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Class file parser

I have an assignment where i need to write a Java program that parses a .class file and retrieves things like :
1.name of the .java file
2.implemented interfaces
3.variables
4.constructors
5.methods
I don't have any ideeas where to begin from?
For example,what kind of Data I/O structure should I use?

You can you ClassParser which is available in Apache commons library. you can read the Javadoc here. You can download apache commons from here
You can also use Java reflection API which provides method such as getDeclaredFileds, getDeclaredMethods etc.

There are already several libraries for classfile parsing out there. Objectweb ASM is the most popular.
If you have to do it from scratch, that I'd recommend starting by the JVM specification, which explains the binary layout of classfiles in detail. After that, parsing is just a simple matter of programming. I've written a classfile parser before, it's not that hard.

You don't need any external library, just use java.lang.Class. Write the name of your class:
[NameOfMyClass].class.getDeclaredFields();
[NameOfMyClass].class.getDeclaredConstructors();
[NameOfMyClass].class.getDeclaredMethods();
It's the same for interfaces and many other attributes.

You can use Java Reflection. Here is a good tutorial -->
Java Reflection Tutorial

OpenJDK actually comes with an API that lets you parse and manipulate class files programmatically that most programmers don't know about. It is located at the package com.sun.org.apache.bcel.internal.

A library to produce canonical XML in JAVA 5?

I'm using org.apache.xml.security.c14n.Canonicalizer which was recommended to me here: Sort xml attributes for pretty print using javax.xml.transform.Transformer. I will need it to run in Java 5 though.. it doesn't seem to work.
Are there any options?

XOM has a Canonicalizer which will do this.
In addition to being a very good general-purpose XML DOM library, it's a much more lightweight solution to canonicalization than your XSLT-based solution.

Best way to parse Java in Java

As the title says, I want to parse some Java source code in Java. I'm pretty sure there are other java libraries that already perform this, but I couldn't find any.

Antlr has a grammar file for Java. See this.

Janino can parse, compile and execute Java code.

You may be looking for something like ANTLR: http://www.antlr.org/

Eclipse exposes the Syntax Tree of it's own Java compiler. You can simply access the elements.
See here.

JavaCC has a Java 1.5 grammar including generics.
the tokens are probably more
fine-grained then what I want
Your first requirement is to get an accurate parse, and you will realistically only get that from an existing parser. What you do with the result is up to you.

What is best practice in converting XML to Java object?

I need to convert XML data to Java objects. What would be best practice to convert this XML data to object?
Idea is to fetch data via a web service (it doesn't use WSDL, just HTTP GET queries, so I cannot use any framework) and answers are in XML. What would be best practice to handle this situation?

JAXB is a standard API for doing this: http://java.sun.com/developer/technicalArticles/WebServices/jaxb/

Have a look at XStream. It might not be the quickest, but it is one of the most user friendly and straightforward converters in Java, especially if your model is not complex.

For a JMS project we were marshalling and unmarshalling (going from java to xml and xml to java) XML embedded in TextMessages (string property). We tried JAXB, Jibx, and XMLBeans. We found that XMLBeans worked best for us. Fast, easily configurable, good documentation, and easy Maven integration.

I have used and will continue to use JDOM -> www.jdom.org

Another option is a Sax Parser. It is procedural - i.e. a visitor pattern - but if the xml is fairly lightweight, (and even medium weight) I have found it to be very useful for this.

JAXB API which comes in Java(In built).

I have used JIBX in MQ module. It works very well. Ant config is simple. Used Xsd2Jibx converter to generate the binding files and Java beans from XML schema. Marshalling and un-marshalling allow to specify character-set parameter. It was useful in my project to handle custom character-set. But I found an issue in the binding compiler. If the Java bean has lengthier path name, it generates class file with lengthier file name which will cause issue in Windows XP(it has a maximum file length limit).
I haven't used other APIs. So I am not trying to compare with others. If you decided to use JIBX, I hope this will be helpful.
More details, please refer JIBX website

I've used XStream as well, it is easy to use and customizable. You can add your own custom converters and that was very handy for me...

So surprised more people have not mentioned Jibx. Amazing lib and i think a lot simpler to use than Jaxb. Performance is also fab!

For this you can also consider apache's bitwixt and simple framework for xml

Code / template generator for Java

For C#, I have often used CodeSmith and lately the T4 generator which is part of Visual Studio.
I'm looking for something similar for Java, in particular an Eclipse add-in since I do all my Java development using the Eclipse IDE.

I've found that freemarker does a pretty good job for generating any type of code. From the website:
FreeMarker is a "template engine"; a generic tool to generate text output (anything from HTML to autogenerated source code) based on templates. It's a Java package, a class library for Java programmers. It's not an application for end-users in itself, but something that programmers can embed into their products.
It is used by struts2 a lot. The website has a long list of other products that use freemarker.

I have worked with both Velocity and StringTemplate. Velocity is a bit more conventional (think JSP/ASP concepts), while StringTemplate seems a bit cleaner. in a sense described in this Artima interview. Both are pure templating engines, and will require you to write some code around them, if you want to do full-blown code generation from a model.
StringTemplate is used internally by ANTLR, which may be useful to your effort.
As an alternative approach, you could go with Eclipse, using EMF and JET.

You should try Telosys Tools, an Eclipse plugin for code generation working from an existing database with customizable Velocity templates
See: http://www.telosys.org/
Eclipse Marketplace : http://marketplace.eclipse.org/content/telosys-tools
The tutorials are here : https://sites.google.com/site/telosystutorial/
See this other question about CodeSmith : Is there any freeware tool available which is like Codesmith?

I use JavaForger to generate code from templates. It parses existing classes so that you can use that class-data inside your templates. It can both create new classes or insert code into existing classes. You can determine where generated code will be inserted based on a string conversion rule (e.g. myProject/dao/ProductDao.java => myProject/service/ProductService.java).
JavaForger is open source and uses FreeMarker as template engine and JavaParser as parser.

This is an old question but the only thing that comes close (for Java) to do what CodeSmith Generator does is Spring Roo.
The reason is that Java does not have Partial Classes like C# does. Spring Roo gets around this by using AspectJ ITDs.

My answer is to use StringTemplate, but there is a bit more to it than just what tool to use.
Is it the issue to generate java code? Or is it to use java tools? Programmers would be normally very comfortable writing code. Therefore, it would not be a leap to write some java classes and write a walk that would generate code using StringTemplate. I personally think it is a good exercise to create example models, generate your java code from the models. And depending on your use case you could end up writing JSON models by hand and never having to write any java code to produce the java code. Or you could end up writing Java classes that produce equivalent models.
You could use the StringTemplate based STST, which reads JSON. STST is command line based, and I am sure you could hook it to both eclipse and/or Visual Studio.
I personally think about portability, JSON is an extremely simple language. And almost every language has libraries that support it.

I'm not a C# man so I don't know what the equivalents would be, however I've found xdoclet to be very good in the past. I don't think it integrates with eclipse as such but you can run it from an ant script. Does things like generating Hibernate mapping files from annotated Java classes. Useful if that's what you're looking for :)

eclipse has a built-in template system.
look in window -> preferences -> java -> code style -> code templates

You might look at my plugin : http://fast-code.sourceforge.net/. It allows one to select multiple fields and generate code using user specified velocity templates.

Take a look at my project https://github.com/karajdaar/templator and see if that helps.

I wrote a simple web based application for my use.
its available at https://github.com/harish2704/templates
and a demo is available at http://templates-harish2704.rhcloud.com/
Its language independent tool. GUI supports several languages ( highlighting, snippet completion ect )