LRUCache.java

/*
 * Copyright 2014 Red Hat, Inc. and/or its affiliates.
 *
 * Licensed 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.guvnor.common.services.backend.cache;

import java.util.Collections;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Set;

import org.uberfire.commons.validation.PortablePreconditions;

/**
 * A simple LRU cache keyed on Paths
 */
public abstract class LRUCache<Path, V> implements Cache<Path, V> {

    private static final int MAX_ENTRIES = 20;

    private Map<Path, V> cache;

    public LRUCache() {
        cache = new LinkedHashMap<Path, V>( MAX_ENTRIES + 1,
                                            0.75f,
                                            true ) {
            public boolean removeEldestEntry( Map.Entry eldest ) {
                return size() > MAX_ENTRIES;
            }
        };
        cache = (Map) Collections.synchronizedMap( cache );
    }

    @Override
    public V getEntry( final Path path ) {
        PortablePreconditions.checkNotNull( "path",
                                            path );
        return cache.get( path );
    }

    @Override
    public void setEntry( final Path path,
                          final V value ) {
        PortablePreconditions.checkNotNull( "path",
                                            path );
        PortablePreconditions.checkNotNull( "value",
                                            value );
        cache.put( path,
                   value );
    }

    @Override
    public void invalidateCache() {
        this.cache.clear();
    }

    @Override
    public void invalidateCache( final Path path ) {
        PortablePreconditions.checkNotNull( "path",
                                            path );
        this.cache.remove( path );
    }

    public Set<Path> getKeys() {
        return cache.keySet();
    }

}