在GSP中導入和使用Groovy代碼

Question

我想在GSP中使用groovy函數。請大家幫忙，因爲我正要把我的頭髮放在這裏。

在我GSP的頂部，我有<%@ page import = company.ConstantsFile %>

裏面我GSP我有

<p> 
I have been in the heating and cooling business for <%(ConstantsFile.daysBetween())%> 
</p> 

和我ConstantsFile.groovy

package company 

import static java.util.Calendar.* 

class ConstantsFile { 

    def daysBetween() { 
     def startDate = Calendar.instance 
     def m = [:] 
     m[YEAR] = 2004 
     m[MONTH] = "JUNE" 
     m[DATE] = 26 
     startDate.set(m) 
     def today = Calendar.instance 

     render today - startDate 
    } 
} 

我也試圖改變租車人要放， system.out等，但這不是我的主要問題。

Error 500: Internal Server Error 
URI 
/company/ 
Class 
java.lang.NullPointerException 
Message 
Cannot invoke method daysBetween() on null object 

所以我嘗試

<p> 
    I have been in the heating and cooling business for <%(new ConstantsFile.daysBetween())%> 
    </p> 

但後來我得到

Class: org.codehaus.groovy.control.MultipleCompilationErrorsException 

unable to resolve class ConstantsFile.daysBetween @ line 37, column 1. (new ConstantsFile.daysBetween())^1 error 

請人幫助我，或指向我一個網站，顯示做什麼..我試着用搜索引擎和一切都會談到ag：select或者其他類型的標籤......我只是想像我以前在JSP中那樣輸出函數的結果。

Answer 1

首先，你的普惠制的進口應該是：

<%@ page import="company.ConstantsFile" %> 

其次，你的daysBetween應該是靜態的（它更有意義），你不會從任何渲染，但控制器：

class ConstantsFile { 

    static daysBetween() { 
     def startDate = Calendar.instance 
     def m = [:] 
     m[YEAR] = 2004 
     m[MONTH] = "JUNE" 
     m[DATE] = 26 
     startDate.set(m) 
     def today = Calendar.instance 

     return today - startDate 
    } 
} 

三，獲得它以下列方式：

<p>I have been in the heating and cooling business for ${ConstantsFile.daysBetween}</p> 

最後，你應該使用標籤庫本。我編輯我的職務，以添加例如

class MyTagLib { 

    static namespace = "my" 

    def daysBetween = { attr -> 
    out << ConstantsFile.daysBetween() 
    } 
} 

然後在你的GSP使用

<p>I have been in the heating and cooling business for <my:daysBetween /></p>