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本帖最后由 liyihongcug 于 2015-4-8 11:23 编辑
pReduce WordCount教程对于如何编译WordCount.java几乎是一笔带过… 而有写到的，大多又是 0.20 等旧版本版本的做法，即 javac -classpath /usr/local/Hadoop/hadoop-1.0.1/hadoop-core-1.0.1.jar WordCount.java，但较新的 2.X 版本中，已经没有 hadoop-core*.jar 这个文件，因此编辑和打包自己的MapReduce程序与旧版本有所不同。
本文以 Hadoop 2.4.1 环境下的WordCount实例来介绍 2.x 版本中如何编辑自己的MapReduce程序。
Hadoop 2.x 版本中的依赖 jar
Hadoop 2.x 版本中jar不再集中在一个 hadoop-core*.jar 中，而是分成多个 jar，如运行WordCount实例需要如下三个 jar:
$HADOOP_HOME/share/hadoop/common/hadoop-common-2.4.1.jar
$HADOOP_HOME/share/hadoop/mapreduce/hadoop-mapreduce-client-core-2.4.1.jar
$HADOOP_HOME/share/hadoop/common/lib/commons-cli-1.2.jar
编译、打包 Hadoop MapReduce 程序
将上述 jar 添加至 classpath 路径：
export CLASSPATH="$HADOOP_HOME/share/hadoop/common/hadoop-common-2.4.1.jar:$HADOOP_HOME/share/hadoop/mapreduce/hadoop-mapreduce-client-core-2.4.1.jar:$HADOOP_HOME/share/hadoop/common/lib/commons-cli-1.2.jar:$CLASSPATH"
接着就可以编译 WordCount.java 了（使用的是 2.4.1 源码中的 WordCount.java，源码在文本最后面）：
javac WordCount.java
编译时会有警告，可以忽略。编译后可以看到生成了几个.class文件。
使用Javac编译自己的MapReduce程序使用Javac编译自己的MapReduce程序
接着把 .class 文件打包成 jar，才能在 Hadoop 中运行：
jar -cvf WordCount.jar ./WordCount*.class
打包完成后，运行试试，创建几个输入文件：
Mkdir input
echo "echo of the rainbow" > ./input/file0
echo "the waiting game" > ./input/file1
创建WordCount的输入创建WordCount的输入
开始运行：
/usr/local/hadoop/bin/hadoop jar WordCount.jar WordCount input output
不过这边可能会遇到如下的提示 Exception in thread "main" java.lang.NoClassDefFoundError: WordCount ：
提示找不到 WordCount 类提示找不到 WordCount 类
因为程序中声明了 package ，所以在命令中也要 org.apache.hadoop.examples 写完整：
/usr/local/hadoop/bin/hadoop jar WordCount.jar org.apache.hadoop.examples.WordCount input output
正确运行后的结果如下：
WordCount 运行结果WordCount 运行结果
进阶：使用Eclipse编译运行MapReduce程序
使用命令行编译运行MapReduce程序毕竟有些麻烦，修改一次就得手动编译、打包一次，使用Eclipse编译运行MapReduce程序会更加方便。
WordCount.java 源码
文件位于 hadoop-2.4.1-src\hadoop-mapreduce-project\hadoop-mapreduce-examples\src\main\java\org\apache\hadoop\examples 中：
/**
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.hadoop.examples;
import java.io.IOException;
import java.util.StringTokenizer;
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.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import org.apache.hadoop.util.GenericOptionsParser;
publicclassWordCount{
publicstaticclassTokenizerMapper
extendsMapper<Object,Text,Text,IntWritable>{
privatefinalstaticIntWritable one =newIntWritable(1);
privateText word =newText();
publicvoid map(Object key,Text value,Context context
)throwsIOException,InterruptedException{
StringTokenizer itr =newStringTokenizer(value.toString());
while(itr.hasMoreTokens()){
word.set(itr.nextToken());
context.write(word, one);
}
}
}
publicstaticclassIntSumReducer
extendsReducer<Text,IntWritable,Text,IntWritable>{
privateIntWritable result =newIntWritable();
publicvoid reduce(Text key,Iterable<IntWritable> values,
Context context
)throwsIOException,InterruptedException{
int sum =0;
for(IntWritable val : values){
sum += val.get();
}
result.set(sum);
context.write(key, result);
}
}
publicstaticvoid main(String[] args)throwsException{
Configuration conf =newConfiguration();
String[] otherArgs =newGenericOptionsParser(conf, args).getRemainingArgs();
if(otherArgs.length !=2){
System.err.println("Usage: wordcount <in> <out>");
System.exit(2);
}
Job job =newJob(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,newPath(otherArgs[0]));
FileOutputFormat.setOutputPath(job,newPath(otherArgs[1]));
System.exit(job.waitForCompletion(true)?0:1);
}
}
CentOS安装和配置Hadoop2.2.0 http://www.linuxidc.com/Linux/2014-01/94685.htm
Ubuntu 13.04上搭建Hadoop环境 http://www.linuxidc.com/Linux/2013-06/86106.htm
Ubuntu 12.10 +Hadoop 1.2.1版本集群配置 http://www.linuxidc.com/Linux/2013-09/90600.htm
Ubuntu上搭建Hadoop环境（单机模式+伪分布模式） http://www.linuxidc.com/Linux/2013-01/77681.htm
Ubuntu下Hadoop环境的配置 http://www.linuxidc.com/Linux/2012-11/74539.htm
单机版搭建Hadoop环境图文教程详解 http://www.linuxidc.com/Linux/2012-02/53927.htm
搭建Hadoop环境（在Winodws环境下用虚拟机虚拟两个Ubuntu系统进行搭建） http://www.linuxidc.com/Linux/2011-12/48894.htm
更多Hadoop相关信息见Hadoop 专题页面 http://www.linuxidc.com/topicnews.aspx?tid=13
本文永久更新链接地址：http://www.linuxidc.com/Linux/2015-02/113489.htm
/**
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.hadoop.examples;
import java.io.IOException;
import java.util.StringTokenizer;
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.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import org.apache.hadoop.util.GenericOptionsParser;
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> [<in>...] <out>");
System.exit(2);
}
Job job = new Job(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);
for (int i = 0; i < otherArgs.length - 1; ++i) {
FileInputFormat.addInputPath(job, new Path(otherArgs));
}
FileOutputFormat.setOutputPath(job,
new Path(otherArgs[otherArgs.length - 1]));
System.exit(job.waitForCompletion(true) ? 0 : 1);
}
} javac WordCount.java
/usr/local/hadoop/share/hadoop/common/hadoop-common-2.6.0.jar(org/apache/hadoop/fs/Path.class): warning: Cannot find annotation method 'value()' in type 'LimitedPrivate': class file for org.apache.hadoop.classification.InterfaceAudience not found
Note: WordCount.java uses or overrides a deprecated API.
Note: Recompile with -Xlint:deprecation for details.
1 warning'develop envirmont http://momodev.blog.51cto.com/4916132/1186313 eclplise-plugin
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