org.apache.calcite.rel.metadata.ChainedRelMetadataProvider.java Source code

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Here is the source code for org.apache.calcite.rel.metadata.ChainedRelMetadataProvider.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.apache.calcite.rel.metadata;

import org.apache.calcite.rel.RelNode;
import org.apache.calcite.util.Util;

import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableMultimap;
import com.google.common.collect.Lists;
import com.google.common.collect.Multimap;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.util.ArrayList;
import java.util.List;

/**
 * Implementation of the {@link RelMetadataProvider}
 * interface via the
 * {@link org.apache.calcite.util.Glossary#CHAIN_OF_RESPONSIBILITY_PATTERN}.
 *
 * <p>When a consumer calls the {@link #apply} method to ask for a provider
 * for a particular type of {@link RelNode} and {@link Metadata}, scans the list
 * of underlying providers.</p>
 */
public class ChainedRelMetadataProvider implements RelMetadataProvider {
    //~ Instance fields --------------------------------------------------------

    private final ImmutableList<RelMetadataProvider> providers;

    //~ Constructors -----------------------------------------------------------

    /**
     * Creates a chain.
     */
    protected ChainedRelMetadataProvider(ImmutableList<RelMetadataProvider> providers) {
        this.providers = providers;
        assert !providers.contains(this);
    }

    //~ Methods ----------------------------------------------------------------

    @Override
    public boolean equals(Object obj) {
        return obj == this || obj instanceof ChainedRelMetadataProvider
                && providers.equals(((ChainedRelMetadataProvider) obj).providers);
    }

    @Override
    public int hashCode() {
        return providers.hashCode();
    }

    public <M extends Metadata> UnboundMetadata<M> apply(Class<? extends RelNode> relClass,
            final Class<? extends M> metadataClass) {
        final List<UnboundMetadata<M>> functions = new ArrayList<>();
        for (RelMetadataProvider provider : providers) {
            final UnboundMetadata<M> function = provider.apply(relClass, metadataClass);
            if (function == null) {
                continue;
            }
            functions.add(function);
        }
        switch (functions.size()) {
        case 0:
            return null;
        case 1:
            return functions.get(0);
        default:
            return new UnboundMetadata<M>() {
                public M bind(RelNode rel, RelMetadataQuery mq) {
                    final List<Metadata> metadataList = Lists.newArrayList();
                    for (UnboundMetadata<M> function : functions) {
                        final Metadata metadata = function.bind(rel, mq);
                        if (metadata != null) {
                            metadataList.add(metadata);
                        }
                    }
                    return metadataClass.cast(Proxy.newProxyInstance(metadataClass.getClassLoader(),
                            new Class[] { metadataClass }, new ChainedInvocationHandler(metadataList)));
                }
            };
        }
    }

    public <M extends Metadata> Multimap<Method, MetadataHandler<M>> handlers(MetadataDef<M> def) {
        final ImmutableMultimap.Builder<Method, MetadataHandler<M>> builder = ImmutableMultimap.builder();
        for (RelMetadataProvider provider : providers.reverse()) {
            builder.putAll(provider.handlers(def));
        }
        return builder.build();
    }

    /** Creates a chain. */
    public static RelMetadataProvider of(List<RelMetadataProvider> list) {
        return new ChainedRelMetadataProvider(ImmutableList.copyOf(list));
    }

    /** Invocation handler that calls a list of {@link Metadata} objects,
     * returning the first non-null value. */
    private static class ChainedInvocationHandler implements InvocationHandler {
        private final List<Metadata> metadataList;

        public ChainedInvocationHandler(List<Metadata> metadataList) {
            this.metadataList = ImmutableList.copyOf(metadataList);
        }

        public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
            for (Metadata metadata : metadataList) {
                try {
                    final Object o = method.invoke(metadata, args);
                    if (o != null) {
                        return o;
                    }
                } catch (InvocationTargetException e) {
                    if (e.getCause() instanceof CyclicMetadataException) {
                        continue;
                    }
                    Util.throwIfUnchecked(e.getCause());
                    throw new RuntimeException(e.getCause());
                }
            }
            return null;
        }
    }
}

// End ChainedRelMetadataProvider.java