Java tutorial
package hdfs.hdfsadapter; /** * 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. */ import com.google.common.io.Closeables; import org.apache.commons.io.Charsets; import org.apache.hadoop.conf.Configuration; import org.apache.hadoop.fs.FSDataInputStream; import org.apache.hadoop.fs.FileSystem; import org.apache.hadoop.fs.Path; import org.apache.hadoop.io.DataOutputBuffer; import org.apache.hadoop.io.LongWritable; import org.apache.hadoop.io.Text; import org.apache.hadoop.mapreduce.InputSplit; import org.apache.hadoop.mapreduce.RecordReader; import org.apache.hadoop.mapreduce.TaskAttemptContext; import org.apache.hadoop.mapreduce.lib.input.FileSplit; import org.apache.hadoop.mapreduce.lib.input.TextInputFormat; import java.io.IOException; import org.apache.hadoop.fs.BlockLocation; import org.apache.hadoop.fs.FileStatus; /** * Reads records that are delimited by a specific begin/end tag. */ public class XmlInputFormatOneBufferSolution extends TextInputFormat { public static String STARTING_TAG; public static String ENDING_TAG; @Override public RecordReader<LongWritable, Text> createRecordReader(InputSplit split, TaskAttemptContext context) { try { STARTING_TAG = context.getConfiguration().get("start_tag"); ENDING_TAG = context.getConfiguration().get("end_tag"); return new XmlRecordReader((FileSplit) split, context.getConfiguration()); } catch (IOException ioe) { return null; } } /** * XMLRecordReader class to read through a given xml document to output xml blocks as records as specified * by the end tag * */ public static class XmlRecordReader extends RecordReader<LongWritable, Text> { private final byte[] end_tag; private final byte[] start_tag; private final long start; private final long end; private int current_block = 0; private final FSDataInputStream fsin; private final DataOutputBuffer buffer = new DataOutputBuffer(); private LongWritable currentKey; private Text currentValue; BlockLocation[] blocks; public XmlRecordReader(FileSplit split, Configuration conf) throws IOException { end_tag = ENDING_TAG.getBytes(Charsets.UTF_8); start_tag = ENDING_TAG.getBytes(Charsets.UTF_8); // open the file and seek to the start of the split start = split.getStart(); // set the end of the file end = start + split.getLength(); Path file = split.getPath(); FileSystem fs = file.getFileSystem(conf); FileStatus fStatus = fs.getFileStatus(file); blocks = fs.getFileBlockLocations(fStatus, 0, fStatus.getLen()); // seek the start of file fsin = fs.open(split.getPath()); fsin.seek(start); } /** * Get next block item * @param key * @param value * @return * @throws IOException */ private boolean next(LongWritable key, Text value) throws IOException { current_block = nextBlock(); if (fsin.getPos() < end && current_block < blocks.length) { if (current_block > 0) { readUntilMatch(end_tag, false); } try { if (readBlock(true)) { key.set(fsin.getPos()); value.set(buffer.getData(), 0, buffer.getLength()); return true; } } finally { buffer.reset(); } } return false; } @Override public void close() throws IOException { Closeables.close(fsin, true); } @Override public float getProgress() throws IOException { return (fsin.getPos() - start) / (float) (end - start); } /** * Read the block from start till end and after that until you find a closing tag * @param withinBlock * @return * @throws IOException */ private boolean readBlock(boolean withinBlock) throws IOException { boolean read = false; while (true) { if (fsin.getPos() < end) { if (readUntilMatch(start_tag, false)) { buffer.write(start_tag); readUntilMatch(end_tag, true); read = true; } } else { return read; } } } /** * Read from block(s) until you reach the end of file or find a matching bytes with match[] * @param match * @param withinBlock * @return * @throws IOException */ private boolean readUntilMatch(byte[] match, boolean withinBlock) throws IOException { int i = 0; while (true) { int b = fsin.read(); // end of file: if (b == -1) { return false; } // save to buffer: if (withinBlock) { buffer.write(b); } // check if we're matching: if (b == match[i]) { i++; if (i >= match.length) { return true; } } else { i = 0; } // see if we've passed the stop point: if (!withinBlock && i == 0 && fsin.getPos() >= end) { return false; } } } private int nextBlock() throws IOException { long pos = fsin.getPos(); long block_length; for (int i = 0; i < blocks.length; i++) { block_length = blocks[i].getOffset() + blocks[i].getLength(); if (pos == block_length) { return i + 1; } } return 0; } @Override public LongWritable getCurrentKey() throws IOException, InterruptedException { return currentKey; } @Override public Text getCurrentValue() throws IOException, InterruptedException { return currentValue; } @Override public void initialize(InputSplit split, TaskAttemptContext context) throws IOException, InterruptedException { } @Override public boolean nextKeyValue() throws IOException, InterruptedException { currentKey = new LongWritable(); currentValue = new Text(); return next(currentKey, currentValue); } } }