需要全部代码请点赞关注收藏后评论区留言私信~~~
下面通过WordCount，WordMean等几个例子讲解MapReduce的实际应用，编程环境都是以Hadoop MapReduce为基础
一、WordCount
WordCount用于计算文件中每个单词出现的次数，非常适合采用MapReduce进行处理，处理单词计数问题的思路很简单，在 Map阶段处理每个文本split中的数据,产生<word,1> 这样的键-值对，在Reduce阶段对相同的关键字求和,最后生成所有的单词计数 。
运行示意图如下
运行结果如下
二、WordMean
对上面例子的代码稍作修改，改成计算所有文件中单词的平均长度，单词长度的定义是单词的字符个数，现在HDFS集群中有大量的文件，需要统计所有文件中所出现单词的平均长度。
三、Grep
还是进行大规模文本中单词的相关操作，现在希望提供类似Linux系统中的Grep命令的功能，找出匹配目标串的所有文件，并统计出每个文件中出现目标字符串的个数。
在 Map阶段根据提供的文件split信息、给定的每个字符串输出 <filename,1> 这样 的键-值对信息
在 Reduce阶段根据filename对 Map阶段产生的结果进行合并
运行效果如下
四、代码
部分代码如下 全部代码请点赞关注收藏后评论区留言私信~
package alibook.odps; import java.io.IOException; import java.util.Iterator; import com.aliyun.odps.data.Record; import com.aliyun.odps.data.TableInfo; import com.aliyun.odps.mapred.JobClient; import com.aliyun.odps.mapred.MapperBase; import com.aliyun.odps.mapred.ReducerBase; import com.aliyun.odps.mapred.conf.JobConf; import com.aliyun.odps.mapred.utils.InputUtils; import com.aliyun.odps.mapred.utils.OutputUtils; import com.aliyun.odps.mapred.utils.SchemaUtils; public class wordcount { public static class TokenizerMapper extends MapperBase { private Record word; private Record one; @Override public void setup(TaskContext context) throws IOException { word = context.createMapOutputKeyRecord(); one = context.createMapOutputValueRecord(); one.set(new Object[] { 1L }); System.out.println("TaskID:" + context.getTaskID().toString()); } @Override public void map(long recordNum, Record record, TaskContext context) throws IOException { for (int i = 0; i < record.getColumnCount(); i++) { word.set(new Object[] { record.get(i).toString() }); context.write(word, one); } } } /** * A combiner class that combines map output by sum them. **/ public static class SumCombiner extends ReducerBase { private Record count; @Override public void setup(TaskContext context) throws IOException { count = context.createMapOutputValueRecord(); } @Override public void reduce(Record key, Iterator<Record> values, TaskContext context) throws IOException { long c = 0; while (values.hasNext()) { Record val = values.next(); c += (Long) val.get(0); } count.set(0, c); context.write(key, count); } } /** * A reducer class that just emits the sum of the input values. **/ public static class SumReducer extends ReducerBase { private Record result = null; @Override public void setup(TaskContext context) throws IOException { result = context.createOutputRecord(); } @Override public void reduce(Record key, Iterator<Record> values, TaskContext context) throws IOException { long count = 0; while (values.hasNext()) { Record val = values.next(); count += (Long) val.get(0); } result.set(0, key.get(0)); result.set(1, count); context.write(result); } } public static void main(String[] args) throws Exception { if (args.length != 2) { System.err.println("Usage: WordCount <in_table> <out_table>"); System.exit(2); } JobConf job = new JobConf(); job.setMapperClass(TokenizerMapper.class); job.setCombinerClass(SumCombiner.class); job.setReducerClass(SumReducer.class); job.setMapOutputKeySchema(SchemaUtils.fromString("word:string")); job.setMapOutputValueSchema(SchemaUtils.fromString("count:bigint")); InputUtils.addTable(TableInfo.builder().tableName(args[0]).build(), job); OutputUtils.addTable(TableInfo.builder().tableName(args[1]).build(), job); JobClient.runJob(job); } }
pom.xml文件代码如下
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"> <modelVersion>4.0.0</modelVersion> <groupId>alibook</groupId> <artifactId>odps</artifactId> <version>0.0.1</version> <packaging>jar</packaging> <name>odps</name> <url>http://maven.apache.org</url> <properties> <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding> </properties> <dependencies> <dependency> <groupId>junit</groupId> <artifactId>junit</artifactId> <version>3.8.1</version> <scope>test</scope> </dependency> <dependency> <groupId>com.aliyun.odps</groupId> <artifactId>odps-sdk-core</artifactId> <version>0.23.3-public</version> </dependency> <dependency> <groupId>com.aliyun.odps</groupId> <artifactId>odps-sdk-commons</artifactId> <version>0.23.3-public</version> </dependency> <dependency> <groupId>com.aliyun.odps</groupId> <artifactId>odps-sdk-mapred</artifactId> <version>0.23.3-public</version> </dependency> </dependencies> </project>
创作不易 觉得有帮助请点赞关注收藏~~~
