startserver.java

db4o db4o是一个嵌入式的开源对象数据库引擎.对于Java与.NET开发者来说都是一个非常好的对象持久化工具. db4o性能高并且安装简单.

package com.db4o.f1.chapter5;

import com.db4o.*;
import com.db4o.messaging.*;

/**
 * starts a db4o server with the settings from {@link ServerConfiguration}. 
 * <br><br>This is a typical setup for a long running server.
 * <br><br>The Server may be stopped from a remote location by running
 * StopServer. The StartServer instance is used as a MessageRecipient and
 * reacts to receiving an instance of a StopServer object.
 * <br><br>Note that all user classes need to be present on the server
 * side and that all possible Db4o.configure() calls to alter the db4o
 * configuration need to be executed on the client and on the server.
 */
public class StartServer
    implements ServerConfiguration, MessageRecipient {
  
  /**
   * setting the value to true denotes that the server should be closed
   */
  private boolean stop = false;
  
  /**
   * starts a db4o server using the configuration from
   * {@link ServerConfiguration}.
   */
  public static void main(String[] arguments) {
    new StartServer().runServer();
  } 
  
  /**
   * opens the ObjectServer, and waits forever until close() is called
   * or a StopServer message is being received.
   */
  public void runServer(){
    synchronized(this){
      ObjectServer db4oServer = Db4o.openServer(FILE, PORT);
      db4oServer.grantAccess(USER, PASS);
      
      // Using the messaging functionality to redirect all
      // messages to this.processMessage
      db4oServer.ext().configure().setMessageRecipient(this);
      
      // to identify the thread in a debugger
      Thread.currentThread().setName(this.getClass().getName());
      
      // We only need low priority since the db4o server has
      // it's own thread.
      Thread.currentThread().setPriority(Thread.MIN_PRIORITY);
      try {
          if(! stop){
            // wait forever for notify() from close()
            this.wait(Long.MAX_VALUE);   
          }
      } catch (Exception e) {
        e.printStackTrace();
      }
      db4oServer.close();
    }
  }
  
  /**
   * messaging callback
   * @see com.db4o.messaging.MessageRecipient#processMessage(ObjectContainer, Object)
   */
  public void processMessage(ObjectContainer con, Object message) {
    if(message instanceof StopServer){
      close();
    }
  }
  
  /**
   * closes this server.
   */
  public void close(){
    synchronized(this){
      stop = true;
      this.notify();
    }
  }
}