A good Design-by-Contract library for Java?

There is a nice overview on WikiPedia about Design by Contract, at the end there is a section regarding languages with third party support libraries, which includes a nice serie of Java libraries. Most of these Java libraries are based on Java Assertions.

In the case you only need Precondition Checking there is also a lightweight Validate Method Arguments solution, at SourceForge under Java Argument Validation (Plain Java implementation).

Depending on your problem, maybe the OVal framework, for field/property Constraints validation is a good choice. This framework lets you place the Constraints in all kind of different forms (Annotations, POJO, XML). Create customer constraints through POJO or scripting languages (JavaScript, Groovy, BeanShell, OGNL, MVEL). And it also party implements Programming by Contract.

I tested contract4J one time and found it usable but not perfect. You are creating contracts for for and after method calls and invars over the whole class.

The contract is created as an assertion for the method. The Problem is that the contract itself is written in a string so you don't have IDE support for the contracts or compile time cheching if the contract still works.

A link to the library

It's been a long time since I've looked at these, but found some old links. One was for JASS.

The other one that I had used (and liked) was iContract by Reliable Systems. It had an ant task that you would run as a preprocessor. However, I can't seem to find it with some google searches, it looks like it has vanished. The original site is now a link farm. Check out this link for some possible ways to get to it.

I think that many DbC libraries were surclassed by the builtin assert keyword, introduced since Java 1.4:

• it is a built-in, no other library is required
• it works with inheritance
• you can activate/deactivate on package basis
• easy to refactoring (e.g. no assertions in comments)