nullproof

A Java null arguments proofed object constructor by Guice AOP or AspectJ

Purpose

If you have a Class which conatains 20 methods and each method takes 2 arguments, you probably need to repeat following line of code 40 times!!

if(arg == null)
    throw new NullPointerException("Your error message");

With NullProof, you don't need to do it anymore.

Maven Repo

<dependency>
    <groupId>com.github.wnameless</groupId>
    <artifactId>nullproof</artifactId>
    <version>0.5.0</version>
</dependency>

AspectJ is supported since v0.2.0.

Quick Start

With AspectJ

@RejectNull
public class Foo { ... }

With Guice

Class with 0-argument constructor

Foo foo = NullProof.of(Foo.class);
foo.bar(null); // throws NullPointerException

Class with single implementation arguments constructor

Foo foo = NullProof.of(Foo.class, 123, "abc");
foo.bar(null); // throws NullPointerException

Class with generic and upcasting arguments constructor

Foo foo = new NullProof.Constructor<Foo>(Foo.class)
        .forType(new TypeLiteral<Map<String, Integer>>() {})
        .addArgument(new HashMap<String, Integer>()).create();
foo.bar(null); // throws NullPointerException

Feature

Both runtime Guice AOP and AspectJ are supported.

The first difference shows in following codes:

Foo foo1 = NullProof.of(Foo.class); // Works even there is no @RejectNull found on the class.
Foo foo2 = new Foo(); // Works only if there is @RejectNull annotated on the class (and of course you have to compile it with AspectJ).

The second difference is that AspectJ blocks null arguments of constructors(since v0.3.0), but Guice simply not allows null arguments to bind with constructors.

Annotation-Driven configuration:

@RejectNull // On Type or Method.
@Argument   // Can only used within RejectNull
@AcceptNull // On Type or Method.

@RejectNull can be used to set up the default behavior of NullProof.

@RejectNull({
    @Argument(type = String.class, message = "Oop!"),
    @Argument(type = Integer.class, ignore = true) })

@AcceptNull can be used to ignore certain methods.

@AcceptNull({ "bar1", "bar2" }) // Works on Type
@AcceptNull // Works on Method

Descriptive default error message, the original line number is kept:

java.lang.NullPointerException: Parameter<String> is not nullable
    at com.github.wnameless.nullproof.Foo.bar(Foo.java:16)
        ...

Best Practice with Guice

Using NullProof with static factory pattern to ensure every instance is prevented from null arguments.

public Foo { // Non-final class is required
    public static Foo create() {
      return NullProof.of(Foo.class);
    }

    Foo () {} // At least 1 package-private(non-private) constuctor is required to let Guice do the AOP
    ...
}

Tip for AspectJ

If you are using aspectj-maven-plugin with Eclipse AJDT. Try to create a java file with following content in your project. It allows AJDT to help you indentify all the AspectJ advice in your source codes during development.

@Aspect
public class NullProofAspect extends AbstractNullProofAspect {}