In this short example, a parser state machine processes raw XML from a ByteBuffer. Each state has its own process method and if there is not enough data available, the state machine can return to retrieve more data. Each transition between states is well defined and the code for all states is together in one enum.
interface Context {
ByteBuffer buffer();
State state();
void state(State state);
}
interface State {
/**
* @return true to keep processing, false to read more data.
*/
boolean process(Context context);
}
enum States implements State {
XML {
public boolean process(Context context) {
if (context.buffer().remaining() < 16) return false;
// read header
if(headerComplete)
context.state(States.ROOT);
return true;
}
}, ROOT {
public boolean process(Context context) {
if (context.buffer().remaining() < 8) return false;
// read root tag
if(rootComplete)
context.state(States.IN_ROOT);
return true;
}
}
}
public void process(Context context) {
socket.read(context.buffer());
while(context.state().process(context));
}
Related Article:
Reference: Java Secret: Using an enum to build a State machine from our JCG partner Peter Lawrey at the Vanilla Java
