Java 14 is introducing Records as a preview feature. Since Java 9, features in Java are being released in stages. While the Java 14 version of records is fantastic, it's currently missing an important feature for data classes: a builder. This project is an annotation processor that creates companion builder classes for Java records.

Example

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

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

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

// generate a copy with a changed value
var 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);
var n3 = builder.build();

The full builder class is defined as:

public class NameAndAgeBuilder {
    private String name;

    private int age;

    private NameAndAgeBuilder() {
    }

    private NameAndAgeBuilder(String name, int age) {
        this.name = name;
        this.age = 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 new record instance with all fields set to the current values in this builder
     */
    public NameAndAge build() {
        return new NameAndAge(name, age);
    }

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

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

    @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 b)
                && Objects.equals(name, b.name)
                && (age == b.age));
    }
}

Usage

Maven

1. Add the dependency that contains the @RecordBuilder annotation.

<dependency>
    <groupId>io.soabase.record-builder</groupId>
    <artifactId>record-builder-core</artifactId>
    <version>set-version-here</version>
</dependency>

2. Enable the annotation processing for the Maven Compiler Plugin:

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-compiler-plugin</artifactId>
    <version>set-version-here</version>
    <configuration>
        <annotationProcessorPaths>
            <annotationProcessorPath>
                <groupId>io.soabase.record-builder</groupId>
                <artifactId>record-builder-processor</artifactId>
                <version>set-version-here</version>
            </annotationProcessorPath>
        </annotationProcessorPaths>
        <annotationProcessors>
            <annotationProcessor>io.soabase.recordbuilder.processor.RecordBuilderProcessor</annotationProcessor>
        </annotationProcessors>

        
        <!-- "release" and "enable-preview" are required while records are preview features -->
        <release>14</release>
        <compilerArgs>
            <arg>--enable-preview</arg>
        </compilerArgs>

        ... any other options here ...
    </configuration>
</plugin>

IDE

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

Enable Preview

Note: records are a preview feature only. You'll need take a number of steps in order to try RecordBuilder:

Install and make active Java 14 or later
Make sure your development tool is using Java 14 or later and is configured to enable preview features (for Maven I've documented how to do this here: https://stackoverflow.com/a/59363152/2048051)
Bear in mind that this is not yet meant for production and there are numerous bugs in the tools and JDKs.

Note: I've seen some very odd compilation bugs with the current Java 14 and Maven. If you get internal Javac errors I suggest rebuilding with mvn clean package and/or mvn clean install.

TODOs

Document how to integrate with Gradle
Keep up with changes
Testing
Etc.