提醒：看博客的过程一定要自己点开源码，跟着一步步走，只看博客容易懵逼
一、自己对Retrofit的理解
Retrofit的中文翻译是改造，改造什么呢？
我认为是对OkHttp的使用、RxJava的使用进行改造。
具体体现在哪里？
在使用OkHttp请求前：
1.用注解统一配置网络请求头和请求参数
2.通过动态代理统一获取注解的请求头和请求参数然后一致组装适配成请求的request，交给okHttp进行请求
使用OkHttp结果返回后:
1.线程切换
线程切换分为两种一种是用Retrofit默认的，另一种是使用RxJava
2.把返回的数据json适配成javabean
简单总结，Retrofit就是为了让OkHttp、RxJava使用的更加简洁的一个封装
二、Retrofit的简单使用，没有添加RxJava
class RetrofitActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
//初始化一个Retrofit对象
val retrofit = Retrofit.Builder()
.baseUrl("https://api.github.com/")
.addConverterFactory(GsonConverterFactory.create())
.client(OkHttpClientProvider.client()) // 这个OkHttpClientProvider.client()是我自己封装的，就是简单提供一个OkHttpClient
.build()
//创建出GitHubApiService这个GitHubApiService的动态代理对象service
val service = retrofit.create(GitHubApiService::class.java)
//返回一个Okhttp的请求 Call 对象repos
val repos = service.listRepos("octocat")
//调用 enqueue 方法在回调方法里处理结果
repos.enqueue(object : Callback<List<Repo>?> {
override fun onFailure(call: Call<List<Repo>?>, t: Throwable) {
t.printStackTrace()
}
override fun onResponse(call: Call<List<Repo>?>, response: Response<List<Repo>?>) {
"response.code() = ${response.code()}".logE()
}
})
}
}
//自己定义的 API 请求接口
interface GitHubApiService {
@GET("users/{user}/repos")
fun listRepos(@Path("user") user: String?): Call<List<Repo>>
}三、请求前Retrofit所做的工作
1.以统一的方式为网络请求准备各种参数
(1).Retrofit的创建，把BaseUrl、OkHttpClient和Gson的实例保存在Retrofit对象中
Retrofit.Builder()的build()方法:
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> adapterFactories = new ArrayList<>(this.adapterFactories);
adapterFactories.add(platform.defaultCallAdapterFactory(callbackExecutor));
// Make a defensive copy of the converters.
List<Converter.Factory> converterFactories = new ArrayList<>(this.converterFactories);
return new Retrofit(callFactory, baseUrl, converterFactories, adapterFactories,
callbackExecutor, validateEagerly);
}首先看这个callFactory，因为我们已经.client(OkHttpClientProvider.client())方法设置了我们的okhttpclient，所以这里callFactory不为null:
public Builder client(OkHttpClient client) {
return callFactory(checkNotNull(client, "client == null"));
}
public Builder callFactory(okhttp3.Call.Factory factory) {
this.callFactory = checkNotNull(factory, "factory == null");
return this;
}我们没有添加CallbackExecutor(这个看名字就知道是用来处理返回值的)，所以这里用的是默认的:
? ? ? Executor callbackExecutor = this.callbackExecutor;
? ? ? if (callbackExecutor == null) {
? ? ? ? callbackExecutor = platform.defaultCallbackExecutor();
? ? ? }
记住这个CallbackExecutor，后面会用到
接下来重点看:
List<CallAdapter.Factory> adapterFactories = new ArrayList<>(this.adapterFactories); adapterFactories.add(platform.defaultCallAdapterFactory(callbackExecutor));
这个很重要，我们没有调用addCallAdapterFactory方法另外添加AdapterFactory，所以这里第一句的this.adapterFactories是一个空集合，之后调用add方法添加了一个默认的platform.defaultCallAdapterFactory(callbackExecutor)，这个很重要需要记住。
接下来把我们的Gson解析器添加到了converterFactories中
最后创建了Retrofit对象，把上面的对象都维护在了Retrofit中，这些都是网络请求需要的工具。
(2).用注解来表示请求头和请求的参数等
看一下注解的具体使用:
@GET("users/{user}/repos")
fun listRepos(@Path("user") user: String?): Call<List<Repo>>这个就是注解提供的请求方式、请求地址、请求参数等，这个是接口类中的一个方法，后面这个接口类会被动态代理来代理这个接口。
(3).用动态代理来把Retrofit和代理接口的方法上的请求信息，组装成一个OkHttp的请求
如果不知道动态代理本质的小伙伴点击传送门:
//创建出GitHubApiService这个GitHubApiService的动态代理对象service
val service = retrofit.create(GitHubApiService::class.java)
//返回一个Okhttp的请求 Call 对象repos
val repos = service.listRepos("octocat")看Retrofit的create方法:
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();
@Override public Object invoke(Object proxy, Method method, @Nullable Object[] args)
throws Throwable {
......
ServiceMethod<Object, Object> serviceMethod =
(ServiceMethod<Object, Object>) loadServiceMethod(method);
OkHttpCall<Object> okHttpCall = new OkHttpCall<>(serviceMethod, args);
return serviceMethod.callAdapter.adapt(okHttpCall);
}
});
}可以看到就是创建了一个动态代理，动态代理的作用就是代理类的任何一个方法的调用，都会走这个动态代理的invoke方法，即service.listRepos("octocat")的调用会走这个invoke方法。
下面我们具体分析，动态代理的invoke方法如何把各种请求的信息，组装成一个OkHttpCall的:
? ? ? ? ? ? ServiceMethod<Object, Object> serviceMethod =
? ? ? ? ? ? ? ? (ServiceMethod<Object, Object>) loadServiceMethod(method);
这个ServiceMethod是一个重点,它是真正执行把所有的请求信息，拼成一个Okhttp的请求Call的类:
ServiceMethod<?, ?> loadServiceMethod(Method method) {
ServiceMethod<?, ?> result = serviceMethodCache.get(method);
if (result != null) return result;
synchronized (serviceMethodCache) {
result = serviceMethodCache.get(method);
if (result == null) {
result = new ServiceMethod.Builder<>(this, method).build();
serviceMethodCache.put(method, result);
}
}
return result;
}?这里有一个缓存，serviceMethodCache是一个ConcurrentHashMap来缓存serviceMethod。
然后是ServiceMethod的创建，主要看build方法:
public ServiceMethod build() {
callAdapter = createCallAdapter();
responseType = callAdapter.responseType();
......
responseConverter = createResponseConverter();
for (Annotation annotation : methodAnnotations) {
parseMethodAnnotation(annotation);
}
......
int parameterCount = parameterAnnotationsArray.length;
parameterHandlers = new ParameterHandler<?>[parameterCount];
for (int p = 0; p < parameterCount; p++) {
Type parameterType = parameterTypes[p];
......
Annotation[] parameterAnnotations = parameterAnnotationsArray[p];
......
parameterHandlers[p] = parseParameter(p, parameterType, parameterAnnotations);
}
......
return new ServiceMethod<>(this);
}可以看出来，这里都在把之前的注解、请求参数、请求地址等解析出来，存到serviceMethod中:
ServiceMethod(Builder<R, T> builder) {
this.callFactory = builder.retrofit.callFactory();
this.callAdapter = builder.callAdapter;
this.baseUrl = builder.retrofit.baseUrl();
this.responseConverter = builder.responseConverter;
this.httpMethod = builder.httpMethod;
this.relativeUrl = builder.relativeUrl;
this.headers = builder.headers;
this.contentType = builder.contentType;
this.hasBody = builder.hasBody;
this.isFormEncoded = builder.isFormEncoded;
this.isMultipart = builder.isMultipart;
this.parameterHandlers = builder.parameterHandlers;
}这个ServiceMethod大家现在不用细看它，知道它是解析了我们之前统一用注解格式表示的请求信息，后保存在了自己serviceMethoed的对象中。后面用到的时候，大家自然能体会到。
然后回到动态代理的invoke方法:
OkHttpCall<Object> okHttpCall = new OkHttpCall<>(serviceMethod, args);
这个OkHttpCall就是具体发出请求的类，它持有serviceMethod，这里我们先不分析它，继续往下看:
return serviceMethod.callAdapter.adapt(okHttpCall);
这里就和我们调用的地方联系起来了，这个return的是一个okHttp的call:
//创建出GitHubApiService这个GitHubApiService的动态代理对象service
val service = retrofit.create(GitHubApiService::class.java)
//返回一个Okhttp的请求 Call 对象repos ???注意这里变化了
val repos = serviceMethod.callAdapter.adapt(okHttpCall)注意上面service.listRepos("octocat")等于动态代理调用invoke方法的返回值即:
serviceMethod.callAdapter.adapt(okHttpCall)
那我们重点分析:
serviceMethod.callAdapter.adapt(okHttpCall)
首先这个serviceMethod.callAdapter是什么:
callAdapter是在serviceMethod中的build方法中赋值的:
public ServiceMethod build() {
callAdapter = createCallAdapter();
......
}
private CallAdapter<T, R> createCallAdapter() {
......
try {
//noinspection unchecked
return (CallAdapter<T, R>) retrofit.callAdapter(returnType, annotations);
} catch (RuntimeException e) { // Wide exception range because factories are user code.
throw methodError(e, "Unable to create call adapter for %s", returnType);
}
}
public CallAdapter<?, ?> callAdapter(Type returnType, Annotation[] annotations) {
return nextCallAdapter(null, returnType, annotations);
}
public CallAdapter<?, ?> nextCallAdapter(@Nullable CallAdapter.Factory skipPast, Type returnType,
Annotation[] annotations) {
......
int start = adapterFactories.indexOf(skipPast) + 1;
for (int i = start, count = adapterFactories.size(); i < count; i++) {
CallAdapter<?, ?> adapter = adapterFactories.get(i).get(returnType, annotations, this);
if (adapter != null) {
return adapter;
}
}
......
}上面是整个callAdapter的调用链，最后是：
adapterFactories.get(i).get(returnType, annotations, this);
这句确定的CallAdapter:
adapterFactoris之前我们提到过要记住的，在Retrofit的build方法中:
List<CallAdapter.Factory> adapterFactories = new ArrayList<>(this.adapterFactories);
adapterFactories.add(platform.defaultCallAdapterFactory(callbackExecutor));上面分析了，adapterFactories中只有platform.defaultCallAdapterFactory(callbackExecutor)，这一个CallAdapter，adapterFactories.get(i)就是获取platform.defaultCallAdapterFactory(callbackExecutor)的。
接下来看platform.defaultCallAdapterFactory(callbackExecutor)是什么:
@Override CallAdapter.Factory defaultCallAdapterFactory(@Nullable Executor callbackExecutor) {
if (callbackExecutor == null) throw new AssertionError();
return new ExecutorCallAdapterFactory(callbackExecutor);
}所以我们得到结论，adapterFactories.get(i)是new ExecutorCallAdapterFactory(callbackExecutor)
?注意我们要的是adapterFactories.get(i).get(returnType, annotations, this)，所以我们要看ExecutorCallAdapterFactory的get方法:
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<Object, Call<?>>() {
@Override public Type responseType() {
return responseType;
}
@Override public Call<Object> adapt(Call<Object> call) {
return new ExecutorCallbackCall<>(callbackExecutor, call);
}
};
}?返回的是:
new CallAdapter<Object, Call<?>>() {
@Override public Type responseType() {
return responseType;
}
@Override public Call<Object> adapt(Call<Object> call) {
return new ExecutorCallbackCall<>(callbackExecutor, call);
}
};所以：
serviceMethod.callAdapter是adapterFactories.get(i).get(returnType, annotations, this)是上面这段代码new CallAdapter
?那我们要分析的serviceMethod.callAdapter.adapt(okHttpCall)，所以我们要的是new CallAdapter的adaptger方法:它返回的是new ExecutorCallbackCall<>(callbackExecutor, call)
这里要注意，这两个参数：
callbackExecutor是我们上面提到过的处理返回值的：
? ? ? Executor callbackExecutor = this.callbackExecutor;
? ? ? if (callbackExecutor == null) {
? ? ? ? callbackExecutor = platform.defaultCallbackExecutor();
? ? ? }
call是：
OkHttpCall<Object> okHttpCall = new OkHttpCall<>(serviceMethod, args);
好现在我们知道了:
//创建出GitHubApiService这个GitHubApiService的动态代理对象service
val service = retrofit.create(GitHubApiService::class.java)
//返回一个Okhttp的请求 Call 对象repos ???注意这里变化了
val repos = serviceMethod.callAdapter.adapt(okHttpCall)其实是：
//创建出GitHubApiService这个GitHubApiService的动态代理对象service
val service = retrofit.create(GitHubApiService::class.java)
//返回一个Okhttp的请求 Call 对象repos ???注意这里变化了
Call repos = new ExecutorCallbackCall<>(callbackExecutor, call)到这里我们分析了第三小节的题目：如何用动态代理来把Retrofit和代理接口的方法上的请求信息组装成一个OkHttp的请求
(4).发起请求的调用链细节
我们知道发起请求的代码:
val service = retrofit.create(GitHubApiService::class.java)
//返回一个Okhttp的请求 Call 对象repos
val repos = service.listRepos("octocat")
//调用 enqueue 方法在回调方法里处理结果
repos.enqueue(object : Callback<List<Repo>?> {
override fun onFailure(call: Call<List<Repo>?>, t: Throwable) {
t.printStackTrace()
}
override fun onResponse(call: Call<List<Repo>?>, response: Response<List<Repo>?>) {
"response.code() = ${response.code()}".logE()
}
})这里的repos已经分析了是ExecutorCallbackCall，调用的enqueue方法，接下来我们来看调用链ExecutorCallbackCall的enqueue方法：
final Executor callbackExecutor;
final Call<T> delegate;
ExecutorCallbackCall(Executor callbackExecutor, Call<T> delegate) {
this.callbackExecutor = callbackExecutor;
this.delegate = delegate;
}
@Override public void enqueue(final Callback<T> callback) {
checkNotNull(callback, "callback == null");
delegate.enqueue(new Callback<T>() {
@Override public void onResponse(Call<T> call, final Response<T> response) {
callbackExecutor.execute(new Runnable() {
@Override public void run() {
if (delegate.isCanceled()) {
// Emulate OkHttp's behavior of throwing/delivering an IOException on cancellation.
callback.onFailure(ExecutorCallbackCall.this, new IOException("Canceled"));
} else {
callback.onResponse(ExecutorCallbackCall.this, response);
}
}
});
}
@Override public void onFailure(Call<T> call, final Throwable t) {
callbackExecutor.execute(new Runnable() {
@Override public void run() {
callback.onFailure(ExecutorCallbackCall.this, t);
}
});
}
});
}首先我们已经知道构造方法的两个参数是什么:
delegate 是OkHttpCall
callbackExecutor是platform.defaultCallbackExecutor();
然后我们继续看delegate即OkHttpCall的enqueue方法（上面提到的掠过的OkhttpCall这里用到了）:
@Override public void enqueue(final Callback<T> callback) {
checkNotNull(callback, "callback == null");
okhttp3.Call call;
Throwable failure;
synchronized (this) {
if (executed) throw new IllegalStateException("Already executed.");
executed = true;
call = rawCall;
failure = creationFailure;
if (call == null && failure == null) {
try {
//?? 重点
call = rawCall = createRawCall();
} catch (Throwable t) {
failure = creationFailure = t;
}
}
}
if (failure != null) {
callback.onFailure(this, failure);
return;
}
if (canceled) {
call.cancel();
}
//?? 重点
call.enqueue(new okhttp3.Callback() {
@Override public void onResponse(okhttp3.Call call, okhttp3.Response rawResponse)
throws IOException {
Response<T> response;
try {
response = parseResponse(rawResponse);
} catch (Throwable e) {
callFailure(e);
return;
}
//?? 重点
callSuccess(response);
}
@Override public void onFailure(okhttp3.Call call, IOException e) {
try {
callback.onFailure(OkHttpCall.this, e);
} catch (Throwable t) {
t.printStackTrace();
}
}
private void callFailure(Throwable e) {
try {
callback.onFailure(OkHttpCall.this, e);
} catch (Throwable t) {
t.printStackTrace();
}
}
private void callSuccess(Response<T> response) {
try {
callback.onResponse(OkHttpCall.this, response);
} catch (Throwable t) {
t.printStackTrace();
}
}
});
}上面我们标记了三个重点:
1.第一个重点call = rawCall = createRawCall();
private okhttp3.Call createRawCall() throws IOException {
Request request = serviceMethod.toRequest(args);
okhttp3.Call call = serviceMethod.callFactory.newCall(request);
if (call == null) {
throw new NullPointerException("Call.Factory returned null.");
}
return call;
}这里用到了上面提到了serviceMethod，之前我们已经总结，它是保存了所有请求需要的信息和请求需要的工具，这里就要使用了:
? ? Request request = serviceMethod.toRequest(args);
? ? okhttp3.Call call = serviceMethod.callFactory.newCall(request);
就这两句，先把保存的请求头和参数等信息，拼凑成OkHttpClient需要的Request，然后调用serviceMethod.callFactory.newCall(request)，这个serviceMethod.callFactory就是我们之前设置的OkHttpClient，调用的它的newCall方法，得到一个OkHttp的Call请求对象，其实是RealCall对象
2.第二个重点call.enqueue(new okhttp3.Callback() {｝
?这是调用的OkHttpClient的enqueue方法，所以我们之前总结Retrofit就是对OkHttp请求之前和之后的工作的封装，使其有一致、简单、可复用等等。
3.第三个重点callSuccess(response);
private void callSuccess(Response<T> response) {
try {
callback.onResponse(OkHttpCall.this, response);
} catch (Throwable t) {
t.printStackTrace();
}
}callback.onResponse(OkHttpCall.this, response);，这个callback是之前delegate调用enqueue方法时的参数：
final Executor callbackExecutor;
final Call<T> delegate;
ExecutorCallbackCall(Executor callbackExecutor, Call<T> delegate) {
this.callbackExecutor = callbackExecutor;
this.delegate = delegate;
}
@Override public void enqueue(final Callback<T> callback) {
checkNotNull(callback, "callback == null");
delegate.enqueue(new Callback<T>() {
@Override public void onResponse(Call<T> call, final Response<T> response) {
callbackExecutor.execute(new Runnable() {
@Override public void run() {
if (delegate.isCanceled()) {
// Emulate OkHttp's behavior of throwing/delivering an IOException on cancellation.
callback.onFailure(ExecutorCallbackCall.this, new IOException("Canceled"));
} else {
callback.onResponse(ExecutorCallbackCall.this, response);
}
}
});
}
@Override public void onFailure(Call<T> call, final Throwable t) {
callbackExecutor.execute(new Runnable() {
@Override public void run() {
callback.onFailure(ExecutorCallbackCall.this, t);
}
});
}
});
}注意这个callback是delegate.enqueue方法的参数，不是外层enqueue方法的callback,所以这个回调执行的这个callback的onResponse方法代码:
callbackExecutor.execute(new Runnable() {
@Override public void run() {
if (delegate.isCanceled()) {
// Emulate OkHttp's behavior of throwing/delivering an IOException on cancellation.
callback.onFailure(ExecutorCallbackCall.this, new IOException("Canceled"));
} else {
callback.onResponse(ExecutorCallbackCall.this, response);
}
}
});callbackExecutor之前提到过是platform.defaultCallbackExecutor()：
@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);
}
}可以看到就是把Runnable来交给handler执行，实现的线程切换
?到这里发起请求的调用逻辑分析清楚了。