JsonSequenceFileViewer.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.PrintWriter;

import org.apache.hadoop.io.BytesWritable;
import org.apache.hadoop.io.SequenceFile;
import org.apache.hadoop.io.SequenceFile.Reader;
import org.apache.hadoop.io.Text;
import org.apache.log4j.Logger;

import voldemort.serialization.json.JsonTypeSerializer;

public class JsonSequenceFileViewer extends HdfsSequenceFileViewer {

	private static Logger logger = Logger.getLogger(JsonSequenceFileViewer.class);

	public boolean canReadFile(Reader reader) {
		Text keySchema = reader.getMetadata().get(new Text("key.schema"));
		Text valueSchema = reader.getMetadata().get(new Text("value.schema"));

		return keySchema != null && valueSchema != null;
	}

	public void displaySequenceFile(SequenceFile.Reader reader,
			PrintWriter output,
			int startLine,
			int endLine) throws IOException {

		if(logger.isDebugEnabled())
			logger.debug("display json file");

		try {
			BytesWritable keyWritable = new BytesWritable();
			BytesWritable valueWritable = new BytesWritable();
			Text keySchema = reader.getMetadata().get(new Text("key.schema"));
			Text valueSchema = reader.getMetadata().get(new Text("value.schema"));

			JsonTypeSerializer keySerializer = new JsonTypeSerializer(keySchema.toString());
			JsonTypeSerializer valueSerializer = new JsonTypeSerializer(valueSchema.toString());

			// skip lines before the start line
			for(int i = 1; i < startLine; i++)
				reader.next(keyWritable, valueWritable);

			// now actually output lines
			for(int i = startLine; i <= endLine; i++) {
				boolean readSomething = reader.next(keyWritable, valueWritable);
				if(!readSomething)
					break;
				output.write(safeToString(keySerializer.toObject(keyWritable.getBytes())));
				output.write("\t=>\t");
				output.write(safeToString(valueSerializer.toObject(valueWritable.getBytes())));
				output.write("\n");
				output.flush();
			}
		} finally {
			reader.close();
		}
	}

	private String safeToString(Object value) {
		if(value == null)
			return "null";
		else
			return value.toString();
	}

}