前言
retrofit 是一个类型安全的http 客户端库。是对okhttp的封装。
使用：
* Retrofit retrofit = new Retrofit.Builder()
* .baseUrl("https://api.example.com/")
* .addConverterFactory(GsonConverterFactory.create())
* .build();
*
* MyApi api = retrofit.create(MyApi.class);
* Response user = api.getUser().execute();
1.retrofit创建：
retrofit主要包括：
callFactory --OkHttpClient
baseUrl --传入的域名
converterFactories
转换器的工厂列表， Converter.Factory 接口实现， 抽象工厂模式。
包括responseBodyConverter,
requestBodyConverter, RequestFactory解析@body标签时 使用。
stringConverter RequestFactory解析@query标签时 使用。
默认，加入BuiltInConverters。callAdapterFactories
默认时 接口返回Call<ResponseBody>类型。
CallAdpater用于将Call<?>适配到其他类型。
注 ： ResponseBody由Converter负责转换。
默认时 java平台加入DefaultCallAdapterFactory
android 加入ExecutorCallAdapterFactory:不改变返回值类型，只做线程切换。
2.创建接口代理实现:
public <T> T create(final Class<T> 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();
private final Object[] emptyArgs = new Object[0];
@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);
}
return loadServiceMethod(method).invoke(args != null ? args : emptyArgs);
}
});
}
生成的代理 调用时，相当于调用
loadServiceMethod(method).invoke()
每个接口方法对应于一个ServiceMethod对象。
abstract class ServiceMethod<T> {
static <T> ServiceMethod<T> parseAnnotations(Retrofit retrofit, Method method) {
RequestFactory requestFactory = RequestFactory.parseAnnotations(retrofit, method);
Type returnType = method.getGenericReturnType();
if (Utils.hasUnresolvableType(returnType)) {
throw methodError(method,
"Method return type must not include a type variable or wildcard: %s", returnType);
}
if (returnType == void.class) {
throw methodError(method, "Service methods cannot return void.");
}
return HttpServiceMethod.parseAnnotations(retrofit, method, requestFactory);
}
abstract T invoke(Object[] args);
}
static <ResponseT, ReturnT> HttpServiceMethod<ResponseT, ReturnT> parseAnnotations(
Retrofit retrofit, Method method, RequestFactory requestFactory) {
CallAdapter<ResponseT, ReturnT> callAdapter = createCallAdapter(retrofit, method);
Type responseType = callAdapter.responseType();
if (responseType == Response.class || responseType == okhttp3.Response.class) {
throw methodError(method, "'"
+ Utils.getRawType(responseType).getName()
+ "' is not a valid response body type. Did you mean ResponseBody?");
}
if (requestFactory.httpMethod.equals("HEAD") && !Void.class.equals(responseType)) {
throw methodError(method, "HEAD method must use Void as response type.");
}
Converter<ResponseBody, ResponseT> responseConverter =
createResponseConverter(retrofit, method, responseType);
okhttp3.Call.Factory callFactory = retrofit.callFactory;
return new HttpServiceMethod<>(requestFactory, callFactory, callAdapter, responseConverter);
}
ServiceMethod对象 根据注解创建。
3.调用接口:
HttpServiceMethod.java
@Override ReturnT invoke(Object[] args) {
return callAdapter.adapt(
new OkHttpCall<>(requestFactory, args, callFactory, responseConverter));
}
生成OkHttpCall对象，并通过callAdapter适配到特定类型。
