FSM Implementation

fsm

// Model:


/*
 * Copyright (c) 2004 jPOS.org 
 *
 * See terms of license at http://jpos.org/license.html
 *
 */
package org.jpos.fsm;

import java.util.*;
import org.jdom.Element;

/**
 * @author Alejandro Revilla
 */
public class Model {
    HashMap states;
    State initialState = null;

    public Model (Element model) {
        super ();
        states = new HashMap ();
        initModel (model);
    }
    private void initModel (Element e) {
        Iterator iter = e.getChildren ("state").iterator ();
        while (iter.hasNext ()) {
            initState ((Element) iter.next ());
        }
    }
    public State getInitialState () {
        return initialState;
    }
    private void initState (Element e) {
        State s = new State (e.getAttributeValue ("name"));
        states.put (s.getName (), s);
        if (initialState == null)
            initialState = s;

        s.setSelector (e.getChildTextTrim ("selector"));
        Iterator iter = e.getChildren ("transition").iterator ();
        while (iter.hasNext ()) {
            initTransition (s, (Element) iter.next ());
        }
    }
    private void initTransition (State s, Element e) {
        s.addTransition (
            e.getAttributeValue ("name"),
            e.getAttributeValue ("next", "nil"),
            e.getAttributeValue ("action")
        );
    }
    public State getState (String name) {
        return (State) states.get (name);
    }
}

// State

/*
 * Copyright (c) 2004 jPOS.org 
 *
 * See terms of license at http://jpos.org/license.html
 *
 */

package org.jpos.fsm;

import java.util.Map;
import java.util.HashMap;

/**
 * @author Alejandro Revilla
 */
public class State {
    String name;
    String selector;
    Map state;
    Map action;
    
    public State (String name) {
        super ();
        this.name = name;
        this.state  = new HashMap ();
        this.action = new HashMap ();
    }
    public String getName () {
        return name;
    }
    public boolean equals (Object obj) {
        if (name == null)
            return false;
        return name.equals (obj);
    }
    public void addTransition (String t, String s, String a) {
        state.put (t, s);
        if (a != null)
            action.put (t, a);
    }
    public String getNext (String t) {
        if (t == null)
            return this.getName();
        return (String) state.get (t);
    }
    public String getAction (String t) {
        if (t == null)
            return null;
        return (String) action.get (t);
    }
    public void setSelector (String selector) {
        this.selector = selector;
    }
    public String getSelector () {
        return selector;
    }
}

// StateMachine

/*
 * Copyright (c) 2004 jPOS.org 
 *
 * See terms of license at http://jpos.org/license.html
 *
 */

package org.jpos.fsm;

import org.jpos.util.Log;

/**
 * @author Alejandro Revilla
 */
public class StateMachine {
    Model model;
    State current;
    Log log;

    public StateMachine (Model model) {
        super ();
        this.model = model;
        current = model.getInitialState ();
    }
    public State getCurrent () {
        return current;
    }
    public void setLog (Log log) {
        this.log = log;
    }
    public String event (String s) {
        StringBuffer sb = new StringBuffer ();
        String info = current.getName() + " --> " + s;
        String next   = current.getNext (s);
        String action = current.getAction (s);
        if (next == null || "nil".equals (next)) {
            next = "invalid-transition";
        }
        State state = model.getState (next);
        if (state == null) {
            throw new IllegalArgumentException (
                "Invalid transition: " +info + " " + next
            );
        }
        if (log != null) {
            sb.append (info);
            sb.append (" -> ");
            sb.append (next);
            if (action != null) {
                sb.append (" (");
                sb.append (action);
                sb.append (')');
            }
            log.info (sb.toString());
        }
        current = state;

        return action;
    }
}