Apache Hadoop中的Combiner函数可以在MapReduce作业的Map阶段之后,Reduce阶段之前对Map输出进行本地合并,以减少数据传输量。Gora是一个开源的数据存储、查询和处理框架,用于在Apache Hadoop生态系统中处理大规模数据。
下面是一个使用Combiner函数和Gora的代码示例:
import java.io.IOException;
import java.util.Iterator;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.Reducer;
import org.apache.gora.mapreduce.GoraMapper;
import org.apache.gora.mapreduce.GoraReducer;
import org.apache.gora.store.DataStoreFactory;
import org.apache.gora.store.DataStore;
import org.apache.gora.util.GoraException;
public class WordCount {
public static class WordCountMapper extends GoraMapper {
private final static IntWritable one = new IntWritable(1);
private Text word = new Text();
@Override
public void map(Long key, Text value, Context context) throws IOException, InterruptedException {
String line = value.toString();
String[] words = line.split(" ");
for (String w : words) {
word.set(w);
context.write(word, one);
}
}
}
public static class WordCountReducer extends GoraReducer {
private IntWritable result = new IntWritable();
@Override
protected void reduce(Text key, Iterable values, Context context) throws IOException, InterruptedException {
int sum = 0;
for (IntWritable val : values) {
sum += val.get();
}
result.set(sum);
context.write(key, result);
}
}
public static void main(String[] args) throws IOException, ClassNotFoundException, InterruptedException, GoraException {
DataStore dataStore = DataStoreFactory.getDataStore(Long.class, MyCustomObject.class, new Configuration());
Job job = Job.getInstance(new Configuration());
job.setJarByClass(WordCount.class);
job.setMapperClass(WordCountMapper.class);
job.setCombinerClass(WordCountReducer.class);
job.setReducerClass(WordCountReducer.class);
job.setOutputKeyClass(Text.class);
job.setOutputValueClass(IntWritable.class);
GoraMapper.initMapperJob(job, dataStore, Long.class, MyCustomObject.class, WordCountMapper.class, true);
GoraReducer.initReducerJob(job, dataStore, WordCountReducer.class);
job.waitForCompletion(true);
}
}
上述示例中,使用了Apache Gora中的GoraMapper和GoraReducer类来处理数据存储和查询。在main方法中,我们首先初始化了一个Gora DataStore实例来连接到数据存储中。
然后,我们创建一个MapReduce作业,并设置了Mapper和Reducer的类。我们还设置了Combiner函数,即WordCountReducer类,以进行本地合并。最后,我们通过调用GoraMapper和GoraReducer类的initMapperJob和initReducerJob方法来初始化Mapper和Reducer作业。
请注意,上述代码示例中的MyCustomObject类是一个自定义的数据对象,你可以根据自己的需求进行修改。另外,你还需要根据实际情况进行相关的配置和依赖项设置。
希望这个示例能够帮助你理解如何在Apache Hadoop中使用Combiner函数和Gora。