MRUnit减速器测试:值类不匹配

Question

我的reducer单元测试在迁移到MapReduce 2后抛出了一个"Mismatch in value class"异常:

Mismatch in value class: expected: class org.apache.hadoop.io.IntWritable actual: class com.company.MyWritable

错误信息本身对我来说是清楚的，但我不明白为什么MRUnit得到临时可写类而不是IntWritable。

reducer实现:

public static class TestCountReduce extends
        Reducer<Text, MyWritable, Text, IntWritable> {
    public void reduce(Text key, Iterator<MyWritable> values,
            Context context) throws IOException, InterruptedException {
        ...
        context.write(key, new IntWritable(s.size()));
    }
}

测试设置:

public void setUp() throws IOException {
    Mapper<Object, Text, Text, MyWritable> mapper = new MyMapper();
    Reducer<Text, MyWritable, Text, IntWritable> reducer = new MyReducer();
    mapDriver = new MapDriver<Object, Text, Text, MyWritable>();
    mapDriver.setMapper(mapper);
    reduceDriver = new ReduceDriver<Text, MyWritable, Text, IntWritable>();
    reduceDriver.setReducer(reducer);
}

最后是测试用例:

@Test
public void testReducer() throws IOException {
    List<MyWritable> values = new ArrayList<MyWritable>();
    values.add(new MyWritable("1"));
    values.add(new MyWritable("1"));
    reduceDriver.withInput(new Text("testkey"), values);
    reduceDriver.withOutput(new Text("testkey"), new IntWritable(1));
    reduceDriver.runTest();
}

Answer 1

请检查您的reducer实现中的reduce方法签名

应该是

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

代替

public void reduce(Text key, Iterator<MyWritable> values, Context context) throws IOException, InterruptedException {