Support i18n and nested template loading in ScriptTemplateView render function [SPR-15064]

[spring-projects-issues]

Sébastien Deleuze opened SPR-15064 and commented

The render function called by ScriptTemplateView has currently 3 parameters provided:

• String template: the content of the template resource
• Map<String, Object>: the model to use to render the view
• String url: the url of the 2 view

To achieve i18n support for messages and nested template loading, we need to provide these additional informations:

• a ResourceBundleMessageSource instance (or the ApplicationContext that allows to retrieve it)
• the view Locale
• a Function<String, String> that allows the render function to call ScriptTemplateView#getTemplate(String)

I see mainly 2 ways to support that:

1. We could be possible leverage setExposeContextBeansAsAttributes() or setExposedContextBeanNames() to access to context beans and expose them via model attributes.

2. We could transform the 3rd parameter passed to the script function (currently String url) to RenderingContext that would contains String url, Locale locale, ResourceBundleMessageSource messageSource and Function<String, String> templateLoader properties. This would be a breaking change for people using url but ScriptTemplateView is a rather feature, and url is not widely used, so I consider this as an option in order to be consistent and provide such flexible mechanism for further needs + it provides these properties in a type-safe way which would be valuable for Kotlin JSR-223 support.

---

Issue Links:

• Add Kotlin ScriptTemplateView tests [SPR-15059] #19625 Add Kotlin ScriptTemplateView tests ("depends on")
• Expose view url to render function in ScriptTemplateView [SPR-13453] #18033 Expose view url to render function in ScriptTemplateView
• Update and improve script templating documentation [SPR-16447] #20992 Update and improve script templating documentation

Referenced from: commits 7ff257c, 98642c7, 2d95199, 2a5d1b0

[spring-projects-issues]

Yevhenii Melnyk commented

Not sure if the following stuff is appropriate here but I didn't want to open a new issue without discussion. So, the situation is following:

I was trying to use two different template view resolvers in my Spring mvc app. For example, kotlin and javascript at the same time. Creation of 2 ViewResolver beans is not the problem. It seems impossible to use two ScriptTemplateConfigurer because ScriptTemplateConfig is being acquired in ScriptTemplateView.autodetectViewConfig by ScriptTemplateConfig.class from Spring context.

Is there a way to use two scripting engines at the same time or this feature is not supported currently?

[spring-projects-issues]

Sébastien Deleuze commented

Indeed this is currently not supported out of the box, but maybe you could make it works for your use case by extending ScriptTemplateConfig* classes for Kotlin or Javascript with specify dedicated View and ViewConfigurer classes.

[spring-projects-issues]

Yevhenii Melnyk commented

I'll leave the stackoverflow post regarding multiple configurers here in case somebody has a same question I've got. The implementation is really easy. Thank you Sébastien Deleuze.

[spring-projects-issues]

Sébastien Deleuze commented

See also this related pull request for providing i18n support, I will try to provide a solution that fulfill that need too.

[spring-projects-issues]

Sébastien Deleuze commented

Juergen Hoeller Could you please have a look to this pull request I have just submitted to say me if you are ok with such approach.

This change would be breaking (on the script side, not on java side) for people using the third url parameter that we introduced as part of #18033 in 4.2.2, but ScriptTemplateView is a rather young functionality, and this variant with an url parameter is likely to not being used very widely, so I would take the opportunity of our major 5.0 release to define a consistent and future proof render function SPI.

As you can see here the migration path is trivial.

I preferred this option over using setExposeContextBeansAsAttributes() or setExposedContextBeanNames() because:

• It allows to be consistent about the various parameters we pass to the rendering function (url versus others)
• It is type-safe which matters for Kotlin Script and more discoverable than something based on model attributes
• It avoids to mix model attributes designed to be rendered in the template, and those informations designed to be used in the rendering function
• It will allow us to add new rendering properties without breaking the script API

I also choose to provide the ApplicationContext rather than directly the ResourceBundleMessageSource bean because that avoids to make assumption about how to retrieve it (by type, by name) and allows a wide range of use cases in addition to i18n. See it in action in this Kotlin Script example.

[spring-projects-issues]

Sébastien Deleuze commented

Notice that this improvement allow this kind of Kotlin type-safe templates with i18n and nested template support:

import org.springframework.web.reactive.result.view.script.*

"""${include("header") }
<p>${i18n("hello")} $foo</p>
${include("footer")}"""