org.apache.lens.server.api.driver.hooks.ChainedDriverQueryHook.java Source code

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Here is the source code for org.apache.lens.server.api.driver.hooks.ChainedDriverQueryHook.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.lens.server.api.driver.hooks;

import java.util.List;

import org.apache.lens.server.api.driver.LensDriver;
import org.apache.lens.server.api.error.LensException;
import org.apache.lens.server.api.query.AbstractQueryContext;
import org.apache.lens.server.api.query.QueryContext;

import org.apache.hadoop.conf.Configurable;
import org.apache.hadoop.conf.Configuration;

import com.google.common.collect.Lists;
import lombok.Data;

/**
 * This hook allows chaining of different hooks. A driver can specify multiple hooks for itself by providing
 * `query.hook.classes` in its configuration. The value should be a comma separated list of class names, each
 * of which should be an implementation of org.apache.lens.server.api.driver.hooks.DriverQueryHook. This hook
 * stores instances of those classes.
 * All the methods of this class invokes the same method on each of the hooks in the chain.
 */
@Data
public class ChainedDriverQueryHook extends NoOpDriverQueryHook {

    private final Iterable<DriverQueryHook> hooks;

    @Override
    public void setDriver(LensDriver driver) {
        super.setDriver(driver);
        for (DriverQueryHook hook : hooks) {
            hook.setDriver(driver);
        }
    }

    @Override
    public void preRewrite(AbstractQueryContext ctx) throws LensException {
        super.preRewrite(ctx);
        for (DriverQueryHook hook : hooks) {
            hook.preRewrite(ctx);
        }
    }

    @Override
    public void postRewrite(AbstractQueryContext ctx) throws LensException {
        super.postRewrite(ctx);
        for (DriverQueryHook hook : hooks) {
            hook.postRewrite(ctx);
        }
    }

    @Override
    public void preEstimate(AbstractQueryContext ctx) throws LensException {
        super.preEstimate(ctx);
        for (DriverQueryHook hook : hooks) {
            hook.preEstimate(ctx);
        }
    }

    @Override
    public void postEstimate(AbstractQueryContext ctx) throws LensException {
        super.postEstimate(ctx);
        for (DriverQueryHook hook : hooks) {
            hook.postEstimate(ctx);
        }
    }

    @Override
    public void postDriverSelection(AbstractQueryContext ctx) throws LensException {
        super.postDriverSelection(ctx);
        for (DriverQueryHook hook : hooks) {
            hook.postDriverSelection(ctx);
        }
    }

    @Override
    public void preLaunch(QueryContext ctx) throws LensException {
        super.preLaunch(ctx);
        for (DriverQueryHook hook : hooks) {
            hook.preLaunch(ctx);
        }
    }

    public static ChainedDriverQueryHook from(Configuration conf, String key) throws LensException {
        String[] classNames = conf.getStrings(key);
        List<DriverQueryHook> hooks = Lists.newArrayList();
        if (classNames != null) {
            for (String className : classNames) {
                Class<? extends DriverQueryHook> clazz;
                try {
                    clazz = conf.getClassByName(className).asSubclass(DriverQueryHook.class);
                } catch (ClassNotFoundException e) {
                    throw new LensException("Couldn't load class " + className, e);
                }
                DriverQueryHook instance;
                try {
                    instance = clazz.newInstance();
                } catch (InstantiationException | IllegalAccessException e) {
                    throw new LensException("Couldn't create instance of class " + clazz.getName(), e);
                }
                if (instance instanceof Configurable) {
                    ((Configurable) instance).setConf(conf);
                }
                hooks.add(instance);
            }
        }
        return new ChainedDriverQueryHook(hooks);
    }
}