How to load classes which are not in your classpath

By mkyong | Updated: August 30, 2012

Viewed: 656 (+5 pv/w)

Tags: classpath java

In certain scenario, you may need to load some classes which are not in your classpath.

Java Example

Assume folder “c:\\other_classes\\” is not in your project classpath, here’s an example to show how to load a Java class from this folder. The code and comments are self-explanatory.

import java.io.File;
import java.net.URL;
import java.net.URLClassLoader;
import java.security.CodeSource;
import java.security.ProtectionDomain;

public class App{

	public static void main(String[] args) {
		
	try{
	
		File file = new File("c:\\other_classes\\"); 

                //convert the file to URL format
		URL url = file.toURI().toURL(); 
		URL[] urls = new URL[]{url}; 
			
                //load this folder into Class loader
		ClassLoader cl = new URLClassLoader(urls); 

                //load the Address class in 'c:\\other_classes\\'
		Class  cls = cl.loadClass("com.mkyong.io.Address");		
		
                //print the location from where this class was loaded
		ProtectionDomain pDomain = cls.getProtectionDomain(); 
		CodeSource cSource = pDomain.getCodeSource(); 
		URL urlfrom = cSource.getLocation();
		System.out.println(urlfrom.getFile());
	
	}catch(Exception ex){
		ex.printStackTrace();
	}
  }
}

Output

/c:/other_classes/

You will notice this class is loaded from “/c:/other_classes/“, which is not in your project classpath.