mapreduce demo实现

mapreduce主要的实现需要三个类:主方法类、map类、reduce类。

1. 主方法类：

public class BreadPointDriver {
    /**
     *
     * @param args
     * @throws IOException
     * @throws ClassNotFoundException
     * @throws InterruptedException
     */
    public static void main(String[] args) throws IOException, ClassNotFoundException, InterruptedException {
        //配置项
        Configuration conf = new Configuration();

	//定义任务，第一个参数设定配置项,第二个参数设置任务名称
	Job job = new Job(conf, "bscreenUserCount");
	//设置输入文件格式化类
	job.setInputFormatClass(FileInputFormat.class);
	//设置输出文件格式化类
	job.setOutputFormatClass(FileOutputFormat.class);
	//设置启动类
	job.setJarByClass(BreadPointDriver.class);
	//设置mapper
	job.setMapperClass(UserCountMapper.class);
	//设置reducer
	job.setReducerClass(UserCountReducer.class);
	//设置reducer数量, 如果不设置默认为1,如果设置0则不执行reducer,设置1以上需要编写partition类
	job.setNumReduceTasks(0);
	job.setMapOutputKeyClass(Text.class);//map输出key数据类型
	job.setMapOutputValueClass(Text.class);//map输出value数据类型
	job.setOutputKeyClass(BscreenUseCount.class);//reducer输出key数据类型
	job.setOutputValueClass(NullWritable.class);//reducer输出value数据类型
        FileInputFormat.addInputPath(job, new Path(inputPath));//输入路径
        FileOutputFormat.addInputPath(job, new Path(outputPath));//输入路径
        job.waitForCompletion(true);//执行任务
    }
}

2. map类

public class BreadPointMapper extends Mapper {
    /**
     * 
     * @param key 行索引
     * @param value 行内容
     * @param context 容器
     * @throws IOException
     * @throws InterruptedException
     */
    @Override
    protected void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
        String outKey = "";
        String outValue = "";
        context.write(new Text(outKey),new Text(outValue));
    }
}

3. reducer类

public class BreadPointReducer extends Reducer {

	/**
     * 
     * @param key map中存储的key,每个key会执行一次reduce
     * @param value 对应的value列表
     * @param context
     * @throws IOException
     * @throws InterruptedException
     */
    @Override
    protected void reduce(Text key, Iterable value, Context context) throws IOException, InterruptedException {
    	//处理key和value
    	//...
        String outKey = "";
        String outValue = "";
        context.write(new Text(outKey),new Text(outValue));
    }
}