BuildGraph.XmlInputFormat.java Source code

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Here is the source code for BuildGraph.XmlInputFormat.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 BuildGraph;

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;

/**
 * Reads records that are delimited by a specific begin/end tag.
 */
public class XmlInputFormat extends TextInputFormat {

    public static final String START_TAG_KEY = "xmlinput.start";
    public static final String END_TAG_KEY = "xmlinput.end";

    @Override
    public RecordReader<LongWritable, Text> createRecordReader(InputSplit split, TaskAttemptContext context) {
        try {
            return new XmlRecordReader((FileSplit) split, context);
        } catch (IOException e) {
            throw new RuntimeException("TODO : refactor this...");
        }
    }

    /**
     * XMLRecordReader class to read through a given xml document to output xml
     * blocks as records as specified by the start tag and end tag
     */
    public static class XmlRecordReader extends RecordReader<LongWritable, Text> {
        private final byte[] startTag;
        private final byte[] endTag;
        private final long start;
        private final long end;
        private final FSDataInputStream fsin;
        private final DataOutputBuffer buffer = new DataOutputBuffer();

        private LongWritable key = new LongWritable();
        private Text value = new Text();

        public XmlRecordReader(FileSplit split, TaskAttemptContext context) throws IOException {
            Configuration conf = context.getConfiguration();
            startTag = conf.get(START_TAG_KEY).getBytes("utf-8");
            endTag = conf.get(END_TAG_KEY).getBytes("utf-8");

            // open the file and seek to the start of the split
            start = split.getStart();
            end = start + split.getLength();
            Path file = split.getPath();
            FileSystem fs = file.getFileSystem(conf);
            fsin = fs.open(split.getPath());
            fsin.seek(start);
        }

        @Override
        public void initialize(InputSplit split, TaskAttemptContext context)
                throws IOException, InterruptedException {
        }

        @Override
        public boolean nextKeyValue() throws IOException, InterruptedException {
            if (fsin.getPos() < end) {
                if (readUntilMatch(startTag, false)) {
                    try {
                        buffer.write(startTag);
                        if (readUntilMatch(endTag, true)) {
                            key.set(fsin.getPos());
                            value.set(buffer.getData(), 0, buffer.getLength());
                            return true;
                        }
                    } finally {
                        buffer.reset();
                    }
                }
            }
            return false;
        }

        @Override
        public LongWritable getCurrentKey() throws IOException, InterruptedException {
            return key;
        }

        @Override
        public Text getCurrentValue() throws IOException, InterruptedException {
            return value;
        }

        @Override
        public void close() throws IOException {
            fsin.close();
        }

        @Override
        public float getProgress() throws IOException {
            return (fsin.getPos() - start) / (float) (end - start);
        }

        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;
            }
        }
    }
}