Retrofit 与 annotation Processor

Retrofit 与 annotation Processor ，EventBus结合使用的一个简单示例

代码地址：https://github.com/baofei/RetrofitAnnotation

用annotation processor 把Retrofit的接口生成Manager，网络请求成功的数据将会使用EventBus post出去

简单介绍下(Annotation Processing )，在Java中有一个apt的命令行工具（也包含了javac命令的功能，即编译功能），它的作用是在编译源文件(.java)之前，通过一个自定义的注解处理器(AnnotationProcessor)解释并处理源文件中的注解，由注解处理器生成一些新的源文件，字节码文件(.class)，或其他的文本文件，APT也会对新生成源文件进行编译，直到没有新的文件生成。具体的Google下就有了。

APT需要实现AbstractProcessor，可以看看大神们写的文章。

部分代码
RetrofitManager , 实现Retrofit的单例
<pre>public class RetrofitManager {
public static RetrofitManager mManager = new RetrofitManager();
public static OkHttpClient mClient;
private Retrofit retrofit;
public String mBaseUrl;
public HashMap<String, String> mHeader;
private int mRetrofitCode;
private Context mContext;
private RetrofitManager() {
}
public static RetrofitManager getInstance() {
return mManager;
}
public void init(Context context, String url) {
mBaseUrl = url;
mClient = createClient();
mContext = context.getApplicationContext();
createRetrofit();
}
private OkHttpClient createClient() {
return new OkHttpClient.Builder().build();
}
private void createRetrofit() {
retrofit = new Retrofit.Builder()
.baseUrl(mBaseUrl)
.addConverterFactory(GsonConverterFactory.create())
.client(mClient)
.build();
mRetrofitCode = retrofit.hashCode();
}
public synchronized Retrofit getRetrofit() {
return retrofit;
}
public int getRetrofitCode() {
return mRetrofitCode;
}
public synchronized void resetRetrofit(String url) {
mBaseUrl = url;
mClient = null;
mClient = createClient();
retrofit = null;
createRetrofit();
}

}</pre>
实现Callback，请求完成后用EventBus post出数据
<pre>
public class ApCallBack<T extends BaseResponse> implements Callback<T> {
T body;
private Object extra;
public ApCallBack(Class<? extends BaseResponse> body) {
this(body, null);
}
public ApCallBack(Class<? extends BaseResponse> body, Object extra) {
this.extra = extra;
try {
this.body = (T) body.newInstance();
} catch (InstantiationException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
}
}
@Override
public void onResponse(Call<T> call, Response<T> response) {
if (response.isSuccessful()) {
BaseResponse bean = response.body();
if (extra != null) {
bean.extra = extra;
}
EventBus.getDefault().post(bean);
} else {
onFailure(call, new Throwable("HTTP STATUS CODE " + response.code()));
}
}
@Override
public void onFailure(Call<T> call, Throwable t) {
if (body == null) {
body = (T) new BaseResponse();
}
if (extra != null) {
body.extra = extra;
}
body.code = Http.ERROR_CODE_FAILURE;
body.desc = getFailureDesc();
EventBus.getDefault().post(body);
}
protected String getFailureDesc() {
return "network error";
}

}</pre>
Manager的一个基类， annotation processor 把Retrofit的接口生成Manager的基类

/**
 * 基类，用于创建接口相关service
 * Created by baofei on 2016/9/22.
 */
public class BaseManager<T> {
    private int mRetrofitCode;
    private T service;
    public BaseManager() {
      create();
    }
    private void create() {
    mRetrofitCode = RetrofitManager.getInstance().getRetrofitCode();
     service =  (T) RetrofitManager.getInstance().getRetrofit().create(getT());
    }
    private Class getT() {
            Type genType = getClass().getGenericSuperclass();
            Type[] params = ((ParameterizedType) genType).getActualTypeArguments();
return (Class) params[0];
    }

    /**
     * 获取T相关接口service类
     *
     * @return T的具体实现
     */
    public T getService() {
        if(mRetrofitCode != RetrofitManager.getInstance().getRetrofitCode()){
            resetService();
        }
        return service;
    }

    /**
     * 切换环境重置service
     */
    public void resetService() {
        create();
    }
}```
http请求接口
``` @Manager
public interface ApiService {

    @POST("/api/addr/getDefaultAddr")
    Call<ResultBean> getDefaultAddr();
}```

 运行编译时，annotation processor根据ApiService 和BaseManager生成如下代码,代码生成位置为build/generated/source/apt里

public final class ApiServiceManager extends BaseManager<ApiService> {
private static ApiServiceManager sApiServiceManager;

public static synchronized ApiServiceManager getInstance() {
if (sApiServiceManager == null) {
sApiServiceManager = new ApiServiceManager();
}
return sApiServiceManager;
}

public Call<ResultBean> getDefaultAddr() {
Call<ResultBean> call = getService().getDefaultAddr();
call.enqueue(new ApCallBack<ResultBean>(ResultBean.class));
return call;
}
}

代码中就可以使用 ApiServiceManager.getInstance().getDefaultAddr();