hadoop programming 0715 ¶

• 整理出hadoop programming 的完全公式

		輸入 key		輸入 value		輸出 Key		輸出 Value
Mapper	<	A	,	B	,	C	,	D	>
map	(	A	,	B	,	OutputCollector < C , D >	,	Reporter reporter	)
output	.	collect	(	c	,	d	)
Reducer	<	C	,	D	,	E	,	F	>
reduce	(	C	,	D	,	OutputCollector < E , F >	,	Reporter reporter	)
output	.	collect	(	e	,	f	)

public static class Map extends MapReduceBase implements Mapper<LongWritable, Text, Text, IntWritable> {
public void map(LongWritable key, Text value, OutputCollector<Text, IntWritable> output, Reporter reporter) throws IOException {

while (tokenizer.hasMoreTokens()) {
		private final static IntWritable one = new IntWritable(1);
		private Text word = new Text();
		output.collect(word, one);

public static class Reduce extends MapReduceBase implements Reducer<Text, IntWritable, Text, IntWritable> {
public void reduce(Text key, Iterator<IntWritable> values,OutputCollector<Text, IntWritable> output, Reporter reporter)	throws IOException {
int sum = 0;
while (values.hasNext()) {
	sum += values.next().get();
}
output.collect(key, new IntWritable(sum));