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Running Java classes

What is it?​

The Java Agent runs Java classes defined in OpCon job definitions. It supports two entry points: a named method (any non-main method in the class) and the default main method. Parameters can be passed to either entry point from the OpCon job definition using typed identifiers.

  • Use named method when the class contains specific business logic methods you want OpCon to call directly
  • Use main method when the class follows a standard command-line entry point pattern or accepts arguments as a string array

When the Java Agent is installed on the same system as the Java classes, the agent needs access to the Java libraries (.jar files) that contain the classes. All required libraries must be loaded into the agent's class path before a job runs. For information on loading libraries, refer to Managing Software Libraries.

The Java Agent can run classes that contain either a named method or the default main method of the class.

Named method​

When a named method (not the default main method) runs, parameters can be passed to the method as part of the run. The parameters must be defined using an identifier and a value. The supported identifiers are STRING, INTEGER, LONG, and BOOLEAN. The agent passes the parameters to the method, casting them to the identified type using the identifier, in the order that the parameters are defined in the job definition.

Example

A Java class com.sma.test.execution has a method execute with four parameters defined as String, String, int, and boolean objects.

package com.sma.test;

public class execution {

public void execute(String name, String surname, int age, boolean male){

}
}

The parameters passed to the class would need to be defined in the Java job definition as follows:

STRING John
STRING Simpson
INTEGER 35
BOOLEAN True

The Java Agent would run the method mapping the parameters according to the identifiers as follows:

com.sma.test.execution.execute("John", "Simpson", 35, true);

Main method​

When a main method runs, parameters can be passed to the method as part of the run. The parameters must be defined using either an identifier or a name and a value. If an identifier such as STRING, INTEGER, LONG, or BOOLEAN is used, the identifier is not passed as part of the run — only the value is passed. If a name definition is used (for example, -age), the name is passed as part of the run. The agent passes the parameters to the method in the order that the parameters are defined in the job definition.

Example

A Java class com.sma.test.execution has a main method that accepts multiple arguments.

package com.sma.test;

public class execution {

public static void main(String[] args){

}
}

The parameters for this would be defined in the Java job definition as follows:

STRING John
STRING Simpson
-age 35
-male True

The Java Agent would run the main method passing the parameters as follows:

com.sma.test.execution "John" "Simpson" -age 35 -male True

FAQs​

What is the difference between a named method and the main method? A named method is any specific non-main method in a class that you want the agent to call directly. The main method is the standard Java entry point (public static void main(String[] args)). Named method runs happen within a thread of the agent's JVM. Main method runs spawn a separate JVM process.

What type identifiers does the Java Agent support? The agent supports STRING, INTEGER, LONG, and BOOLEAN. These identifiers tell the agent what Java type to use when passing the parameter value to the method.

Does the identifier appear in the method call for named methods? No. For named methods, the identifier is used only to determine the Java type for casting. The identifier itself is not passed to the method — only the value is passed, cast to the specified type.

Does the identifier appear in the command line for main method runs? No. When you use a type identifier (STRING, INTEGER, LONG, BOOLEAN) with a main method, only the value is passed as a command-line argument. When you use a name definition (for example, -age), both the name and the value are passed.

What happens if the class or method is not found? The agent logs an error message: Method <name> not found in class <name> or Class <name> not found in libraries. The job fails with an error return code. Verify that the required .jar files are loaded into the agent's class path.

Glossary​

Named method — A specific non-main method within a Java class, identified by name, that the agent calls directly. Parameters are passed using typed identifiers (STRING, INTEGER, LONG, BOOLEAN).

Main method — The standard Java entry point method (public static void main(String[] args)). When using the main method, the agent spawns a separate JVM process. Parameters are passed as command-line arguments.

Type identifier — A keyword (STRING, INTEGER, LONG, BOOLEAN) used in the OpCon job definition to specify the Java type for a parameter value. The agent casts the value to this type before passing it to the method.

Class path — The list of directories and .jar files that the JVM searches when loading Java classes. All required libraries must be in the class path before a job runs.