Hadoop 简单示例
1.云计算的概念
狭义云计算是指IT基础设施的交付和使用模式,通过网络以按需、易扩展的方式获得所需的资源(硬件、平台、软件)。
广义云计算是指服务的交付和使用模式,通过网络以按需、易扩展的方式获得所需的服务。这种服务可以是IT和软件、互联网相关的,也可以是任意其他的服务。
2.三层模型
Saas:more
Paas:hadoop
Iaas: openstack
3.google VS hadoop
google concept | hadoop concept |
MapReduce | Hadoop |
GFS | HDFS |
Bigtable | HBase |
Chubby | Zookeeper |
4.hadoop 编写map和reduce函数
4.1 map函数
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); //设置 key value } } }
说明: map的输出key 、value和reduce的输入key、value要一致
4.2 reduce
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(); //聚集操作 } result.set(sum); context.write(key, result); } }
说明: map的输出key 、value和reduce的输入key、value要一致,见上面红色部分
4.3 job的配置
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 = new Job(conf, "word count"); //job name 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])); //file input FileOutputFormat.setOutputPath(job, new Path(otherArgs[1])); //file output System.exit(job.waitForCompletion(true) ? 0 : 1); }
5.命令行运行
步骤:
a.打包mapreduce函数,wordcount.jar 设类名WordCount
b.进入hadoop安装目录
c.执行方式:hadoop jar 本地jar包目录 类名 hdfs输入文件目录 hdfs输入文件目录
例如:hadoop jar /home/deke/wordcount.jar WordCount hdfs输入文件目录 hdfs输出文件目录
6.eclipse配置
步骤:
a.下载eclipse
b.将 hadoop 文件夹下的 contrib/eclipse-plugin/hadoop-*-eclipse- plugin.jar ,
拷贝到 eclipse 文件夹下的/plugins 文件夹里
c.启动 Eclipse
d.设置 Hadoop 安装文件夹的路径
Window->Preferences—>hadoop Map/Reduce设置 hadoop的linux下文件位置,如:/usr/hadoop
e.window->show view->other->MapReduce Tool ->Map/Reduce Location,在Map/Reduce Location控制台空白处,右击选择“New Map/Reduce Location”,在弹出的对话框里,根据core-site.xml和maperd-site.xml里的端口填写
转自:hadoop基础学习(一)