環境：Hadoop1.2.1
例：直接使用FileSystem以標準輸出格式顯示Hadoop文件系統中的文件
編寫JAVA文件
import org.Apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IOUtils;
import java.io.InputStream;
import java.net.URI;
public class FileSystemCat {
public static void main(String[] args) throws Exception {
String uri = args[0];
Configuration conf = new Configuration();
FileSystem fs = FileSystem.get(URI.create(uri), conf);
InputStream in = null;
try {
in = fs.open(new Path(uri));
IOUtils.copyBytes(in, System.out, 4096, false);
} finally {
IOUtils.closeStream(in);
}
}
}
設置JAVA_HOME環境變量，將$JAVA_HOME/bin添加到PATH環境變量
設置Hadoop的類目錄( HADOOP_CLASSPATH)
[grid@hadoop1 hadoop-1.2.1]# vi conf/hadoop-env.sh # The java implementation to use. Required. export JAVA_HOME=/usr/java/jdk1.7.0_72 # Extra Java CLASSPATH elements. Optional. export HADOOP_CLASSPATH=/home/grid/hadoop-1.2.1/myclasses
上傳編輯好的JAVA文件
[grid@hadoop1 hadoop-1.2.1]$ mkdir myclasses [grid@hadoop1 hadoop-1.2.1]$ cd myclasses [grid@hadoop1 myclasses]$ rz
編譯java文件
[grid@hadoop1 myclasses]$ javac -classpath ../hadoop-core-1.2.1.jar FileSystemCat.java
執行：
[grid@hadoop1 hadoop-1.2.1]$ ./bin/hadoop FileSystemCat hdfs://hadoop1:9000/user/grid/in/test3.txt Hello Hadoop Java API
