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我正在 Hadoop MapReduce 框架中编写一个 Java 实现程序。我正在写一个名为CombinePatternReduce.class. 为了在 Eclipse 中调试 reducer，我编写了main()如下函数：

@SuppressWarnings("unchecked")
public static void main(String[] args) throws IOException, InterruptedException{
    Text key = new Text("key2:::key1:::_ performs better than _");
    IntWritable count5 = new IntWritable(5);
    IntWritable count3 = new IntWritable(3);
    IntWritable count8 = new IntWritable(8);
    List<IntWritable> values = new ArrayList<IntWritable>();
    values.add(count5);
    values.add(count3);
    values.add(count8);
    CombinePatternReduce reducer = new CombinePatternReduce();
    Context dcontext = new DebugTools.DebugReducerContext<Text, IntWritable, KeyPairWritableComparable, WrapperDoubleOrPatternWithWeightWritable>(reducer, key, count3); // here is the problem
    reducer.reduce(key, values, dcontext);      
}

这DebugTools.DebugReducerContext是我编写的一个类，用于使调试过程更易于执行，如下所示：

public static class DebugReducerContext<KIN, VIN, KOUT, VOUT> extends Reducer<KIN, VIN, KOUT, VOUT>.Context {
    DebugTools dtools = new DebugTools();
    DataOutput out = dtools.new DebugDataOutputStream(System.out);

    public DebugReducerContext(Reducer<KIN, VIN, KOUT, VOUT> reducer, Class<KIN> keyClass, Class<VIN> valueClass) throws IOException, InterruptedException{
        reducer.super(new Configuration(), new TaskAttemptID(), new DebugRawKeyValueIterator(), null, null, 
                null, null, null, null, keyClass, valueClass);
    }

    @Override
    public void write(Object key, Object value) throws IOException, InterruptedException {
        writeKeyValue(key, value, out);
    }

    @Override
    public void setStatus(String status) {
        System.err.println(status);
    }
}

问题出在代码的第一部分，即main(). 当我写

Context dcontext = new DebugTools.DebugReducerContext<Text, IntWritable, KeyPairWritableComparable, WrapperDoubleOrPatternWithWeightWritable>(reducer, key, count3);

有一个错误是

The constructor DebugTools.DebugReducerContext<Text,IntWritable,KeyPairWritableComparable,WrapperDoubleOrPatternWithWeightWritable>(CombinePatternReduce, Text, IntWritable) is undefined.

当我写

Context dcontext = new DebugTools.DebugReducerContext<Text, IntWritable, KeyPairWritableComparable, WrapperDoubleOrPatternWithWeightWritable>(reducer, key, values);

有一个错误是

The constructor DebugTools.DebugReducerContext<Text,IntWritable,KeyPairWritableComparable,WrapperDoubleOrPatternWithWeightWritable>(CombinePatternReduce, Text, List<IntWritable>) is undefined.

由于文档Reducer.Context是

public Reducer.Context(Configuration conf,
                       TaskAttemptID taskid,
                       RawKeyValueIterator input,
                       Counter inputKeyCounter,
                       Counter inputValueCounter,
                       RecordWriter<KEYOUT,VALUEOUT> output,
                       OutputCommitter committer,
                       StatusReporter reporter,
                       RawComparator<KEYIN> comparator,
                       Class<KEYIN> keyClass,
                       Class<VALUEIN> valueClass)
                throws IOException,
                       InterruptedException

我需要传入一个Class<KEYIN> keyClassand Class<VALUEIN> valueClass。那么如何编写 main() 函数（尤其是有错误的句子）来调试 reducer 类呢？

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1 回答 1

0

很明显，类构造函数需要 3 个参数。一个 reducer 的实例，一个 key 的 class，一个 value 的 class。

而不是实际传递键和值。您需要为其提供课程链接

Context dcontext = new DebugTools.DebugReducerContext<Text, IntWritable, KeyPairWritableComparable, WrapperDoubleOrPatternWithWeightWritable>(reducer, Text.class, IntWritable.class);

本质上，这是重申上下文应该能够处理减少的值的类型。

于 2012-11-08T14:44:23.097 回答