JBPM与软件架构模式之命令模式

JBPM与软件架构模式之命令模式

       前面我们介绍了JBPM的长事务设计，其中用到了职责链模式和命令模式，其中职责链模式我们已经介绍过了，今天我们来看看JBPM是怎样使用命令模式的。
       命令模式定义
             将请求封装成一个对象，使你可以使用不同的请求对客户端进行参数化；对请求排队和记录请求队列，并支持对请求的撤销操作。
       命令模式UML类图
      
     命令模式代码示例

    

package org.jbpm.pvm.internal.svc;

public abstract class Command {

    protected Reciever reviever;
    
    public Command(Reciever reviever)
    {
        this.reviever=reviever;
    }
    
    public abstract void Execution();
}

 

package org.jbpm.pvm.internal.svc;

public class ConcreteCommand  extends Command{

    public ConcreteCommand(Reciever reviever) {
        super(reviever);
        // TODO Auto-generated constructor stub
    }

    @Override
    public void Execution() {
        // TODO Auto-generated method stub
        reviever.Action();
    }
    
}

package org.jbpm.pvm.internal.svc;

public class Invoker {
    private Command command;
    
    public void SetCommand(Command command)
    {
        this.command=command;
    }
    public void ExecutionCommand()
    {
        this.command.Execution();
    }
}

package org.jbpm.pvm.internal.svc;

public class Reciever {
    public void Action(){}
}

package org.jbpm.pvm.internal.svc;

public class Client {

    /**
     * @param args
     */
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Reciever r=new Reciever();
        Command c=new ConcreteCommand(r);
        Invoker i=new Invoker();
        i.SetCommand(c);
        i.ExecutionCommand();
        
    }

}

 

      命令模式的优点
            可以比较容易的设置一个命令队列
            在需要的情况下可以很容易的将命令记录下来
            允许接受请求的一方决定是否否决命令
            很容易实现对请求的撤销和重做

      JBPM的命令模式实现
     

   

package org.jbpm.api;

import org.jbpm.api.history.HistoryComment;
import org.jbpm.api.history.HistoryActivityInstance;
import org.jbpm.api.task.Participation;
import org.jbpm.api.task.Task;

import java.util.List;
import java.util.Map;
import java.util.Set;

public interface TaskService {
   Task getTask(String taskId);
}

package org.jbpm.pvm.internal.svc;

import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;

import org.jbpm.api.TaskQuery;
import org.jbpm.api.TaskService;
import org.jbpm.api.history.HistoryComment;
import org.jbpm.api.task.Participation;
import org.jbpm.api.task.Task;
import org.jbpm.pvm.internal.cmd.AddParticipationCmd;
import org.jbpm.pvm.internal.cmd.AddReplyCommentCmd;
import org.jbpm.pvm.internal.cmd.AddTaskCommentCmd;
import org.jbpm.pvm.internal.cmd.AssignTaskCmd;
import org.jbpm.pvm.internal.cmd.CompositeCmd;
import org.jbpm.pvm.internal.cmd.DeleteTaskCmd;
import org.jbpm.pvm.internal.cmd.CompleteTaskCmd;
import org.jbpm.pvm.internal.cmd.CreateTaskQueryCmd;
import org.jbpm.pvm.internal.cmd.DeleteCommentCmd;
import org.jbpm.pvm.internal.cmd.GetOutcomes;
import org.jbpm.pvm.internal.cmd.GetParticipantsCmd;
import org.jbpm.pvm.internal.cmd.GetSubTasksCmd;
import org.jbpm.pvm.internal.cmd.GetTaskCmd;
import org.jbpm.pvm.internal.cmd.GetTaskCommentsCmd;
import org.jbpm.pvm.internal.cmd.GetTaskVariableNamesCmd;
import org.jbpm.pvm.internal.cmd.GetTaskVariablesCmd;
import org.jbpm.pvm.internal.cmd.NewTaskCmd;
import org.jbpm.pvm.internal.cmd.RemoveParticipantCmd;
import org.jbpm.pvm.internal.cmd.SaveTaskCmd;
import org.jbpm.pvm.internal.cmd.SetTaskVariablesCmd;
import org.jbpm.pvm.internal.query.TaskQueryImpl;
import org.jbpm.pvm.internal.task.TaskImpl;


public class TaskServiceImpl extends AbstractServiceImpl implements TaskService {

 

  public Task getTask(String taskId) {
    return commandService.execute(new GetTaskCmd(taskId));
  }
}

public interface CommandService {
  
  String NAME_TX_REQUIRED_COMMAND_SERVICE = "txRequiredCommandService";
  String NAME_NEW_TX_REQUIRED_COMMAND_SERVICE = "newTxRequiredCommandService";

  /**
   * @throws JbpmException if command throws an exception.
   */
  <T> T execute(Command<T> command);
}

package org.jbpm.pvm.internal.svc;

import org.jbpm.pvm.internal.cmd.CommandService;



public class AbstractServiceImpl {
  
  protected CommandService commandService;

  public CommandService getCommandService() {
    return commandService;
  }

  public void setCommandService(CommandService commandService) {
    this.commandService = commandService;
  }
}

public interface Command<T> extends Serializable {
  
  T execute(Environment environment) throws Exception;
}

public class GetTaskCmd extends Command<Task> {

  private static final long serialVersionUID = 1L;
  
  protected String taskId;
  
  public GetTaskCmd(String taskId) {
    if (taskId==null) {
      throw new JbpmException("taskId is null");
    }
    this.taskId = taskId;
  }

  public Task execute(Environment environment) throws Exception {
    DbSession dbSession = environment.get(DbSession.class);
    return dbSession.get(TaskImpl.class, Long.parseLong(taskId));
  }
}

    JBPM使用命令模式的设计的优点请参见 JBPM长事务设计