dow.ngra.de

Today’s software is so much about integration. You can have a cool Java utility but if you don’t have an Eclipse plugin for that, a large % of Eclipse users won’t adopt (IDEA & NetBeans users require plugins just as much). In the consumer market the same goes for browser extensions and iPhone apps that support the main service with better accessibility.

There are different ways for integration. Usually it is done via an API. The host platform offers some hooks into the system and you can use them to add some custom functionality on top of the host (or maybe just integrate your own product with the host). The result of this in the IDE world is a plugin. JRebel (the product our team is spending the most development time on) has plugins for application servers, frameworks and even IDEs.

If you’re in luck you can achieve everything with the API, if not you need other tricks. If the API does not offer certain public methods or access to some internal fields you can go in with reflection and still use them (of course there are no guarantees if the internals stay the same on version changes).

One step further to the darkside is binary patching. By binary patching I mean adding/changing/removing methods/fields/classes in runtime. This is the approach that we had to take when writing the JRebel NetBeans plugin.

On NetBeans startup we lookup a debugger class and on success try to patch it. In 2009 and using the JVM (not native apps) it is quite an easy task, at least for the most part. No assembler involved (of course you could be using a bytecode generation library), no need to do jumps to correct offsets or even read assembler (or bytecode).

In our case we use the Javassist library. It is a matter of inserting Java code embedded into a String to methods looked up via reflection. For example the following code adds some new code into the beginning of a method.

ctc.getDeclaredMethod("setRequests").insertAfter(
  "org.netbeans.api.debugger.jpda.LineBreakpoint _breakpoint = getBreakpoint();" +
  "java.lang.String _className = _breakpoint.getPreferredClassName();" +
  "if (_className == null) {" +
  "  _className = reader.findCachedClassName(_breakpoint);" +
  "  if (_className == null) {" +
  "    _className = org.netbeans.modules.debugger.jpda.EditorContextBridge.getContext().getClassName (" +
  "      _breakpoint.getURL ()," +
  "      lineNumber);" +
  "    if (_className != null && _className.length() > 0) {" +
  "      reader.storeCachedClassName(_breakpoint, _className);" +
  "    }" +
  "  }" +
  "}"

For the complete source code of the patch see the src folder of the nb-plugin.

In conclusion, the best way to integrate with any system is via the API it provides. If it does not cut it then look into reflection and start using internals. You will lose on maintainability of course. Still not happy? Look into binary patching and have your fingers crossed whenever the target platform releases a new version.