HTTP GET requests

INFO

Java does have a built-in java.net.http, but it's quite verbose. It's easier to get started with a library such as Unirest.

<dependency>
  <groupId>com.konghq</groupId>
  <artifactId>unirest-java</artifactId>
  <version>3.13.10</version>
</dependency>

Making a GET request

Making a GET request with Unirest looks like this:

public class BoredApi {

  public static String getActivity(String endpoint) throws Exception {
    String url = "https://bored-api.appbrewery.com/random";

    var response = Unirest
        .get(url)
        .header("Accept", "application/json")
        .asString();

    String json = response.getBody();
  }

}

For comparison, the equivalent request in java.net.http looks like this.

Details

public class BoredApi {

  public static String getRandomActivity() throws Exception {
    // Create a HTTP client
    HttpClient client = HttpClient.newHttpClient();

    // Create a URI
    URI uri = new URI("https://bored-api.appbrewery.com/random");

    // Create a new request
    HttpRequest request = HttpRequest.newBuilder()
        .uri(uri)
        .GET()
        .build();

    // Use the client to send the request
    HttpResponse<String> response = client.send(request, HttpResponse.BodyHandlers.ofString());

    return response.body();
  }

}

Mapping to an object

The response.body() is a JSON string.

If we make a class which maps some of the keys in the JSON string, we can convert the JSON into an object.

import com.fasterxml.jackson.annotation.JsonIgnoreProperties;

@JsonIgnoreProperties(ignoreUnknown = true)
public class Activity {
  private String activity;
  private double price;

  public Activity() {
  }

  public String summary() {
    return String.format("Try: %s, it costs £%.2f", this.activity, this.price * 100);
  }
}

TIP

The decorator @JsonIgnoreProperties(ignoreUnknown = true) allows us to pick just certain properties out of the JSON.

In this case, we only extract the activity and price properties.

To convert the JSON into an instance of Activity we use Jackson's ObjectMapper.

String json = response.getBody();

// Parse into an Activity
ObjectMapper mapper = new ObjectMapper();
Activity activity = mapper.readValue(json, Activity.class);

System.out.println(activity.summary());
// Try: Learn calligraphy, it costs £10.00