grails - 在GSP中导入和使用Groovy代码

Question

我正在尝试在GSP中使用常规功能。请帮忙，因为我要在这里整理头发。

在我的GSP顶部，我有<%@ page import = company.ConstantsFile %>
在我的GSP中，我有

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

和我的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
    }
}

我也尝试过将承租人更改为puts，system.out等，但这不是我的主要问题。

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

所以我尝试

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

但后来我明白了

Class: org.codehaus.groovy.control.MultipleCompilationErrorsException

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

请有人帮助我或将我指向一个显示操作说明的网站。.我尝试了谷歌搜索，所有内容都在讨论ag:select或其他某种标记...我只想输出该函数的结果，就像我以前使用的那样到JSP中。

Answer 1

首先，您的GSP导入应为:

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

其次，您的daysBetween应该是静态的(更有意义)，并且除了 Controller 之外，您不会从其他任何对象进行渲染:

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
    }
}

第三，通过以下方式访问它:

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

最后，您应该为此使用taglib。我现在正在编辑我的帖子以添加示例

class MyTagLib {

  static namespace = "my"

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

然后在您的GSP中使用

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