Issue #64 - Add Transformer/Function support

Author: boretti

src/main/java/ch/powerunit/extensions/exceptions/CommonsCollections4Helper.java

@@ -21,11 +21,13 @@
 
 import static ch.powerunit.extensions.exceptions.Constants.verifySupplier;
 import static ch.powerunit.extensions.exceptions.Constants.verifyPredicate;
+import static ch.powerunit.extensions.exceptions.Constants.verifyFunction;
 
 import java.util.function.Function;
 
 import org.apache.commons.collections4.Factory;
 import org.apache.commons.collections4.FunctorException;
+import org.apache.commons.collections4.Transformer;
 
 /**
  * This class provides several helper methods for the functional interface of
@@ -90,4 +92,28 @@ public static <T> org.apache.commons.collections4.Predicate<T> asPredicate(Predi
 	public static <T> Factory<T> asFactory(SupplierWithException<T, ?> supplier) {
 		return SupplierWithException.unchecked(verifySupplier(supplier), FunctorException::new)::get;
 	}
+
+	/**
+	 * Transforms a {@link FunctionWithException} to the one from
+	 * commons-collections.
+	 * 
+	 * @param function
+	 *            the {@link FunctionWithException} to be transformed to the one
+	 *            from commons-collections.
+	 * @param <I>
+	 *            the input argument type of the function
+	 * @param <O>
+	 *            the result type of the function
+	 * @return the {@link Transformer transformer} from commons-collections. The
+	 *         ClassCastException and IllegalArgumentException are not wrapped and
+	 *         the other exception are wrapped in a FunctorException.
+	 * @throws NoClassDefFoundError
+	 *             In case the commons-collections4 library is not available.
+	 * @throws NullPointerException
+	 *             if function is null.
+	 * @see org.apache.commons.collections4.Transformer
+	 */
+	public static <I, O> Transformer<I, O> asTransformer(FunctionWithException<I, O, ?> function) {
+		return FunctionWithException.unchecked(verifyFunction(function), DEFAULT_EXCEPTION_MAPPER)::apply;
+	}
 }

src/test/java/ch/powerunit/extensions/exceptions/CommonsCollections4HelperTest.java

@@ -19,6 +19,8 @@
  */
 package ch.powerunit.extensions.exceptions;
 
+import org.apache.commons.collections4.FunctorException;
+
 import ch.powerunit.Test;
 import ch.powerunit.TestSuite;
 
@@ -48,7 +50,7 @@ public void testAsPredicateIllegalArgumentException() {
 	@Test
 	public void testAsPredicateOtherException() {
 		assertWhen(() -> CommonsCollections4Helper.asPredicate(PredicateWithException.failing(Exception::new))
-				.evaluate("x")).throwException(instanceOf(Exception.class));
+				.evaluate("x")).throwException(instanceOf(FunctorException.class));
 	}
 
 	// AsFactory
@@ -64,4 +66,30 @@ public void testAsFactoryOtherException() {
 				.throwException(instanceOf(Exception.class));
 	}
 
+	// AsTransformer
+
+	@Test
+	public void testAsTransformerNoException() {
+		assertThat(CommonsCollections4Helper.asTransformer(x -> "y").transform("x")).is("y");
+	}
+
+	@Test
+	public void testAsTransformerClassCastException() {
+		assertWhen(() -> CommonsCollections4Helper.asTransformer(FunctionWithException.failing(ClassCastException::new))
+				.transform("x")).throwException(instanceOf(ClassCastException.class));
+	}
+
+	@Test
+	public void testAsTransformerIllegalArgumentException() {
+		assertWhen(() -> CommonsCollections4Helper
+				.asTransformer(FunctionWithException.failing(IllegalArgumentException::new)).transform("x"))
+						.throwException(instanceOf(IllegalArgumentException.class));
+	}
+
+	@Test
+	public void testAsTransformerOtherException() {
+		assertWhen(() -> CommonsCollections4Helper.asTransformer(FunctionWithException.failing(RuntimeException::new))
+				.transform("x")).throwException(instanceOf(FunctorException.class));
+	}
+
 }