How to integrate beanshell

Question

I am developing a component based game engine in java, right now when i have changes to the components I need to rebuild and restart the editor for the changes to take effect (or i can use some limited hot code injection if the application is running in debug mode).

I am looking for a way to allow the user to modify the source of the components and reload them without having to restart the application (maybe just exit and enter game mode instead). Also a important feature that I need is that the final exported code should be native Java code(so no interpreter should be used in the final result)).

Can you give me any pointers on how to integrate the beanshell interpreter in the project? I can manually monitor the source folder for changes and feed the updated java classes to it, but how is the hotswap going to occur really?

Answer 1

First of all, the title is a bit confusing. You don't need to integrate a BeanShell. What you actually need are:

1. to define a proper architecture
2. to use Java Compiler API in order to work with java classes

Architecture

Let's say you have an object graph. There are lots of objects, references, etc. So it will be really a tricky task to replace some instance with the new one. Instead of solving this problem you can hide dynamic part behind a "static" proxy. Proxy will handle all reloading stuff (including source folder monitoring).

Before reload:

After reload:

Having that done you can easily track changes and update dynamic part when needed.

Java Compiler API

Instead of using interpreted languages you can use Java, compiling it on the fly and loading using 'Class.forName()'. There are a lot of different examples due to the fact this approach was there for a while.

Here are some details:

• Add dynamic Java code to your application
• Compiling fully in memory with javax.tools.JavaCompiler