Hadoop源码工程结构
引言
Hadoop是一个开源的分布式计算框架,它能够处理大规模数据集并运行在大型集群上。Hadoop的源码工程结构是一个复杂而庞大的系统,它由许多模块和组件组成。本文将介绍Hadoop源码工程的结构,并通过代码示例来解释其中的关键概念。
Hadoop源码工程结构
Hadoop源码工程结构包括三个主要部分:Hadoop Common、Hadoop HDFS和Hadoop MapReduce。
Hadoop Common
Hadoop Common模块提供了一系列通用的工具和类,供其他Hadoop模块使用。它包含了文件系统、网络通信、IO操作、安全认证等功能。其中一个重要的类是Configuration
,它负责读取和解析配置文件,为Hadoop集群提供统一的配置管理。以下是一个使用Configuration
的示例代码:
import org.apache.hadoop.conf.Configuration;
public class MyApp {
public static void main(String[] args) {
Configuration conf = new Configuration();
conf.set("fs.defaultFS", "hdfs://localhost:9000");
String defaultFS = conf.get("fs.defaultFS");
System.out.println("Default FileSystem: " + defaultFS);
}
}
Hadoop HDFS
Hadoop HDFS是Hadoop的分布式文件系统,它可在大型集群上存储和处理大规模数据。HDFS将文件切分成多个块,并将这些块分布式存储在集群的不同节点上。以下是一个使用Hadoop HDFS的示例代码:
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
public class HdfsExample {
public static void main(String[] args) throws Exception {
Configuration conf = new Configuration();
conf.set("fs.defaultFS", "hdfs://localhost:9000");
FileSystem fs = FileSystem.get(conf);
Path path = new Path("/user/hadoop/input.txt");
fs.copyFromLocalFile(new Path("input.txt"), path);
fs.close();
}
}
Hadoop MapReduce
Hadoop MapReduce是Hadoop的分布式计算框架,它能够并行处理大规模数据集。MapReduce模型由Map和Reduce两个阶段组成,其中Map负责将输入数据切分成多个子问题,并由Reduce负责将Map阶段的输出结果进行计算和整合。以下是一个使用Hadoop MapReduce的示例代码:
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.Reducer;
import org.apache.hadoop.util.GenericOptionsParser;
import java.io.IOException;
import java.util.StringTokenizer;
public class WordCount {
public static class TokenizerMapper extends Mapper<Object, Text, Text, IntWritable>{
private final static IntWritable one = new IntWritable(1);
private Text word = new Text();
public void map(Object key, Text value, Context context) throws IOException, InterruptedException {
StringTokenizer itr = new StringTokenizer(value.toString());
while (itr.hasMoreTokens()) {
word.set(itr.nextToken());
context.write(word, one);
}
}
}
public static class IntSumReducer extends Reducer<Text,IntWritable,Text,IntWritable> {
private IntWritable result = new IntWritable();
public void reduce(Text key, Iterable<IntWritable> 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 Exception {
Configuration conf = new Configuration();
String[] otherArgs = new GenericOptionsParser(conf, args).getRemainingArgs();
if (otherArgs.length != 2) {
System.err.println("Usage: wordcount <in> <out>");
System.exit(2);
}
Job job = Job.getInstance(conf, "word count");
job.setJarByClass(WordCount.class);
job.setMapperClass(TokenizerMapper.class);
job.setCombinerClass(IntSumReducer.class);
job.setReducerClass(IntSumReducer.class);
job.setOutputKeyClass(Text.class);
job.setOutputValueClass(IntWritable.class);
FileInputFormat.addInputPath(job, new Path(otherArgs[0]));
FileOutputFormat.setOutputPath(job, new Path(otherArgs[1]));
System.exit(job.waitForCompletion(true)