Fail-safe Resource Initialization

VolatileResources.java

/*
 * This module, both source code and documentation,
 * is in the Public Domain, and comes with NO WARRANTY.
 */
//package ;

import java.util.ArrayList;
import java.util.List;

/**
 * Temporary collection for initializing multiple {@code AutoCloseable}
 * resources.  If initialization of a resource fails, all previously opened
 * resources get automatically closed as with {@code try-with-resources} block:
 * <pre>
 *     private FileInputStream in;
 *     private FileOutputStream out;
 *
 *     Constructor() throws IOException {
 *         VolatileResources resources = VolatileResource.open();
 *         this.in = resources.add(() -> new FileInputStream("..."));
 *         this.out = resources.add(() -> new FileOuputStream("..."));
 *     }</pre>
 * <p>
 * If all resource initialization succeeds, the volatile collection is
 * normally discarded.  It is then responsibility of the user to close the
 * initialized resources.</p>
 */
public class VolatileResources {

    private final List<AutoCloseable> resources = new ArrayList<>(3);

    public static VolatileResources open() {
        return new VolatileResources();
    }

    public <R extends AutoCloseable, E extends Throwable>
            R add(ThrowingSupplier<R, E> resourceInitializer) throws E {
        try {
            R res = resourceInitializer.get();
            resources.add(res);
            return res;
        } catch (Throwable e) {
            closeSafely(e);
            throw e;
        }
    }

    private void closeSafely(Throwable root) {
        resources.forEach(it -> {
            try {
                it.close();
            } catch (Throwable e) {
                root.addSuppressed(e);
            }
        });
    }


    @FunctionalInterface
    public static interface ThrowingSupplier<R, E extends Throwable> {
        R get() throws E;
    }


}