valid4j is a simple assertion and validation library for Java which makes it possible to use your favorite hamcrest-matchers to express pre- and post-conditions in your code in a design by contract style.

valid4j provides you with an option to customize the global assertion policy by implementing an org.valid4j.AssertiveProvider and register it as a service loader in META-INF/services.

valid4j also provides support for regular input validation using hamcrest-matchers throwing custom recoverable exceptions if validation fails.

More info found here.

Installation

This library is available at Maven Central Repository. Add this dependency to your pom.xml

<dependency>
  <groupId>org.valid4j</groupId>
  <artifactId>valid4j</artifactId>
  <version>0.5.0</version>
</dependency>

Getting started

Statically import the library entry point:

import static org.valid4j.Assertive.*;

Use assertive preconditions to check for programming errors in calling clients:

// Use hamcrest-matchers to specify your preconditions
require(list, everyItem(greaterThanOrEqualTo(3)));

// Or express your preconditions using plain boolean expressions
require(v > 0.0, "The value (%f) must be positive", v);

Use assertive postconditions to check for programming errors in your supplied code:

ensure(result != null);
ensure(result, greaterThan(3.0));

Make use of the convenient pass-through of valid objects:

// Initialize members with valid arguments
this.message = require(message, containsString("Greetings"));

// Return valid results
return ensure(list, hasSize(greaterThan(1)));

Clearly express what you assume is unreachable code:

neverGetHere("This should never happen");

// If needed, give the compiler a hint that this branch won't return
throw neverGetHereError("Really...!?");

More info found here.

Validation

Statically import the library entry point:

import static org.valid4j.Validation.*;

Use condition checking to perform simpler error handling and throw recoverable exceptions:

// Use expressive hamcrest-matchers
validate(v, containsString("Greetings"), otherwiseThrowing(MissingGreatException.class));

// Or use plain boolean expressions
validate(v > 0.0, otherwiseThrowing(NotAPositiveNumberException.class));

More info found here.

Motivation for valid4j

The rationale behind valid4j (that we think is lacking from comparable alternatives from e.g. Google Guava, or Apache Commons):

  • provide better support for design by contract, using pre- and post-conditions
  • similar support for recoverable exceptions, as for programming errors
  • make use of hamcrest library for extensibility
  • make it possible to customize the global policy for contract violations

Project license

This software is licensed under Apache Software License, Version 2.0

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