How does a wsimport generated client work?

Question

Before anything else, I want you to know that I can already connect to the web service server. I'm asking this question because I want to gain a deeper knowledge on how a wsimport generated client works. Based from my research, wsimport uses JAXWS. Please note that I have no knowledge from JAXWS.

I generated my client using wsimport. The WSDL I used is from an Axis2 web service and was automatically generated by Axis2. The classes below are the results of wsimport:

Under com.datamodel.xsd

• DataBeanRequest.java
• DataBeanResponse.java
• ObjectFactory.java
• package-info.java

Under com.service

• MyWebService.java
• MyWebServicePortType.java
• MyMethod.java
• MyMethodResponse.java
• ObjectFactory.java
• package-info.java

With the classes above, I can that tell that com.datamodel.xsd contains the beans used by the web service server (excluding ObjectFactory and package-info). Meanwhile, MyMethod and MyMethodResponse are also beans used to set the request and response parameter of the web service method/operation.

Below are my questions: (You don't really have to answer all of it if you don't know the answers on some of my questions. :) And please feel free to share any info that you think I might find useful.)

Am I correct with

• Am I correct with my assumptions above?
• What are the function of the other classes?
• I inspected MyWebService and it contains an annotation referring to the absolute location of the WSDL I used to generate the client. What is the relevance of specifying the wsdllocation in the client? How does the client use that info?
• I noticed that the actual URL of the web service is not declared in any of the classes generated. How does the client know where it needs to connect to?
• Was the WSDL file annotated so that the client can read the URL on the WSDL file upon connection? If so, then does it mean that the WSDL file is always read when a new connection must be established?
• Since there's a need for me to compile my application and install it on a different server, the will become invalid. Can I set it to a relative path instead of an absolute path? How? (Answer: Yes, it can be set to a relative path. The wsimport command has a wsdllocation attribute wherein the value of the wsdllocation can be specified.)
• What if I need to connect to an HTTPS. How can I set the server certificate?
• Is there any difference when I generate my client using wsimport and when I generate it using Axis2 or Apache CXF.

Stanford

Answer 1

Before I answer the questions, some clarification: JAX-WS is a specification for implementing web services in Java. It describes how WSDL artifacts can be mapped to Java classes and how this mapping can be applied using annotations. You can download the specification here. The tool wsimport is part of the reference implementation of this specification and the reference implementation is part of the Java class library. There are several alternative implementations, such as Axis2, CXF or Metro, that enhance the basic JAX-WS support with support for additional standards such as WS-ReliableMessaging or WS-Security.

Now to your questions:

Am I correct with my assumptions above?

Yes, you are.

What are the function of the other classes?

The package-info exists to map the XML namespace used in the web service to the package in which your implementation classes reside. The namespace normally looks different from a Java package name (normally, it is a URL) and this makes the mapping necessary.

The ObjectFactory allows you to create any of the messages sent and received by the service. You need this if you want to hook in code in front of your stub class, provide modified messages or similar things.

I can't see the content of your classes, but if I understand it right MyWebServicePortType is an interface that resembles the portType in your WSDL. That is, it maps the operations and their signatures in the WSDL to Java methods. If you want to provide the service (which you don't, you are asking about the client), you would need to implement this interface. As you implement the client, you simply use it.

Finally, the class MyWebService contains the client stub you need if you want to invoke the web service.

I inspected MyWebService and it contains an annotation referring to the absolute location of the WSDL I used to generate the client. What is the relevance of specifying the wsdllocation in the client? How does the client use that info?

The interface you generated contains the signature of the portType of the service, but it does not explain how you can talk to the service. This is part of the binding in the WSDL. The most basic setting is a document/literal style for the messages using SOAP over HTTP. Other configurations, such as SOAP over JMS, are possible and your client needs to know what protocol to use. Therefore it needs the binding WSDL. Also, as you state later, there is no endpoint address in your Java files. This address is also read from the WSDL.

I noticed that the actual URL of the web service is not declared in any of the classes generated. How does the client know where it needs to connect to?

It reads the address from the port of the service in the WSDL. This is located of the end of the WSDL.

Was the WSDL file annotated so that the client can read the URL on the WSDL file upon connection?

No, the port is a typical element of a concrete web service endpoint. There's nothing special needed here.

If so, then does it mean that the WSDL file is always read when a new connection must be established?

Well, there could be caching at the client side (I don't know about the details of the reference implementation on this one). From a conceptual point of view: yes, it is.

What if I need to connect to an HTTPS. How can I set the server certificate

This can be tricky, I can't give you an out-of-the-box answer. I would suggest to read through questions on this topic, such as this one.

Is there any difference when I generate my client using wsimport and when I generate it using Axis2 or Apache CXF

Yes, there is. wsimport is better, don't use wsdl2java. Here is a description, why.

Georginageorgine

Thanks again! :D You're also the one who answered my previous question. I just want to clarify this: JAXWS is a Java specification for web services. Java, CXF, Axis2 and others are examples of APIs/frameworks which implemented the JAXWS specification. Am I right with this? Also, what can you say on wsimport vs CXF when generating client stubs? The link you gave me only compares wsimport to Axis2. Is the additional features of Axis2, CXF really useful compare to the plain JAXWS of Java (Considering you're going to use it to develop a web service client, not a server.)? – Stanford

Yes, I am into this atm as well :) Yes, you are right in what you say. Concerning wsdl2java vs wsimport: Unfortunately, I can't give you hard facts, but only word of mouth advise. CXF and Axis2 name their code generation tools equally, but they are different. I have had bad experiences with axis2 wsdl2java, but no experience with cxf wsdl2java. So far, I have had no negative experience with wsimport. I even use it for generating client stubs that also use CXF. From what I have experienced and read, CXF is a fine WS-stack. – Georginageorgine

Concerning the additional features: Do you need things like docs.oasis-open.org/ws-rx/wsrm/200702 or oasis-open.org/committees/tc_home.php?wg_abbrev=wss ? Put differently: Does the service you call use a policy? (Look for policy elements in the WSDL). If no, the reference implementation will very likely be enough. There may be performance advantages for one of the stacks, but there is hardly any data on that out there. – Georginageorgine

Thanks! I also have no experience with CXF. On the other hand, I only have a basic knowledge on Axis2 and a very little knowledge on JAX-WS. Regarding the additional features, to be honest, I'm not sure what I need. I just want to ask it if it can make certain things easier. I might need to research what is a policy. I've read a WS-POLICY before but I'm not sure what it does. – Stanford

WS-Policy allows you to configure non-functional properties (message encryption, ...) for the service. The idea is that the service defines a policy and the WS-stack (axis2, cxf, ...) of client and service make it work, without additional coding necessary at the client or service side. As you can already connect to the service, I assume it does not define a policy and you can are safe to use the reference implementation. – Georginageorgine

Answer 2

You asked: I noticed that the actual URL of the web service is not declared in any of the classes generated. How does the client know where it needs to connect to?

If the WSDL was downloaded using a browser and passed as input to wsimport, then the local wsdl file location is embedded into the generated code. That is why you don't see the actual service location in the generated code. It also means if you deleted the local copy of the wsdl file the generated code will not work (when inovked using a main method) .

If the URL of the wsdl was passed as input to wsimport then that URL is embedded in the generated code, which is further used to get the actual service location. The idea is that the WSDL locations are fixed. They are expected to be in a UDDI or as a local file. This allows the actual services to move around and if they do move, you just have to modify the local copy of the wsdl file alone or update the wsdl in the UDDI. [mostly this does not happen as service locations are never IP but DNS names]

This is why it is never a good idea to publish the wsdl in the same server where your webservice is running

Ramrod