TypeLiteral¶

public abstract class org.apache.commons.lang3.reflect.TypeLiteral<T> implements Typed<T>[source]¶

Type literal comparable to javax.enterprise.util.TypeLiteral, made generally available outside the JEE context. Allows the passing around of a “token” that represents a type in a typesafe manner, as opposed to passing the (non-parameterized) Type object itself. Consider:

You might see such a typesafe API as:

class Typesafe {
  <T> T obtain(Class<T> type, ...);
}

Consumed in the manner of:

Foo foo = typesafe.obtain(Foo.class, ...);

Yet, you run into problems when you want to do this with a parameterized type:

List<String> listOfString = typesafe.obtain(List.class, ...); // could only give us a raw List

java.lang.reflect.Type might provide some value:

Type listOfStringType = ...; // firstly, how to obtain this? Doable, but not straightforward.
List<String> listOfString = (List<String>) typesafe.obtain(listOfStringType, ...); // nongeneric Type would necessitate a cast

The “type literal” concept was introduced to provide an alternative, i.e.:

class Typesafe {
  <T> T obtain(TypeLiteral<T> type, ...);
}

Consuming code looks like:

List<String> listOfString = typesafe.obtain(new TypeLiteral<List<String>>() {}, ...);

This has the effect of “jumping up” a level to tie a java.lang.reflect.Type to a type variable while simultaneously making it short work to obtain a Type instance for any given type, inline.

Additionally TypeLiteral implements the Typed interface which is a generalization of this concept, and which may be implemented in custom classes. It is suggested that APIs be defined in terms of the interface, in the following manner: