Hadoop 2.7.1 使用minicluster進行單元測試

目的是要跑通這個單元測試:hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/TestClose.java

這個Java文件比較簡單：

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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();
      }
    }
  }
  
}

通過實例化一個minicluster來測試hdfs的關閉功能是否正常。

直接運行Junit，將會報錯，因為在CLASSPATH中找不到webapps/hdfs。

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

要現在~/CVS/hadoop目錄下執行如下兩條命令：

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

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

執行完這兩條命令后，會在如下目錄生成webapps目錄：

也就是說這個webapps目錄是通過上面兩條命令生成的，如果沒有執行上面兩條命令，那么這個目錄下就不會有這個文件，導致java在運行時無法在CLASSPATH中找到這個文件夾。一切准備就緒，運行Junit，可以看到單元測試成功通過：