record-builder/README.md

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# RecordBuilder

## What is RecordBuilder

Java 16 introduces [Records](https://openjdk.java.net/jeps/395). While this version of records is fantastic, 
it's currently missing some important features normally found in data classes: a builder 
and "with"ers. This project is an annotation processor that creates:
 
- a companion builder class for Java records
- an interface that adds "with" copy methods
- an annotation that generates a Java record from an Interface template

_Details:_

- [RecordBuilder Details](#RecordBuilder-Example)
- [Wither Details](#Wither-Example)
- [RecordBuilder Full Definition](#Builder-Class-Definition)
- [Record From Interface Details](#RecordInterface-Example)
- [Generation Via Includes](#generation-via-includes)
- [Usage](#usage)
- [Customizing](customizing.md) (e.g. add immutable collections, etc.)

## RecordBuilder Example

```java
@RecordBuilder
public record NameAndAge(String name, int age){}
```

This will generate a builder class that can be used ala:

```java
// build from components
NameAndAge n1 = NameAndAgeBuilder.builder().name(aName).age(anAge).build();

// generate a copy with a changed value
NameAndAge n2 = NameAndAgeBuilder.builder(n1).age(newAge).build(); // name is the same as the name in n1

// pass to other methods to set components
var builder = new NameAndAgeBuilder();
setName(builder);
setAge(builder);
NameAndAge n3 = builder.build();

// use the generated static constructor/builder
import static NameAndAgeBuilder.NameAndAge;
...
var n4 = NameAndAge("hey", 42);
```

## Wither Example

```java
@RecordBuilder
public record NameAndAge(String name, int age) implements NameAndAgeBuilder.With {}
```

In addition to creating a builder, your record is enhanced by "wither" methods ala:

```java
NameAndAge r1 = new NameAndAge("foo", 123);
NameAndAge r2 = r1.withName("bar");
NameAndAge r3 = r2.withAge(456);

// access the builder as well
NameAndAge r4 = r3.with().age(101).name("baz").build();

// alternate method of accessing the builder (note: no need to call "build()")
NameAndAge r5 = r4.with(b -> b.age(200).name("whatever"));

// perform some logic in addition to changing values
NameAndAge r5 = r4.with(b -> {
   if (b.age() > 13) {
       b.name("Teen " + b.name());
   } else {
       b.name("whatever"));
   }
});

// or, if you cannot add the "With" interface to your record...
NameAndAge r6 = NameAndAgeBuilder.from(r5).with(b -> b.age(200).name("whatever"));
NameAndAge r7 = NameAndAgeBuilder.from(r5).withName("boop");
```

_Hat tip to [Benji Weber](https://benjiweber.co.uk/blog/2020/09/19/fun-with-java-records/) for the Withers idea._

## Builder Class Definition

(Note: you can see a builder class built using `@RecordBuilderFull` here: [FullRecordBuilder.java](https://gist.github.com/Randgalt/8aa487a847ea2acdd76d702f7cf17d6a))

The full builder class is defined as:

```java
public class NameAndAgeBuilder {
    private String name;

    private int age;

    private NameAndAgeBuilder() {
    }

    private NameAndAgeBuilder(String name, int age) {
        this.name = name;
        this.age = age;
    }

    /**
     * Static constructor/builder. Can be used instead of new NameAndAge(...)
     */
    public static NameAndAge NameAndAge(String name, int age) {
        return new NameAndAge(name, age);
    }

    /**
     * Return a new builder with all fields set to default Java values
     */
    public static NameAndAgeBuilder builder() {
        return new NameAndAgeBuilder();
    }

    /**
     * Return a new builder with all fields set to the values taken from the given record instance
     */
    public static NameAndAgeBuilder builder(NameAndAge from) {
        return new NameAndAgeBuilder(from.name(), from.age());
    }

    /**
     * Return a "with"er for an existing record instance
     */
    public static NameAndAgeBuilder.With from(NameAndAge from) {
        return new _FromWith(from);
    }

    /**
     * Return a stream of the record components as map entries keyed with the component name and the value as the component value
     */
    public static Stream<Map.Entry<String, Object>> stream(NameAndAge record) {
        return Stream.of(new AbstractMap.SimpleImmutableEntry<>("name", record.name()),
                 new AbstractMap.SimpleImmutableEntry<>("age", record.age()));
    }

    /**
     * Return a new record instance with all fields set to the current values in this builder
     */
    public NameAndAge build() {
        return new NameAndAge(name, age);
    }

    @Override
    public String toString() {
        return "NameAndAgeBuilder[name=" + name + ", age=" + age + "]";
    }

    @Override
    public int hashCode() {
        return Objects.hash(name, age);
    }

    @Override
    public boolean equals(Object o) {
        return (this == o) || ((o instanceof NameAndAgeBuilder r)
                && Objects.equals(name, r.name)
                && (age == r.age));
    }

    /**
     * Set a new value for the {@code name} record component in the builder
     */
    public NameAndAgeBuilder name(String name) {
        this.name = name;
        return this;
    }

    /**
     * Return the current value for the {@code name} record component in the builder
     */
    public String name() {
        return name;
    }

    /**
     * Set a new value for the {@code age} record component in the builder
     */
    public NameAndAgeBuilder age(int age) {
        this.age = age;
        return this;
    }

    /**
     * Return the current value for the {@code age} record component in the builder
     */
    public int age() {
        return age;
    }

    /**
     * Add withers to {@code NameAndAge}
     */
    public interface With {
        /**
         * Return the current value for the {@code name} record component in the builder
         */
        String name();

        /**
         * Return the current value for the {@code age} record component in the builder
         */
        int age();

        /**
         * Return a new record builder using the current values
         */
        default NameAndAgeBuilder with() {
            return new NameAndAgeBuilder(name(), age());
        }

        /**
         * Return a new record built from the builder passed to the given consumer
         */
        default NameAndAge with(Consumer<NameAndAgeBuilder> consumer) {
            NameAndAgeBuilder builder = with();
            consumer.accept(builder);
            return builder.build();
        }

        /**
         * Return a new instance of {@code NameAndAge} with a new value for {@code name}
         */
        default NameAndAge withName(String name) {
            return new NameAndAge(name, age());
        }

        /**
         * Return a new instance of {@code NameAndAge} with a new value for {@code age}
         */
        default NameAndAge withAge(int age) {
            return new NameAndAge(name(), age);
        }
    }

    private static final class _FromWith implements NameAndAgeBuilder.With {
        private final NameAndAge from;

        private _FromWith(NameAndAge from) {
            this.from = from;
        }

        @Override
        public String name() {
            return from.name();
        }

        @Override
        public int age() {
            return from.age();
        }
    }
}
```

## RecordInterface Example

```java
@RecordInterface
public interface NameAndAge {
    String name(); 
    int age();
}
```

This will generate a record ala:

```java
@RecordBuilder
public record NameAndAgeRecord(String name, int age) implements 
    NameAndAge, NameAndAgeRecordBuilder.With {}
```

Note that the generated record is annotated with `@RecordBuilder` so a record
builder is generated for the new record as well.

Notes:

- Non static methods in the interface...
  - ...cannot have arguments
  - ...must return a value
  - ...cannot have type parameters
- Methods with default implementations are used in the generation unless they are annotated with `@IgnoreDefaultMethod`
- If you do not want a record builder generated, annotate your interface as `@RecordInterface(addRecordBuilder = false)`
- If your interface is a JavaBean (e.g. `getThing()`, `isThing()`) the "get" and "is" prefixes are
stripped and forwarding methods are added.

## Generation Via Includes

An alternate method of generation is to use the Include variants of the annotations. These variants
act on lists of specified classes. This allows the source classes to be pristine or even come from
libraries where you are not able to annotate the source. 

E.g.

```java
import some.library.code.ImportedRecord
import some.library.code.ImportedInterface

@RecordBuilder.Include({
    ImportedRecord.class    // generates a record builder for ImportedRecord  
})
@RecordInterface.Include({
    ImportedInterface.class // generates a record interface for ImportedInterface 
})
public void Placeholder {
}
```

`@RecordBuilder.Include` also supports a `packages` attribute that includes all records
in the listed packages.

The target package for generation is the same as the package that contains the "Include"
annotation. Use `packagePattern` to change this (see Javadoc for details).  

## Usage

### Maven

Add a dependency that contains the discoverable annotation processor:

```xml
<dependency>
    <groupId>io.soabase.record-builder</groupId>
    <artifactId>record-builder-processor</artifactId>
    <version>${record.builder.version}</version>
    <scope>provided</scope>
</dependency>
```

### Gradle

Add the following to your build.gradle file:

```groovy
dependencies {
    annotationProcessor 'io.soabase.record-builder:record-builder-processor:$version-goes-here'
    compileOnly 'io.soabase.record-builder:record-builder-core:$version-goes-here'
}
```

### IDE

Depending on your IDE you are likely to need to enable Annotation Processing in your IDE settings.

## Customizing

RecordBuilder can be customized to your needs and you can even create your
own custom RecordBuilder annotations. See [Customizing RecordBuilder](customizing.md)
for details.