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How to pull detailed schema info from a WSDL based web service?

Assuming I am developing a client for a known, WSDL-based, web service (of which source code is not available to me):
Is there a way I can validate various fields (e.g. string lengths not exceeding limit) based on the inline schema in that WSDL, at runtime?
If so, how do I interact with that web service to get its inline XSD information?

If you want to make this really dynamic, than you have to assume that the URI to the WSDL is accessible to you, along with all other external references the WSDL might use, to other WSDL files and/or XSD files.
First step, you will have to download files to a temp folder, or create I/O streams to those URIs for in memory loading, to load a schema (a javax.xml.validation.Schema). I am not aware of a Java API which would make this task easy (get a schema out of WSDL reference, such as one available to developers on the .NET platform) - hopefully if there is one, someone might chime in. Otherwise, it shouldn't be that difficult to write one.
I have to warn you that many people may consider this (loading external URIs, particularly one pointing to the Internet) as a security issue in a production environment, so be careful here with your design. Since you're saying "a known, WSDL-based, web service", I would probably aquire the XSDs at design time, and bundle them as resources in my Jar files which would go with the client code.
The next thing is how do you create your XML... Let's say you're using something such as JAXB, then a post such as this one will give an idea how to tackle your problem, and what exactly do you need to validate. If you're not using JAXB, then explore what your API is doing, and how it would actually allow you to interject your validation...
I hope that this at least gives you an idea around the kind of details you need to have in this kind of question, to get a more specific answer.

creating a .xml file from .xsd with java

I'm a quite new to java world and I have a requirement of generating an .xml file from an .xsd file
I did some research and found that 'jaxb' could do it. And I found some example too, but the problem is, almost all the examples uses 'xjc' tool to do this. But I want a way to do this through my java code.
Os this possible?
if yes, I'm thinking something like this, from my java code
load the .xsd file
generate the .xml
save the .xml file
Can someone direct me to a good resource and or tell me if my thinking is wrong

I've had good experiences using XMLBeans, however I've always had the XSD available at compile time. It integrates nicely with Maven (plus potentially other build systems). The compilation produces a series of Java classes that can be used to construct an XML document that conforms to the XSD or process an XML file you've received.
You can potentially do some runtime processing of an XSD using the org.apache.xmlbeans.XmlBeans.compileXsd class, but I've never experimented with it. Just seen a reference from an FAQ.

I think the main problem is that to do it in a clean way you should have classes reflecting your xsd. Xsd defines a data model, so the important part is to recreate it with classes. If you want to do it dynamically it could be rather difficult. If you want to do it at compile time- jaxb is the way to go. There is very interesting article talking about problems related with parsing xml (it goes from a different perspective than you describe), but I think there is a wealth of knowledge to be learned from here:
http://elegantcode.com/2010/08/07/dont-parse-that-xml/

Set up maven build for xjc for multiple schemas in the same xml namespace?

I'm working on a project where we have Jersey/JaxB based serialization system to talk to a web service. The service in question returns data wrapped inside an Atom feed.
An older part of the system wrote a one-off specific to their service XSD for Atom that was hard wired with only their particular elements. I now need to add support for a new service, which is doing a similar thing (using Atom as a "envelope"), but using significantly different elements and content schema.
I don't want to disturb the existing code, so ideally I'd like to do the same thing the previous project did: define my own schema for the parts of Atom that the new service is using.
I'm running into:
org.xml.sax.SAXParseException: 'feed' is already defined
I'm apparently hitting the limitation described in the XJC release notes: It is not legal to have more than one <jaxb:schemaBindings> per namespace.
Is there a way to set things up in our build so that if I have separate xjb files, I can run xjc independently over the two distinct schemas and generate code for each of them into separate packages? How do I work around this limitation?
We're using the maven jaxb plugin.

Just for the record, what we ended up doing was generating the code from the schema separately, and checking in the generated code. Since the ATOM schema's not changing, it was reasonably safe. Annoying to have to do it that way though.

How to parse wsdl and xsd files?

I've been looking for a way to programmatically parse WSDL and associated XSD files to get values from annotation / documentation tags. I managed to get values from wsdl using wsdl4j, but how do i do this for XSD files? I tried to use XSOM but for some reason i always get null.

1). Hope this link will be useful for you to choose the best parser, Parse WSDL Effectively.
I have tried using Apache Woden, WSDL4J and Membrane SOA. Among these, Membrane SOA seems to be developer friendly.
2). Place the dependent XSD's in the folder where you have placed the WSDL. Then try parsing your WSDL, it should work fine.

Maybe the JWSDL help will be of service. It also makes calls to the services.
Here a discussion on the subject

How to create WSDL file given SOAP WSDL operations

I haven't had any experience with web service related development. So, any ideas will be greatly appreciated.
Suppose, I have a file listing draft specification of WSDL operations. Following is one example. How would I go about creating the WSDL file. Is notepad sufficient or do I need to have WSDL editor?
getHostSystemInfo
Returns detailed information about host systems specified via given IDs.
input HostSystemIdCollection(Collection of Strings)
Output HostSystemInfoCollection
HostSystemInfo
Id: mandatory
Properties: Following properties should be provided for host systems
HostSystemName
HostSystemProperty1
HostSystemProperty2
HostSystemProperty3
....
....

If the question is just "how do I create the WSDL" then you could indeed use Notepad and just write it, it's only XML after all. However, writing syntactically correct XML by hand is pretty dull, and error prone. So I would recommend using WSDL aware tooling for example an Eclipse editor
An alternative is to write some Java which expresses the interface, and from it generate the WSDL. There are many ways of doing this, including starting with an EJB and annotating it accordingly. A few googles should help you find what you need.
My experience is that simple POC situations tend to work well starting at the Java. Larger scale projects benfit from considered designs starting at the WSDL.

coding WSDL by hand is a big pain! i used a XML editor for creation of and then generated the stubs with JAXWS. It is important to understand and differences of the WSDL styles, which is not trivial (have a look at WSDL styles). a good help is to import the WSDL schema to your IDE (eclipse, idea) and then work with autocompletion.
just for interest, why are you using WSDL + SOAP. if you have a choice and you use anyway HTTP, have a look at REST. It can make implementation of web-api a LOT easier, both on server side and for api-clients.

If you haven't done any web services before, I would strongly recommend a WSDL Editor. The Netbeans has a plugin that should help.
The other way of doing it, which may be easier is by using the Java annotations defined in JSR 181.

Of course you could use the worst text editor in the world (!) but I'd seriously consider using any decent XML editor or IDE (Eclipse's WSDL support is pretty decent). This will save you a lot of pain and suffer.
Or, if this is an option, you could just annotate a Java class with JAX-WS annotations and have your WSDL dynamically generated from the Java code. Personally, I prefer the WSDL-first approach, the Java-first approach is just a suggestion to get you started.

You could use Axis2 to create that for you.