core/src/com/google/inject/TypeLiteral.java
public TypeLiteral<?> getReturnType(Method method) {
    checkArgument(
        method.getDeclaringClass().isAssignableFrom(rawType),
        "%s is not defined by a supertype of %s",
        method,
        type);
    return resolve(method.getGenericReturnType());
  }
public TypeLiteral<?> getReturnType(Method method) {
    checkArgument(
        method.getDeclaringClass().isAssignableFrom(rawType),
        "%s is not defined by a supertype of %s",
        method,
        type);
    return resolve(method.getGenericReturnType());
  }
Returns the resolved generic return type of {@code method}.

@param method a method defined by this or any supertype.
@since 2.0