我有大量需要分析的 WIKI 数据。这些转储基本上是 XML 文件。如何使用 HADOOP Map Reduce 解析 XML 文件？
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标签： hadoop
import java.io.ByteArrayInputStream;
import java.io.IOException;
import javax.xml.stream.XMLInputFactory;
import javax.xml.stream.XMLStreamConstants;
import javax.xml.stream.XMLStreamReader;
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.Job;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.RecordReader;
import org.apache.hadoop.mapreduce.Reducer;
import org.apache.hadoop.mapreduce.TaskAttemptContext;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.input.FileSplit;
import org.apache.hadoop.mapreduce.lib.input.TextInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import org.apache.hadoop.mapreduce.lib.output.TextOutputFormat;
public class XmlDriver
{
public static class XmlInputFormat1 extends TextInputFormat {
public static final String START_TAG_KEY = "xmlinput.start";
public static final String END_TAG_KEY = "xmlinput.end";
public RecordReader<LongWritable, Text> createRecordReader(
InputSplit split, TaskAttemptContext context) {
return new XmlRecordReader();
}
/**
* 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 byte[] startTag;
private byte[] endTag;
private long start;
private long end;
private FSDataInputStream fsin;
private DataOutputBuffer buffer = new DataOutputBuffer();
private LongWritable key = new LongWritable();
private Text value = new Text();
@Override
public void initialize(InputSplit split, TaskAttemptContext context)
throws IOException, InterruptedException {
Configuration conf = context.getConfiguration();
startTag = conf.get(START_TAG_KEY).getBytes("utf-8");
endTag = conf.get(END_TAG_KEY).getBytes("utf-8");
FileSplit fileSplit = (FileSplit) split;
// open the file and seek to the start of the split
start = fileSplit.getStart();
end = start + fileSplit.getLength();
Path file = fileSplit.getPath();
FileSystem fs = file.getFileSystem(conf);
fsin = fs.open(fileSplit.getPath());
fsin.seek(start);
}
@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;
}
}
}
}
public static class Map extends Mapper<LongWritable, Text,
Text, Text> {
@Override
protected void map(LongWritable key, Text value,
Mapper.Context context)
throws
IOException, InterruptedException {
String document = value.toString();
System.out.println("‘" + document + "‘");
try {
XMLStreamReader reader =
XMLInputFactory.newInstance().createXMLStreamReader(new
ByteArrayInputStream(document.getBytes()));
String propertyName = "";
String propertyValue = "";
String currentElement = "";
while (reader.hasNext()) {
int code = reader.next();
switch (code) {
case XMLStreamConstants.START_ELEMENT: //START_ELEMENT:
currentElement = reader.getLocalName();
break;
case XMLStreamConstants.CHARACTERS: //CHARACTERS:
if (currentElement.equalsIgnoreCase("name")) {
propertyName += reader.getText();
System.out.println("propertName"+propertyName);
} else if (currentElement.equalsIgnoreCase("value")) {
propertyValue += reader.getText();
System.out.println("propertyValue"+propertyValue);
}
break;
}
}
reader.close();
context.write(new Text(propertyName.trim()), new Text(propertyValue.trim()));
}
catch(Exception e){
throw new IOException(e);
}
}
}
public static class Reduce
extends Reducer<Text, Text, Text, Text> {
@Override
protected void setup(
Context context)
throws IOException, InterruptedException {
context.write(new Text("<configuration>"), null);
}
@Override
protected void cleanup(
Context context)
throws IOException, InterruptedException {
context.write(new Text("</configuration>"), null);
}
private Text outputKey = new Text();
public void reduce(Text key, Iterable<Text> values,
Context context)
throws IOException, InterruptedException {
for (Text value : values) {
outputKey.set(constructPropertyXml(key, value));
context.write(outputKey, null);
}
}
public static String constructPropertyXml(Text name, Text value) {
StringBuilder sb = new StringBuilder();
sb.append("<property><name>").append(name)
.append("</name><value>").append(value)
.append("</value></property>");
return sb.toString();
}
}
public static void main(String[] args) throws Exception
{
Configuration conf = new Configuration();
conf.set("xmlinput.start", "<property>");
conf.set("xmlinput.end", "</property>");
Job job = new Job(conf);
job.setJarByClass(XmlDriver.class);
job.setOutputKeyClass(Text.class);
job.setOutputValueClass(Text.class);
job.setMapperClass(XmlDriver.Map.class);
job.setReducerClass(XmlDriver.Reduce.class);
job.setInputFormatClass(XmlInputFormat1.class);
job.setOutputFormatClass(TextOutputFormat.class);
FileInputFormat.addInputPath(job, new Path(args[0]));
FileOutputFormat.setOutputPath(job, new Path(args[1]));
job.waitForCompletion(true);
}
}
参数：- /home/test.xml /home/out
Xml 文件（test.xml）：
<configuration>
<property>
<name>dfs.replication</name>
<value>1</value>
</property>
<property>
<name>dfs</name>
<value>2</value>
</property>
</configuration>
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