Overview
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