Android进阶必学retrofit源码解析，最新Android面试合集

Call listRepos(&＃64;Path(“user”) String user);
}

创建Retrofit并生成API的实现

Retrofit retrofit &＃61; new Retrofit.Builder()
.baseUrl(“https://api.github.com/”)
.build();
GitHubService service &＃61; retrofit.create(GitHubService.class);

调用API方法&＃xff0c;生成Call

Call repos &＃61; service.listRepos(“octocat”);

Retrofit的创建

retrofit实例的创建&＃xff0c;使用了builder模式&＃xff0c;从下面的源码中可以看出

public static final class Builder {
Builder(Platform platform) {
this.platform &＃61; platform;
converterFactories.add(new BuiltInConverters());
}
public Builder() {
// Platform.get()方法可以用于判断当前的环境
this(Platform.get());
}
public Builder baseUrl(String baseUrl) {
checkNotNull(baseUrl, “baseUrl &＃61;&＃61; null”);
HttpUrl httpUrl &＃61; HttpUrl.parse(baseUrl);
if (httpUrl &＃61;&＃61; null) {
throw new IllegalArgumentException("Illegal URL: " &＃43; baseUrl);
}
return baseUrl(httpUrl);
}

public Retrofit build() {
if (baseUrl &＃61;&＃61; null) {
throw new IllegalStateException(“Base URL required.”);
}
okhttp3.Call.Factory callFactory &＃61; this.callFactory;
if (callFactory &＃61;&＃61; null) {
callFactory &＃61; new OkHttpClient();// 新建Client&＃xff0c;留到之后newCall什么的
}
Executor callbackExecutor &＃61; this.callbackExecutor;
if (callbackExecutor &＃61;&＃61; null) {
callbackExecutor &＃61; platform.defaultCallbackExecutor();
}
// Make a defensive copy of the adapters and add the default Call adapter.
List adapterFactories &＃61; new ArrayList<>(this.adapterFactories);
adapterFactories.add(platform.defaultCallAdapterFactory(callbackExecutor));
// Make a defensive copy of the converters.
List converterFactories &＃61; new ArrayList<>(this.converterFactories);
return new Retrofit(callFactory, baseUrl, converterFactories, adapterFactories,
callbackExecutor, validateEagerly);
}
}

retrofit.create

好玩的地方开始了&＃xff0c;我们先来看看这个方法

public T create(final Class service) {
Utils.validateServiceInterface(service);
if (validateEagerly) {
eagerlyValidateMethods(service);
}
// 动态代理&＃xff0c;啦啦啦
return (T) Proxy.newProxyInstance(service.getClassLoader(), new Class[] { service },
new InvocationHandler() {
// platform 可以分辨出你是在android&＃xff0c;还是java8&＃xff0c;又或者别的
private final Platform platform &＃61; Platform.get();
&＃64;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.
// 这里的invoke&＃xff0c;Object方法都走这里&＃xff0c;比如equals、toString、hashCode什么的
if (method.getDeclaringClass() &＃61;&＃61; Object.class) {
return method.invoke(this, args);
}
// java8默认方法&＃xff0c;1.8的新特性
if (platform.isDefaultMethod(method)) {
return platform.invokeDefaultMethod(method, service, proxy, args);
}
// 这里是核心代码了
ServiceMethod serviceMethod &＃61;
(ServiceMethod) loadServiceMethod(method);
OkHttpCall okHttpCall &＃61; new OkHttpCall<>(serviceMethod, args);
return serviceMethod.callAdapter.adapt(okHttpCall);
}
});
}

可以看出创建API使用了动态代理&＃xff0c;根据接口动态生成的代理类&＃xff0c;将接口的都转发给了负责连接代理类和委托类的InvocationHandler实例&＃xff0c;接口方法也都通过其invoke方法来处理。
在invoke方法中&＃xff0c;首先会通过Platform.get()方法判断出当前代码的执行环境&＃xff0c;之后会先把Object和Java8的默认方法进行一个处理&＃xff0c;也是在进行后续处理之前进行去噪。其中的关键代码其实就是最后三句&＃xff0c;这也是这篇文章将要分析的

创建ServiceMethod

erviceMethod loadServiceMethod(Method method) {
// 从缓存里面取出&＃xff0c;如果有的话&＃xff0c;直接返回好了
ServiceMethod result &＃61; serviceMethodCache.get(method);
if (result !&＃61; null) return result;
synchronized (serviceMethodCache) {
result &＃61; serviceMethodCache.get(method);
if (result &＃61;&＃61; null) {
// 为null的话&＃xff0c;解析方法的注解和返回类型、参数的注解he参数类型&＃xff0c;新建一个ServiceMethod
result &＃61; new ServiceMethod.Builder<>(this, method).build();// ->
// 新建的ServiceMethod加到缓存列表里面
serviceMethodCache.put(method, result);
}
}
return result;
}

注解的解析

CallAdapter和Converter等到后面再分析&＃xff0c;这里先看看parseMethodAnnotation(annotation)&＃xff0c;功能和其名字一样&＃xff0c;其对方法注解进行了解析

/**

• 解析方法注解&＃xff0c;呜啦啦
• 通过判断注解类型来解析
• &＃64;param annotation
  */
  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);
  }
  // 其他的一些方法注解的解析
  …
  }
  private void parseHttpMethodAndPath(String httpMethod, String value, boolean hasBody) {
  if (this.httpMethod !&＃61; null) {// 已经赋值过了
  throw methodError(“Only one HTTP method is allowed. Found: %s and %s.”,
  this.httpMethod, httpMethod);
  }
  this.httpMethod &＃61; httpMethod;
  this.hasBody &＃61; hasBody;
  // value为设置注解方法时候&＃xff0c;设置的值&＃xff0c;官方例子中的users/{user}/repos or user
  if (value.isEmpty()) {
  return;
  }
  // 查询条件的一些判断
  …
  this.relativeUrl &＃61; value;
  this.relativeUrlParamNames &＃61; parsePathParameters(value);
  }
  &＃96;

在解析注解时&＃xff0c;先通过instanceof判断出注解的类型&＃xff0c;之后调用parseHttpMethodAndPath方法解析注解参数值&＃xff0c;并设置httpMethod、relativeUrl、relativeUrlParamNames等属性。

上面说了API中方法注解的解析&＃xff0c;现在来看看方法参数注解的解析&＃xff0c;这是通过调用parseParameterAnnotation方法生成ParameterHandler实例来实现的&＃xff0c;代码比较多&＃xff0c;这里挑选&＃64;Query来看看。

else if (annotation instanceof Query) {
Query query &＃61; (Query) annotation;
String name &＃61; query.value();
boolean encoded &＃61; query.encoded();
Class rawParameterType &＃61; Utils.getRawType(type);// 返回基础的类
gotQuery &＃61; true;
// 可以迭代&＃xff0c;Collection
if (Iterable.class.isAssignableFrom(rawParameterType)) {
if (!(type instanceof ParameterizedType)) {
throw parameterError(p, rawParameterType.getSimpleName()

• " must include generic type (e.g., "
• rawParameterType.getSimpleName()
• “)”);
  }
  ParameterizedType parameterizedType &＃61; (ParameterizedType) type;
  Type iterableType &＃61; Utils.getParameterUpperBound(0, parameterizedType);// 返回基本类型
  Converter converter &＃61;
  retrofit.stringConverter(iterableType, annotations);
  return new ParameterHandler.Query<>(name, converter, encoded).iterable();
  } else if (rawParameterType.isArray()) {// Array
  Class arrayComponentType &＃61; boxIfPrimitive(rawParameterType.getComponentType());// 如果是基本类型&＃xff0c;自动装箱
  Converter converter &＃61;
  retrofit.stringConverter(arrayComponentType, annotations);
  return new ParameterHandler.Query<>(name, converter, encoded).array();
  } else {// Other
  Converter converter &＃61;
  retrofit.stringConverter(type, annotations);
  return new ParameterHandler.Query<>(name, converter, encoded);
  }

在&＃64;Query中&＃xff0c;将分成Collection、array、other三种情况处理参数&＃xff0c;之后根据这些参数&＃xff0c;调用ParameterHandler中的Query静态类&＃xff0c;创建出一个ParameterHandler实例。这样循环直到解析了所有的参数注解&＃xff0c;组合成为全局变量parameterHandlers&＃xff0c;之后构建请求时会用到

OkHttpCall

ServiceMethod创建完成之后&＃xff0c;我们来看看下一行代码中的OkHttpCall类&＃xff0c;里面的包含了请求的执行和响应处理&＃xff0c;我们来看看异步请求的做法

OkHttpCall(ServiceMethod serviceMethod, Object[] args) {
this.serviceMethod &＃61; serviceMethod;
this.args &＃61; args;
}
&＃64;Override public void enqueue(final Callback callback) {
checkNotNull(callback, “callback &＃61;&＃61; null”);
okhttp3.Call call;
Throwable failure;
synchronized (this) {
if (executed) throw new IllegalStateException(“Already executed.”);
executed &＃61; true;
call &＃61; rawCall;
failure &＃61; creationFailure;
if (call &＃61;&＃61; null && failure &＃61;&＃61; null) {
try {
call &＃61; rawCall &＃61; createRawCall();// 创建OkHttp3.Call
} catch (Throwable t) {
failure &＃61; creationFailure &＃61; t;
}
}
}
if (failure !&＃61; null) {
callback.onFailure(this, failure);
return;
}
if (canceled) {
call.cancel();
}
call.enqueue(new okhttp3.Callback() {

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