11. Grape

Whilst you can use Maven or (even better) Gradle to grab dependencies, Groovy includes a dependency manager called Grape that you can start using straight away.

Say I wanted to grab a copy of my favourite web page and had worked out that Apache’s HTTP Components would really help me. I can search the Maven Central Repository and find what I need. In fact, that web page even tells me how to use the library with Grape:

@Grapes(
@Grab(group='org.apache.httpcomponents', module='httpcomponents-client', version\
='4.4')
)

Grape uses annotations - essentially the “at” (@) sign followed by a name - to do its thing. In the example above:

• @Grapes starts of the grape listing
  • You need this if you’re grabbing several libraries in the same segment (node) of your code - we can actually ignore this in smaller examples.
• Each grape is declared using @Grab and providing the following:
  • The group that holds the module
  • The name of the module
  • The required version of the module

In the code below I use the Apache HTTP Components library to report on the HTTP status line from my request to “http://www.example.org”. I’ve trimmed off the @Grapes as I just need to Grab one module:

@Grab(group='org.apache.httpcomponents', module='httpclient', version='4.3.6')
import org.apache.http.impl.client.HttpClients
import org.apache.http.client.methods.HttpGet

def httpclient = HttpClients.createDefault()
def httpGet = new HttpGet('http://www.example.org')
def response = httpclient.execute(httpGet)

println response.getStatusLine()

You can use a short-form version of @Grab using the format <group>:<module>:<version> - this would let us use the following:

@Grab('org.apache.httpcomponents:httpclient:4.3.6')

Once you start building more complex programs you will probably turn to Gradle but Grape works just fine for these tutorials.