AutoValue: Node Extension

An extension for Google's AutoValue that:

• Eliminates null checks when accessing AutoValue object fields;
• Prevents NullPointerException's;
• Increases code readability and maintainability (less if-else blocks);
• Easier to read and understand than Java 8 Optionals
• Works great with Lambdas;

Use case

Suppose you have the following data structure:

Car
    String model
    Driver driver
        String name
        Club club
            String title
            Integer members
            Contact contact
                String email
                String phone

Let's say you want to print the email for the club a car's driver is member of:

System.out.println(car.driver().club().contact().email());

What if the car doesn't have a driver? Well, our code will break with a NullPointerException. What if the car has a driver that is not a member of any club. Or, what if the driver is member of a club, but its email is not listed? We will have to check all those before printing. We will end up with this:

if(car.driver()!=null && car.driver().club()!= null && car.driver().club().contact() != null){
    System.out.println(car.driver().club().contact().email());
}

This works but it is hard to read and to maintain. And most likely you'll have plenty of places in your code where you'll need to write similar checks.

Using auto-value-node the code above will become like this (assuming you use lambdas):

car.node().driver().club().contact().email().ifPresent(System.out::println);

Usage

Integrating auto-value-node takes very little effort. First add the dependencies, then add the following method to each AutoValue class:

public abstract Node_<your_class_name> node();

Make sure to replace "<your_class_name>" with the actual class name. That is all.

Node methods

• withValue(Action1) executes an action with the value;
• ifPresent(Action1) executes an action with the value if it is not null, followed by
  • otherwise(Action) executes an action if the value is null;
• ifAbsent(Action) executes an action if the value is null, followed by
  • otherwise(Acton1) applies an action on the value if it is not null;
• match(Predicate) returns a Node with the value if the predicate is true; a Node with null otherwise
• map(Mapper) returns a mapped value defined by Mapper (e.g.: car.node().driver().club().map(Observable::just) == Observable.just(car.driver().club()));
• orAlernative(alternativeValue) returns a Node containing the value if it is not null; a Node with alternativeValue otherwise
• isPresent() returns true if the value is not null; false otherwise;
• isAbsent() returns false if the value is not null; true otherwise;
• value() returns the value contained by the node;
• value(alternativeValue) returns the value contained by the node if it is present; alternativeValue otherwise;

Download

annotationProcessor 'com.ccheptea.auto.value:auto-value-node:0.2.8'
compile 'com.ccheptea.auto.value:auto-value-node-runtime:0.2.8'

Snapshots of the development version are available in Sonatype's snapshots repository.

License

Copyright 2017 Constantin Cheptea.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

   http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.