title: Replace content of some methods at runtime
body: <p>I would like to replace the content of some methods at runtime.</p>
  
  <p>I know I can use <em>javassist</em> for this but it does not work because the classes I would like to enhance are already loaded by the system <em>classLoader</em>.</p>
  
  <p>How can I do, to replace the content of a method at runtime ? Should I try to unload the class ? How can I do that ? I saw it was possible but I could not figure out how to do it.</p>
  
  <p>If possible, I would like to avoid using an external lib for this, I would like to code it my-self.</p>
  
  <p><strong>More information:</strong>
  - The class I would like to enhance is contained in a framework (in a jar file)
  - My code is actually a plugin of this framework
  - The framework in which my plugin runs has its own <em>classLoader</em>, but this <em>classLoader</em> does not load its own classes (it delegates them to the system class loader)
  - The framework I'm using is <em>Play</em>.</p>
  
  <p>Thank you for your help !</p>