Grails features 5 dependency resolution configurations (or 'scopes') which you can take advantage of:

Within the dependencies block you can specify a dependency that falls into one of these configurations by calling the equivalent method. For example if your application requires the MySQL driver to function at runtime you can specify as such:

runtime 'com.mysql:mysql-connector-java:5.1.5'

The above uses the string syntax which is group:name:version. You can also use a map-based syntax:

runtime group:'com.mysql', name:'mysql-connector-java', version:'5.1.5'

In Maven terminology, group corresponds to an artifact's groupId and name corresponds to its artifactId.

Multiple dependencies can be specified by passing multiple arguments:

runtime 'com.mysql:mysql-connector-java:5.1.5',
        'net.sf.ehcache:ehcache:1.6.1'

// Or

runtime( [group:'com.mysql', name:'mysql-connector-java', version:'5.1.5'], [group:'net.sf.ehcache', name:'ehcache', version:'1.6.1'] )

Disabling transitive dependency resolution

By default, Grails will not only get the JARs and plugins that you declare, but it will also get their transitive dependencies. This is usually what you want, but there are occasions where you want a dependency without all its baggage. In such cases, you can disable transitive dependency resolution on a case-by-case basis:

runtime('com.mysql:mysql-connector-java:5.1.5', 'net.sf.ehcache:ehcache:1.6.1') {
    transitive = false
}

// Or runtime group:'com.mysql', name:'mysql-connector-java', version:'5.1.5', transitive:false

Excluding specific transitive dependencies

A far more common scenario is where you want the transitive dependencies, but some of them cause issues with your own dependencies or are unnecessary. For example, many Apache projects have 'commons-logging' as a transitive dependency, but it shouldn't be included in a Grails project (we use SLF4J). That's where the excludes option comes in:

runtime('com.mysql:mysql-connector-java:5.1.5', 'net.sf.ehcache:ehcache:1.6.1') {
    excludes "xml-apis", "commons-logging"
}

// Or runtime(group:'com.mysql', name:'mysql-connector-java', version:'5.1.5') { excludes([ group: 'xml-apis', name: 'xml-apis'], [ group: 'org.apache.httpcomponents' ], [ name: 'commons-logging' ])

As you can see, you can either exclude dependencies by their artifact ID (also known as a module name) or any combination of group and artifact IDs (if you use the map notation). You may also come across exclude as well, but that can only accept a single string or map:

runtime('com.mysql:mysql-connector-java:5.1.5', 'net.sf.ehcache:ehcache:1.6.1') {
    exclude "xml-apis"
}