code: public boolean isProxyClassDefined(ClassLoader classLoader) {
          try {
              // first check that the proxy has not already been created
              classLoader.loadClass(this.className);
              return true;
          } catch (ClassNotFoundException e) {
              return false;
          }
      }
docs: Checks if the proxy class has been defined in the given class loader
  
  @param classLoader The class loader to check
  @return true if the proxy is defined in the class loader