A good Design-by-Contract library for Java? [closed]

Answer 1

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.

Answer 2

Google has a open source library called contracts for java.

Contracts for Java is our new open source tool. Preconditions, postconditions, and invariants are added as Java boolean expressions inside annotations. By default these do nothing, but enabled via a JVM argument, they’re checked at runtime.

• @Requires, @Ensures, @ThrowEnsures and @Invariant specify contracts as Java boolean expressions
• Contracts are inherited from both interfaces and classes and can be selectively enabled at runtime

contracts for java.

Answer 3

I personally think that the DbC libraries available at present have left a lot to be desired, none of the libraries i looked at played well with the Bean Validation API.

The libraries i looked at have been documented here

The Bean Validation API has a lot of over lap with the concepts from DbC. In certain cases Bean Validation API cannot be used like simple POJO's (non CDI managed code). IMO a think wrapper around the Bean Validation API should suffice.

I found that the existing libraries are a little tricky to add into existing web projects given that they are implemented either via AOP or Byte code instrumentation. Probably with the advent of Bean Validation API this kind of complexity to implement DbC is unwarranted.

I have also documented my rant in this post and hope to build a small library which leverages on the Bean Validation API

Answer 4

If you want a plain and simple basic support for expressing your contracts, have a look on valid4j (found on Maven Central as org.valid4j:valid4j). It lets you express your contracts using regular hamcrest-matchers in plain code (no annotations, nor comments).

For preconditions and postconditions (basically assertions -> throwing AssertionError):

import static org.valid4j.Assertive.*;

require(inputList, hasSize(greaterThan(0)));
...
ensure(result, lessThan(4.0));

If you are not happy with the default global policy (throwing AssertionError), valid4j provides a customization mechanism that let's you provide your own implementation of org.valid4j.AssertiveProvider.

Links:

• http://www.valid4j.org/
• https://github.com/helsing/valid4j