如何在FreeMarker（FTL）中从自己的类创建实例

Question

I wish to instantiate a java class that I have defined in my domain and I want to use it from my FTL code in this way, but I'm getting an error.

<#assign myClassInstance = "com.domain.MyClass"?new())>

Is it possible? What I should change to do it?

MyClass doesn't implements the TemplateModel

Thanks!

Answer 1

There's no built-in function for instantiating arbitrary non- TemplateModel classes... maybe there should be a setting to allow that for ?new . Anyway, for now you can write a TemplateMethodModelEx that does that, and then you can pull that into some of your commonly included/imported templates like <#assign unrestrictedNew = "com.example.UnrestrictedNewMethodModel"?new()> (or just put the instance into the data-model or into the Configuration as a shared variable) and then you can do <#assign myClassInstance = unrestrictedNew("com.domain.MyClass")(arg1, arg2, argN)> in your templates. There are two tricky parts in implementing such a TemplateMethodModel . One is resolving the class name to a Class , for which I recommend env.getNewBuiltinClassResolver().resolve(className, env, null) , where env is the current freemarker.core.Environment object. The other is calling the constructor, as then you have to convert parameter values and possibly chose an overloaded constructor. For that I recommend calling ow = env.getObjectWrapper() , see if ow instanceof BeansWrapper (throw exception if it isn't), then do return ((BeansWrapper) ow).newInstance(cl, arguments) .