org.apache.hadoop.fs.shell.Head.java Source code

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Here is the source code for org.apache.hadoop.fs.shell.Head.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.hadoop.fs.shell;

import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import org.apache.hadoop.fs.FSDataInputStream;
import org.apache.hadoop.fs.PathIsDirectoryException;
import org.apache.hadoop.io.IOUtils;

import java.io.IOException;
import java.util.LinkedList;
import java.util.List;

/**
 * Show the first 1KB of the file.
 */
@InterfaceAudience.Private
@InterfaceStability.Unstable

class Head extends FsCommand {
    public static void registerCommands(CommandFactory factory) {
        factory.addClass(Head.class, "-head");
    }

    public static final String NAME = "head";
    public static final String USAGE = "<file>";
    public static final String DESCRIPTION = "Show the first 1KB of the file.\n";

    private long endingOffset = 1024;

    @Override
    protected void processOptions(LinkedList<String> args) throws IOException {
        CommandFormat cf = new CommandFormat(1, 1);
        cf.parse(args);
    }

    @Override
    protected List<PathData> expandArgument(String arg) throws IOException {
        List<PathData> items = new LinkedList<PathData>();
        items.add(new PathData(arg, getConf()));
        return items;
    }

    @Override
    protected void processPath(PathData item) throws IOException {
        if (item.stat.isDirectory()) {
            throw new PathIsDirectoryException(item.toString());
        }

        dumpToOffset(item);
    }

    private void dumpToOffset(PathData item) throws IOException {
        FSDataInputStream in = item.fs.open(item.path);
        try {
            IOUtils.copyBytes(in, System.out, endingOffset, false);
        } finally {
            in.close();
        }
    }
}