如何在Grails中动态选择一项服务 [英] How to dynamically select a service in Grails

问题描述

在我的控制器中，我希望根据参数动态选择服务。

目前我有一个基本服务和一些其他服务来扩展这个基本服务。根据参数我调用一个类，该类创建一个基于param的bean名称，并最终调用以下内容：

  import org .codehaus.groovy.grails.web.context.ServletContextHolder as SCH 
 import org.codehaus.groovy.grails.web.servlet.GrailsApplicationAttributes as GA 
 
 class Resolver {
 def ctx 
 $ b $ getBean（String beanName）{
 if（！ctx）{
 ctx = SCH.servletContext.getAttribute（GA.APPLICATION_CONTEXT）
} 
返回ctx。$ {beanName}
} 
  

}

这会返回我想要的服务。不过，我觉得这样做很脏。有没有人有更好的方式来处理基于某些参数获取服务（或任何其他bean）？

谢谢。

解决方案

ctx。$ {beanName}被添加到 ApplicationContext metaclass，所以你可以做一些像 def userService = ctx.userService 的东西。它只是 ctx.getBean（'userService'）的一个快捷方式，因此您可以将代码更改为

  return ctx.getBean（beanName）
  

它会是一样的，但不那么神奇。

由于您是从控制器或服务调用它的，我会跳过 ServletContextHolder stuff并通过依赖注入 grailsApplication bean（ def grailsApplication ）并通过<$ c获取它$ c> def ctx = grailsApplication.mainContext 。然后将它传递给这个帮助类（记住Spring的大范例是依赖注入，而不是老派的依赖拉），然后它就会简单地变成：

  class Resolver {
 def getBean（ctx，String beanName）{
 ctx.getBean（beanName）
} 
} 
  
 
 $ b 
但是这很简单，我根本不用打扰辅助类：）
From my controller I would like to dynamically select a service based on a parameter.

Currently I have a base service and some other services that extent this base service.  Based on the parameter I call a class that does creates a bean name based on the param and eventually calls the following:
import org.codehaus.groovy.grails.web.context.ServletContextHolder as SCH
import org.codehaus.groovy.grails.web.servlet.GrailsApplicationAttributes as GA

class Resolver {
    def ctx

def getBean(String beanName) {
    if(!ctx) {
        ctx = SCH.servletContext.getAttribute(GA.APPLICATION_CONTEXT)
    }
    return ctx."${beanName}"
}
}

This returns the service I want.  However I feel rather dirty doing it this way.  Does anyone have a better way to handle getting a service (or any other bean) based on some parameter?

Thank you.
解决方案
ctx."${beanName}" is added to the ApplicationContext metaclass so you can do stuff like def userService = ctx.userService. It's just a shortcut for ctx.getBean('userService') so you could change your code to 
return ctx.getBean(beanName)
and it would be the same, but less magical.

Since you're calling this from a controller or a service, I'd skip the ServletContextHolder stuff and get the context by dependency-injecting the grailsApplication bean (def grailsApplication) and getting it via def ctx = grailsApplication.mainContext. Then pass it into this helper class (remember the big paradigm of Spring is dependency injection, not old-school dependency-pulling) and then it would be simply
class Resolver {
   def getBean(ctx, String beanName) {
      ctx.getBean(beanName)
   }
}
But then it's so simple that I wouldn't bother with the helper class at all :)

                        
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