Retrofit是对网络请求实现了一套请求架构封装，屏蔽底层网络实现，使网络请求像调用本地接口一样
基本使用例子
public interface GitHubService {//定义request方法以及返回需要的response类型
@GET("users/{user}/repos")
List<Repo> listRepos(@Path("user") String user);
@GET("users/{user}/repos")
Call<List<Repo>> listRepos2(@Path("user") String user,Callback<List<Repo>> calback);
}
void usetest(){
static final String BASE_URL = "http://yourwebsite/services/";
Retrofit retrofit = new Retrofit.Builder()
.baseUrl(BASE_URL)
.addConverterFactory(GsonConverterFactory.create())//Response转换器，这里以GsonConvert为例
.addCallAdapterFactory(Java8CallAdapterFactory.create())//request处理Adapter
.build();
GitHubService service = retrofit.create(GitHubService.class);
// 直接调用
List<Repo> data = service.listRepos("user1");
// 异步callback方式
service.listRepos2("user2",new Callback<List<Repo>>() {
@Override
public void onResponse(Call<List<Repo>> call,
Response<List<Repo>> response) {
data=response.body();
}
@Override
public void onFailure(Call<List<Repo>> call, Throwable t) {
Log.e("error",t.getMessage());
}
});
}
调用流程
分析调用实现：首先从create开始
public <T> T create(final Class<T> service) {
Utils.validateServiceInterface(service);//校验service接口定义是否合法
if (validateEagerly) {
eagerlyValidateMethods(service);
}
return (T) Proxy.newProxyInstance(service.getClassLoader(), new Class<?>[] { service },//产生代理，实现对service接口调用
new InvocationHandler() {
private final Platform platform = Platform.get();
@Override public Object invoke(Object proxy, Method method, Object... args)
throws Throwable {
...
//每个接口最终转换为ServiceMethod,存储在serviceMethodCache中
ServiceMethod<Object, Object> serviceMethod =
(ServiceMethod<Object, Object>) loadServiceMethod(method);
//网络访问与okhttp结合生成OkHttpCall
OkHttpCall<Object> okHttpCall = new OkHttpCall<>(serviceMethod, args);
//发起请求，返回结果，解析返回
return serviceMethod.callAdapter.adapt(okHttpCall);
}
});
}
这里的OkHttpCall是Retrofit对自身Call接口实现，并不是okhttp3里的对象，通过实现接口内部封装okhttp3.Call，当然也可以替换其它网络库
看看call接口
public interface Call<T> extends Cloneable {
...
Response<T> execute() throws IOException;
...
void enqueue(Callback<T> callback);
...
boolean isExecuted();
...
void cancel();
/** The original HTTP request. */
Request request();
}
与okhttp里面call类似，只不过自身重新定义一下，降低耦合度
看看Okhttp3实现类
final class OkHttpCall<T> implements Call<T> {
private final ServiceMethod<T, ?> serviceMethod;
private final Object[] args;
private volatile boolean canceled;
// All guarded by this.
private okhttp3.Call rawCall;
private Throwable creationFailure; // Either a RuntimeException or IOException.
private boolean executed;
OkHttpCall(ServiceMethod<T, ?> serviceMethod, Object[] args) {
this.serviceMethod = serviceMethod;
this.args = args;
}
......
@Override public void enqueue(final Callback<T> callback) {//异步请求
if (callback == null) throw new NullPointerException("callback == null");
okhttp3.Call call;
Throwable failure;
synchronized (this) {
if (executed) throw new IllegalStateException("Already executed.");
executed = true;
...
if (failure != null) {
callback.onFailure(this, failure);
return;
}
if (canceled) {
call.cancel();
}
call.enqueue(new okhttp3.Callback() {
@Override public void onResponse(okhttp3.Call call, okhttp3.Response rawResponse)
throws IOException {
Response<T> response;
try {
response = parseResponse(rawResponse);//解析response
} catch (Throwable e) {
callFailure(e);
return;
}
callSuccess(response);
}
......
});
}
@Override public Response<T> execute() throws IOException {//同步调用请求
okhttp3.Call call;
synchronized (this) {
if (executed) throw new IllegalStateException("Already executed.");
executed = true;
......
call = rawCall;
if (call == null) {
try {
call = rawCall = createRawCall();
} catch (IOException | RuntimeException e) {
creationFailure = e;
throw e;
}
}
}
if (canceled) {
call.cancel();
}
return parseResponse(call.execute());//执行请求并解析
}
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;
}
Response<T> parseResponse(okhttp3.Response rawResponse) throws IOException {
ResponseBody rawBody = rawResponse.body();
// Remove the body's source (the only stateful object) so we can pass the response along.
rawResponse = rawResponse.newBuilder()
.body(new NoContentResponseBody(rawBody.contentType(), rawBody.contentLength()))
.build();
......
ExceptionCatchingRequestBody catchingBody = new ExceptionCatchingRequestBody(rawBody);
try {
T body = serviceMethod.toResponse(catchingBody);//调用指定的Convert对response进行泛型转换
return Response.success(body, rawResponse);
} catch (RuntimeException e) {
// If the underlying source threw an exception, propagate that rather than indicating it was
// a runtime exception.
catchingBody.throwIfCaught();
throw e;
}
}
convert最终调用来源Retrofit里的在builder里加入Converter.Factory
public <T> Converter<ResponseBody, T> nextResponseBodyConverter(Converter.Factory skipPast,
Type type, Annotation[] annotations) {
checkNotNull(type, "type == null");
checkNotNull(annotations, "annotations == null");
int start = converterFactories.indexOf(skipPast) + 1;
for (int i = start, count = converterFactories.size(); i < count; i++) {
Converter<ResponseBody, ?> converter =
converterFactories.get(i).responseBodyConverter(type, annotations, this);
if (converter != null) {
//noinspection unchecked
return (Converter<ResponseBody, T>) converter;
}
}
public Builder addConverterFactory(Converter.Factory factory) {
converterFactories.add(checkNotNull(factory, "factory == null"));
return this;
}
看看GsonResponseBodyConverter实现
final class GsonResponseBodyConverter<T> implements Converter<ResponseBody, T> {
private final Gson gson;
private final TypeAdapter<T> adapter;
GsonResponseBodyConverter(Gson gson, TypeAdapter<T> adapter) {
this.gson = gson;
this.adapter = adapter;
}
@Override public T convert(ResponseBody value) throws IOException {//通过TypeAdapter转换为对应实体类型T
JsonReader jsonReader = gson.newJsonReader(value.charStream());
try {
return adapter.read(jsonReader);
} finally {
value.close();
}
}
}
整理一下，Retrofit使用Jdk里的Proxy动态代理方式实现对接口方法调用，即当调用接口方法listRepos时，调用了Proxy中的invoke，将对应接口方法及注解封装为ServiceMethod对象，通过CallAdapter对OkHttpCall调用获取Response并将数据转换为T返回给调用者
Retrofit中build构建方法：
public Retrofit build() {
if (baseUrl == null) {
throw new IllegalStateException("Base URL required.");
}
okhttp3.Call.Factory callFactory = this.callFactory;
if (callFactory == null) {//检测网络请求client，如果没有指定则创建一个client
callFactory = new OkHttpClient();
}
Executor callbackExecutor = this.callbackExecutor;
if (callbackExecutor == null) {//回调执行callback的线程，如果没有指定则采用默认主线程
callbackExecutor = platform.defaultCallbackExecutor();
}
//CallAdapter指的是对request处理的CallAdapter，可以添加多个
List<CallAdapter.Factory> adapterFactories = new ArrayList<>(this.adapterFactories);
adapterFactories.add(platform.defaultCallAdapterFactory(callbackExecutor));
// Converter是对response执行转换处理返回的T,可以添加多个
List<Converter.Factory> converterFactories = new ArrayList<>(this.converterFactories);
return new Retrofit(callFactory, baseUrl, converterFactories, adapterFactories,
callbackExecutor, validateEagerly);
}
CallAdapter接口定义
public interface CallAdapter<R, T> {
//http 解析response 返回类型,不是咱接口定义泛型
Type responseType();
//处理response并转换为指定类型T
T adapt(Call<R> call);
//CallAdapter 创建获取
abstract class Factory {
/**
* Returns a call adapter for interface methods that return {@code returnType}, or null if it
* cannot be handled by this factory.
*根据接口返回类型，注解类型判断当前CallAdapter是否支持，不支持返回为null
*/
public abstract CallAdapter<?, ?> get(Type returnType, Annotation[] annotations,
Retrofit retrofit);
/**
* Extract the upper bound of the generic parameter at {@code index} from {@code type}. For
* example, index 1 of {@code Map<String, ? extends Runnable>} returns {@code Runnable}.
*获取指定index泛型参数上限，例如Map<String, ? extends Runnable> index为1参数上限为Runnable
*/
protected static Type getParameterUpperBound(int index, ParameterizedType type) {
return Utils.getParameterUpperBound(index, type);
}
/**
* Extract the raw class type from {@code type}. For example, the type representing
* {@code List<? extends Runnable>} returns {@code List.class}.
*/
//获取解析类型class，例如List<? extends Runnable>，返回List.class
protected static Class<?> getRawType(Type type) {
return Utils.getRawType(type);
}
}
项目中有三种实现
RxJava Observable & Single - com.squareup.retrofit2:adapter-rxjava
Guava ListenableFuture - com.squareup.retrofit2:adapter-guava
Java 8 CompleteableFuture - com.squareup.retrofit2:adapter-java8
看一下java8实现
Java8CallAdapterFactory
private static final class BodyCallAdapter<R> implements CallAdapter<R, CompletableFuture<R>> {
private final Type responseType;
BodyCallAdapter(Type responseType) {
this.responseType = responseType;
}
@Override public Type responseType() {
return responseType;
}
@Override public CompletableFuture<R> adapt(final Call<R> call) {
final CompletableFuture<R> future = new CompletableFuture<R>() {
@Override public boolean cancel(boolean mayInterruptIfRunning) {
if (mayInterruptIfRunning) {
call.cancel();
}
return super.cancel(mayInterruptIfRunning);
}
};
call.enqueue(new Callback<R>() {//调用okhttp Call方法异步调用
@Override public void onResponse(Call<R> call, Response<R> response) {
if (response.isSuccessful()) {
future.complete(response.body());
} else {
future.completeExceptionally(new HttpException(response));
}
}
@Override public void onFailure(Call<R> call, Throwable t) {
future.completeExceptionally(t);
}
});
return future;
}
}
到这里我们已取到数据结果，再看看转换如何实现ServiceMethod的toResponse
/** Builds a method return value from an HTTP response body. */
R toResponse(ResponseBody body) throws IOException {
return responseConverter.convert(body);
}
通过serviceMethod 中的Converter<ResponseBody, R> responseConverter;实现进行解析
Converter为转换接口，实现类有以下
Gson - com.squareup.retrofit2:converter-gson
Jackson - com.squareup.retrofit2:converter-jackson
Moshi - com.squareup.retrofit2:converter-moshi
Protobuf - com.squareup.retrofit2:converter-protobuf
Wire - com.squareup.retrofit2:converter-wire
Simple Framework - com.squareup.retrofit2:converter-simpleframework
Scalars - com.squareup.retrofit2:converter-scalars
当然也可以自定义实现Converter，定制出符合自己需求转换器
从上面分析看出Retorfit中的3个核心部分：
1，Proxy 代理实现接口调用
2，CallAdapters request网络t处理
3，Converters response解析转换对应泛型T返回数据结果