Retrofit2源码试读（一）
2018-12-14 本文已影响21人
Young_Allen
1.文章介绍
Retrofit2+Rxjava2+Glide+MVP架构正是火热，以学习角度出发，分模块来熟悉下这种架构的各个模块源码以及实现方式。
什么情况下使用Retrofit2+Rxjava2呢？Retrofit2+Rxjava2的主要优势是它的解耦性，在项目越复杂时体现出的优势越明显。
2.干货
那么就先从Retrofit的使用开始说起，然后再说Rxjava2：
public static Retrofit getDeafault(String url) {
Retrofit sRetrofit;
OkHttpClient.Builder builder = new OkHttpClient.Builder();
OkHttpClient okHttpClient = builder.build();
if (BuildConfig.DEBUG) {
// Log信息拦截器
HttpLoggingInterceptor loggingInterceptor = new HttpLoggingInterceptor();
loggingInterceptor.setLevel(HttpLoggingInterceptor.Level.BODY);
builder.addInterceptor(loggingInterceptor);
}
sRetrofit = new Retrofit.Builder()
.baseUrl(url)
//设置数据转换工厂类eg:把json数据转换为对象使用GsonConverterFactory
.addConverterFactory(GsonConverterFactory.create())
//设置数据适配转换工厂类eg:把Callback的接口转化为对RxJava的回调
.addCallAdapterFactory(RxJava2CallAdapterFactory.create())
.client(okHttpClient)
.build();
return sRetrofit;
}
以上代码就是关于一个Retrofit简单的初始化。初始化后就可以关联需要请求的数据实现业务处理了:
public void requesetWeatherInfo() {
Call<DataModel> call = RetrofitUtils.getDeafault(WeatherService.WEATHERSERVICE_URL)
.create(WeatherService.class)
.loadWeatherInfo("101190201");
call.enqueue(new Callback<DataModel>() {
@Override
public void onResponse(Call<DataModel> call, Response<DataModel> response) {
DataModel model = response.body();
DataModel.WeatherInfoBean bean = model.getWeatherinfo();
Log.d(TAG, "onResponse:" + bean.getCity());
}
@Override
public void onFailure(Call<DataModel> call, Throwable t) {
Log.d(TAG, "onFailure:" + t.getMessage());
}
});
}
这是最基本的Retrofit的使用，为了方便分析先不涉及与Rxjava相关的内容。
从Retrofit的初始化开始说起，new Retrofit.Builder()使用了建造者模式:
public static final class Builder {
private final Platform platform;
private @Nullable okhttp3.Call.Factory callFactory;
private @Nullable HttpUrl baseUrl;
private final List<Converter.Factory> converterFactories = new ArrayList<>();
private final List<CallAdapter.Factory> callAdapterFactories = new ArrayList<>();
private @Nullable Executor callbackExecutor;
private boolean validateEagerly;
Builder(Platform platform) {
this.platform = platform;
}
public Builder() {
this(Platform.get());
}
Builder(Retrofit retrofit) {
platform = Platform.get();
callFactory = retrofit.callFactory;
baseUrl = retrofit.baseUrl;
// Do not add the default BuiltIntConverters and platform-aware converters added by build().
for (int i = 1,
size = retrofit.converterFactories.size() - platform.defaultConverterFactoriesSize();
i < size; i++) {
converterFactories.add(retrofit.converterFactories.get(i));
}
// Do not add the default, platform-aware call adapters added by build().
for (int i = 0,
size = retrofit.callAdapterFactories.size() - platform.defaultCallAdapterFactoriesSize();
i < size; i++) {
callAdapterFactories.add(retrofit.callAdapterFactories.get(i));
}
callbackExecutor = retrofit.callbackExecutor;
validateEagerly = retrofit.validateEagerly;
}
...
/**
* Create the {@link Retrofit} instance using the configured values.
* <p>
* Note: If neither {@link #client} nor {@link #callFactory} is called a default {@link
* OkHttpClient} will be created and used.
*/
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<CallAdapter.Factory> callAdapterFactories = new ArrayList<>(this.callAdapterFactories);
callAdapterFactories.addAll(platform.defaultCallAdapterFactories(callbackExecutor));
// Make a defensive copy of the converters.
List<Converter.Factory> converterFactories = new ArrayList<>(
1 + this.converterFactories.size() + platform.defaultConverterFactoriesSize());
// 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);
converterFactories.addAll(platform.defaultConverterFactories());
return new Retrofit(callFactory, baseUrl, unmodifiableList(converterFactories),
unmodifiableList(callAdapterFactories), callbackExecutor, validateEagerly);
}
...
}
源码中有converterFactories、callAdapterFactories分别是对数据格式适配和网络请求的适配。最后这些参数都保存在Retrofit这个对象里：
new Retrofit(callFactory, baseUrl, unmodifiableList(converterFactories),
unmodifiableList(callAdapterFactories), callbackExecutor, validateEagerly);
另外需要创建业务数据的关联：
@SuppressWarnings("unchecked") // Single-interface proxy creation guarded by parameter safety.
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);
}
});
}
在这里使用了动态代理模式，这个传入的参数service就是定义的接口类如：
public interface WeatherService {
String WEATHERSERVICE_URL = "http://www.weather.com.cn/";
/**
* 单独使用Retrofit
* @param cityId
* @return
*/
@GET("adat/sk/{cityId}.html")
Call<DataModel> loadWeatherInfo(@Path("cityId")String cityId);
｝
使用了Java的反射机制创建类的实例：
@CallerSensitive
public static Object newProxyInstance(ClassLoader loader,
Class<?>[] interfaces,
InvocationHandler h)
throws IllegalArgumentException
{
Objects.requireNonNull(h);
final Class<?>[] intfs = interfaces.clone();
// Android-removed: SecurityManager calls
/*
final SecurityManager sm = System.getSecurityManager();
if (sm != null) {
checkProxyAccess(Reflection.getCallerClass(), loader, intfs);
}
*/
/*
* Look up or generate the designated proxy class.
*/
Class<?> cl = getProxyClass0(loader, intfs);
/*
* Invoke its constructor with the designated invocation handler.
*/
try {
// Android-removed: SecurityManager / permission checks.
/*
if (sm != null) {
checkNewProxyPermission(Reflection.getCallerClass(), cl);
}
*/
final Constructor<?> cons = cl.getConstructor(constructorParams);
final InvocationHandler ih = h;
if (!Modifier.isPublic(cl.getModifiers())) {
// BEGIN Android-changed: Excluded AccessController.doPrivileged call.
/*
AccessController.doPrivileged(new PrivilegedAction<Void>() {
public Void run() {
cons.setAccessible(true);
return null;
}
});
*/
cons.setAccessible(true);
// END Android-removed: Excluded AccessController.doPrivileged call.
}
return cons.newInstance(new Object[]{h});
} catch (IllegalAccessException|InstantiationException e) {
throw new InternalError(e.toString(), e);
} catch (InvocationTargetException e) {
Throwable t = e.getCause();
if (t instanceof RuntimeException) {
throw (RuntimeException) t;
} else {
throw new InternalError(t.toString(), t);
}
} catch (NoSuchMethodException e) {
throw new InternalError(e.toString(), e);
}
}
private static Class<?> getProxyClass0(ClassLoader loader,
Class<?>... interfaces) {
if (interfaces.length > 65535) {
throw new IllegalArgumentException("interface limit exceeded");
}
// If the proxy class defined by the given loader implementing
// the given interfaces exists, this will simply return the cached copy;
// otherwise, it will create the proxy class via the ProxyClassFactory
return proxyClassCache.get(loader, interfaces);
}
重写了InvocationHandler的invoke方法。
如果是Object类的方法直接通过invoke反射处理：
if (method.getDeclaringClass() == Object.class) {
return method.invoke(this, args);
}
如果是相关平台的基础方法则默认处理：
if (platform.isDefaultMethod(method)) {
return platform.invokeDefaultMethod(method, service, proxy, args);
}
其他情况如开发者自定义的，就通过ServiceMethod处理：
return loadServiceMethod(method).invoke(args != null ? args : emptyArgs);
ServiceMethod<?> loadServiceMethod(Method method) {
ServiceMethod<?> result = serviceMethodCache.get(method);
if (result != null) return result;
synchronized (serviceMethodCache) {
result = serviceMethodCache.get(method);
if (result == null) {
result = ServiceMethod.parseAnnotations(this, method);
serviceMethodCache.put(method, result);
}
}
return result;
}
需要去解析注解字段，为了优化速度把方法类缓存在serviceMethodCache里
static <T> ServiceMethod<T> parseAnnotations(Retrofit retrofit, Method method) {
RequestFactory requestFactory = RequestFactory.parseAnnotations(retrofit, method);
//按本篇文章来分析 这个返回的就是Call<DataModel>
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);
}
final class RequestFactory {
static RequestFactory parseAnnotations(Retrofit retrofit, Method method) {
return new Builder(retrofit, method).build();
}
...
Builder(Retrofit retrofit, Method method) {
this.retrofit = retrofit;
this.method = method;
this.methodAnnotations = method.getAnnotations();
this.parameterTypes = method.getGenericParameterTypes();
this.parameterAnnotationsArray = method.getParameterAnnotations();
}
RequestFactory build() {
for (Annotation annotation : methodAnnotations) {
parseMethodAnnotation(annotation);
}
if (httpMethod == null) {
throw methodError(method, "HTTP method annotation is required (e.g., @GET, @POST, etc.).");
}
if (!hasBody) {
if (isMultipart) {
throw methodError(method,
"Multipart can only be specified on HTTP methods with request body (e.g., @POST).");
}
if (isFormEncoded) {
throw methodError(method, "FormUrlEncoded can only be specified on HTTP methods with "
+ "request body (e.g., @POST).");
}
}
int parameterCount = parameterAnnotationsArray.length;
parameterHandlers = new ParameterHandler<?>[parameterCount];
for (int p = 0; p < parameterCount; p++) {
parameterHandlers[p] = parseParameter(p, parameterTypes[p], parameterAnnotationsArray[p]);
}
if (relativeUrl == null && !gotUrl) {
throw methodError(method, "Missing either @%s URL or @Url parameter.", httpMethod);
}
if (!isFormEncoded && !isMultipart && !hasBody && gotBody) {
throw methodError(method, "Non-body HTTP method cannot contain @Body.");
}
if (isFormEncoded && !gotField) {
throw methodError(method, "Form-encoded method must contain at least one @Field.");
}
if (isMultipart && !gotPart) {
throw methodError(method, "Multipart method must contain at least one @Part.");
}
return new RequestFactory(this);
}
...
private void parseMethodAnnotation(Annotation annotation) {
if (annotation instanceof DELETE) {
parseHttpMethodAndPath("DELETE", ((DELETE) annotation).value(), false);
} else if (annotation instanceof GET) {
parseHttpMethodAndPath("GET", ((GET) annotation).value(), false);
} else if (annotation instanceof HEAD) {
parseHttpMethodAndPath("HEAD", ((HEAD) annotation).value(), false);
} else if (annotation instanceof PATCH) {
parseHttpMethodAndPath("PATCH", ((PATCH) annotation).value(), true);
} else if (annotation instanceof POST) {
parseHttpMethodAndPath("POST", ((POST) annotation).value(), true);
} else if (annotation instanceof PUT) {
parseHttpMethodAndPath("PUT", ((PUT) annotation).value(), true);
} else if (annotation instanceof OPTIONS) {
parseHttpMethodAndPath("OPTIONS", ((OPTIONS) annotation).value(), false);
} else if (annotation instanceof HTTP) {
HTTP http = (HTTP) annotation;
parseHttpMethodAndPath(http.method(), http.path(), http.hasBody());
} else if (annotation instanceof retrofit2.http.Headers) {
String[] headersToParse = ((retrofit2.http.Headers) annotation).value();
if (headersToParse.length == 0) {
throw methodError(method, "@Headers annotation is empty.");
}
headers = parseHeaders(headersToParse);
} else if (annotation instanceof Multipart) {
if (isFormEncoded) {
throw methodError(method, "Only one encoding annotation is allowed.");
}
isMultipart = true;
} else if (annotation instanceof FormUrlEncoded) {
if (isMultipart) {
throw methodError(method, "Only one encoding annotation is allowed.");
}
isFormEncoded = true;
}
}
...
}
这样就把如下注解的方法解析成一个GET请求，并且请求的地址根据参数cityId转换为"http:***/adat/sk/0124.html"等地址：
@GET("adat/sk/{cityId}.html")
Call<DataModel> loadWeatherInfo(@Path("cityId")String cityId);
那么这个返回值Call的泛型是在哪处理，答案是在解析完Annotations后：
static <ResponseT, ReturnT> HttpServiceMethod<ResponseT, ReturnT> parseAnnotations(
Retrofit retrofit, Method method, RequestFactory requestFactory) {
// 根据本文的分析，这里使用的CallAdapter是ExecutorCallAdapterFactory
CallAdapter<ResponseT, ReturnT> callAdapter = createCallAdapter(retrofit, method);
// 这里是泛型的实际类型，本文这里是DataModel
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);
}
private static <ResponseT, ReturnT> CallAdapter<ResponseT, ReturnT> createCallAdapter(
Retrofit retrofit, Method method) {
// 这里的retrunType就是方法的返回值 即Call<DataModel>
Type returnType = method.getGenericReturnType();
Annotation[] annotations = method.getAnnotations();
try {
//noinspection unchecked
return (CallAdapter<ResponseT, ReturnT>) retrofit.callAdapter(returnType, annotations);
} catch (RuntimeException e) { // Wide exception range because factories are user code.
throw methodError(method, e, "Unable to create call adapter for %s", returnType);
}
}
注意returnType很重要，之后有多处需要用到。
这一步就要开始涉及到CallAdapter，还记得在初始化的时候会有一个callAdapterFactories的列表吧，在这个时候就要派上用场了：
public CallAdapter<?, ?> callAdapter(Type returnType, Annotation[] annotations) {
return nextCallAdapter(null, returnType, annotations);
}
public CallAdapter<?, ?> nextCallAdapter(@Nullable CallAdapter.Factory skipPast, Type returnType,
Annotation[] annotations) {
checkNotNull(returnType, "returnType == null");
checkNotNull(annotations, "annotations == null");
int start = callAdapterFactories.indexOf(skipPast) + 1;
for (int i = start, count = callAdapterFactories.size(); i < count; i++) {
CallAdapter<?, ?> adapter = callAdapterFactories.get(i).get(returnType, annotations, this);
if (adapter != null) {
return adapter;
}
}
StringBuilder builder = new StringBuilder("Could not locate call adapter for ")
.append(returnType)
.append(".\n");
if (skipPast != null) {
builder.append(" Skipped:");
for (int i = 0; i < start; i++) {
builder.append("\n * ").append(callAdapterFactories.get(i).getClass().getName());
}
builder.append('\n');
}
builder.append(" Tried:");
for (int i = start, count = callAdapterFactories.size(); i < count; i++) {
builder.append("\n * ").append(callAdapterFactories.get(i).getClass().getName());
}
throw new IllegalArgumentException(builder.toString());
}
当我们没有addCallAdapterFactory时，Retrofit是如何处理的呢？
Executor callbackExecutor = this.callbackExecutor;
if (callbackExecutor == null) {
callbackExecutor = platform.defaultCallbackExecutor();
}
// Make a defensive copy of the adapters and add the default Call adapter.
List<CallAdapter.Factory> callAdapterFactories = new ArrayList<>(this.callAdapterFactories);
callAdapterFactories.addAll(platform.defaultCallAdapterFactories(callbackExecutor));
这里要注意参数callbackExecutor是Android的MainThreadExecutor：
static class Android extends Platform {
@IgnoreJRERequirement // Guarded by API check.
@Override boolean isDefaultMethod(Method method) {
if (Build.VERSION.SDK_INT < 24) {
return false;
}
return method.isDefault();
}
@Override public Executor defaultCallbackExecutor() {
return new MainThreadExecutor();
}
static class MainThreadExecutor implements Executor {
private final Handler handler = new Handler(Looper.getMainLooper());
@Override public void execute(Runnable r) {
handler.post(r);
}
}
...
}
List<? extends CallAdapter.Factory> defaultCallAdapterFactories(
@Nullable Executor callbackExecutor) {
if (callbackExecutor != null) {
return singletonList(new ExecutorCallAdapterFactory(callbackExecutor));
}
return singletonList(DefaultCallAdapterFactory.INSTANCE);
}
除了添加用户定义的callAdapter外，会默认添加defaultCallAdapter或者ExecutorCallAdapterFactory。
由于简书的字数限制，把分析放在了Retrofit2源码试读（二）中 。
3.结束语
比较简陋的把Retrofit的源码摸了一遍，了解了其中部分实现机制，发现确实解耦的比较好，目前只是初试Retrofit源码，有个框架上的认识而已，通过积累会完善这个系列。
Rxjava的分析会是下一步的计划，反正都是难啃的骨头，一起加油！文章的分析流程不确保完全正确，有分析的不对的地方欢迎指正。
