HdfsAvroFileViewer.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.InputStream;
import java.io.OutputStream;

import org.apache.avro.Schema;
import org.apache.avro.file.DataFileStream;
import org.apache.avro.generic.GenericDatumReader;
import org.apache.avro.generic.GenericDatumWriter;
import org.apache.avro.io.DatumWriter;
import org.apache.avro.io.Encoder;
import org.apache.avro.io.JsonEncoder;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.log4j.Logger;
import org.codehaus.jackson.JsonEncoding;
import org.codehaus.jackson.JsonFactory;
import org.codehaus.jackson.JsonGenerator;

/**
 * This class implements a viewer of avro files
 * 
 * @author lguo
 * 
 */
public class HdfsAvroFileViewer implements HdfsFileViewer {

	private static Logger logger = Logger.getLogger(HdfsAvroFileViewer.class);
	// Will spend 5 seconds trying to pull data and then stop.
	private static long STOP_TIME = 2000l;
	
	@Override
	public boolean canReadFile(FileSystem fs, Path path) {

		if(logger.isDebugEnabled())
			logger.debug("path:" + path.toUri().getPath());

		try {
			DataFileStream<Object> avroDataStream = getAvroDataStream(fs, path);
			Schema schema = avroDataStream.getSchema();
			avroDataStream.close();
			return schema != null;
		} catch(IOException e) {
			if(logger.isDebugEnabled()) {
				logger.debug(path.toUri().getPath() + " is not an avro file.");
				logger.debug("Error in getting avro schema: " + e.getLocalizedMessage());
			}
			return false;
		}
	}

	private DataFileStream<Object> getAvroDataStream(FileSystem fs, Path path) throws IOException {
		if(logger.isDebugEnabled())
			logger.debug("path:" + path.toUri().getPath());

		GenericDatumReader<Object> avroReader = new GenericDatumReader<Object>();
		InputStream hdfsInputStream = fs.open(path);
		return new DataFileStream<Object>(hdfsInputStream, avroReader);

	}

	@Override
	public void displayFile(FileSystem fs,
			Path path,
			OutputStream outputStream,
			int startLine,
			int endLine) throws IOException {

		if(logger.isDebugEnabled())
			logger.debug("display avro file:" + path.toUri().getPath());

		DataFileStream<Object> avroDatastream = null;

		try {
			avroDatastream = getAvroDataStream(fs, path);
			Schema schema = avroDatastream.getSchema();
			DatumWriter<Object> avroWriter = new GenericDatumWriter<Object>(schema);

			JsonGenerator g = new JsonFactory().createJsonGenerator(outputStream, JsonEncoding.UTF8);
			g.useDefaultPrettyPrinter();
			Encoder encoder = new JsonEncoder(schema, g);

			long endTime = System.currentTimeMillis() + STOP_TIME;
			int lineno = 1; // line number starts from 1
			while(avroDatastream.hasNext() && lineno <= endLine && System.currentTimeMillis() <= endTime) {
				Object datum = avroDatastream.next();
				if(lineno >= startLine) {
					String record = "\n\n Record " + lineno + ":\n";
					outputStream.write(record.getBytes("UTF-8"));
					avroWriter.write(datum, encoder);
					encoder.flush();
				}
				lineno++;
			}
		} catch(IOException e) {
			outputStream.write(("Error in display avro file: " + e.getLocalizedMessage()).getBytes("UTF-8"));
			throw e;
		} finally {
			avroDatastream.close();
		}
	}

}