mapreduce实现按日期统计访问次数

MapReduce 是一个分布式计算框架，用于处理大规模数据集。要按日期统计访问次数，可以采用以下步骤：

1. Map 阶段：将日志文件中的每一行数据作为输入，key 是日期，value 是 1。

2. Reduce 阶段：计算每个日期的访问次数，将相同日期的 value 值相加即可。

具体实现步骤如下：

1. 编写 Map 函数

public class Map extends Mapper<LongWritable, Text, Text, IntWritable> {
    private final static IntWritable one = new IntWritable(1);
    private Text word = new Text();

    public void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
        String line = value.toString();
        String[] fields = line.split("\t");
        String date = fields[0].substring(0, 10); // 获取日期
        word.set(date);
        context.write(word, one);
    }
}

2. 编写 Reduce 函数

public class Reduce 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);
    }
}

3. 编写 Main 函数

public static void main(String[] args) throws Exception {
    Configuration conf = new Configuration();
    Job job = Job.getInstance(conf, "word count");
    job.setJarByClass(WordCount.class);
    job.setMapperClass(Map.class);
    job.setCombinerClass(Reduce.class);
    job.setReducerClass(Reduce.class);
    job.setOutputKeyClass(Text.class);
    job.setOutputValueClass(IntWritable.class);
    FileInputFormat.addInputPath(job, new Path(args[0]));
    FileOutputFormat.setOutputPath(job, new Path(args[1]));
    System.exit(job.waitForCompletion(true) ? 0 : 1);
}

4. 运行程序

将日志文件作为输入，运行程序，输出结果即为按日期统计的访问次数。