我是 hadoop 新手，使用 Hadoop 2.6.0 版本并尝试解析复杂的 XML。
经过一段时间的搜索，我了解到，对于 XML 解析，我们需要编写自定义的 InputFormat，即 mahout 的 XMLInputFormat。
我也得到了帮助这个例子 http://xmlandhadoop.blogspot.in/
但是，当我在传递 XMLInputformat 类之后运行代码时，如果我使用示例中给出的 XMLInputFormat，它不会调用我自己的 Mapper 类，并且输出文件中的数据为 0。
令人惊讶的是，如果我不将 XMLInputFormat 类传递给我的作业，那么我的映射器可以正常工作并正确提供输出。有人会在这里帮忙指出我在这里缺少什么吗？
我的工作配置类是：
public static void runParserJob(String inputPath, String outputPath) throws IOException {
LOGGER.info("-----runParserJob()-----Start");
Configuration configuration = new Configuration(); configuration.set("xmlinput.start",Constants.XML_INPUT_START_TAG_PRODUCT);
configuration.set("xmlinput.end",Constants.XML_INPUT_END_TAG_PRODUCT);
configuration.set("io.serializations",Constants.XML_IO_SERIALIZATIONS);
Job job = new Job(configuration,Constants.JOB_TITLE);
FileInputFormat.setInputPaths(job, inputPath);
job.setJarByClass(ParserDriver.class);
job.setMapperClass(XMLMapper.class);
job.setNumReduceTasks(0);
job.setInputFormatClass(XmlInputFormat.class);
job.setOutputKeyClass(NullWritable.class);
job.setOutputValueClass(Text.class);
Path hdfsOutputPath = new Path(outputPath);
FileOutputFormat.setOutputPath(job, hdfsOutputPath);
FileSystem dfs = FileSystem.get(hdfsOutputPath.toUri(),configuration);
/**Using this condition it will create output at same location
* by deleting older data in that location**/
if(dfs.exists(hdfsOutputPath)){
dfs.delete(hdfsOutputPath,true);
}
try{
job.waitForCompletion(true);
}catch(InterruptedException ie){
LOGGER.error("-----Process interrupted in between Exception-----", ie);
}catch(ClassNotFoundException ce){
LOGGER.error("-----Class not found while running the job-----",ce);
}
}
我的 XMLInputFormat 类是：
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 is, TaskAttemptContext tac) {
return new XmlRecordReader();
}
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 inputSplit, TaskAttemptContext taskAttemptContext)
throws IOException, InterruptedException {
FileSplit fileSplit = (FileSplit)inputSplit;
startTag = taskAttemptContext.getConfiguration().get(START_TAG_KEY).getBytes("utf-8");
endTag = taskAttemptContext.getConfiguration().get(END_TAG_KEY).getBytes("utf-8");
start = fileSplit.getStart();
end = start + fileSplit.getLength();
Path file = fileSplit.getPath();
FileSystem hdfs = file.getFileSystem(taskAttemptContext.getConfiguration());
fsin = hdfs.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)) {
value.set(buffer.getData(), 0, buffer.getLength());
key.set(fsin.getPos());
return true;
}
} finally {
buffer.reset();
}
}
}
return false;
}
@Override
public void close() throws IOException {
}
@Override
public LongWritable getCurrentKey() throws IOException,InterruptedException {
return null;
}
@Override
public Text getCurrentValue() throws IOException, InterruptedException {
return null;
}
@Override
public float getProgress() throws IOException, InterruptedException {
return 0;
}
private boolean readUntilMatch(byte[] match, boolean withinBlock) throws IOException{
int i = 0;
while(true){
int b = fsin.read();
//If reaches to EOF
if(b == -1){
return false;
}
//If not then save into the 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;
}
}
}
}
有人可以帮我从这里出去吗？提前致谢。如果我哪里出错了请纠正我。
