This example is showing how to download a jar file into the jvm and use the classes in that jar file.
First we create a jar file with a Hello.class in it.
The Hello.class does some logging when its get called.
After creating the jar file we set up a HTTP server which alows us to download the jar file from a url.
The next step is creating a Jython application which after is start will download the jar, put in into the system class loader and run the Hello.class.
1) Creating the Hello.class.
This is a very basic class, which is printing if a method is called.
package nl.sysgarden;
public class Hello {
public Hello() {
System.out.println("Hello.function.Constuctor");
}
public static void main (String[] args){
System.out.println("Hello.function.main");
}
public void p1(){
System.out.println("Hello.funtion.p1");
}
}
2) Creating a jar file:
After compile 'javac nl/sysgarden/Hello.java' we put the class in the jar file httpjartest.jar
user$ jar cvf httpjartest.jar nl/sysgarden/Hello.*
added manifest
adding: nl/sysgarden/Hello.class(in = 540) (out= 343)(deflated 36%)
adding: nl/sysgarden/Hello.java(in = 272) (out= 146)(deflated 46%)
Testing the jar file bij calling the Hello class main function
user$ java -cp httpjartest.jar nl.sysgarden.Hello
Hello.function.main
3) Putting up the http deamon.
Go to the directory where the jarfile is and activate the python webserver.
python -m SimpleHTTPServer 8080
Now we can download the jar file bij it's url http://localhost:8080/httpjartest.jar
Next and final is creating the Jython app that starts and dynamicly adds the httpjartest.jar file to the systemclassloader.
$ cat classloaderExample.py
import java.lang.System
import java.net.URLClassLoader
import java.net.URL
def printObject(obj):
print 'obj:' + str(obj)
print 'cls:' + str(obj.getClass().getName())
def addJarToClassLoader(u):
sysloader = java.lang.ClassLoader.getSystemClassLoader()
sysclass = sysloader.getClass()
#print str(sysclass.getDeclaredMethods())
method = sysclass.getDeclaredMethod("addAppURL", [java.net.URL])
print 'method= ' + str(method)
method.setAccessible(1)
jar_a = java.net.URL(u)
b = method.invoke(sysloader, [jar_a])
return sysloader
print 'step 1 download jar file and add it to the systemclass loader'
sysloader = addJarToClassLoader('http://localhost:8080/httpjartest.jar' )
import nl.sysgarden.Hello
print 'step 2 create Hello object and print output'
a=nl.sysgarden.Hello()
a.p1()
printObject(a)
Running the classloaderExample.py file
bash-3.2$ java -jar jython-standalone-2.5.3.jar classloaderExample.py
step 1 download jar file and add it to the systemclass loader
method= void sun.misc.Launcher$AppClassLoader.addAppURL(java.net.URL)
step 2 create Hello object and print output
Hello.function.Constuctor
Hello.funtion.p1
obj:nl.sysgarden.Hello@6da05bdb
cls:nl.sysgarden.Hello
