com.cloudera.bigdata.analysis.index.util.WritableUtil.java Source code

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Here is the source code for com.cloudera.bigdata.analysis.index.util.WritableUtil.java

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/*
 * Copyright 2010 The Apache Software Foundation
 *
 * 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 com.cloudera.bigdata.analysis.index.util;

import org.apache.hadoop.hbase.util.Bytes;
import org.apache.hadoop.io.Writable;

import java.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;

/**
 * A collection of writable utils.
 */
public class WritableUtil {
    private WritableUtil() {
    }

    /**
     * Helper method to instantiate an expression instance using the provided
     * className.
     *
     * @param className the class name
     * @param baseClass the base class type (the class must be or inherit from
     *                  this type)
     * @return the instance
     */
    @SuppressWarnings("unchecked")
    public static <T extends Writable> T instanceForName(String className, Class<T> baseClass) {
        try {
            Class<T> clazz = (Class<T>) Class.forName(className);
            return clazz.newInstance();
        } catch (Exception e) {
            throw new IllegalArgumentException("Can't find or instantiate class " + className, e);
        }
    }

    /**
     * Reads an instance of provided clazz (or one of it's subclasses) from the
     * provided data input.
     *
     * @param in    the data into
     * @param clazz the class that the instance will be or extend from
     * @param <T>   the type
     * @return the instance
     * @throws java.io.IOException if an io error occurs
     */
    public static <T extends Writable> T readInstance(DataInput in, Class<T> clazz) throws IOException {
        String className = Bytes.toString(Bytes.readByteArray(in));
        T instance = instanceForName(className, clazz);
        instance.readFields(in);
        return instance;
    }

    /**
     * Reads an instance of provided clazz (or one of it's subclasses) from the
     * provided data input.
     * <p/>
     * <p>Note: It's assumed that the {@link #writeInstanceNullable(java.io.DataOutput,
     * org.apache.hadoop.io.Writable)} method was used to write out the instance.
     *
     * @param in    the data into
     * @param clazz the class that the instance will be or extend from
     * @param <T>   the type
     * @return the instance (or null)
     * @throws java.io.IOException if an io error occurs
     */
    public static <T extends Writable> T readInstanceNullable(DataInput in, Class<T> clazz) throws IOException {
        if (in.readBoolean()) {
            return readInstance(in, clazz);
        } else {
            return null;
        }
    }

    /**
     * Writes out the provided writable instance to the data outout.
     *
     * @param out      the data output
     * @param writable the writable isntance (must not be null)
     * @throws java.io.IOException if an io error occurs
     */
    public static void writeInstance(DataOutput out, Writable writable) throws IOException {
        if (writable == null) {
            throw new IllegalArgumentException("The writable instance must not be null");
        }
        Bytes.writeByteArray(out, Bytes.toBytes(writable.getClass().getName()));
        writable.write(out);
    }

    /**
     * Writes out the provided writable instance to the data outout.
     *
     * @param out      the data output
     * @param writable the writable isntance (can be null)
     * @throws java.io.IOException if an io error occurs
     */
    public static void writeInstanceNullable(DataOutput out, Writable writable) throws IOException {
        if (writable == null) {
            out.writeBoolean(false);
        } else {
            out.writeBoolean(true);
            writeInstance(out, writable);
        }
    }
}