publiccIass4020601092430027extendsMapper<loneuritableText,Text,Intwritable> private static final IntWritable one=new Intritable(1); private static final Text word-new Text() public void map(Longwritable key ,Text value .MappercLongWritable,Text,Text,Intwritable>,Context context) throws IOException,InterruptedException String lineString=value.tostring(); Stringl7 words=lineString,split(" for(String w;words) word.set( w): context.write(word, one); } } }
时间: 2024-03-30 13:34:42 浏览: 21
这段代码是一个MapReduce中的Mapper类,用于统计文本中每个单词出现的次数。具体来说,它将文本中每一行的单词拆分出来,然后对于每个单词,将其作为key,值为1的IntWritable对象作为value,写入到上下文中。这样,在MapReduce框架中,所有相同key的value会被汇总在一起,从而得到每个单词出现的次数。
相关问题
public class IntSortReducer extends Reducer<IntWritable, IntWritable, IntWritable, IntWritable> { private static final IntWritable lineNumber = new IntWritable(0); @Override protected void reduce(IntWritable key, Iterable<IntWritable> values, Context context) throws IOException, InterruptedException { // ignore values: they'll always be 1 (as long as paired with IntMapper) synchronized (lineNumber) { /* TODO: Advance line number */ context.write(/* TODO: Write new, reduced <K,V> pair to context */); } } }
补全后的代码如下:
```
public class IntSortReducer extends Reducer<IntWritable, IntWritable, IntWritable, IntWritable> {
private static final IntWritable lineNumber = new IntWritable(0);
private int count = 0;
@Override
protected void reduce(IntWritable key, Iterable<IntWritable> values, Context context) throws IOException, InterruptedException {
// ignore values: they'll always be 1 (as long as paired with IntMapper)
synchronized (lineNumber) {
/* Advance line number */
count++;
lineNumber.set(count);
/* Write new, reduced <K,V> pair to context */
context.write(lineNumber, key);
}
}
}
```
在补全的代码中,我们通过使用 count 计数器和线程安全的 synchronized 关键字来实现了一个自增的 lineNumber,然后将新生成的键值对通过调用 context.write() 写入到 context 中。
补全public class IntSortReducer extends Reducer<IntWritable, IntWritable, IntWritable, IntWritable> { private static final IntWritable lineNumber = new IntWritable(0); @Override protected void reduce(IntWritable key, Iterable<IntWritable> values, Context context) throws IOException, InterruptedException { // ignore values: they'll always be 1 (as long as paired with IntMapper) synchronized (lineNumber) { /* TODO: Advance line number */ context.write(/* TODO: Write new, reduced <K,V> pair to context */); } } }
补全后的代码如下:
```
public class IntSortReducer extends Reducer<IntWritable, IntWritable, IntWritable, IntWritable> {
private static final IntWritable lineNumber = new IntWritable(0);
private int count = 0;
@Override
protected void reduce(IntWritable key, Iterable<IntWritable> values, Context context) throws IOException, InterruptedException {
// ignore values: they'll always be 1 (as long as paired with IntMapper)
synchronized (lineNumber) {
/* Advance line number */
count++;
lineNumber.set(count);
/* Write new, reduced <K,V> pair to context */
context.write(lineNumber, key);
}
}
}
```
在补全的代码中,我们通过使用 count 计数器和线程安全的 synchronized 关键字来实现了一个自增的 lineNumber,然后将新生成的键值对通过调用 context.write() 写入到 context 中。