Java 8 Lambda function that throws exception?

Question

I know how to create a reference to a method that has a String parameter and returns an int, it\'s:

Function         


        

Answer 1

Sneaky throw idiom enables bypassing CheckedException of Lambda expression. Wrapping a CheckedException in a RuntimeException is not good for strict error handling.

It can be used as a Consumer function used in a Java collection.

Here is a simple and improved version of jib's answer.

import static Throwing.rethrow;

@Test
public void testRethrow() {
    thrown.expect(IOException.class);
    thrown.expectMessage("i=3");

    Arrays.asList(1, 2, 3).forEach(rethrow(e -> {
        int i = e.intValue();
        if (i == 3) {
            throw new IOException("i=" + i);
        }
    }));
}

This just wrapps the lambda in a rethrow. It makes CheckedException rethrow any Exception that was thrown in your lambda.

public final class Throwing {
    private Throwing() {}

    @Nonnull
    public static  Consumer rethrow(@Nonnull final ThrowingConsumer consumer) {
        return consumer;
    }

    /**
     * The compiler sees the signature with the throws T inferred to a RuntimeException type, so it
     * allows the unchecked exception to propagate.
     * 
     * http://www.baeldung.com/java-sneaky-throws
     */
    @SuppressWarnings("unchecked")
    @Nonnull
    public static  void sneakyThrow(@Nonnull Throwable ex) throws E {
        throw (E) ex;
    }

}

Find a complete code and unit tests here.