// Create a very simple REST adapter which points the GitHub API.
Retrofit retrofit = new Retrofit.Builder()
.baseUrl("https://api.github.com")
.addConverterFactory(GsonConverterFactory.create())
.build();
// Create an instance of our GitHub API interface.
GitHub github = retrofit.create(GitHub.class);
通过baseUrl接口声明接口请求域名；
配置对象的序列化和反序列化转换工厂；
Step3：通过API接口方法创建Call实例并发起请求
// Create a call instance for looking up Retrofit contributors.
Call> call = github.contributors("square", "retrofit");
// Fetch and print a list of the contributors to the library.
List contributors = call.execute().body();
Retrofit的实现就是这么简单优雅，业务层只需要像调用普通接口一样即可完成网络请求。
Retrofit源码解析
首先要构建一个Retrofit实例，其作用是把接口方法注解转换为OKHttp请求。
Retrofit.Builder.build
public Retrofit build() {
if (baseUrl == null) {
throw new IllegalStateException("Base URL required.");
}
okhttp3.Call.Factory callFactory = this.callFactory;
if (callFactory == null) {
callFactory = new OkHttpClient();
}
Executor callbackExecutor = this.callbackExecutor;
if (callbackExecutor == null) {
callbackExecutor = platform.defaultCallbackExecutor();
}
// Make a defensive copy of the adapters and add the default Call adapter.
List callAdapterFactories = new ArrayList<>(this.callAdapterFactories);
callAdapterFactories.add(platform.defaultCallAdapterFactory(callbackExecutor));
// Make a defensive copy of the converters.
List converterFactories =
new ArrayList<>(1 + this.converterFactories.size());
// Add the built-in converter factory first. This prevents overriding its behavior but also
// ensures correct behavior when using converters that consume all types.
converterFactories.add(new BuiltInConverters());
converterFactories.addAll(this.converterFactories);
return new Retrofit(callFactory, baseUrl, unmodifiableList(converterFactories),
unmodifiableList(callAdapterFactories), callbackExecutor, validateEagerly);
}
}
public T create(final Class service) {
Utils.validateServiceInterface(service);
if (validateEagerly) {
eagerlyValidateMethods(service);
}
return (T) Proxy.newProxyInstance(service.getClassLoader(), new Class[] { service },
new InvocationHandler() {
private final Platform platform = Platform.get();
@Override public Object invoke(Object proxy, Method method, @Nullable Object[] args)
throws Throwable {
// If the method is a method from Object then defer to normal invocation.
if (method.getDeclaringClass() == Object.class) {
return method.invoke(this, args);
}
if (platform.isDefaultMethod(method)) {
return platform.invokeDefaultMethod(method, service, proxy, args);
}
ServiceMethod serviceMethod =
(ServiceMethod) loadServiceMethod(method);
OkHttpCall
@Override
public Response execute() throws IOException {
okhttp3.Call call;
synchronized (this) {
if (executed) throw new IllegalStateException("Already executed.");
executed = true;
if (creationFailure != null) {
if (creationFailure instanceof IOException) {
throw (IOException) creationFailure;
} else if (creationFailure instanceof RuntimeException) {
throw (RuntimeException) creationFailure;
} else {
throw (Error) creationFailure;
}
}
call = rawCall;
if (call == null) {
try {
call = rawCall = createRawCall();
} catch (IOException | RuntimeException | Error e) {
throwIfFatal(e); // Do not assign a fatal error to creationFailure.
creationFailure = e;
throw e;
}
}
}
if (canceled) {
call.cancel();
}
return parseResponse(call.execute());
}
ExecutorCallbackCall把网络请求委派给OKHttpCall，后者主要负责：
把接口注解参数转换为okhttp3.Call原始请求
执行okhttp3.Call接口请求,获取Response结果
把ResponseBody转换为接口返回数据类型并回调
1. ServiceMethod.toCall负责将注解参数转换为okhttp3.Call
/** Builds an HTTP request from method arguments. */
okhttp3.Call toCall(@Nullable Object... args) throws IOException {
RequestBuilder requestBuilder = new RequestBuilder(httpMethod, baseUrl, relativeUrl, headers,
contentType, hasBody, isFormEncoded, isMultipart);
@SuppressWarnings("unchecked") // It is an error to invoke a method with the wrong arg types.
ParameterHandler
/** Builds a method return value from an HTTP response body. */
R toResponse(ResponseBody body) throws IOException {
return responseConverter.convert(body);
}
