3,InvocableServlet base class for the called servlet.

• By David Tayouri
• November 17, 2000

/** Extend this servlet to have the ability of
    method invocation.
    The caller applet/application should send
    the name of the method to be invoked and
    a vector of the method parameters.
 */
public abstract class InvocableServlet
  extends HttpServlet
{
  //===========================================
  /** Reads the name of method to be invoked
      and its parameters from request input
      stream, invokes the method and sends
      the return value of the method through
      response output stream. If an exception
      is thrown, it is returned as output value.
   */
  protected void invokeMethod(
    HttpServletRequest request,
    HttpServletResponse response)
    throws ServletException, IOException
  {
    Object returnValue = null;
    // Read name of method to be invoked and
    // its params (as Vector)
    ObjectInputStream in = 
      new ObjectInputStream(
        request.getInputStream());
    String methodName = null;
    Vector parameters = null;
    try {
      methodName = (String)in.readObject();
      parameters = (Vector)in.readObject();
      in.close();

      // Prepare param-type and param-
      // value arrays (if any param)
      Class paramTypes[] = null;
      Object paramValues[] = null;
      if (   parameters != null
          && !parameters.isEmpty()) {
        paramTypes = new 
          Class[parameters.size()];
        for (int i = 0;
             i < parameters.size();
             i++) {
          paramTypes[i] =
          parameters.elementAt(i).getClass();
          // Change classes to primitive types
          // See below
        }
        paramValues = 
          new Object[parameters.size()];
        parameters.copyInto(paramValues);
      }

      // Invoke the method
      Method method =
        getClass().getMethod(
          methodName, paramTypes);
      returnValue = method.invoke(
        this, paramValues);

      // Exceptions are thrown in case of
      // inappropriate input, method
      // non-existence and illegal access
      // There can be also method specific
      // exceptions
    } catch (Exception e) {
      returnValue = e;
    }

    // Send the return value of the method
    ObjectOutputStream out = 
      new ObjectOutputStream(
        response.getOutputStream());
    out.writeObject(returnValue);
    out.close();
  }
}