用RMI实现基于Java的分布式计算

以下接口定义展示了java.rmi.Remote接口最典型的用法：

import java.rmi.Remote;
import java.rmi.RemoteException;
public interface TimeKeeper extends Remote
{
  public String currentDate() throws RemoteException;
  public String currentTime() throws RemoteException;
}

由于String类声明为实现了java.io.Serializable接口，所以String是远程方法的有效返回类型。

以下代码展示了如何实现TimeKeeper接口，以便定义一个有效的远程对象：

import java.rmi.RemoteException;
import java.util.Calendar;
import java.util.GregorianCalendar;
public class TimeKeeperImpl implements TimeKeeper
{
  public TimeKeeperImpl()
  throws RemoteException
  {
  }
  public String currentDate() throws RemoteException
  {
  Calendar cal = new GregorianCalendar();
  String retVal = (cal.get(Calendar.MONTH) + "/" +
      cal.get(Calendar.DAY_OF_MONTH) + "/" +
      cal.get(Calendar.YEAR));
  return retVal;
  }
  public String currentTime() throws RemoteException
  {
  Calendar cal = new GregorianCalendar();
  String retVal = (cal.get(Calendar.HOUR_OF_DAY) + ":" +
      cal.get(Calendar.MINUTE) + ":" +
      cal.get(Calendar.SECOND));
  return retVal;
  }
}