Hadoop 2.7.1 使用minicluster进行单元测试

目的是要跑通这个单元测试:hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/TestClose.java

这个Java文件比较简单：

/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.hadoop.hdfs;

import static org.junit.Assert.fail;

import java.io.IOException;
import java.io.OutputStream;
import java.nio.channels.ClosedChannelException;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.test.GenericTestUtils;
import org.junit.Test;

public class TestClose {

  @Test
  public void testWriteAfterClose() throws IOException {
    Configuration conf = new Configuration();
    MiniDFSCluster cluster = new MiniDFSCluster.Builder(conf)
        .build();
    
    try {
      final byte[] data = "foo".getBytes();
      
      FileSystem fs = FileSystem.get(conf);
      OutputStream out = fs.create(new Path("/test"));
      
      out.write(data); 
      out.close();
      try {
        // Should fail.
        out.write(data);
        fail("Should not have been able to write more data after file is closed.");
      } catch (ClosedChannelException cce) {
        // We got the correct exception. Ignoring.
      }
      // Should succeed. Double closes are OK.
      out.close();
    } finally {
      if (cluster != null) {
        cluster.shutdown();
      }
    }
  }
  
}

通过实例化一个minicluster来测试hdfs的关闭功能是否正常。

直接运行Junit，将会报错，因为在CLASSPATH中找不到webapps/hdfs。

正确的做法（https://hadoop.apache.org/docs/current/hadoop-project-dist/hadoop-common/CLIMiniCluster.html ）

要现在~/CVS/hadoop目录下执行如下两条命令：

hadoop@ubuntu:~/CVS/hadoop$ mvn clean install –DskipTests

hadoop@ubuntu:~/CVS/hadoop$ mvn package -Pdist -Dtar -DskipTests -Dmaven.javadoc.skip

执行完这两条命令后，会在如下目录生成webapps目录：

也就是说这个webapps目录是通过上面两条命令生成的，如果没有执行上面两条命令，那么这个目录下就不会有这个文件，导致java在运行时无法在CLASSPATH中找到这个文件夹。一切准备就绪，运行Junit，可以看到单元测试成功通过：