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

Another solution using a Function wrapper would be to return either an instance of a wrapper of your result, say Success, if everything went well, either an instance of, say Failure.

Some code to clarify things :

public interface ThrowableFunction {
    B apply(A a) throws Exception;
}

public abstract class Try {

    public static boolean isSuccess(Try tryy) {
        return tryy instanceof Success;
    }

    public static  Function> tryOf(ThrowableFunction function) {
        return a -> {
            try {
                B result = function.apply(a);
                return new Success(result);
            } catch (Exception e) {
                return new Failure<>(e);
            }
        };
    }

    public abstract boolean isSuccess();

    public boolean isError() {
        return !isSuccess();
    }

    public abstract A getResult();

    public abstract Exception getError();
}

public class Success extends Try {

    private final A result;

    public Success(A result) {
        this.result = result;
    }

    @Override
    public boolean isSuccess() {
        return true;
    }

    @Override
    public A getResult() {
        return result;
    }

    @Override
    public Exception getError() {
        return new UnsupportedOperationException();
    }

    @Override
    public boolean equals(Object that) {
        if(!(that instanceof Success)) {
            return false;
        }
        return Objects.equal(result, ((Success) that).getResult());
    }
}

public class Failure extends Try {

    private final Exception exception;

    public Failure(Exception exception) {
        this.exception = exception;
    }

    @Override
    public boolean isSuccess() {
        return false;
    }

    @Override
    public A getResult() {
        throw new UnsupportedOperationException();
    }

    @Override
    public Exception getError() {
        return exception;
    }
}

A simple use case :

List> result = Lists.newArrayList(1, 2, 3).stream().
    map(Try.tryOf(i -> someMethodThrowingAnException(i))).
    collect(Collectors.toList());