HdfsSequenceFileViewer.java

/*
 * Copyright 2012 LinkedIn, 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 azkaban.fsviewers;

import java.io.IOException;
import java.io.OutputStream;
import java.io.PrintWriter;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.SequenceFile;

public abstract class HdfsSequenceFileViewer implements HdfsFileViewer {

	protected abstract boolean canReadFile(SequenceFile.Reader reader);

	protected abstract void displaySequenceFile(SequenceFile.Reader reader,
			PrintWriter output,
			int startLine,
			int endLine) throws IOException;

	public boolean canReadFile(FileSystem fs, Path file) {
		boolean result = false;
		try {
			SequenceFile.Reader reader = new SequenceFile.Reader(fs, file, new Configuration());
			result = canReadFile(reader);
			reader.close();
		} catch(IOException e) {
			return false;
		}

		return result;
	}

	public void displayFile(FileSystem fs,
			Path file,
			OutputStream outputStream,
			int startLine,
			int endLine) throws IOException {
		SequenceFile.Reader reader = null;
		PrintWriter writer = new PrintWriter(outputStream);
		try {
			reader = new SequenceFile.Reader(fs, file, new Configuration());
			displaySequenceFile(reader, writer, startLine, endLine);
		} catch(IOException e) {
			writer.write("Error opening sequence file " + e);
		} finally {
			if(reader != null) {
				reader.close();
			}
		}
	}
}