java - 如何构建 buildOutputValue 方法

Question

拜托，我需要这段代码的帮助:

public class ThirdQueryReducer extends
    Reducer<IntWritable, Text, NullWritable, Text> {

private NullWritable nullWritableKey = NullWritable.get();
private Text outputValue = new Text();

private StringBuilder buildOutputValue(IntWritable key,
        StringBuilder reduceValueBuilder, Text value) {


}

@Override
public void reduce(IntWritable key, Iterable<Text> values, Context context)
        throws IOException, InterruptedException {


}}

我如何实现 buildOutputValue？知道映射器中的输出是这样的:mapDriver.withOutput(new IntWritable(1981), new Text("Mercurey"));

并且 buildOutputValue() 必须像这样处理日期:

List<Text> values = new ArrayList<Text>();
values.add(new Text("Pommard"));
values.add(new Text("Gentil"));
reduceDriver.withInput(new IntWritable(1980), values);

reducer 中的输出是这样的:

reduceDriver.withOutput(NullWritable.get(), new Text("Pommard\nGentil"));

提前致谢

Answer 1

你可以像下面这样实现它:

公共(public)类 ThirdQueryReducer 扩展 reducer {

private NullWritable nullWritableKey = NullWritable.get();
private Text outputValue = new Text();

private StringBuilder buildOutputValue(IntWritable key,
        StringBuilder reduceValueBuilder, Text value) {
    return reduceValueBuilder.append(value);
}

@Override
public void reduce(IntWritable key, Iterable<Text> values, Context context)
        throws IOException, InterruptedException {
    Iterator<Text> valueIter = values.iterator();
    StringBuilder reduceValueBuilder = new StringBuilder();
    while (valueIter.hasNext()) {
        buildOutputValue(key, valueIter.next(), reduceValueBuilder);
        if (valueIter.hasNext()) {
            reduceValueBuilder.append("\n");
        }
    }
    context.write(NullWritable.get(), new Text(reduceValueBuilder.toString()));
}