Call the Hadoop Java API for the first time

Environment: Hadoop1.2.1

Example: Displaying files in a Hadoop file system directly using filesystem in a standard output format
Writing Java files

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);}}    }

Set the JAVA_HOME environment variable to add $java_home/bin to the PATH environment variable

Set the class directory for Hadoop ( Hadoop_classpath)

[Email protected] 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

Upload the edited Java file

[[email protected] hadoop-1.2.1]$ mkdir myclasses[[email protected] hadoop-1.2.1]$ CD Myclasses[[email protected] myclasses]$ RZ

compiling Java files

[Email protected] myclasses]$ Javac-classpath. /hadoop-core-1.2.1.jar  Filesystemcat.java

Perform:

[[email protected] hadoop-1.2.1]$./bin/hadoop filesystemcat Hdfs://hadoop1:9000/user/grid/in/test3.txthello Hadoop Java API

Call the Hadoop Java API for the first time