Retrofit ver2.0.0の使い方 ref: http://qiita.com/kiimiiis/items/9e1078c66646c02cc103

file0.java

compile 'com.squareup.retrofit2:retrofit:2.0.0-beta3'
compile 'com.squareup.retrofit2:converter-gson:latest.release'

file1.java

compile 'com.google.code.gson:gson:2.3.1'
compile 'org.glassfish:javax.annotation:10.0-b28'

MainActivity.java

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        //QiitaApiの使用
        Retrofit retrofit = new Retrofit.Builder()
                .baseUrl("https://qiita.com")
                .addConverterFactory(GsonConverterFactory.create())
                .build();

        QiitaApiService qiitaApiservice = retrofit.create(QiitaApiService.class);
        Call<List<QiitaGsonResponse>> call = qiitaApiservice.getData("1", "20", "android");
        try {
                call.enqueue(new Callback<List<QiitaGsonResponse>>() {
                    @Override
                    public void onResponse(Response<List<QiitaGsonResponse>> response) {
                        String title = response.body().get(0).getTitle();
                        Log.d("Qiita",title);
                    }

                    @Override
                    public void onFailure(Throwable t) {
                        Log.d("Qiita", "error");
                    }
                });
        } catch (Exception e) {
            Log.d("Qiita", "レスポンスエラー");
        }
    }

QiitaApiService.java

/**
 * Created by hanasjima on 2016/01/28.
 */
public interface QiitaApiService {
    @GET("/api/v2/items")
    Call<List<QiitaGsonResponse>> getData(@Query("page") String page, @Query ("per_page") String per_page, @Query("query") String query);
}

QiitaGsonResponse.java

@Generated("org.jsonschema2pojo")
public class QiitaGsonResponse {

    @SerializedName("rendered_body")
    @Expose
    private String renderedBody;
    @SerializedName("body")
    @Expose
    private String body;
    @SerializedName("coediting")
    @Expose
    private Boolean coediting;
    @SerializedName("created_at")
    @Expose
    private String createdAt;
    @SerializedName("id")
    @Expose
    private String id;
    @SerializedName("private")
    @Expose
    private Boolean _private;
    @SerializedName("tags")
    @Expose
    private List<Tag> tags = new ArrayList<Tag>();
    @SerializedName("title")
    @Expose
    private String title;
    @SerializedName("updated_at")
    @Expose
    private String updatedAt;
    @SerializedName("url")
    @Expose
    private String url;
    @SerializedName("user")
    @Expose
    private User user;

    /**
     *
     * @return
     * The renderedBody
     */
    public String getRenderedBody() {
        return renderedBody;
    }

    /**
     *
     * @param renderedBody
     * The rendered_body
     */
    public void setRenderedBody(String renderedBody) {
        this.renderedBody = renderedBody;
    }

    /**
     *
     * @return
     * The body
     */
    public String getBody() {
        return body;
    }

    /**
     *
     * @param body
     * The body
     */
    public void setBody(String body) {
        this.body = body;
    }

    /**
     *
     * @return
     * The coediting
     */
    public Boolean getCoediting() {
        return coediting;
    }

    /**
     *
     * @param coediting
     * The coediting
     */
    public void setCoediting(Boolean coediting) {
        this.coediting = coediting;
    }

    /**
     *
     * @return
     * The createdAt
     */
    public String getCreatedAt() {
        return createdAt;
    }

    /**
     *
     * @param createdAt
     * The created_at
     */
    public void setCreatedAt(String createdAt) {
        this.createdAt = createdAt;
    }

    /**
     *
     * @return
     * The id
     */
    public String getId() {
        return id;
    }

    /**
     *
     * @param id
     * The id
     */
    public void setId(String id) {
        this.id = id;
    }

    /**
     *
     * @return
     * The _private
     */
    public Boolean getPrivate() {
        return _private;
    }

    /**
     *
     * @param _private
     * The private
     */
    public void setPrivate(Boolean _private) {
        this._private = _private;
    }

    /**
     *
     * @return
     * The tags
     */
    public List<Tag> getTags() {
        return tags;
    }

    /**
     *
     * @param tags
     * The tags
     */
    public void setTags(List<Tag> tags) {
        this.tags = tags;
    }

    /**
     *
     * @return
     * The title
     */
    public String getTitle() {
        return title;
    }

    /**
     *
     * @param title
     * The title
     */
    public void setTitle(String title) {
        this.title = title;
    }

    /**
     *
     * @return
     * The updatedAt
     */
    public String getUpdatedAt() {
        return updatedAt;
    }

    /**
     *
     * @param updatedAt
     * The updated_at
     */
    public void setUpdatedAt(String updatedAt) {
        this.updatedAt = updatedAt;
    }

    /**
     *
     * @return
     * The url
     */
    public String getUrl() {
        return url;
    }

    /**
     *
     * @param url
     * The url
     */
    public void setUrl(String url) {
        this.url = url;
    }

    /**
     *
     * @return
     * The user
     */
    public User getUser() {
        return user;
    }

    /**
     *
     * @param user
     * The user
     */
    public void setUser(User user) {
        this.user = user;
    }

}