes on
both platforms.

What you'll wind up with is what's known as a Data Transfer Object (as
opposed to a Business Object). Define your operations in terms of this DTO.
It means you'll have to pack or unpack your complex objects or DataSets into
and out of the DTO, which is tedious to code. But it means that you will be
communicating at all levels in XML and in OO structures which map to the
XML.

Sorry for the mini-lecture; I hope that helps.

John