Builder plugin for Intellij

An Intellij plugin to generate a nested static Builder for a Class.

• Why another Builder plugin?
• Install
• Use
• Features
• Why a Builder?
• Example

Why another Builder plugin? --------------------------- There were several Builder plugins already out there, but none that generated a Builder that conformed to the pattern laid out in [Effective Java](http://www.informit.com/articles/article.aspx?p=1216151&seqNum=2), which we use extensively. In addition, the [Features](/README.md#features) outlines other goodies.

Install

• Download the latest release.
• From Intellij: Preferences -> Plugins -> Install plugin from disk...
• Restart Intellij

Use

• From a Class, right click -> Generate... -> Builder...
• Remove any fields you don't want and select which fields are nullable

Features

• Creates a static nested Builder that conforms to the pattern in Effective Java.
• Select what fields you want to include in the Builder.
• A Guava Preconditions.checkNotNull will be added to the constructor for non-null fields.
• If javax.persistence annotations exist on fields, nullable will be inferred for the UI dialog box.
• Can optionally generate getters, which will return an Optional if the field is nullable.

Why a Builder? -------------- [Effective Java](http://www.informit.com/articles/article.aspx?p=1216151&seqNum=2) already advocates using a Builder when your class has a handful of dependencies. I would take it even further and argue for a Builder when you have 2 or more dependencies. It makes your Tests more readable and easier to construct. Usually a Test might look something like this:

public void testBarThingIsDifferent() {
  Bar bar1 = ... // complicated construction code with many fields
  bar1.setThing("thing1");
  Bar bar2 = ... // more construction code
  bar2.setThing("thing2");
  Zen zen = ... // still more setup code
  Foo foo1 = new Foo(bar1, zen);
  Foo foo2 = new Foo(bar2, zen);
  assertSomethingAboutBar(foo1, foo2);
}

Now if we use a Builder and write a test fixture method once:

public class TestFixtures {
  ...
  public Foo.Builder newFooBuilder() {
    return new Foo.Builder()
      .bar(newBar())
      .zen(newZen());
  }
  ...
}

Now we can reuse the fixture method everywhere and only override exactly what we care about.

public void testBarThingIsDifferent() {
  Bar bar1 = testFixtures.newBarBuilder()
     .thing1("thing1")
     .build();
  Bar bar2 = testFixtures.newBarBuilder()
     .thing2("thing2")
     .build();
  Foo foo1 = testFixtures.newFooBuilder()
    .bar(bar1)
    .build();
  Foo foo2 = testFixtures.newFooBuilder()
    .bar(bar2)
    .build();
  assertSomethingAboutBar(foo1, foo2);
}

Some good things about the new Test:

1. We've completely removed the construction of objects we don't care about, like Zen
2. It's very clear that thing is different and that's what we're testing.

Example

The main drawback to using a Builder is the tedious overhead to write one. The fewer dependencies you have, the less inclined you are to write one. But we just argued for a Builder with only 2 depenencies? That's where the plugin comes in! Say you have the given class:

  public class Foo {
     private final Bar bar;
     private final Zen zen; // This can be null.
  }

With the click of a button you can generate the following code:

public class Foo {

  private Bar bar;
  private Zen zen;

  private Foo(Builder builder) {
    this.bar = Preconditions.checkNotNull(builder.bar);
    this.zen = builder.zen;
  }

  public Bar getBar() {
    return bar;
  }

  public Optional<Zen> getZen() {
    return Optional.ofNullable(zen);
  }

  public static class Builder {
    private Bar bar;
    private Zen zen;

    public Builder bar(Bar bar) {
      this.bar = bar;
      return this;
    }

    public Builder zen(Zen zen) {
      this.zen = zen;
      return this;
    }

    public Builder fromPrototype(Foo prototype) {
      bar = prototype.bar;
      zen = prototype.zen;
      return this;
    }

    public Foo build() {
      return new Foo(this);
    }
  }
}