How to launch One Java Program from another Java Program

[joshivaibhav]

Hello,

I am new to Java and here is my question:

How to launch another Java program from within a Java program?

I have tried using Runtime.getRuntime() and it works for launching
applications.

But if I need to launch another java program do I have to use:

"Java <another Java program name>" => This string as an input to exec()
method to run another Java program?

Both the programs will run on the same machine. Can these program share
the same JVM and run in the same process?

I want to avoid using RMI.

Please advice.

Thanks,

Vaibhav

 

[Jeff]

Hello,

I am new to Java and here is my question:

How to launch another Java program from within a Java program?

I have tried using Runtime.getRuntime() and it works for launching
applications.

But if I need to launch another java program do I have to use:

"Java <another Java program name>" => This string as an input to exec()
method to run another Java program?

Both the programs will run on the same machine. Can these program share
the same JVM and run in the same process?

I want to avoid using RMI.

Please advice.

Thanks,

Vaibhav

It seems to me that you would just use a classLoader to load the class
and execute the main method.

 

[Thomas Hawtin]

Both the programs will run on the same machine. Can these program share
the same JVM and run in the same process?

You can, but they wont be entirely independent.

o Create a new ClassLoader with the URLs of the program code. null as
the parent class loader will stop the libraries you are using interfere
with the libraries it is using.

ClassLoader loader = URLClassLoader.newInstance(new URL[] { url },
null);

http://download.java.net/jdk6/docs/api/java/net/URLClassLoader.html#newInstance(java.net.URL[],
java.lang.ClassLoader)

o Find you the applications main class (I guess you could look up
Main-Class in its manifest).

Class<?> mainClass = Class.forName(mainName, false, loader);

http://download.java.net/jdk6/docs/api/java/lang/Class.html#forName(java.lang.String,
boolean, java.lang.ClassLoader)

o Find the main method.

Method mainMethod = mainClass.getMethod("main", String[].class);

http://download.java.net/jdk6/docs/api/java/lang/Class.html#getMethod(java.lang.String,
java.lang.Class...)

o Invoke main method. Note how varargs doesn't work too well.

mainMethod.invoke(null, new Object[] { new String[] { /* args */ }});

http://download.java.net/jdk6/docs/api/java/lang/reflect/Method.html#invoke(java.lang.Object,
java.lang.Object...)

(Disclaimer: I've not tested or even compiled this code. However, I have
written similar stuff before).

You will be sharing the JVM, but for AWT/Swing applications you wont be
able to do the separate AppContext thing. You can create a new
ThreadGroup for the application if you so wish.

> I want to avoid using RMI.

It's not *that* bad is it?

Tom Hawtin

 

[joshivaibhav]

Thanks !!!

I will try this out and see if it solves my problem.

Both the programs will run on the same machine. Can these program share
the same JVM and run in the same process?

You can, but they wont be entirely independent.

o Create a new ClassLoader with the URLs of the program code. null as
the parent class loader will stop the libraries you are using interfere
with the libraries it is using.

ClassLoader loader = URLClassLoader.newInstance(new URL[] { url },
null);

http://download.java.net/jdk6/docs/api/java/net/URLClassLoader.html#newInstance(java.net.URL[],
java.lang.ClassLoader)

o Find you the applications main class (I guess you could look up
Main-Class in its manifest).

Class<?> mainClass = Class.forName(mainName, false, loader);

http://download.java.net/jdk6/docs/api/java/lang/Class.html#forName(java.lang.String,
boolean, java.lang.ClassLoader)

o Find the main method.

Method mainMethod = mainClass.getMethod("main", String[].class);

http://download.java.net/jdk6/docs/api/java/lang/Class.html#getMethod(java.lang.String,
java.lang.Class...)

o Invoke main method. Note how varargs doesn't work too well.

mainMethod.invoke(null, new Object[] { new String[] { /* args */ }});

http://download.java.net/jdk6/docs/api/java/lang/reflect/Method.html#invoke(java.lang.Object,
java.lang.Object...)

(Disclaimer: I've not tested or even compiled this code. However, I have
written similar stuff before).

You will be sharing the JVM, but for AWT/Swing applications you wont be
able to do the separate AppContext thing. You can create a new
ThreadGroup for the application if you so wish.

I want to avoid using RMI.

It's not *that* bad is it?

Tom Hawtin