摘要：此前在例子中調(diào)用的，就是設(shè)置返回的數(shù)據(jù)支持轉(zhuǎn)換為對(duì)象。最終會(huì)返回配置好的類。注釋處遍歷方法來對(duì)請(qǐng)求方式比如和請(qǐng)求地址進(jìn)行解析。的方法主要做的就是用來請(qǐng)求網(wǎng)絡(luò)并將返回的進(jìn)行數(shù)據(jù)轉(zhuǎn)換并回調(diào)給線程。至此，的源碼就講到這里。
前言
最近文章的產(chǎn)出確實(shí)很少，因?yàn)槲艺趯懸槐続ndroid進(jìn)階書籍，兩頭很難兼顧，但是每個(gè)月也得至少發(fā)一篇博客。上一篇我們介紹了Retrofit的使用方法，這一篇我們照例來學(xué)習(xí)Retrofit的源碼。
1.Retrofit的創(chuàng)建過程
當(dāng)我們使用Retrofit請(qǐng)求網(wǎng)絡(luò)時(shí)，首先要寫請(qǐng)求接口：
public interface IpService {
@GET("getIpInfo.php?ip=59.108.54.37")
Call getIpMsg();
接著我們通過調(diào)用如下代碼來創(chuàng)建Retrofit：
Retrofit retrofit = new Retrofit.Builder()
.baseUrl(url)
.addConverterFactory(GsonConverterFactory.create())
.build();
Retrofit 是通過建造者模式構(gòu)建出來的，接下來查看Builder方法做了什么：
public Builder() {
this(Platform.get());
}
很簡(jiǎn)短，查看Platform的get方法，如下所示。
private static final Platform PLATFORM = findPlatform();
static Platform get() {
return PLATFORM;
}
private static Platform findPlatform() {
try {
Class.forName("android.os.Build");
if (Build.VERSION.SDK_INT != 0) {
return new Android();
}
} catch (ClassNotFoundException ignored) {
}
try {
Class.forName("java.util.Optional");
return new Java8();
} catch (ClassNotFoundException ignored) {
}
try {
Class.forName("org.robovm.apple.foundation.NSObject");
return new IOS();
} catch (ClassNotFoundException ignored) {
}
return new Platform();
}
Platform的get方法最終調(diào)用的是findPlatform方法，根據(jù)不同的運(yùn)行平臺(tái)來提供不同的線程池。接下來查看build方法，代碼如下所示。
public Retrofit build() {
if (baseUrl == null) {//1
throw new IllegalStateException("Base URL required.");
}
okhttp3.Call.Factory callFactory = this.callFactory;//2
if (callFactory == null) {
callFactory = new OkHttpClient();//3
}
Executor callbackExecutor = this.callbackExecutor;
if (callbackExecutor == null) {
callbackExecutor = platform.defaultCallbackExecutor();//4
}
List adapterFactories = new ArrayList<>(this.adapterFactories);//5
adapterFactories.add(platform.defaultCallAdapterFactory(callbackExecutor));
List converterFactories = new ArrayList<>(this.converterFactories);//6
return new Retrofit(callFactory, baseUrl, converterFactories, adapterFactories,
callbackExecutor, validateEagerly);
}
從注釋1處可以看出baseUrl 是必須指定的。注釋2處callFactory默認(rèn)為this.callFactory，this.callFactory就是我們?cè)跇?gòu)建Retrofit時(shí)調(diào)用callFactory方法所傳進(jìn)來的，如下所示。
public Builder callFactory(okhttp3.Call.Factory factory) {
this.callFactory = checkNotNull(factory, "factory == null");
return this;
}
因此，如果需要對(duì)OkHttpClient進(jìn)行設(shè)置，則可以構(gòu)建OkHttpClient對(duì)象，然后調(diào)用callFactory方法將設(shè)置好的OkHttpClient傳進(jìn)去。注釋3處，如果沒有設(shè)置callFactory則直接創(chuàng)建OkHttpClient。注釋4的callbackExecutor用來將回調(diào)傳遞到UI線程。注釋5的adapterFactories主要用于存儲(chǔ)對(duì)Call進(jìn)行轉(zhuǎn)化的對(duì)象，后面在Call的創(chuàng)建過程會(huì)再次提到它。注釋6處的converterFactories主要用于存儲(chǔ)轉(zhuǎn)化數(shù)據(jù)對(duì)象，后面也會(huì)提及到。此前在例子中調(diào)用的addConverterFactory(GsonConverterFactory.create())，就是設(shè)置返回的數(shù)據(jù)支持轉(zhuǎn)換為Gson對(duì)象。最終會(huì)返回配置好的Retrofit類。
2.Call的創(chuàng)建過程
緊接著我們創(chuàng)建Retrofit實(shí)例并調(diào)用如下代碼來生成接口的動(dòng)態(tài)代理對(duì)象：
IpService ipService = retrofit.create(IpService.class);
接下來看Retrofit的create方法做了什么，代碼如下所示。
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, 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 = loadServiceMethod(method);//1
OkHttpCall okHttpCall = new OkHttpCall<>(serviceMethod, args);
return serviceMethod.callAdapter.adapt(okHttpCall);
}
});
}
可以看到create方法返回了一個(gè)Proxy.newProxyInstance動(dòng)態(tài)代理對(duì)象，當(dāng)我們調(diào)用IpService的getIpMsg方法最終會(huì)調(diào)用InvocationHandler的invoke 方法，它有3個(gè)參數(shù)，第一個(gè)是代理對(duì)象，第二個(gè)是調(diào)用的方法，第三個(gè)是方法的參數(shù)。注釋1處的loadServiceMethod(method)中的method就是我們定義的getIpMsg方法。接下來查看loadServiceMethod方法里做了什么：
private final Map serviceMethodCache = new LinkedHashMap<>();
ServiceMethod loadServiceMethod(Method method) {
ServiceMethod result;
synchronized (serviceMethodCache) {
result = serviceMethodCache.get(method);
if (result == null) {
result = new ServiceMethod.Builder(this, method).build();
serviceMethodCache.put(method, result);
}
}
return result;
}
首先會(huì)從serviceMethodCache查詢傳入的方法是否有緩存，如果有就用緩存的ServiceMethod，如果沒有就創(chuàng)建一個(gè)，并加入serviceMethodCache緩存起來。接下來看ServiceMethod是如何構(gòu)建的，代碼如下所示。
public ServiceMethod build() {
callAdapter = createCallAdapter();//1
responseType = callAdapter.responseType();//2
if (responseType == Response.class || responseType == okhttp3.Response.class) {
throw methodError("""
+ Utils.getRawType(responseType).getName()
+ "" is not a valid response body type. Did you mean ResponseBody?");
}
responseConverter = createResponseConverter();//3
for (Annotation annotation : methodAnnotations) {
parseMethodAnnotation(annotation);//4
}
...
int parameterCount = parameterAnnotationsArray.length;
parameterHandlers = new ParameterHandler[parameterCount];
for (int p = 0; p < parameterCount; p++) {
Type parameterType = parameterTypes[p];
if (Utils.hasUnresolvableType(parameterType)) {
throw parameterError(p, "Parameter type must not include a type variable or wildcard: %s",
parameterType);
}
Annotation[] parameterAnnotations = parameterAnnotationsArray[p];//5
if (parameterAnnotations == null) {
throw parameterError(p, "No Retrofit annotation found.");
}
parameterHandlers[p] = parseParameter(p, parameterType, parameterAnnotations);
}
...
return new ServiceMethod<>(this);
}
注釋1處調(diào)用了createCallAdapter方法，它最終會(huì)得到我們?cè)跇?gòu)建Retrofit調(diào)用build方法時(shí)adapterFactories添加的對(duì)象的get方法，Retrofit的build方法部分代碼：
List adapterFactories = new ArrayList<>(this.adapterFactories);
adapterFactories.add(platform.defaultCallAdapterFactory(callbackExecutor));
adapterFactories列表默認(rèn)會(huì)添加defaultCallAdapterFactory，defaultCallAdapterFactory指的是ExecutorCallAdapterFactory，ExecutorCallAdapterFactory的get方法如下所示。
public CallAdapter> get(Type returnType, Annotation[] annotations, Retrofit retrofit) {
if (getRawType(returnType) != Call.class) {
return null;
}
final Type responseType = Utils.getCallResponseType(returnType);
return new CallAdapter>() {
@Override public Type responseType() {
return responseType;
}
@Override public Call adapt(Call call) {
return new ExecutorCallbackCall<>(callbackExecutor, call);
}
};
}
get方法會(huì)得到CallAdapter對(duì)象，它的responseType方法會(huì)返回?cái)?shù)據(jù)的真實(shí)類型，比如 Call，它就會(huì)返回IpModel。adapt方法會(huì)創(chuàng)建ExecutorCallbackCall，它會(huì)將call的回調(diào)轉(zhuǎn)發(fā)至UI線程。
接著回到ServiceMethod的 build方法，注釋2處調(diào)用CallAdapter的responseType得到的是返回?cái)?shù)據(jù)的真實(shí)類型。
注釋3處調(diào)用createResponseConverter方法來遍歷converterFactories列表中存儲(chǔ)的Converter.Factory，并返回一個(gè)合適的Converter用來轉(zhuǎn)換對(duì)象。此前我們?cè)跇?gòu)建Retrofit 調(diào)用了addConverterFactory(GsonConverterFactory.create())將GsonConverterFactory（Converter.Factory的子類）添加到converterFactories列表中，表示返回的數(shù)據(jù)支持轉(zhuǎn)換為Json對(duì)象。
注釋4處遍歷parseMethodAnnotation方法來對(duì)請(qǐng)求方式（比如GET、POST）和請(qǐng)求地址進(jìn)行解析。注釋5處對(duì)方法中的參數(shù)注解進(jìn)行解析（比如@Query、@Part）。最后創(chuàng)建ServiceMethod類并返回。
接下來回過頭來查看Retrofit的create方法，在調(diào)用了loadServiceMethod方法后會(huì)創(chuàng)建OkHttpCall，OkHttpCall的構(gòu)造函數(shù)只是進(jìn)行了賦值操作。緊接著調(diào)用serviceMethod.callAdapter.adapt(okHttpCall)，callAdapter的adapt方法前面講過，它會(huì)創(chuàng)建ExecutorCallbackCall，ExecutorCallbackCall的部分代碼如下所示。
ExecutorCallbackCall(Executor callbackExecutor, Call delegate) {
this.callbackExecutor = callbackExecutor;
this.delegate = delegate;
}
@Override public void enqueue(final Callback callback) {
if (callback == null) throw new NullPointerException("callback == null");
delegate.enqueue(new Callback() {//1
@Override public void onResponse(Call call, final Response response) {
callbackExecutor.execute(new Runnable() {
@Override public void run() {
if (delegate.isCanceled()) {
callback.onFailure(ExecutorCallbackCall.this, new IOException("Canceled"));
} else {
callback.onResponse(ExecutorCallbackCall.this, response);
}
}
});
}
@Override public void onFailure(Call call, final Throwable t) {
callbackExecutor.execute(new Runnable() {
@Override public void run() {
callback.onFailure(ExecutorCallbackCall.this, t);
}
});
}
});
}
可以看出ExecutorCallbackCall是對(duì)Call的封裝，它主要添加了通過callbackExecutor將請(qǐng)求回調(diào)到UI線程。
當(dāng)我們得到Call對(duì)象后會(huì)調(diào)用它的enqueue方法，其實(shí)調(diào)用的是ExecutorCallbackCall的enqueue方法，而從注釋1處可以看出ExecutorCallbackCall的enqueue方法最終調(diào)用的是delegate的enqueue方法。delegate從Retrofit的create方法的代碼中我們知道它其實(shí)就是OkHttpCall。
3.Call的enqueue方法
接下來我們就來查看OkHttpCall的enqueue方法，代碼如下所示。
public void enqueue(final Callback callback) {
if (callback == null) throw new NullPointerException("callback == null");
okhttp3.Call call;
...
call.enqueue(new okhttp3.Callback() {//1
@Override public void onResponse(okhttp3.Call call, okhttp3.Response rawResponse)
throws IOException {
Response response;
try {
response = parseResponse(rawResponse);//2
} catch (Throwable e) {
callFailure(e);
return;
}
callSuccess(response);
}
...
}
注釋1處調(diào)用了okhttp3.Call的enqueue方法。注釋2處調(diào)用parseResponse方法：
Response parseResponse(okhttp3.Response rawResponse) throws IOException {
ResponseBody rawBody = rawResponse.body();
...
int code = rawResponse.code();
if (code < 200 || code >= 300) {
try {
ResponseBody bufferedBody = Utils.buffer(rawBody);
return Response.error(bufferedBody, rawResponse);
} finally {
rawBody.close();
}
}
if (code == 204 || code == 205) {
return Response.success(null, rawResponse);
}
ExceptionCatchingRequestBody catchingBody = new ExceptionCatchingRequestBody(rawBody);
try {
T body = serviceMethod.toResponse(catchingBody);//2
return Response.success(body, rawResponse);
} catch (RuntimeException e) {
catchingBody.throwIfCaught();
throw e;
}
}
根據(jù)返回的不同的狀態(tài)碼code值來做不同的操作，如果順利則會(huì)調(diào)用注釋2處的代碼，接下來看toResponse方法里做了什么：
T toResponse(ResponseBody body) throws IOException {
return responseConverter.convert(body);
}
這個(gè)responseConverter就是此前講過在ServiceMethod的build方法調(diào)用createResponseConverter方法返回的Converter，在此前的例子中我們傳入的是GsonConverterFactory，因此可以查看GsonConverterFactory的代碼，如下所示。
public final class GsonConverterFactory extends Converter.Factory {
...
@Override
public Converter responseBodyConverter(Type type, Annotation[] annotations,
Retrofit retrofit) {
TypeAdapter adapter = gson.getAdapter(TypeToken.get(type));
return new GsonResponseBodyConverter<>(gson, adapter);
}
...
}
在GsonConverterFactory 中有一個(gè)方法responseBodyConverter，它最終會(huì)創(chuàng)建GsonResponseBodyConverter：
final class GsonResponseBodyConverter implements Converter {
private final Gson gson;
private final TypeAdapter adapter;
GsonResponseBodyConverter(Gson gson, TypeAdapter adapter) {
this.gson = gson;
this.adapter = adapter;
}
@Override public T convert(ResponseBody value) throws IOException {
JsonReader jsonReader = gson.newJsonReader(value.charStream());
try {
return adapter.read(jsonReader);
} finally {
value.close();
}
}
}
在GsonResponseBodyConverter的convert方法里會(huì)將回調(diào)的數(shù)據(jù)轉(zhuǎn)換為Json格式。因此我們也知道了此前調(diào)用responseConverter.convert是為了轉(zhuǎn)換為特定的數(shù)據(jù)格式。
Call的enqueue方法主要做的就是用OKHttp來請(qǐng)求網(wǎng)絡(luò)并將返回的Response進(jìn)行數(shù)據(jù)轉(zhuǎn)換并回調(diào)給UI線程。
至此，Retrofit的源碼就講到這里。
