.addInterceptor(logInterceptor)//日志拦截器，按照需要添加
.connectTimeout(10, TimeUnit.SECONDS).build();//连接超时时间
}
向外提供一个方法，用于获取刚才的API接口
private volatile static API aPI = null;
public static API createAPI() {
if (aPI == null) {
synchronized (RetrofitService.class) {
if (aPI == null) {
initOkHttpClient();
aPI = new Retrofit.Builder()
.client(mOkHttpClient)
.baseUrl(“服务器地址”)
.addConverterFactory(GsonConverterFactory.create())//指定json处理库
.build().create(API.class);//将第一步创建的API接口传入
}
}
}
return aPI;
}
3.开始发送请求
Call = call = RetrofitService.getInstance()
.createShowAPI()
.get(“参数1”, “参数2”);
call.enqueue(new Callback() {
@Override
public void onResponse(Call call, Response response) {
//请求成功的处理
}
@Override
public void onFailure(Call<ShowApiResponse> call, Throwable t) {
//请求失败的处理
}
});
Retrofit的核心-动态代理
Retrofit是如何将我们定义的接口方法最后转化成请求发送出去呢，这里就到源码去看看
创建者模式
首先来看Retrofit的创建，这里使用了创建者模式
new Retrofit.Builder()
.client(mOkHttpClient)
.baseUrl(“服务器地址”)
.addConverterFactory(GsonConverterFactory.create())//指定json处理库
.build().create(API.class);//将第一步创建的API接口传入
首先来看Retrofit.Builder()这个类的构造方法
public static final class Builder {
public Builder() {
this(Platform.get());
}
}
这里调用了一个带参数的构造方法，先看看Platform.get()是什么
private static final Platform PLATFORM = findPlatform();
static Platform get()
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{
return PLATFORM;
}
Platform.findPlatform
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) {
}
return new Platform();
}
可以看到，这个Platform类，顾名思义其实就是平台。在Retrofit中，内置了两种平台，一种是Android，一种是Java8。不同的平台，处理的方式不同。继续往下看代码就明白了
static class Android extends Platform {
@Override public Executor defaultCallbackExecutor() {
return new MainThreadExecutor();
}
@Override CallAdapter.Factory defaultCallAdapterFactory(@Nullable Executor callbackExecutor) {
if (callbackExecutor == null) throw new AssertionError();
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®;
}
}
}
这里先不深入探究，后面还会再回来，不过我们已经可以看到，Executor类在Android平台里是返回了MainThreadExecutor，里面提供了一个handler，并且这个handler是传入的主线程的Looper，也就是说在execute方法里面，handler.post实际上是在主线程（UI线程）执行的。
这里再回到Retrofit.Builder()，看看那个带参数的构造方法：
public Builder() {
this(Platform.get());
}
Builder(Retrofit retrofit) {
platform = Platform.get();
callFactory = retrofit.callFactory;
baseUrl = retrofit.baseUrl;
converterFactories.addAll(retrofit.converterFactories);
adapterFactories.addAll(retrofit.adapterFactories);
// Remove the default, platform-aware call adapter added by build().
adapterFactories.remove(adapterFactories.size() - 1);
callbackExecutor = retrofit.callbackExecutor;
validateEagerly = retrofit.validateEagerly;
}
在这个构造方法里，对各种属性进行了初始化，来看看这些属性的定义
private final Platform platform;//刚才看到的平台，这里是Android
private @Nullable okhttp3.Call.Factory callFactory;//后面在分析
private HttpUrl baseUrl;//服务器地址
private final List<Converter.Factory> converterFactories = new ArrayList<>();//json解析工厂列表
private final List<CallAdapter.Factory> adapterFactories = new ArrayList<>();//后面再分析
private @Nullable Executor callbackExecutor;//这里是Android的Executor，在主线程执行回调
private boolean validateEagerly;//是否提前创建的标志
挨个看看这几个属性，这里有些属性的作用我们后面才知道，不过大部分看命名已经可以看到一些蹊跷：主要是callFactory和adapterFactories我们现在暂时不知道作用，继续往下看，在构造方法初始化之后，是调用Builder.build()方法
Builder.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<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);
}
}
在这里是将Builder的属性，再传给Retrofit的构造方法，来看看我们刚才疑惑的那两个属性怎么赋值：
callFactory
okhttp3.Call.Factory callFactory = this.callFactory;
if (callFactory == null) {
callFactory = new OkHttpClient();
}
callFactory在默认的情况下，其实是一个OkHttpClient，也就是说Retrofit的内部请求原理其实是用的OkHttp。还记得我们最开始创建的时候也传入了一个静态类OkHttpClient么，这之间有什么关系呢？
new Retrofit.Builder().client(mOkHttpClient)
Retrofit.Builder().client
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;
}
其实client里面传入的OkHttpClient也是赋值给了callFactory，所以callFactory就是OkHttp的网络请求客户端
adapterFactories
// 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));
创建了一个新的列表，并且加入了默认的CallAdapterFactory，刚才我们知道platform是Android，所以再看看之前的代码：
Platform.Android
static class Android extends Platform {
@Override public Executor defaultCallbackExecutor() {
return new MainThreadExecutor();
}
@Override CallAdapter.Factory defaultCallAdapterFactory(@Nullable Executor callbackExecutor) {
if (callbackExecutor == null) throw new AssertionError();
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®;
}
}
}
defaultCallAdapterFactory返回的是ExecutorCallAdapterFactory
final class ExecutorCallAdapterFactory extends CallAdapter.Factory {
final Executor callbackExecutor;
ExecutorCallAdapterFactory(Executor callbackExecutor) {
this.callbackExecutor = callbackExecutor;
}
}
可以看到构造方法并没有做什么，只是将回调处理类传入。里面的其他方法后面调用的时候再来看。所以到这里我们还是不知道adapterFactories是干嘛的，但是我们看到了这个类里面有enqueue方法，还有一些处理响应的一些方法，所以我们可以知道它的作用是处理请求和响应，具体的用法后面继续看源码可以看到。
Retrofit.creat
在创建者初始化了所有属性之后，来到了Retrofit.creat方法
aPI = new Retrofit.Builder()
.client(mOkHttpClient)
.baseUrl(“服务器地址”)