visitor.java

Java Pattern Oriented Framework (Jt) 是为了实现Java快速开发的面向模式的框架。

package Jt.examples.patterns;
import java.beans.*;
import java.lang.reflect.Method;
import Jt.*;
import Jt.examples.HelloWorld;


/**
 * Demonstrates the use of the Visitor pattern.
 */


public class Visitor extends JtObject {

    public static final String JtCLASS_NAME = Visitor.class.getName();   
    private static final long serialVersionUID = 1L;

    public Visitor() {
    }



    // Print the object attributes. This is the new functionality.

    private void printObject (Object obj) {

        PropertyDescriptor[] prop;
        int i;
        Method m;
        BeanInfo info = null;
        Object value;

        if (obj == null)
            return;

        try {

            info = Introspector.getBeanInfo(
                    obj.getClass (), obj.getClass ().getSuperclass());
        } catch(Exception e) {
            handleException (e);
            return;
        }

        prop = info.getPropertyDescriptors();
        for(i = 0; i < prop.length; i++) {


            try {
                m = prop[i].getReadMethod ();
                if (m == null) {
                    handleError 
                    ("getReadMethod returned null");
                    return;
                }

                value = m.invoke (obj, null);

                if (value != null)
                    System.out.print (obj.getClass ().getName () + "." +
                            prop[i].getName() + ":" + value);


            } catch (Exception e) {
                handleException(e);
                return;
            }
        }

    }



    /**
     * Process object messages. 
     * <ul>
     * <li>JtVISIT - visit the object specified by msgContent.
     * </ul>
     * @param event Jt Message    
     */

    public Object processMessage (Object event) {

        String msgid = null;
        JtMessage e = (JtMessage) event;
        Object content;


        if (e == null)
            return null;

        msgid = (String) e.getMsgId ();

        if (msgid == null)
            return null;

        content = e.getMsgContent();

        if (msgid.equals (JtObject.JtREMOVE)) {
            return (null);     
        }

        if (msgid.equals (JtObject.JtVISIT)) {

            printObject (content);
            return (null);
        }

        return (super.processMessage(event));

    }

    /**
     * Test program   
     */

    public static void main(String[] args) {

        JtObject main = new JtFactory ();
        JtMessage msg;
        Visitor visitor;
        JtInterface node;


        // Create an instance of JtVisitor

        visitor = (Visitor)
        main.createObject (Visitor.JtCLASS_NAME, "visitor");


        node = (JtInterface) main.createObject (HelloWorld.JtCLASS_NAME, "helloWorld");
        ((HelloWorld)node).setGreetingMessage("my hello message");

        System.out.println ("This visitor prints the object using a custom format ...\n");

        // Send an JtACCEPT message to the node. The message contains
        // a reference to the visitor

        msg = new JtMessage (JtObject.JtACCEPT);
        msg.setMsgContent (visitor);
        main.sendMessage (node, msg);


        // Remove objects

        main.removeObject (visitor);
        main.removeObject (node);



    }
}