Package org.cactoos.func

Class FuncWithFallback<X,​Y>

  • Type Parameters:
    X - Type of input
    Y - Type of output
    All Implemented Interfaces:
    Func<X,​Y>
    public final class FuncWithFallback<X,​Y>
extends Object
implements Func<X,​Y>
    Func with fallbacks that enable it to recover from errors.

    You may register several fallbacks, each for any type of exception whatsoever. If the decorated Func throws an exception that has an IS-A relationship with a registered fallback's exception, then that fallback's alternative Func will be used to provide a result.

    Example scenario: you need to fetch product data from a database which may potentially not be available (SQLException). As a fallback, you then fetch the data from a local cache that is guaranteed not to fail. This is a sketch of what this code may look like: 

     
    final Product product = new FuncWithFallback<>(
        id -> new SqlProduct().apply(id),
        new Fallback.From<>(
            SQLException.class,
            id -> new CachedProduct().apply(id)
        )
    ).apply(id);

    If you register several fallback plans for exception types belonging to the same hierarchy, then the fallback plan whose exception type has the closest InheritanceLevel to the exception thrown will be used.

    Example scenario: sometimes SqlProduct from above will throw SQLRecoverableException (a sub class of SQLException). In such cases you may want to simply retry the same Func: 

     
    final Product product = new FuncWithFallback<>(
        id -> new SqlProduct().apply(id),
        new IterableOf<>(
            new Fallback.From<>(
                SQLException.class,
                id -> new CachedProduct().apply(id)
            ),
            new Fallback.From<>(
                SQLRecoverableException.class,
                id -> new SqlProduct().apply(id)    // run it again
            )
        )
    ).apply(id);

    There is no thread-safety guarantee.

    Since:
    0.2
    See Also:
    ScalarWithFallback

    • Constructor Detail

      • FuncWithFallback

        @SafeVarargs
public FuncWithFallback​(Func<? super X,​? extends Y> fnc,
                        Fallback<? extends Y>... fbks)
        Ctor.
        Parameters:
        fnc - The func
        fbks - The fallbacks

      • FuncWithFallback

        public FuncWithFallback​(Func<? super X,​? extends Y> fnc,
                        Iterable<? extends Fallback<? extends Y>> fbks)
        Ctor.
        Parameters:
        fnc - The func
        fbks - The fallbacks

    • Method Detail

      • apply

        public Y apply​(X input)
        throws Exception
        Description copied from interface: Func
        Apply it.
        Specified by:
        apply in interface Func<X,​Y>
        Parameters:
        input - The argument
        Returns:
        The result
        Throws:
        Exception - If fails