Hadoop Learning (1)

My Demo
Statistic.java
1. 初始化配置文件，临时文件存放目录，还有具体的Job。

Configuration defaults = new Configuration();
File tempDir = new File("tmp/stat-temp-"+Integer.toString(
new Random().nextInt(Integer.MAX_VALUE)));
JobConf statJob = new JobConf(defaults, Statistic.class);

2. 设置Job的相关参数

statJob.setJobName("StatTestJob");
statJob.setInputDir(new File("tmp/input/"));
statJob.setMapperClass(StatMapper.class);
statJob.setReducerClass(StatReducer.class);
statJob.setOutputDir(tempDir);

3. 运行Job，清理临时文件

JobClient.runJob(statJob);
new JobClient(defaults).getFs().delete(tempDir);

4. 运行这个Demo，会输出
060328 151414 parsing jar:file:/E:/workground/opensource/hadoop-nightly/hadoop-nightly.jar!/hadoop-default.xml
060328 151414 parsing file:/E:/workground/opensource/hadoop-nightly/bin/mapred-default.xml
060328 151414 parsing file:/E:/workground/opensource/hadoop-nightly/bin/hadoop-site.xml
060328 151414 parsing jar:file:/E:/workground/opensource/hadoop-nightly/hadoop-nightly.jar!/hadoop-default.xml
060328 151414 parsing file:/E:/workground/opensource/hadoop-nightly/bin/mapred-default.xml
060328 151414 parsing file:/E:/workground/opensource/hadoop-nightly/bin/mapred-default.xml
060328 151414 parsing file:/E:/workground/opensource/hadoop-nightly/bin/hadoop-site.xml
060328 151414 parsing jar:file:/E:/workground/opensource/hadoop-nightly/hadoop-nightly.jar!/hadoop-default.xml
Key: 0, Value: For the latest information about Hadoop, please visit our website at:
Key: 70, Value:
Key: 71, Value: http://lucene.apache.org/hadoop/
Key: 107, Value:
Key: 108, Value: and our wiki, at:
Key: 126, Value:
Key: 127, Value: http://wiki.apache.org/hadoop/
060328 151414 parsing file:/E:/workground/opensource/hadoop-nightly/bin/mapred-default.xml
060328 151414 parsing build\test\mapred\local\job_lck1iq.xml\localRunner
060328 151414 parsing file:/E:/workground/opensource/hadoop-nightly/bin/hadoop-site.xml
060328 151414 Running job: job_lck1iq
060328 151414 parsing jar:file:/E:/workground/opensource/hadoop-nightly/hadoop-nightly.jar!/hadoop-default.xml
060328 151414 parsing file:/E:/workground/opensource/hadoop-nightly/bin/mapred-default.xml
060328 151414 parsing build\test\mapred\local\job_lck1iq.xml\localRunner
060328 151414 parsing file:/E:/workground/opensource/hadoop-nightly/bin/mapred-default.xml
060328 151414 parsing file:/E:/workground/opensource/hadoop-nightly/bin/hadoop-site.xml
060328 151414 E:\workground\opensource\hadoop-nightly\tmp\input\README.txt:0+161
060328 151414 parsing jar:file:/E:/workground/opensource/hadoop-nightly/hadoop-nightly.jar!/hadoop-default.xml
060328 151414 parsing file:/E:/workground/opensource/hadoop-nightly/bin/mapred-default.xml
060328 151414 parsing file:/E:/workground/opensource/hadoop-nightly/bin/mapred-default.xml
060328 151414 parsing file:/E:/workground/opensource/hadoop-nightly/bin/hadoop-site.xml
060328 151414 parsing jar:file:/E:/workground/opensource/hadoop-nightly/hadoop-nightly.jar!/hadoop-default.xml
060328 151415 parsing file:/E:/workground/opensource/hadoop-nightly/bin/mapred-default.xml
060328 151415 parsing build\test\mapred\local\job_lck1iq.xml\localRunner
060328 151415 parsing file:/E:/workground/opensource/hadoop-nightly/bin/mapred-default.xml
060328 151415 parsing file:/E:/workground/opensource/hadoop-nightly/bin/hadoop-site.xml
060328 151415 reduce > reduce
060328 151415 map 100% reduce 100%
060328 151415 Job complete: job_lck1iq
060328 151415 parsing jar:file:/E:/workground/opensource/hadoop-nightly/hadoop-nightly.jar!/hadoop-default.xml
060328 151415 parsing file:/E:/workground/opensource/hadoop-nightly/bin/hadoop-site.xml

5. 分析一下输出。
刚开始hadoop加载了一大堆配置文件，这里先不管。接着程序对 tmp/input/ 下面的 readme.txt 进行了解析，调用我的 StatMapper.map(WritableComparable key, Writable value, OutputCollector output, Reporter reporter) ，程序输出了key和value的值。可见key是当前指针在文件中的位置，而value是当前行的内容。接着还看到了解析xml文件的log，估计是程序框架启动了多个线程来进行操作，提高效率。
因为我的 StatMapper 只输出key-value，没有做其它事情，reduce这步被略过了。

6. 想办法让Reduce执行，看来要在StatMapper那里动动手脚。

StatMapper.java：
public void map(WritableComparable key, Writable value, OutputCollector output, Reporter reporter)
throws IOException
{
String tokenLength = String.valueOf(value.toString().split(" ").length);
output.collect(new UTF8(""), new LongWritable(1));
}
每行的单词数作key，1作value提交给output.collect()，这样应该就能够统计文件里面每行的单词数频率了。

7. 接着还要修改Statistic.java:

statJob.setOutputDir(tempDir);
statJob.setOutputFormat(SequenceFileOutputFormat.class);
statJob.setOutputKeyClass(UTF8.class);
statJob.setOutputValueClass(LongWritable.class);

8. 以及StatReducer.java:

public void reduce(WritableComparable key, Iterator values, OutputCollector output, Reporter reporter)
throws IOException
{
long sum = 0;
while (values.hasNext())
{
sum += ((LongWritable)values.next()).get();
}
System.out.println("Length: " + key + ", Count: " + sum);
output.collect(key, new LongWritable(sum));
}

9. 放一堆java文件到input目录下面，再次运行。

（省略无数的xml解析log）
Length: 0, Count: 359
Length: 1, Count: 3474
Length: 10, Count: 1113
Length: 11, Count: 1686
Length: 12, Count: 1070
Length: 13, Count: 1725
Length: 14, Count: 773
Length: 15, Count: 707
Length: 16, Count: 490
Length: 17, Count: 787
Length: 18, Count: 348
Length: 19, Count: 303
Length: 2, Count: 1543
Length: 20, Count: 227
Length: 21, Count: 421
Length: 22, Count: 155
Length: 23, Count: 143
Length: 24, Count: 109
Length: 25, Count: 219
Length: 26, Count: 83
Length: 27, Count: 70
Length: 28, Count: 55
Length: 29, Count: 107
Length: 3, Count: 681
Length: 30, Count: 53
Length: 31, Count: 43
Length: 32, Count: 38
Length: 33, Count: 66
Length: 34, Count: 36
Length: 35, Count: 26
Length: 36, Count: 42
Length: 37, Count: 52
Length: 38, Count: 32
Length: 39, Count: 33
Length: 4, Count: 236
Length: 40, Count: 17
Length: 41, Count: 40
Length: 42, Count: 15
Length: 43, Count: 23
Length: 44, Count: 14
Length: 45, Count: 27
Length: 46, Count: 15
Length: 47, Count: 30
Length: 48, Count: 2
Length: 49, Count: 18
Length: 5, Count: 1940
Length: 50, Count: 8
Length: 51, Count: 11
Length: 52, Count: 2
Length: 53, Count: 5
Length: 54, Count: 2
Length: 55, Count: 1
Length: 57, Count: 4
Length: 58, Count: 1
Length: 59, Count: 3
Length: 6, Count: 1192
Length: 60, Count: 1
Length: 61, Count: 4
Length: 62, Count: 1
Length: 63, Count: 3
Length: 66, Count: 1
Length: 7, Count: 1382
Length: 8, Count: 1088
Length: 9, Count: 2151
060328 154741 reduce > reduce
060328 154741 map 100% reduce 100%
060328 154741 Job complete: job_q618hy

Cool，统计出来了，但是这些数据有什么意义............. 看来该搞一个(2)来捣鼓一些更有意义的事情了