title: ClassNotFoundException with URLClassLoader in classes.jar (java.net package)
body: <p>On Eclipse Galileo, got the following ClassNotFoundException when doing Debug As/Web Application. But works just fine when doing Run As/Web Application.</p>
  
  <p>I was given message that "The source attachment does not contain the source for the file URLClassLoader.class. You can change the source attachment by clicking the Change Attached Source below:"</p>
  
  <p>In the project window, it seems that the URLClassLoader class is from Java.net package, which is from /System/Library/Frameworks/JavaVM.framework/Versions/1.6.0/Classes/classes.jar. </p>
  
  <p>I found the jar on the machine, what else I am missing? why it's debug only issue?</p>
  
  <p>Could it be possible that the JRE system library that I have on my iMac 10.6.5 machine is outdated? Or somehow install/unstall of some jar/package caused the issue?</p>
  
  <p>This is what I have - JRE System Library [JVM 1.6.0 (MacOS X Default)] - would update it help fixing the issue? but how to get it updated?</p>
  
  <p>Please help!</p>
  
  <pre><code>com.google.appengine.tools.development.DevAppServerMain at localhost:57873 
   Thread [main] (Suspended (exception ClassNotFoundException)) 
    Launcher$ExtClassLoader(URLClassLoader).findClass(String) line: 207 
    Launcher$ExtClassLoader.findClass(String) line: 229 
    Launcher$ExtClassLoader(ClassLoader).loadClass(String, boolean) line: 307 
    Launcher$AppClassLoader(ClassLoader).loadClass(String, boolean) line: 296 
    Launcher$AppClassLoader.loadClass(String, boolean) line: 301 
    Launcher$AppClassLoader(ClassLoader).loadClass(String) line: 248 
    InstrumentationImpl.loadClassAndStartAgent(String, String, String) line: 280 
    InstrumentationImpl.loadClassAndCallPremain(String, String) line: 338 
  /System/Library/Frameworks/JavaVM.framework/Versions/1.6.0/Home/bin/java (Nov 30, 2010 9:40:41 PM) 
  </code></pre>