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Hosts small but useful tools and utilities that didn't fit anywhere else.

There is a newer version: 2.5.0

/*
 * Copyright (C) 2005-2015 Schlichtherle IT Services.
 * All rights reserved. Use is subject to license terms.
 */
package net.java.truecommons.shed;

import java.util.*;
import javax.annotation.CheckForNull;
import javax.annotation.concurrent.NotThreadSafe;

/**
 * Assembles an {@link Exception} from one or more input exceptions by
 * {@linkplain Exception#addSuppressed(Throwable) suppressing} all but the
 * first input exception with the highest priority.
 * The priority of the exceptions is determined by the {@link Comparator}
 * provided to the constructor.
 * 
 * @param   the type of the input and assembled (output) exceptions.
 * @author Christian Schlichtherle
 */
@NotThreadSafe
public class PriorityExceptionBuilder
extends AbstractExceptionBuilder {

    private final Comparator comparator;
    private final List exceptions;

    /**
     * Constructs a new priority exception builder.
     * This builder will use the first input exception as its initial assembly.
     * Whenever a new input exception gets added, the given comparator will get
     * used to determine if the new input exception shall get suppressed by the
     * current assembly or shall suppress the current assembly and take its
     * place.
     * The comparator will get called like this:
     * {@code comparator.compare(input, assembly)} where {@code input}
     * is the input exception to add and {@code assembly} is the current
     * assembly.
     * 
     * @param comparator the comparator used for prioritizing the exceptions in
     *        the assembly.
     */
    public PriorityExceptionBuilder(final Comparator comparator) {
        if (null == (this.comparator = comparator))
            throw new NullPointerException();
        exceptions = new LinkedList<>();
    }

    @Override
    protected final X update(final X input, final @CheckForNull X assembly) {
        exceptions.add(input);
        return null == assembly
                ? input
                : comparator.compare(input, assembly) > 0 ? input : assembly;
    }

    @Override
    protected final X post(final X selection) {
        for (   final Iterator i = exceptions.iterator();
                i.hasNext();
                i.remove()) {
            final X exception = i.next();
            if (selection != exception) selection.addSuppressed(exception);
        }
        assert exceptions.isEmpty();
        return selection;
    }
}