////
Licensed to the Apache Software Foundation (ASF) under one
or more contributor license agreements.  See the NOTICE file
distributed with this work for additional information
regarding copyright ownership.  The ASF licenses this file
to you under the Apache License, Version 2.0 (the
"License"); you may not use this file except in compliance
with the License.  You may obtain a copy of the License at

https://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing,
software distributed under the License is distributed on an
"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
KIND, either express or implied.  See the License for the
specific language governing permissions and limitations
under the License.
////

Grails provides a number of hooks to leverage the different parts of the system and perform runtime configuration by convention.


==== Hooking into the Grails Spring configuration


First, you can hook in Grails runtime configuration overriding the `doWithSpring` method from the link:{api}grails/plugins/Plugin.html[Plugin] class and returning a closure that defines additional beans. For example the following snippet is from one of the core Grails plugins that provides link:i18n.html[i18n] support:

[source,groovy]
----
import org.springframework.web.servlet.i18n.CookieLocaleResolver
import org.springframework.web.servlet.i18n.LocaleChangeInterceptor
import org.springframework.context.support.ReloadableResourceBundleMessageSource
import grails.plugins.*

class I18nGrailsPlugin extends Plugin {

    def version = "0.1"

    Closure doWithSpring() {{->
        messageSource(ReloadableResourceBundleMessageSource) {
            basename = "WEB-INF/grails-app/i18n/messages"
        }
        localeChangeInterceptor(LocaleChangeInterceptor) {
            paramName = "lang"
        }
        localeResolver(CookieLocaleResolver)
    }}
}
----

This plugin configures the Grails `messageSource` bean and a couple of other beans to manage Locale resolution and switching. It using the link:spring.html#theBeanBuilderDSLExplained[Spring Bean Builder] syntax to do so.


==== Customizing the Servlet Environment


In previous versions of Grails it was possible to dynamically modify the generated `web.xml`. From Grails 3.x+ there is no `web.xml` file and it is not possible to programmatically modify the `web.xml` file anymore.

However, it is possible to perform the most commons tasks of modifying the Servlet environment in Grails 3.x and above.


==== Adding New Servlets


If you want to add a new Servlet instance the simplest way is simply to define a new Spring bean in the `doWithSpring` method:

[source,groovy]
----
Closure doWithSpring() {{->
  myServlet(MyServlet)
}}
----

If you need to customize the servlet you can use Spring Boot's {springbootapi}org/springframework/boot/web/servlet/ServletRegistrationBean.html[ServletRegistrationBean]:

[source,groovy]
----
Closure doWithSpring() {{->
  myServlet(ServletRegistrationBean, new MyServlet(), "/myServlet/*") {
    loadOnStartup = 2
  }
}}
----


==== Adding New Servlet Filters


Just like Servlets, the simplest way to configure a new filter is to simply define a Spring bean:

[source,groovy]
----
Closure doWithSpring() {{->
  myFilter(MyFilter)
}}
----

However, if you want to control the order of filter registrations you will need to use Spring Boot's {springbootapi}org/springframework/boot/web/servlet/FilterRegistrationBean.html[FilterRegistrationBean]:

[source,groovy]
----
myFilter(FilterRegistrationBean) {
    filter = bean(MyFilter)
    urlPatterns = ['/*']
    order = Ordered.HIGHEST_PRECEDENCE
}
----

NOTE: Grails' internal registered filters (`GrailsWebRequestFilter`, `HiddenHttpMethodFilter` etc.) are defined by incrementing `HIGHEST_PRECEDENCE` by 10 thus allowing several filters to be inserted before or between Grails' filters.


==== Doing Post Initialisation Configuration


Sometimes it is useful to be able do some runtime configuration after the Spring {springapi}org/springframework/context/ApplicationContext.html[ApplicationContext] has been built. In this case you can define a `doWithApplicationContext` closure property.

[source,groovy]
----
class SimplePlugin extends Plugin{

    def name = "simple"
    def version = "1.1"

    @Override
    void doWithApplicationContext() {
        def sessionFactory = applicationContext.sessionFactory
        // do something here with session factory
    }
}
----
