Calling the GitHub API using Spring’s RestTemplate

GitHub has an RESTful JSON API that we can call from our apps. In this post I’ll show how I’m grabbing a GitHub repo’s watchers and pull them into my own app using Spring’s RestTemplate.

Meet the GitHub API

First, take a quick look at the GitHub Repo Watching API. It’s pretty simple, and it doesn’t require credentials to call. The URL for my Skybase project, for example, is https://api.github.com/repos/williewheeler/skybase/watchers.

Go ahead and click the watcher link above. You’ll see that the response is a JSON array of watcher objects.

Note that since the GitHub API is HTTPS-based, you will need to download the GitHub API certificate (using, e.g., openssl) and then import it into your Java keystore (using keytool) so your Java programs can call the API without running into certificate errors.

Create a User class for object/JSON mapping

We’re going to use Jackson to map the GitHub JSON to Java objects. We’ll need a User class for that. Here it is:

package org.skydingo.skybase.integrations.github.model;

import org.codehaus.jackson.annotate.JsonProperty;

public class User {
    private Long id;
    private String url, login, avatarUrl, gravatarId;

    public Long getId() { return id; }

    public void setId(Long id) { this.id = id; }

    public String getUrl() { return url; }

    public void setUrl(String url) { this.url = url; }

    public String getLogin() { return login; }

    public void setLogin(String login) { this.login = login; }

    @JsonProperty("avatar_url")
    public String getAvatarUrl() { return avatarUrl; }

    public void setAvatarUrl(String avatarUrl) { this.avatarUrl = avatarUrl; }

    @JsonProperty("gravatar_id")
    public String getGravatarId() { return gravatarId; }

    public void setGravatarId(String gravatarId) { this.gravatarId = gravatarId; }
}

Nothing too amazing here. Note that I’m using @JsonProperty to clarify the mapping from the avatar_url and gravatar_id JSON fields to the avatarUrl and gravatarId Java properties, since Jackson doesn’t automatically handle underscores or anything like that.

The Maven dependency for the @JsonProperty annotation is

<dependency>
    <groupId>org.codehaus.jackson</groupId>
    <artifactId>jackson-mapper-asl</artifactId>
    <version>1.9.3</version>
</dependency>

Get the data using RestTemplate

Now that we have User, all we need to do is grab the data using RestTemplate. Easy:

package org.skydingo.skybase.service;

import javax.inject.Inject;
import org.skydingo.skybase.integrations.github.model.User;
import org.skydingo.skybase.model.Application;
import org.springframework.stereotype.Service;
import org.springframework.web.client.RestTemplate;

@Service
public class ApplicationService {
    private static final String GITHUB_WATCHER_URI =
        "https://api.github.com/repos/{user}/{repo}/watchers";

    @Inject private RestTemplate restTemplate;

    public User[] getGithubRepoWatchers(String user, String repo) {
        return restTemplate.getForObject(GITHUB_WATCHER_URI, User[].class, user, repo);
    }
}

Recall that GitHub returns an array of watchers. That’s why we’re using User[].class in the call. RestTemplate substitutes the user and repo values into the GITHUB_WATCHER_URI string for us.

Spring configuration

All we need to do is put a RestTemplate instance on the app context:

<bean class="org.springframework.web.client.RestTemplate" />

Success!

After a little hacking at the UI:

Skybase SCM page

[See my post Skybase/GitHub integration on the Skydingo blog for more context as to why we'd want to integrate our CMDB with GitHub.]