ACTIVITI 研究代碼 之 模版模式

模板方法模式需要開發抽象類和具體子類的設計師之間的協作。一個設計師負責給出一個算法的輪廓和骨架，另一些設計師則負責給出這個算法的各個邏輯步驟。代表這些具體邏輯步驟的方法稱做基本方法(primitive method)；而將這些基本方法匯總起來的方法叫做模板方法(template method)，這個設計模式的名字就是從此而來。

在activit中很多地方用到了此模式，用這個模式可以重用業務邏輯。

實例代碼如下：

比如在ACTIVITI 的設置流程變量代碼就采用了此模式。

1.抽象模板類。

public abstract class NeedsActiveExecutionCmd<T> implements Command<T>, Serializable {
  
  private static final long serialVersionUID = 1L;
  
  protected String executionId;
  
  public NeedsActiveExecutionCmd(String executionId) {
    this.executionId = executionId;
  }
  
  public T execute(CommandContext commandContext) {
    if(executionId == null) {
      throw new ActivitiIllegalArgumentException("executionId is null");
    }
    
    ExecutionEntity execution = commandContext
      .getExecutionEntityManager()
      .findExecutionById(executionId);
    
    if (execution==null) {
      throw new ActivitiObjectNotFoundException("execution "+executionId+" doesn't exist", Execution.class);
    }
    
    if (execution.isSuspended()) {
      throw new ActivitiException(getSuspendedExceptionMessage());
    }
    
    return execute(commandContext, execution);
  }
  
  /**
   * Subclasses should implement this method. 
   * The provided {@link ExecutionEntity} is guaranteed to be active (ie. not suspended).
   */
  protected abstract T execute(CommandContext commandContext, ExecutionEntity execution);

這個代碼可以被其他的子類繼承，這個類實現了根據executionId獲取ExecutionEntity 實例邏輯，其他的子類可以繼承這個類，實現 T execute(CommandContext commandContext, ExecutionEntity execution)方法。重用這此邏輯。

 

子類代碼如下：

public class SetExecutionVariablesCmd extends NeedsActiveExecutionCmd<Object> {

  private static final long serialVersionUID = 1L;
  
  protected Map<String, ? extends Object> variables;
  protected boolean isLocal;
  
  public SetExecutionVariablesCmd(String executionId, Map<String, ? extends Object> variables, boolean isLocal) {
    super(executionId);
    this.variables = variables;
    this.isLocal = isLocal;
  }
  
  protected Object execute(CommandContext commandContext, ExecutionEntity execution) {
    if (isLocal) {
      execution.setVariablesLocal(variables);
    } else {
      execution.setVariables(variables);
    }
    
    // ACT-1887: Force an update of the execution's revision to prevent simultaneous inserts of the same
    // variable. If not, duplicate variables may occur since optimistic locking doesn't work on inserts
    execution.forceUpdate();
    return null;
  }
  
  @Override
  protected String getSuspendedExceptionMessage() {
    return "Cannot set variables because execution '" + executionId + "' is suspended";
  }
  
}

protected Object execute(CommandContext commandContext, ExecutionEntity execution) 這個代碼就是子類實現的邏輯。