使用一个PhaseListener来熟悉JSF 生命周期

JSF新手可能常常听到  "JSF Request Processing Lifecycle" ,但是不一定知道在生命周期中都发生了什么事情.

这里有一点代码, 一个  PhaseListener, 我们可以用她来了解  JSF's Request Processing Lifecycle如何工作的.

下面是一个在生命周期开始和结束时执行的一个简单的PhaseListener

package com.jsf;
import javax.faces.event.PhaseListener;
import javax.faces.event.PhaseEvent;
import javax.faces.event.PhaseId;

public class MyPhaseListener  implements PhaseListener
{

  public MyPhaseListener()
  {
  }

  public void beforePhase(PhaseEvent pe)
  {
   if (pe.getPhaseId() == PhaseId.RESTORE_VIEW)
      System.out.println("Processing new  Request!");
        
   System.out.println("before - " + pe.getPhaseId().toString());
  }

  public void afterPhase(PhaseEvent pe)
  { 
  System.out.println("after - " + pe.getPhaseId().toString());
  
  if (pe.getPhaseId() == PhaseId.RENDER_RESPONSE)
     System.out.println("Done with Request!\n");
  }

  public PhaseId getPhaseId()
  {  
    return PhaseId.ANY_PHASE;
  }
}

当每一个阶段开始和结束的时候,她 在控制台上打印出一些东西. 你需要在 faces-config.xml中来注册该listener

<lifecycle>
<phase-listener>com.jsf.MyPhaseListener />
</lifecycle>

一旦你注册了  PhaseListener, 你就可以开始写个小程序来测试了. 我们使用一个简单的程序,一个输入表单和按钮:

<h:commandButton value="button" action="#{backingbean.button_action}"/>


按钮绑定了一个manage bean的动作方法.:

public String button_action()
  {
    System.out.println("Action event processed...");
    return "success";
  }

运行该页面可以看到下面的输出,.:

05/08/31 20:32:46 Processing new  Request!
05/08/31 20:32:46 before - RESTORE_VIEW 1
05/08/31 20:32:46 after - RESTORE_VIEW 1
05/08/31 20:32:46 before - RENDER_RESPONSE 6
05/08/31 20:32:46 after - RENDER_RESPONSE 6
05/08/31 20:32:46 Done with Request!

05/08/31 20:32:57 Processing new  Request!
05/08/31 20:32:57 before - RESTORE_VIEW 1
05/08/31 20:32:57 after - RESTORE_VIEW 1
05/08/31 20:32:57 before - APPLY_REQUEST_VALUES 2
05/08/31 20:32:57 after - APPLY_REQUEST_VALUES 2
05/08/31 20:32:57 before - PROCESS_VALIDATIONS 3
05/08/31 20:32:57 after - PROCESS_VALIDATIONS 3
05/08/31 20:32:57 before - UPDATE_MODEL_VALUES 4
05/08/31 20:32:57 after - UPDATE_MODEL_VALUES 4
05/08/31 20:32:57 before - INVOKE_APPLICATION 5
05/08/31 20:32:57 Action event processed...
05/08/31 20:32:57 after - INVOKE_APPLICATION 5
05/08/31 20:32:57 before - RENDER_RESPONSE 6
05/08/31 20:32:57 after - RENDER_RESPONSE 6
05/08/31 20:32:57 Done with Request!

注意在第一个请求 (non-postback) ,只有两个阶段, RESTORE_VIEW and RENDER_RESPONSE..这说明她只是创建  UI component tree然后显示她 . 下一步,你点击按钮,注意打印的消息. 这次她通过了整个jsf生命周期. 注意,按钮点击的动作事件在 INVOKE_APPLICATION phase处理...

现在,作为一个实验,把   commandButton 的 immediate  属性改变为 true ,看看如何影响动作事件的处理的.

下一步你可能想添加一个输入表单,并且添加一个  ValueChangeListener 来显示一个值变化事件.

A new input field...

<h:inputText value="foo">
<f:valueChangeListener type="com.jsf.MyValueChangeListener"/>
</h:inputText>
下面是ValueChangeListener代码..

package com.jsf;
import javax.faces.event.ValueChangeListener;
import javax.faces.event.ValueChangeEvent;
import javax.faces.event.AbortProcessingException;

public class MyValueChangeListener implements ValueChangeListener
{

  public MyValueChangeListener()
  {
  }

  public void processValueChange(ValueChangeEvent vce) throws AbortProcessingException
  {
     System.out.println("A value has changed!");
  }
}

这里你不需要在faces配置文件中注册 ValueChangeListener,你可以直接运行程序,看看有什么信息打印出来.

05/08/31 20:41:33 Processing new  Request!
05/08/31 20:41:33 before - RESTORE_VIEW 1
05/08/31 20:41:33 after - RESTORE_VIEW 1
05/08/31 20:41:33 before - RENDER_RESPONSE 6
05/08/31 20:41:33 after - RENDER_RESPONSE 6
05/08/31 20:41:33 Done with Request!
输入一个值在输入表单中, 看看有什么发生.

5/08/31 20:42:42 Processing new  Request!
05/08/31 20:42:42 before - RESTORE_VIEW 1
05/08/31 20:42:42 after - RESTORE_VIEW 1
05/08/31 20:42:42 before - APPLY_REQUEST_VALUES 2
05/08/31 20:42:42 after - APPLY_REQUEST_VALUES 2
05/08/31 20:42:42 before - PROCESS_VALIDATIONS 3
05/08/31 20:42:42 A value has changed!
05/08/31 20:42:42 after - PROCESS_VALIDATIONS 3
05/08/31 20:42:42 before - UPDATE_MODEL_VALUES 4
05/08/31 20:42:42 after - UPDATE_MODEL_VALUES 4
05/08/31 20:42:42 before - INVOKE_APPLICATION 5
05/08/31 20:42:42 Action event processed!
05/08/31 20:42:42 after - INVOKE_APPLICATION 5
05/08/31 20:42:42 before - RENDER_RESPONSE 6
05/08/31 20:42:42 after - RENDER_RESPONSE 6
05/08/31 20:42:42 Done with Request!