AskMeAgain/LazyGen

Java Code Generator to add Lazy/Caching methods to any class/interface. Also compatible with MapStruct!

LazyGen

This annotation processor adds a lazy/cacheable method to any non-final method annotated with @LazyGen via code generation.

Note: A Lazy/Cacheable method is a method which only executes its body once and keeps a copy of the result in memory.

Gradle

annotationProcessor 'io.github.askmeagain:lazygenprocessor:1.2.1'
implementation 'io.github.askmeagain:lazygenprocessor:1.2.1'

Getting Started

1. Add LazyGen package and annotation processor to your project
2. Add @GenerateLazyClass(ResultType.XXX) to a class (or interface in case of MapStruct mapper)
3. Specify how your result should look like:
   1. ResultType.CLASS: Creates a normal class which extends the original class
   2. ResultType.ABSTRACT_CLASS: Creates an abstract class which extends/implements the interface
   3. ResultType.MAPSTRUCT_COMPATIBLE: Creates an abstract class, prepared correctly for usage with MapStruct
   4. ResultType.MAPSTRUCT_COMPATIBLE_WITHOUT_ANNOTATIN is the same as step 3, but the @Mapper annotation is not added
4. Add @LazyGen to any method on this class and any childs (class or interface doesnt matter)
5. Hit build
6. A class is generated which inherits the original class, with Lazy as suffix

OneTimeUsage vs MultiUsage

You can also specify how the caching should be implemented:

• ONE_TIME_USE: returns always the same (cached) value, ignoring the input parameters
• MULTI_USE: will cache the result of the method in a map based on a key. The key is calculated via hashCode() of the input parameters
• PARENT: default on @LazyGen methods, use what the @GenerateLazyClass specified (by default ONE_TIME_USE)

You can configure a general usage, via @GenerateLazyClass(usage = ONE_TIME_USE), but each @LazyGen method can override this behaviour by themselves.

Making MapStruct lazy

1. Add @GenerateLazyClass(ResultType.MAPSTRUCT_COMPATIBLE) to your mapstruct mapper
2. Remove @Mapper annotation from your mapper
3. Add @LazyGen to any method
4. Get your MapStruct mapper via Mappers.getMapper(XXXXXXLazy.class);

Note: Methods which are touched by the MapStruct annotation processor can only be made lazy if they are implemented/referenced via @Named annotation or else MapStruct cannot find the correct method since the @Named annotation is not inheritable.

Examples

Simple Example

Before

@GenerateLazyClass
public class NormalClass {
    
    @LazyGen
    String abc(){
        return "Test";
    }
}

After

public class LazyNormalClass extends NormalClass {
    private java.lang.String _abc;
    
    @Override
    public java.lang.String abc() {
        if (_abc != null) {
            return _abc;
        }
        _abc = super.abc();
        return _abc;
    }
}

MapStruct Example

Before

@GenerateLazyClass(ResultType.MAPSTRUCT_COMPATIBLE)
public interface TestMapper {

    @Mapping(target = ".", source = "input", qualifiedByName = "a")
    String mapSummations(String input);
    
    @LazyGen
    @Named("a")
    default String a(TestMapper calculator) {
        System.out.println("a");
        return "a";
    }
}

After

@Mapper
public abstract class LazyTestMapper implements TestMapper {

    @Named("a")
    @Override
    public java.lang.String a(io.github.askmeagain.lazygen.calculator.simple.MapstructAbstractClass _TestMapper0) {
        if (_a != null) {
            return _a;
        }
        _a = TestMapper.super.a(_TestMapper0);
        return _a;
    }
    private java.lang.String _a;
}