Struts– 和例

比眉伴天荒 2023-02-15 07:49 16阅读 0赞

> 下载此示例– [Struts-Logic-Empty-NotEmpty-Example.zip][]

仅当指定的属性为null，长度为零的String或不存在时，才执行Struts <logic：empty>。 当Struts <logic：notEmpty>做相反的事情时。 如果条件匹配，则将执行标签的主体。

这是显示Struts <logic：empty>和<logic：notEmpty>用法的示例，并使用以下三个列表进行测试。

1.  listMsg0 –列表包含值。
2.  listMsg1 –空列表。
3.  listMsg2 –不存在的列表

**LogicExampleAction.java**

package com.mkyong.common.action;
     
    import java.util.ArrayList;
    import java.util.List;
    
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
     
    import org.apache.struts.action.Action;
    import org.apache.struts.action.ActionForm;
    import org.apache.struts.action.ActionForward;
    import org.apache.struts.action.ActionMapping;
     
    public class LogicExampleAction extends Action{
     
    	public ActionForward execute(ActionMapping mapping,ActionForm form,
    		HttpServletRequest request,HttpServletResponse response) 
            throws Exception {
     
    		//listMsg0 - A list contains values
    		List<String> listMsg0 = new ArrayList<String>();
    		
    		listMsg0.add("Message A");
    		listMsg0.add("Message B");
    		listMsg0.add("Message C");
    		listMsg0.add("Message D");
    		
    		request.setAttribute("listMsg0", listMsg0);
    		
    		//listMsg1 - An empty list
    		List<String> listMsg1 = new ArrayList<String>();
    		request.setAttribute("listMsg1", listMsg1);
    		
                    //listMsg2 - A list which is doesn't exists
    
    		return mapping.findForward("success");
    	}
     
    }

**LogicExample.jsp**

Struts - Test <logic:empty>
    
    
       
    	
        
        
    
        listMag0 is empty
    
       
    
    
       
    	
        
    
        listMag1 is empty
    
       
    
    
       
    	
        listMag2 is empty
    
       
    
    
       Struts - Test <logic:notEmpty>
    
    
       
    	
        listMag0 is not empty
    	
        
    		
         List Messages 0 - 
    	
        
    
    
       
    
    
       
    	
        listMag1 is not empty
    	
        
    		
         List Messages 1 - 
    	
        
    
       
    
    
       
    	
        listMag2 is not empty
    	
        
    		
         List Messages 2 -

**struts-config.xml**

<?xml version="1.0" encoding="UTF-8"?>
    <!DOCTYPE struts-config PUBLIC 
    "-//Apache Software Foundation//DTD Struts Configuration 1.3//EN" 
    "http://jakarta.apache.org/struts/dtds/struts-config_1_3.dtd">
     
    <struts-config>
      <action-mappings>
    
    	 <action
    		path="/LogicTest"
    		type="com.mkyong.common.action.LogicExampleAction">
     
    		<forward name="success" path="/pages/LogicExample.jsp"/>
     
    	</action>
    				
      </action-mappings>
    </struts-config>

## 结果 ##

*http：// localhost：8080 / StrutsExample / LogicTest.do*

![Struts-logic-empty-notempty-example][]![Struts-logic-empty-notempty-example][Struts-logic-empty-notempty-example 1]

**在Struts – Test <logic：empty>中** ，仅显示listMsg1和listMsg2，这是因为listMag1是一个空列表，而listMag2根本不存在。

**在Struts – Test <logic：** notEmpty **>中** ，仅显示listMsg0，因为这是唯一包含值的列表。

标签： [Struts][]

> 翻译自: [https://mkyong.com/struts/struts-logic-empty-logic-notempty-example/][https_mkyong.com_struts_struts-logic-empty-logic-notempty-example]

[Struts-Logic-Empty-NotEmpty-Example.zip]: http://www.mkyong.com/wp-content/uploads/2010/04/Struts-Logic-Empty-NotEmpty-Example.zip
[Struts-logic-empty-notempty-example]: http://imgconvert.csdnimg.cn/aHR0cDovL3d3dy5ta3lvbmcuY29tL3dwLWNvbnRlbnQvdXBsb2Fkcy8yMDEwLzA0L1N0cnV0cy1sb2dpYy1lbXB0eS1ub3RlbXB0eS1leGFtcGxlLmpwZw?x-oss-process=image/format,png
[Struts-logic-empty-notempty-example 1]: http://imgconvert.csdnimg.cn/aHR0cHM6Ly93d3cubWt5b25nLmNvbS93cC1jb250ZW50L3VwbG9hZHMvMjAxMC8wNC9TdHJ1dHMtbG9naWMtZW1wdHktbm90ZW1wdHktZXhhbXBsZS5qcGc?x-oss-process=image/format,png
[Struts]: https://mkyong.com/tag/struts/
[https_mkyong.com_struts_struts-logic-empty-logic-notempty-example]: https://mkyong.com/struts/struts-logic-empty-logic-notempty-example/