Loading classes dynamically from jar

Question

I know that we can load classes dynamically by using custom class loaders. But here my problem is my Class itself is depends upon other classes

My task is to get PigServer object .So I have used following code to load PigServer class

_pigServerClass = _classLoader.loadClass("org.apache.pig.PigServer");

But here PigServer class itself is depends upon so many other classes.

So when i am trying to get instance of PigServer class then it is showing following errors

java.lang.ClassNotFoundException: org.apache.commons.logging.LogFactory
java.lang.ClassNotFoundException:org.apache.log4j.AppenderSkeleton
 etc..

Can anyone tell how to solve this?

score 1 · Answer 1 · answered Sep 24 '12 at 15:05

There seems to be a misunderstanding. If you have all the jars required in a folder, say "lib", you can for example set up a class loader like this:

    File libs = new File("lib");
    File[] jars = libs.listFiles(new FileFilter() {
        public boolean accept(File pathname) {
            return pathname.getName().toLowerCase().endsWith(".jar");
        }
    });

    URL[] urls = new URL[jars.length];
    for (int i=0; i<jars.length; i++) {
        urls[i] = jars[i].toURI().toURL();
    }
    ClassLoader uc = new URLClassLoader(urls,this.getClass().getClassLoader());


    Class<?> pigServerClz = Class.forName("org.apache.pig.PigServer", false, uc);
    Object pigServer = pigServerClz.newInstance();
    // etc...

score 0 · Accepted Answer · answered Sep 13 '12 at 06:55

0

How you created your ClassLoader?

Did you specified another "parent" classloader, on wich classloading can be delegated?

answered Sep 13 '12 at 06:55

Mirko

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I have created class loader ..its take class path and returns **_customClassLoader = new URLClassLoader(urls,PigClassLoader.class.getClassLoader());** – Rajesh Barri Sep 13 '12 at 06:58
that to my class loader is working fine. Thats y it didnt show class not found exception for PigServer Class – Rajesh Barri Sep 13 '12 at 07:04
Are you're sure, that commons-logging and log4j are in the classpath? – Mirko Sep 13 '12 at 07:09
No . I want it as dynamic loading. All those classes are in Pig.jar;I am passing that pig.jar path to my custom classLoader as class path. – Rajesh Barri Sep 13 '12 at 07:45
2

I'm sorry, but I think that I dont understand your what your problem is. In Standard: a class will loaded on demand when it is needed. you only have to configure the classpath. So if you're implementing it by yourself you'll just get the benifit of less classpath-configuration. So why you not add the jars, required at runtime to the Standard-ClassLoader? See: http://stackoverflow.com/questions/1010919/adding-files-to-java-classpath-at-runtime – Mirko Sep 13 '12 at 07:54
My program is working well when i am using static class loading. But according my project requirement, I have to implement it by dynamic class loading only. – Rajesh Barri Sep 13 '12 at 08:01
And why you dont add the required jar @ runtime to your default classloader? – Mirko Sep 13 '12 at 08:57

Loading classes dynamically from jar

2 Answers2