Hadoop Mapper
MapReduce - Mapper
主要是读取InputSplit的每一个Key,Value对并进行处理
public class Mapper<KEYIN, VALUEIN, KEYOUT, VALUEOUT> {/*** 预处理，仅在map task启动时运行一次*/protected void setup(Context context) throws IOException, InterruptedException {}/*** 对于InputSplit中的每一对<key, value>都会运行一次*/@SuppressWarnings("unchecked")protected void map(KEYIN key, VALUEIN value, Context context) throws IOException, InterruptedException {context.write((KEYOUT) key, (VALUEOUT) value);}/*** 扫尾工作，比如关闭流等*/protected void cleanup(Context context) throws IOException, InterruptedException {}/*** map task的驱动器*/public void run(Context context) throws IOException, InterruptedException {setup(context);while (context.nextKeyValue()) {map(context.getCurrentKey(), context.getCurrentValue(), context);}cleanup(context);}
}public class MapContext<KEYIN, VALUEIN, KEYOUT, VALUEOUT> extends TaskInputOutputContext<KEYIN, VALUEIN, KEYOUT, VALUEOUT> {private RecordReader<KEYIN, VALUEIN> reader;private InputSplit split;/*** Get the input split for this map.*/public InputSplit getInputSplit() {return split;}@Overridepublic KEYIN getCurrentKey() throws IOException, InterruptedException {return reader.getCurrentKey();}@Overridepublic VALUEIN getCurrentValue() throws IOException, InterruptedException {return reader.getCurrentValue();}@Overridepublic boolean nextKeyValue() throws IOException, InterruptedException {return reader.nextKeyValue();}
}