README.md

Java type resolver

Resolves types from context for Java 8 and above, among other utilities.

Integration

If you're using Maven, add this to your pom.xml:

<dependencies>
    <dependency>
        <groupId>ch.jalu</groupId>
        <artifactId>typeresolver</artifactId>
        <version>0.1.0</version>
    </dependency>
</dependencies>

Accessing types and type information

Main features:

1. Resolve generic types from context
2. Access generic type arguments safely & conveniently
3. Convert a type to another type, keeping the generic type info

Example:

public class Demo {
  private List<String> list;

  public static void main(String... args) throws Exception {
    TypeInfo listType = TypeInfo.of(Demo.class.getDeclaredField("list"));

    // Outputs: "Generic type of List is class java.lang.String"
    System.out.println("Generic type of List is " + listType.getTypeArgumentAsClass(0));

    // Outputs: "As an Iterable: java.lang.Iterable<java.lang.String>"
    System.out.println("As an Iterable: " + listType.resolveSuperclass(Iterable.class).getType());

    // Outputs: "List#get returns E, which we know is class java.lang.String"
    Type getReturnRaw = List.class.getDeclaredMethod("get", int.class).getGenericReturnType();
    Type getReturnActual = listType.resolve(getReturnRaw).getType();
    System.out.println("List#get returns " + getReturnRaw + ", which we know is " + getReturnActual);
  }
}

Creating a Type of any implementation

You can use TypeReference and NestedTypeReference to create Type instances of any subclass in a compile-safe manner:

1. Create types on the fly with new TypeReference<Map<String, Double>>() { }
2. Implementation of all Type interfaces with equals and hashCode in line with the internal implementations of the JDK

public static void main(String... args) {
  TypeInfo mySetType = new TypeReference<Set<Double>>() { };
  // Outputs: "Created set type: java.util.Set<java.lang.Double>"
  System.out.println("Created set type: " + mySetType.getType());

  Type myWildcard = WildcardTypeImpl.newWildcardExtends(String.class);
  // Outputs: "Created wildcard: ? extends java.lang.String"
  System.out.println("Created wildcard: " + myWildcard);

  // Implementations of Type interfaces which have the same #equals and #hashCode
  // as the JDK impl. are available.
  ParameterizedType pt = new ParameterizedTypeImpl(Set.class, null, Double.class);
  // Outputs: "Set types equal -> true"
  System.out.println("Set types equal -> " + pt.equals(mySetType.getType()));
}

Array type analysis and creation

1. Get dimension & type of array class
2. Create array class of your definition

public static void main(String... args) {
  AbstractArrayProperties arrayInfo = ArrayTypeUtils.getArrayProperty(String[][].class);
  // Outputs: "Component = class java.lang.String, dimension = 2"
  System.out.println("Component = " + arrayInfo.getComponentType() + ", dimension = " + arrayInfo.getDimension());

  Type listType = new TypeReference<List<String>>() { }.getType();
  Type doubleArr = ArrayTypeUtils.createArrayType(listType, 3);
  // Outputs: "Created type: java.util.List<java.lang.String>[][][]"
  System.out.println("Created type: " + doubleArr);
}