versiontracker.java

ajax patterns 这是关于ajax设计模式方面的原代码

/*
    Copyright 2006 Christian Gross http://www.devspace.com
    From the book Ajax Patterns and Best Practices

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.
*/
package devspace.ajax.persistentcommunications;
import javax.servlet.http.*;
import devspace.testDrivenDevelopment.tracer.*;

public class VersionTracker {
    private int _versionNumber;
    private int _defaultTimeout;
    
    private final String constXStateHeader = "X-Last-State";
    
    public VersionTracker(int defaultTimeout) {
        _defaultTimeout = defaultTimeout;
        _versionNumber = 0;
    }
    public synchronized boolean getNew(long version) {
        boolean retval = false;
        if (_versionNumber > version) {
            retval = true;
        }
        else {
            try {
                wait(_defaultTimeout);
            }
            catch (InterruptedException e) {}
            if (_versionNumber > version) {
                retval = true;
            }
        }
        return retval;
    }
    public synchronized boolean getNew( HttpServletRequest request) {
        String lastState = request.getHeader(constXStateHeader);
        if (lastState == null) {
            lastState = request.getParameter(constXStateHeader);
        }
        GenerateOutput.Write("VersionTracker.getNew", "lastState (" + lastState + ")");
        int lastCount = 0;
        if (lastState != null) {
            lastCount = new Integer( lastState);
        }
        return getNew( lastCount);
    }
    public synchronized void writeVersion( HttpServletResponse response) {
        response.addHeader(constXStateHeader, new Integer( getVersionNumber()).toString());
    }
    public synchronized void increment() {
        _versionNumber ++;
        notify();
    }
    public synchronized int getVersionNumber() {
        return _versionNumber;
    }
}