Trying to get a handle on Web Services?

Question

I'm trying to get a handle on web services and was wondering if I get some help from the SO community. In particular, a I'm trying to get a handle on WSDL, UDDI, SOAP AND JAX-P, because I'm most familiar with Java.

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Edit:

Please tell me if I'm right or wrong on these definitions:

• WSDL: This is a schema to describe what kind of XML documents can be passed to and from the WS.

• UDDI: This is the most confusing to me ATM and don't really have a good def.

• SOAP: Basic protocol used.

• JAX-p: This is used for parsing the XML documents.

Answer 1

As an alternative to the SOAP path you might also want to consider looking into REST-based (or RESTful) web services, for Java in particular JAX-RS: The Java API for RESTful Web Services.

Answer 2

That's a very broad question. At a high level, SOAP refers to the XML protocol of the messages that travel back and forth. WSDL is another XML protocol that defines the format of the SOAP messages (very useful for tools that translate SOAP requests and responses for you). Typically a SOAP service endpoint will also have a way to access the static WSDL document about that service (e.g. if a service is hosted at http://myservice.com/services/MyService, the WSDL will usually be served from http://myservice.com/services/MyService?WSDL in most implementations). UDDI is yet another XML protocol that describes queries to a registry asking for information about SOAP services stored there.

Learn SOAP and WSDL first. UDDI is not all that widely used (although getting more so slowly). JAXR is the Java API around UDDI, which means that you probably should never need to write a raw UDDI query yourself.

JAXP is just a Java XML parser API. It can be used for lots of things, not just SOAP and WSDL. Apache Axis is a good Java SOAP client tool, and wsdl4j is a good WSDL parsing tool, although Axis will also autogenerate SOAP requests and responses from Java objects for you by parsing WSDL. Optimally, you should never need to parse a WSDL document yourself, but you often have to in practice when the tool doesn't quite do what you want.

Answer 3

If you want a practical introduction, do the Spring Web Services tutorial: http://static.springframework.org/spring-ws/sites/1.5/reference/html/tutorial.html

Answer 4

Web Services messages are defined according to the WSDL schema. Some parts will define where the message is supposed to go, and some parts will define the message contents.

Good Thomas Erl introduction to whats in the WSDL

They can be embedded in SOAP messages for transmission.

UDDI is like a look up directory to find web services you might use / consume. If you're trying to tie two specific systems together as opposed to broadcast the offering of some services, its probably irrelevant to you.

In Java, you can use a web services containers like Apache Axis to comprise your web services. JaxP could be used to parse XML documents for transmission etc.

You should read some overviews from the web and then post some more specific questions :-) Maybe if you described what you were trying to achieve, some readers would have experience with similar requirements.