co.cask.cdap.internal.app.runtime.flow.SchemaCache.java Source code

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Here is the source code for co.cask.cdap.internal.app.runtime.flow.SchemaCache.java

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/*
 * Copyright  2014 Cask Data, Inc.
 *
 * 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 co.cask.cdap.internal.app.runtime.flow;

import co.cask.cdap.api.data.schema.Schema;
import co.cask.cdap.api.data.schema.SchemaHash;
import com.google.common.base.Preconditions;
import com.google.common.cache.CacheBuilder;
import com.google.common.cache.CacheLoader;
import com.google.common.cache.LoadingCache;
import com.google.common.collect.Maps;

import java.nio.ByteBuffer;
import java.util.Map;
import java.util.concurrent.ExecutionException;

/**
 * Dynamic loading of schema from classloader and caching of known schemas.
 */
public final class SchemaCache {

    private final LoadingCache<SchemaHash, Schema> cache;

    /**
     * Creates the schema cache with a set of know schemas.
     *
     * @param schemas Set of known schemas
     */
    public SchemaCache(Iterable<Schema> schemas, ClassLoader classLoader) {

        // TODO: Later on we should use ClassLoader.getResource
        final Map<SchemaHash, Schema> schemaMap = Maps.newHashMap();
        for (Schema schema : schemas) {
            schemaMap.put(schema.getSchemaHash(), schema);
        }

        cache = CacheBuilder.newBuilder().build(new CacheLoader<SchemaHash, Schema>() {
            @Override
            public Schema load(SchemaHash key) throws Exception {
                Schema schema = schemaMap.get(key);
                Preconditions.checkNotNull(schema);
                // TODO: Load from classloader
                return schema;
            }
        });
    }

    /**
     * Reads a {@link SchemaHash} from the given buffer and returns a {@link Schema} associated
     * with the hash.
     *
     * @param buffer {@link ByteBuffer} for reading in schema hash
     * @return A {@link Schema} or {@code null} if the schema is not found.
     */
    public Schema get(ByteBuffer buffer) {
        return get(new SchemaHash(buffer));
    }

    public Schema get(SchemaHash hash) {
        try {
            return cache.get(hash);
        } catch (ExecutionException e) {
            return null;
        }
    }
}