URLClassLoader problem

[tracey ruark]

I've searched the topics in this forum and cam across many people who seem to have the same problem as me, but my problem remains.

I'm simply trying to load a class that isn't in the classpath of my app. No matter what I do or what I try it simply cannot find the class

Here is my code:

import java.io.*;
import java.net.*;

public class URLClassLoaderTesting {

	public static void main(String[] args) {
		File targetFile = new File("E:\\URLClassLoaderTesting_TEMP\\projects\\project1\\tests\\ClassToBeLoaded.java");
		System.out.println("the file exists? " + targetFile.exists());
		
		File testPath = new File("E:/URLClassLoaderTesting_TEMP/projects/project1/");
		System.out.println("testPath exists? " + testPath.exists());
		
		try {
			URL testRootUrl = testPath.toURI().toURL();
			URL[] urls = new URL[] {testRootUrl};
			ClassLoader loader = new URLClassLoader(urls);
			URL fileFromLoader = loader.getResource("tests/ClassToBeLoaded.java");
			System.out.println("file from loader: " + fileFromLoader.toString());
			Class cls = loader.loadClass("tests.ClassToBeLoaded");
		} catch (Exception e) {
			System.out.println("BONK: " + e.toString());
		}
	}

}

And here is the output:

the file exists? true
testPath exists? true
file from loader: file:/E:/URLClassLoaderTesting_TEMP/projects/project1/tests/ClassToBeLoaded.java
BONK: java.lang.ClassNotFoundException: tests.ClassToBeLoaded

What am I doing wrong?!?!

[David Newton]

Is there a class file there?

[tracey ruark]

David Newton wrote:Is there a class file there?

Yes, I complied the file already to check it.

Here's the contents of the file at E:\URLClassLoaderTesting_TEMP\projects\project1\tests\ClassToBeLoaded.java
(It is just a dummy class for the proof of concept)

package tests;

public class ClassToBeLoaded {
	
	public ClassToBeLoaded() {
		System.out.println("ClassToBeLoaded was initialized");
	}
	
	public void aMethod() {
		System.out.println("ClasToBeLoaded.aMethod() was called");
	}

}

[Rob Spoor]

And where is file ClassToBeLoaded.class located?

[tracey ruark]

Rob Prime wrote:And where is file ClassToBeLoaded.class located?

That is an excellent question. I say that because when I started this whole thing I dropped the .class file right next to the java file. However, when the .java and .class file reside next to each other in the same directory the program spits this out at me:

the file exists? true
testPath exists? true
file from loader: file:/E:/URLClassLoaderTesting_TEMP/projects/project1/tests/ClassToBeLoaded.java
Exception in thread "main" java.lang.NoClassDefFoundError: tests/ClassToBeLoaded (wrong name: ClassToBeLoaded)
	at java.lang.ClassLoader.defineClass1(Native Method)
	at java.lang.ClassLoader.defineClass(Unknown Source)
	at java.security.SecureClassLoader.defineClass(Unknown Source)
	at java.net.URLClassLoader.defineClass(Unknown Source)
	at java.net.URLClassLoader.access$000(Unknown Source)
	at java.net.URLClassLoader$1.run(Unknown Source)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.net.URLClassLoader.findClass(Unknown Source)
	at java.lang.ClassLoader.loadClass(Unknown Source)
	at java.lang.ClassLoader.loadClass(Unknown Source)
	at URLClassLoaderTesting.main(URLClassLoaderTesting.java:20)

[Rob Spoor]

In what folder are you when you're executing the JVM? It should be E:\URLClassLoaderTesting_TEMP\projects\project1. Also, you error tells me that the .class file does not think it belongs in the tests package; the fully qualified name in the .class file is ClassToBeLoaded, not tests.ClassToBeLoaded.

Have you perhaps created the .class file before you added the package statement?

[tracey ruark]

Rob Prime wrote:In what folder are you when you're executing the JVM? It should be E:\URLClassLoaderTesting_TEMP\projects\project1. Also, you error tells me that the .class file does not think it belongs in the tests package; the fully qualified name in the .class file is ClassToBeLoaded, not tests.ClassToBeLoaded.

Have you perhaps created the .class file before you added the package statement?

Ah Hah! Thank you. It's been so many years since I've worked with java I'd completely forgotten about how it works at it's most fundamental levels.

My new code looks like this:

import java.io.*;
import java.net.*;

public class URLClassLoaderTesting {

	public static void main(String[] args) {
		File testPath = new File("E:/URLClassLoaderTesting_TEMP/projects/project1/tests");
		File targetFile = new File("E:\\URLClassLoaderTesting_TEMP\\projects\\project1\\tests\\ClassToBeLoaded.java");
		
		System.setProperty(
				"java.class.path", 
				System.getProperty("java.class.path") + ";" + testPath.getAbsolutePath()
				);
		
		System.out.println("the file exists? " + targetFile.exists());
		
		try {
			URL testRootUrl = testPath.toURI().toURL();
			URL[] urls = new URL[] {testRootUrl};
			ClassLoader loader = new URLClassLoader(urls);
			//URL fileFromLoader = loader.getResource("ClassToBeLoaded.java");
			//System.out.println("file from loader: " + fileFromLoader.toString());
			Class cls = loader.loadClass("ClassToBeLoaded");
			cls.newInstance();
		} catch (Exception e) {
			System.out.println("BONK: " + e.toString());
		}
	}

}

My output now looks like this, which is what I'm after:

ClassToBeLoaded was initialized

Thank you so much Mr. Prime!