Controlling Plug-in Dependencies
Plug-ins often depend on the presence of other plugins and can also adapt depending on the presence of others. To cover this, a plugin can define two properties. The first is called
dependsOn
. For example, take a look at this snippet from the Grails Hibernate plugin:
class HibernateGrailsPlugin {
def version = 1.0
def dependsOn = [dataSource:1.0,
domainClass:1.0,
i18n:1.0,
core: 1.0]}
As the above example demonstrates the Hibernate plugin is dependent on the presence of 4 plugins: The
dataSource
plugin, The
domainClass
plugin, the
i18n
plugin and the
core
plugin.
Essentially the dependencies will be loaded first and then the Hibernate plugin. If all dependencies do not load, then the plugin will not load.
The
dependsOn
property also supports a mini expression language for specifying version ranges. A few examples of the syntax can be seen below:
def dependsOn = [foo:"* > 1.0"]
def dependsOn = [foo:"1.0 > 1.1"]
def dependsOn = [foo:"1.0 > *"]
When the wildcard * character is used it denotes "any" version. The expression syntax also excludes any suffixes such as -BETA, -ALPHA etc. so for example the expression "1.0 > 1.1" would match any of the following versions:
- 1.1
- 1.0
- 1.0.1
- 1.0.3-SNAPSHOT
- 1.1-BETA2
Controlling Load Order
Using
dependsOn
establishes a "hard" dependency in that if the dependency is not resolved, the plugin will give up and won't load. It is possible though to have a "weaker" dependency using the
loadAfter
property:
def loadAfter = ['controllers']
Here the plugin will be loaded after the
controllers
plugin if it exists, otherwise it will just be loaded. The plugin can then adapt to the presence of the other plugin, for example the Hibernate plugin has this code in the
doWithSpring
closure:
if(manager?.hasGrailsPlugin("controllers")) {
openSessionInViewInterceptor(OpenSessionInViewInterceptor) {
flushMode = HibernateAccessor.FLUSH_MANUAL
sessionFactory = sessionFactory
}
grailsUrlHandlerMapping.interceptors << openSessionInViewInterceptor
}
Here the Hibernate plugin will only register an
OpenSessionInViewInterceptor
if the
controllers
plugin has been loaded. The manager variable is an instance of the
GrailsPluginManager interface and it provides methods to interact with other plugins and the
GrailsPluginManager
itself from any plugin.