This document comprehensively describes the procedure of running Java code using Oozie. Its targeted audience is all forms of users who will install, use and operate Oozie.
The Java action will execute the public static void main(String[] args) method of the specified main Java class. The required Java class(es) should be packaged in the form of a JAR and placed within your workflow application's lib directory.
i.e.
When executing a java application without oozie, one specifies the class having the main function (main-class), run-time JVM options and the arguments to be passed.
$ java -Xms512m a.b.c.MyMainClass arg1 arg2
Now with Oozie, they are specified as inline tags in the workflow.xml file.
<action name='java1'>
<java>
...
<main-class> a.b.c.MyJavaMain </main-class>
<java-opts> -Xms512m </java-opts>
<arg> arg1 </arg>
<arg> arg2 </arg>
...
</java>
</action>
The java-opts element, if present, contains the command line parameters which are to be used to start the JVM that will execute the Java application. For multiple command line parameters, there may instead be a java-opt element for each.
The arg elements, if present, contains arguments for the main function. The value of each arg element is considered a single argument and they are passed to the main method in the same order.
Java applications are executed in the Hadoop cluster as map-reduce job with a single Mapper task. Hence the Java action has to be configured with the following properties in the form of XML tags:
<action name='java1'>
<java>
<job-tracker>foo.bar:8021</job-tracker>
<name-node>foo1.bar:8020</name-node>
...
<configuration>
<property>
<name>abc</name>
<value>def</value>
</property>
</configuration>
</java>
</action>
Prepare block
A java action can be configured to perform HDFS files/directories cleanup such as deleting an existing output directory (<delete>) or creating a new one (<mkdir>) before starting the Java application. This capability enables Oozie to retry a Java application in the situation of a transient or non-transient failure (This can be used to cleanup any temporary data which may have been created by the Java application in case of failure).
The prepare element, if present, indicates a list of paths to do file operations upon, before starting the Java application. This should be used exclusively for directory cleanup for the Java application to be executed.
Capture-output element
This function is only applicable to action nodes that produce output data on completion.
The output data is in a Java Properties format and via this EL function it is available as a Map ..
For more details, refer to the section on EL functions in the Workflow functional specification.
The example below illustrates the use of <capture-output> element and the corresponding java main function definition.
<workflow-app xmlns='uri:oozie:workflow:0.1' name='java-wf'>
<start to='java1' />
<action name='java1'>
<java>
<job-tracker>${jobTracker}</job-tracker>
<name-node>${nameNode}</name-node>
<configuration>
<property>
<name>mapred.job.queue.name</name>
<value>${queueName}</value>
</property>
</configuration>
<main-class>org.apache.oozie.test.MyTest</main-class>
<arg>${outputFileName}</arg>
<capture-output/>
</java>
<ok to="pig1" />
<error to="fail" />
</action>
<action name='pig1'>
<pig>
<job-tracker>${jobTracker}</job-tracker>
<name-node>${nameNode}</name-node>
<configuration>
<property>
<name>mapred.job.queue.name</name>
<value>${queueName}</value>
</property>
</configuration>
<script>script.pig</script>
<param>MY_VAR=${wf:actionData('java1')['PASS_ME']}</param>
</pig>
<ok to="end" />
<error to="fail" />
</action>
<kill name="fail">
<message>Pig failed, error message[${wf:errorMessage(wf:lastErrorNode())}]</message>
</kill>
<end name='end' />
</workflow-app>
Java Main Class
The main() method writes a Property file to the path specified in the 'oozie.action.output.properties' ENVIRONMENT variable.
package org.apache.oozie.test;
import java.io.*;
import java.util.Properties;
public class MyTest {
////////////////////////////////
// Do whatever you want in here
////////////////////////////////
public static void main (String[] args)
{
String fileName = args[0];
try{
File file = new File(System.getProperty("oozie.action.output.properties"));
Properties props = new Properties();
props.setProperty("PASS_ME", "123456");
OutputStream os = new FileOutputStream(file);
props.store(os, "");
os.close();
System.out.println(file.getAbsolutePath());
}
catch (Exception e) {
e.printStackTrace();
}
}
}
Launcher configuration properties
Oozie executes the Java action within a Launcher mapper on the compute node. Some commonly used <configuration> properties passed for the java action can be as follows:
<property>
<name>oozie.mapred.child.env</name>
<value>A=foo</value>
</property>
Thus summarily, mapred properties are applied to the java-action map job by prefixing "oozie." to those property names.
The workflow job will wait until the java application completes its execution before continuing to the next action. To indicate an ok action transition, the main Java class must complete gracefully the main method invocation.
To indicate an error action transition, the main Java class must throw an exception.
e.g. If the main Java class calls System.exit(int n) where n is non-zero, this will make the java action to do an error transition regardless of the used exit code.
Non-zero system exit will be error whereas a System.exit(0) will lead to ok transition.
$ jar uf /path/to/jar -C /path/to/a/ a/b/c/myMainClass.class
where a.b.c.myMainClass is the package structure you wish to maintain in the JAR.
Within your Java Main class, you can query for the following system properties pertaining to your Oozie job.
This provides for a convenient way to access these values directly within the action code.
Following are example workflow applications that illustrate use-cases of the Oozie Java action.
I: Using Java-Main action to copy local file to HDFS
Assume a local file $filename can be accessed by all cluster nodes.
<workflow-app xmlns='uri:oozie:workflow:0.3' name='java-filecopy-wf'>
<start to='java1' />
<action name='java1'>
<java>
<job-tracker>${jobTracker}</job-tracker>
<name-node>${nameNode}</name-node>
<configuration>
<property>
<name>mapred.job.queue.name</name>
<value>${queueName}</value>
</property>
</configuration>
<main-class>testCopyFromLocal</main-class>
<arg>${filename}</arg>
<arg>${nameNode}${testDir}</arg>
<capture-output/>
</java>
<ok to="end" />
<error to="fail" />
</action>
<kill name="fail">
<message>Java failed, error message[${wf:errorMessage(wf:lastErrorNode())}]
</message>
</kill>
<end name='end' />
</workflow-app>
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.FSDataInputStream;
import org.apache.hadoop.fs.FSDataOutputStream;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.conf.Configuration;
import java.io.File;
import java.io.IOException;
public class testCopyFromLocal {
public static void main (String[] args) throws IOException {
String src = args[0];
String dst = args[1];
System.out.println("testCopyFromLocal, source= " + src);
System.out.println("testCopyFromLocal, target= " + dst);
Configuration conf = new Configuration();
Path src1 = new Path(src);
Path dst1 = new Path(dst);
FileSystem fs = FileSystem.get(conf);
try{
//delete local file after copy
fs.copyFromLocalFile(true, true, src1, dst1);
}
catch(IOException ex) {
System.err.println("IOException during copy operation " +
ex.toString());
ex.printStackTrace();
System.exit(1);
}
}
}
II: Java-Main Action decision nodes
This example is to illustrate how action output data captured using capture output can be used in decision nodes.
<workflow-app xmlns='uri:oozie:workflow:0.3' name='java-actionprops-wf'>
<start to='java3' />
<action name='java3'>
<java>
<job-tracker>${jobTracker}</job-tracker>
<name-node>${nameNode}</name-node>
<configuration>
<property>
<name>mapred.job.queue.name</name>
<value>${queueName}</value>
</property>
</configuration>
<main-class>exampleDecision</main-class>
<arg>yes</arg>
<capture-output/>
</java>
<ok to="end" />
<error to="fail" />
</action>
<decision name="decision1">
<switch>
<case to="end">${(wf:actionData('java3')['key1'] == "value1") and (wf:actionData('java3')['key2'] == "value2")}</case>
<default to="fail" />
</switch>
</decision>
<kill name="fail">
<message>Java failed, error message[${wf:errorMessage(wf:lastErrorNode())}]
</message>
</kill>
<end name='end' />
<workflow-app>
The corresponding Java class can be as below:
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.util.Properties;
public class exampleDecision {
public static void main (String[] args) {
String text = args[0];
try{
File file = new File(System.getProperty("oozie.action.output.properties"));
Properties props = new Properties();
if (text.equals("yes")) {
props.setProperty("key1", "value1");
props.setProperty("key2", "value2");
} else {
props.setProperty("key1", "novalue");
props.setProperty("key2", "novalue");
}
OutputStream os = new FileOutputStream(file);
props.store(os, "");
os.close();
System.out.println(file.getAbsolutePath());
}
catch (Exception e) {
e.printStackTrace();
}
}
}