Retrofit.Builder()
看看new Retrofit.Builder()调用的代码
public Builder() {
this(Platform.get());
}
Platform.get()又是什么?抱着一贯的好奇,点进去看看。主要代码如下
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();
}
机智的你一定能看出来,主要就是这个findPlatform()方法。这里面的代码,就是判断当前运行的平台。可以看到里面有Android、Java8、IOS。等下,怎会有IOS,什么鬼(为什么会有IOS就交给你去研究了)。
我们在Android上运行的话,就调用了return new Android();。进一步往下看,Android()是什么
static class Android extends Platform {
@Override public Executor defaultCallbackExecutor() {
return new MainThreadExecutor();
}
@Override CallAdapter.Factory defaultCallAdapterFactory(Executor callbackExecutor) {
return new ExecutorCallAdapterFactory(callbackExecutor);
}
static class MainThreadExecutor implements Executor {
private final Handler handler = new Handler(Looper.getMainLooper());
@Override public void execute(Runnable r) {
handler.post(r);
}
}
}
他继承了Platform重写了defaultCallbackExecutor和defaultCallAdapterFactory方法。
defaultCallbackExecutor:返回的是用于执行 Callback 的 线程池。可以看到MainThreadExecutor 获取了主线程的 Looper 并构造了一个主线程的 Handler,调用 Callback 时会将该请求 post 到主线程上去执行。这就解释了为什么请求后完成的回调都是在主线中。
defaultCallAdapterFactory:将返回的适配类型默认为Call类型(如果使用RxJava的话,就可以通过配置.addCallAdapterFactory(RxJavaCallAdapterFactory.create())将配置类型改成Observable。)
public Builder baseUrl(String baseUrl) {
checkNotNull(baseUrl, "baseUrl == null");
HttpUrl httpUrl = HttpUrl.parse(baseUrl);
if (httpUrl == null) {
throw new IllegalArgumentException("Illegal URL: " + baseUrl);
}
return baseUrl(httpUrl);
}
public Builder baseUrl(HttpUrl baseUrl) {
checkNotNull(baseUrl, "baseUrl == null");
List pathSegments = baseUrl.pathSegments();
if (!"".equals(pathSegments.get(pathSegments.size() - 1))) {
throw new IllegalArgumentException("baseUrl must end in /: " + baseUrl);
}
this.baseUrl = baseUrl;
return this;
}
这里有两个重载的方法,创建了okhttp3 的 HttpUrl 实例。public Builder addConverterFactory(Converter.Factory factory) {
converterFactories.add(checkNotNull(factory, "factory == null"));
return this;
}
往转换工厂集合中添加了我们指定的转换工厂,最后将返回的数据类型转换成对应的实体类对象的Converter类型。在我们的例子里面 GsonConverterFactory 将选用 GsonConverter 来转换。.build();
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 adapterFactories = new ArrayList<>(this.adapterFactories);
adapterFactories.add(platform.defaultCallAdapterFactory(callbackExecutor));
// Make a defensive copy of the converters.
List converterFactories = new ArrayList<>(this.converterFactories);
return new Retrofit(callFactory, baseUrl, converterFactories, adapterFactories,
callbackExecutor, validateEagerly);
}
看最后一句
return new Retrofit(callFactory, baseUrl, converterFactories, adapterFactories,
callbackExecutor, validateEagerly);
这里才是创建Retrofit对象的地方,之前的只是一些配置。里面的参数:
callFactory(Call工厂):看到了吧callFactory = new OkHttpClient();,这里用的是okhttp3;
baseUrl(服务器基本地址):这个我们上面配置过;
converterFactories(对象的序列号/反序列化组件):我们上面配置过。
adapterFactories(适配类型)、callbackExecutor(执行 Callback 的线程池):从我们上面提到的platform中获取默认值。
validateEagerly(标识):先不说,后面会用到