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Reading specific strings from XML tags

I am using java, I want to read strings from an XML tag. EX: < blank type="Something">
I need to be able to assign "Something" to a variable. Any ideas?

There are a lot of ways to do this:
You can use the XML APIs provided with Java (SAX or STAX or DOM).
There are libraries that build on the XML APIs (JDOM, DOM4J, or XOM) which are easier to use than the raw APIs.
There's Java-XML databinding, described in Pratik's answer. Java-XML databinding is sometimes overkill, depending on your requirements, and when there are errors they can be hard to figure out. Sometimes it's worthwhile, though. I think JiBX is particularly interesting.
If you don't know where to start, start with XOM. XOM was created by a JDOM contributor, it was designed to be easy to use.

What you want to achieve is referred to as Unmarshalling an XML. Unmarshalling means extracting data from an XML document and using it to construct a Java object or graph of objects. There are various APIs available to do the same. You should have a look at the following links:
JAXB:
http://www.oracle.com/technetwork/articles/javase/index-140168.html
Castor: http://castor.codehaus.org/
JiBX: http://jibx.sourceforge.net/

Best way for building objects out of XMLs at runtime

I'm in a situation that I have a lot of of XMLs, that are sent to me from a server and I'm using JAXB or any API based on that architecture for building instances of objects.
The problem is, I have to per-determine the class that I want to unmarshall for at compile time. My solution that is in my mind, is to read the incoming XML object and based on some tags, I will direct the unmrashaller to make an instance of the specified class. That approach will let me have a lot of IFs statements and big state machine.
Is there a better design pattern or approach ?

Try using Apache digester 3, I think it can save you lots of "if"s and is not difficult to use at all.
Have a look at this article: http://www.javaworld.com/javaworld/jw-10-2002/jw-1025-opensourceprofile.html

rest implementation without annotations

I am trying to learn REST web services. But it seems to use annotations every where. Is there any implementation of Rest framework without using annotations.I have no idea about annotations.
Thanks

REST does not use annotations. REST is just a spec of good wishes. It does not dictate anything. You are right: the most of existing implementations user annotations. And IMHO it is good.
But if you do not want to use them implement REST yourself. It is easy. For POST create servlet that impelments doPost(). Extract data from URL. Call underlying layer with these parameters. For GET method implement doGet() that does pretty the same.
This is the idea of REST. Nothing more. What frameworks do is just the parsing of the arguments and marshalling/unmarshalling of data. But if you data is marshalled as XML or JSON (or any other format) you can implement all this yourself very quickly.
Happy RESTing!

Creating multithreaded Java server and clients, but messages have to be in XML format

I've got to write a multithreaded chat program, using a server and clients but each message sent has to be in XML.
Is it simpler/easier just to write out all the code in java, and then try and somehow alter it so the messages are sent in XMl format, or would it be simpler just to try and go for it in XML and hope it works. I'll admit I don't know that much about XML. :)
Also any links to any relevant online help/tutorials would be much appreciated.
Thanks.

When messing with XML in Java, PLEASE consider using JAXB or something similar. It allows you to work with a normal object graph in memory and then serialize that to XML in one operation (and the other way around).
Manipulating XML through the DOM API is a slow way to lose your sanity, do not do it for any non-trivial amount of XML.
I fail to see what the program being multithreaded or a server have to do with it though...

Check out XStream. You can use this to marshall a normal Java object into XML, and back again into an object, without having to do anything instrusive like define interfaces or specify schema etc. i.e. it works out of the box for objects you already have defined. For most cases it's seamless in its default mode.
XStream produces a direct XML serialised representation of a Java object (i.e. XML elements represent each field of a Java object directly). You can customise this further as/when you require. If you want to define persisted objects in terms of schema (XSD) then it's not appropriate. However if you're transporting objects where persistence is short-term and you're not worried about conforming to some schema then it's definitely of use.
e.g.
Person person = new Person("Brian Agnew");
XStream xStream = new XStream();
System.out.println(xStream.toXML(person));
and conversion from XML to the Person object is similarly trivial.
(note XStream is thread-safe)

There is something called XML RPC. This examples pretty much shows what you're looking for:
http://docstore.mik.ua/orelly/xml/jxml/ch11_02.htm

It would be simpler to use existing XMPP clients and servers and not write your own at all.
If this is in fact homework, then I would suggest writing the client and server as you have suggested, using all java, but use a String as the message. You can then easily add parsing of the string to/from XML when all other parts are working.

I would suggest to also have a look at Betwixt and Digester. For Digester there are some tutorials which can be found in the Digister-wiki. Betwixt provides some pretty good tutorials right on its website.
Additionally to these two tools there is a list of alternatives that can be found in the Reference section of http://wiki.apache.org/commons/Digester/WhyUseDigester

You're on the right page trying to break the task into smaller pieces.

What's the best practice to render JSON data in JSPs?

I need to render JSON data in my JSPs for some AJAX requests. I'd like to know what's the best way to do it in terms of easy to use and stability.

Assuming you want to generate the JSON from one or more Java objects, the following is a fairly straightforward approach:
Set the Java object(s) as attributes in request/session scope
Convert the objects to JSON using a tag library such as http://json-taglib.sourceforge.net/index.html

I'm assuming you have checked out json.org already...
I recently switched from json-lib to XStream:
http://x-stream.github.io/
Definitely much easier. Just a few lines of code and you are done. Note, it started as an XML serializer, deserializer. It now supports JSON ouput.