![](/img/trans.png)
[英]Found interface org.apache.hadoop.mapreduce.TaskAttemptContext, but class was expected
[英]Found class org.apache.hadoop.mapreduce.TaskInputOutputContext, but interface was expected
我正在尝试使用MRUnit 1.0.0测试Hadoop v2 Reducer,但尝试时出现异常:
java.lang.IncompatibleClassChangeError:
Found class org.apache.hadoop.mapreduce.TaskInputOutputContext, but interface was expected
at org.apache.hadoop.mrunit.internal.mapreduce.AbstractMockContextWrapper.createCommon(AbstractMockContextWrapper.java:59)
at org.apache.hadoop.mrunit.internal.mapreduce.MockReduceContextWrapper.create(MockReduceContextWrapper.java:76)
at org.apache.hadoop.mrunit.internal.mapreduce.MockReduceContextWrapper.<init>(MockReduceContextWrapper.java:67)
at org.apache.hadoop.mrunit.mapreduce.ReduceDriver.getContextWrapper(ReduceDriver.java:159)
at org.apache.hadoop.mrunit.mapreduce.ReduceDriver.run(ReduceDriver.java:142)
at org.apache.hadoop.mrunit.TestDriver.runTest(TestDriver.java:574)
at org.apache.hadoop.mrunit.TestDriver.runTest(TestDriver.java:561)
我认为这意味着我在某种程度上与Hadoop API的版本不匹配, 如本SO问题所示 ,但我不确定问题出在哪里。 我正在使用Maven像这样引入依赖关系,使用来自repo.hortonworks.com的Hadoop 2.2.0.2.0.6.0-76和来自repo1.maven.org的MRUnit 1.0.0:
<dependency>
<groupId>org.apache.hadoop</groupId>
<artifactId>hadoop-common</artifactId>
<version>2.2.0.2.0.6.0-76</version>
</dependency>
<dependency>
<groupId>org.apache.hadoop</groupId>
<artifactId>hadoop-hdfs</artifactId>
<version>2.2.0.2.0.6.0-76</version>
</dependency>
<dependency>
<groupId>org.apache.hadoop</groupId>
<artifactId>hadoop-mapreduce-client-core</artifactId>
<version>2.2.0.2.0.6.0-76</version>
</dependency>
<dependency>
<groupId>org.apache.hadoop</groupId>
<artifactId>hadoop-mapreduce-client-common</artifactId>
<version>2.2.0.2.0.6.0-76</version>
</dependency>
<dependency>
<groupId>org.apache.hadoop</groupId>
<artifactId>hadoop-mapreduce-client-jobclient</artifactId>
<version>2.2.0.2.0.6.0-76</version>
</dependency>
<dependency>
<groupId>org.apache.hadoop</groupId>
<artifactId>hadoop-yarn-common</artifactId>
<version>2.2.0.2.0.6.0-76</version>
</dependency>
<dependency>
<groupId>org.apache.mrunit</groupId>
<artifactId>mrunit</artifactId>
<version>1.0.0</version>
<classifier>hadoop2</classifier>
</dependency>
测试用例如下:
@Test
public void testReducer() throws IOException, InterruptedException {
HH.Reduce r = new HH.Reduce();
T1 fx1 = new T1();
T1 fx2 = new T1();
List<T1> values = new ArrayList<T1>();
values.add(fx1);
values.add(fx2);
T1 fxBoth = new T1(fx1.size() + fx2.size());
fxBoth.addValues(fx1);
fxBoth.addValues(fx2);
ReduceDriver<NullWritable, T1, NullWritable, T1> reduceDriver = ReduceDriver.newReduceDriver(r);
reduceDriver.withInput(NullWritable.get(), values);
reduceDriver.withOutput(NullWritable.get(), fxBoth);
// TODO I can't seem to get this test to work.
// Not sure what I'm doing wrong, whether it's a real
// problem or a testing problem.
reduceDriver.runTest();
}
在其他地方,在HH
包中,Reduce定义为非常简单的内部类:
public static class Reduce extends Reducer<NullWritable, T1, NullWritable, T1> {
@Override
public void reduce(NullWritable key, Iterable<T1> values, Context context)
throws InterruptedException, IOException {
// Need to create a new record here, because the one we're handed
// may be recycled by our overlords.
T1 out = new T1();
for (T1 t : values) {
out.addValues(t);
}
context.write(key, out);
}
}
看到什么古怪吗? MRUnit是否正在尝试使用旧版本的API?
我相信我也有同样的问题,但是我使用的是hadoop-core.1.2.1和mrunit-hadoop2-1.1.0。 检查您的Maven依赖项中的版本和分类器(用于测试,而不是pom.xml中声明的版本)。
mrunit maven依赖项中的分类器部分非常重要。
如您所说,您正在使用hadoop-core.1.2.1,TaskAttemptContext是该jar中的一个类。 因此,您需要在mrunit的maven依赖项中将分类器设置为hadoop1。 这样就可以正常工作了。
如果将分类器设置为hadoop2,则需要最新的api,其中TaskAttemptContext是接口。 您可以简单地在junit中运行文件并检查结果。
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.