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<String, Integer>

However, this doesn't work if the function throws an exception, say it's defined as:

Integer myMethod(String s) throws IOException

How would I define this reference?

Answer 1

You can try any of the following.

•  set your own functional interface that represents the checked exception:

@FunctionalInterface

public interface CheckedFunction<T, R> {

   R apply(T t) throws IOException;

}

and then use it:

void foo (CheckedFunction f) { ... }

• Differently, wrap Integer myMethod(String s) in a manner that doesn't represent a checked exception:

public Integer myWrappedMethod(String s) {

    try {

        return myMethod(s);

    }

    catch(IOException e) {

        throw new UncheckedIOException(e);

    }

}

and then:

Function<String, Integer> f = (String t) -> myWrappedMethod(t);

or: 

Function<String, Integer> f =

    (String t) -> {

        try {

           return myMethod(t);

        }

        catch(IOException e) {

            throw new UncheckedIOException(e);

        }

    };