As a starting point, we will use again the same URL class encountered in the previous recipe. This time we'll explore the openConnection method of the URL class in order to have more options for understanding the intricacies of the response returned by the remote server:

The java.net.URLConnection object, returned by the openConnection method, is convenient for getting hold of the additional response data such as, responseCode, contentType, or response headers.

As you can notice, we set the requestMethod property on the connection object to GET value; but, in fact, it's not needed, because it is a default value anyway.

responseCode is the Status Code Definition returned from the web server. For instance, a 404 status code, informs the client that the requested resource doesn't exist.

The connection object has the getContent method, which is declared to return java.lang.Object by the JDK API. The mechanism used by JDK to handle specific content types is out of scope of this recipe. However, the getContent method typically returns an implementation of the InputStream interface. That's why it is safe to retrieve the text property, which is made available by Groovy on all classes that implement the InputStream functionality.

An HTTP GET request often requires additional parameters needed by the server or remote application. These parameters are propagated inside the URL through a query string:

http://groovy.codehaus.org/Project+Information?print=1

The previous URL passes to the server the following key/value information: print=1, which is used to retrieve the Groovy project information page in printer-friendly format. In Groovy, the plain procedure to add a query string to a URL is just to use a string object. For example:

println ('http://groovy.codehaus.org/' + 
         'Project+Information?print=1').toURL().text

Query strings can be way lengthier than a single key/value entry. A Map is the perfect data structure for representing the query string data. Let us see how a Map can be converted into a query string:

def baseUrl = 
     'http://docs.codehaus.org/pages/editpage.action?'

def params = [spaceKey: 'GROOVY',
              title: 'Project+Information']

def query = params.collect { k,v ->
  "$k=${URLEncoder.encode(v)}"
}.join('&')

println "${baseUrl}${query}"

The code yields the following output:

> http://docs.codehaus.org/pages/editpage.action?spaceKey=GROOVY&title=Project+Information

The code snippet that transforms a Map into a query uses the collect method of the Map. It iterates through the Map entries and executes a simple transformation closure returning a List. The closure simply encodes each parameter value using the java.net.URLEncoder class and adds the = sign between a parameter name and its content. Finally, the join method is applied to the resulting collection to concatenate all entries into a single string using & symbol.