As of HttpComponents 4.2+ there is a new class URIBuilder, which provides convenient way for generating URIs.
You can use either create URI directly from String URL:
List<NameValuePair> listOfParameters = ...;
URI uri = new URIBuilder("http://example.com:8080/path/to/resource?mandatoryParam=someValue")
    .addParameter("firstParam", firstVal)
    .addParameter("secondParam", secondVal)
    .addParameters(listOfParameters)
    .build();
Otherwise, you can specify all parameters explicitly:
URI uri = new URIBuilder()
    .setScheme("http")
    .setHost("example.com")
    .setPort(8080)
    .setPath("/path/to/resource")
    .addParameter("mandatoryParam", "someValue")
    .addParameter("firstParam", firstVal)
    .addParameter("secondParam", secondVal)
    .addParameters(listOfParameters)
    .build();
Once you have created URI object, then you just simply need to create HttpGet object and perform it:
//create GET request
HttpGet httpGet = new HttpGet(uri);
//perform request
httpClient.execute(httpGet ...//additional parameters, handle response etc.