org.jclouds.util.Suppliers2.java Source code

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Here is the source code for org.jclouds.util.Suppliers2.java

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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.jclouds.util;

import java.util.Map;

import com.google.common.annotations.Beta;
import com.google.common.base.Function;
import com.google.common.base.Objects;
import com.google.common.base.Supplier;
import com.google.common.base.Suppliers;
import com.google.common.base.Throwables;
import com.google.common.collect.Iterables;

/**
 * 
 * @author Adrian Cole
 */
public class Suppliers2 {

    public static <K, V> Supplier<V> getLastValueInMap(final Supplier<Map<K, Supplier<V>>> input) {
        return new Supplier<V>() {
            @Override
            public V get() {
                Supplier<V> last = Iterables.getLast(input.get().values());
                return last != null ? last.get() : null;
            }

            @Override
            public String toString() {
                return "getLastValueInMap()";
            }
        };
    }

    public static <X> Function<X, Supplier<X>> ofInstanceFunction() {
        return new Function<X, Supplier<X>>() {

            @Override
            public Supplier<X> apply(X arg0) {
                return Suppliers.ofInstance(arg0);
            }

            @Override
            public String toString() {
                return "Suppliers.ofInstance()";
            }
        };
    }

    /**
     * returns the value of the first supplier, or the value of the fallback, if the unlessNull is
     * null.
     */
    @Beta
    public static <T> Supplier<T> or(final Supplier<T> unlessNull, final Supplier<T> fallback) {
        return new Supplier<T>() {

            @Override
            public T get() {
                T val = unlessNull.get();
                if (val != null)
                    return val;
                return fallback.get();
            }

            @Override
            public String toString() {
                return Objects.toStringHelper(this).add("unlessNull", unlessNull).add("fallback", fallback)
                        .toString();
            }
        };
    }

    /**
     * if a throwable of certain type is encountered on getting the first value, use the fallback.
     */
    @Beta
    public static <T, X extends Throwable> Supplier<T> onThrowable(final Supplier<T> unlessThrowable,
            final Class<X> throwable, final Supplier<T> fallback) {
        return new Supplier<T>() {

            @Override
            public T get() {
                try {
                    return unlessThrowable.get();
                } catch (Throwable t) {
                    if (Throwables2.getFirstThrowableOfType(t, throwable) != null)
                        return fallback.get();
                    throw Throwables.propagate(t);
                }
            }

            @Override
            public String toString() {
                return Objects.toStringHelper(this).add("unlessThrowable", unlessThrowable)
                        .add("throwable", throwable.getSimpleName()).add("fallback", fallback).toString();
            }
        };
    }

}