retrofit的实现原理(二)
上篇文章我们已经了解了retrofit的RestAdapter adapter=new RestAdapter.Builder().setEndpoint(url).build()这段代码做了什么.
现在有下面一个接口,
interface SimplePOST{
@POST("/android")
Response getResponse();
}
这篇我们就来了解下 SimplePOST simplePost= adapter.create(SimplePOST.class)的内部逻辑.
public <T> T create(Class<T> service) {
Utils.validateServiceClass(service);
return (T) Proxy.newProxyInstance(service.getClassLoader(), new Class<?>[] { service }, //动态代理
new RestHandler(getMethodInfoCache(service)));
}
static <T> void validateServiceClass(Class<T> service) { //确保create()参数是一个接口类型,且这个接口没有继承其他的接口.(使用动态代理的前提)
if (!service.isInterface()) {
throw new IllegalArgumentException("Only interface endpoint definitions are supported.");
}
if (service.getInterfaces().length > 0) {
throw new IllegalArgumentException("Interface definitions must not extend other interfaces.");
}
}
可以发现adapter.create()方法的内部实现是利用动态代理生成了service接口的一个实现类. 根据动态代理的原理. 可以得知调用实现类的方法其实就是调用InvocationtHandler的对应方法.
这里简单介绍下动态代理.(关于动态代理的原理,可以参考其他博客的文章.)
委托类:被代理类即称为委托类. 一般不直接调用委托类的方法,而是通过代理类来间接调用.
假定有委托类A,通过动态代理生成了代理类B,生成的时候需要建立一个InvocationHandler H. 实际我们调用代理类B的方法时,方法内部调用的是H的invoke()方法. 而一般H的invoke方法会调用A的同名方法,这样就实现了代理类B功能.
虽然这里是运用了动态代理的技术.但是却和一般的动态代理不一样. 一般的动态代理的InvocationHandler应该通过构造函数中传入委托类A.然后在invoke方法中调用A的方法, 但这里是没有委托类的.只是利用动态代理自动生成接口的实现类.
因为java的动态代理是基于接口的,所以retrofit也要求用户自定义的也必须是一个接口.
注意invocationHandler的invoke()方法执行是在我们调用接口的方法的时候执行的.对于上面的代码就simplepost.getResponse()执行的时候.
private class RestHandler implements InvocationHandler {
private final Map<Method, RestMethodInfo> methodDetailsCache;
RestHandler(Map<Method, RestMethodInfo> methodDetailsCache) { //一般的动态代理.InvocationHandler构造函数一般要传入委托类.
this.methodDetailsCache = methodDetailsCache;
}
@SuppressWarnings("unchecked") //
@Override public Object invoke(Object proxy, Method method, final Object[] args) //动态代理的方法实现.调用委托类的方法,最终会调用invoke方法.
throws Throwable {
// If the method is a method from Object then defer to normal invocation.
if (method.getDeclaringClass() == Object.class) { //因为接口默认也继承Object.所以接口也有Object中的方法的. 如继承自Object如equals()方法
return method.invoke(this, args); //这里需要注意下,这里调用的是invocationHandler(H)的方法.一般的动态代理这里应该是调用委托类(A)的方法.
}
// Load or create the details cache for the current method.
final RestMethodInfo methodInfo = getMethodInfo(methodDetailsCache, method); //把method和RestMethodInfo缓存起来.防止重复解析method.(把方法的注解,返回值,同步异步等信息都解析出来储存在RestMethodInfo中.)
if (methodInfo.isSynchronous) { //同步的方式.
try {
return invokeRequest(requestInterceptor, methodInfo, args); //核心方法(网络访问). //可以看到retrofit的synchronous类型方法并不是子线程执行的. 所以在Android平台使用同步方式的retrofit的话要在子线程中.
} catch (RetrofitError error) {
Throwable newError = errorHandler.handleError(error);
if (newError == null) {
throw new IllegalStateException("Error handler returned null for wrapped exception.", //自定义的ErrorHandler的hanleError()方法不能return null.
error);
}
throw newError; //注意,同步的方式,当遇到错误的时候,会抛出一个RuntimeException.在Android下尽量不要使用同步的方式(因为RuntimeException是不提示用户主动捕捉的).
}
}
if (httpExecutor == null || callbackExecutor == null) {
throw new IllegalStateException("Asynchronous invocation requires calling setExecutors.");
}
if (methodInfo.isObservable) { //rx的方式
if (rxSupport == null) {
if (Platform.HAS_RX_JAVA) {
rxSupport = new RxSupport(httpExecutor, errorHandler, requestInterceptor);
} else {
throw new IllegalStateException("Observable method found but no RxJava on classpath.");
}
}
return rxSupport.createRequestObservable(new RxSupport.Invoker() {
@Override public ResponseWrapper invoke(RequestInterceptor requestInterceptor) {
return (ResponseWrapper) invokeRequest(requestInterceptor, methodInfo, args);
}
});
}
//同步, Observable方式都不是的话,肯定是异步的方式了.
// Apply the interceptor synchronously, recording the interception so we can replay it later.
// This way we still defer argument serialization to the background thread.
final RequestInterceptorTape interceptorTape = new RequestInterceptorTape();
requestInterceptor.intercept(interceptorTape);
Callback<?> callback = (Callback<?>) args[args.length - 1];
httpExecutor.execute(new CallbackRunnable(callback, callbackExecutor, errorHandler) { //可以看到在Android上异步方式是通过HttpExecutor执行的.是默认子线程执行的. 所以异步方式的retrofit不需要在子线程中执行.
@Override public ResponseWrapper obtainResponse() {
return (ResponseWrapper) invokeRequest(interceptorTape, methodInfo, args);
}
});
return null; // Asynchronous methods should have return type of void.
}
/**
* Execute an HTTP request.
*
* @return HTTP response object of specified {@code type} or {@code null}.
* @throws RetrofitError if any error occurs during the HTTP request.
*/
private Object invokeRequest(RequestInterceptor requestInterceptor, RestMethodInfo methodInfo,
Object[] args) {
String url = null;
try {
methodInfo.init(); // Ensure all relevant method information has been loaded. --->保证method的参数,返回值,注解都解析完成. 可以得到网络访问的url,header,query,访问方式等信息.
String serverUrl = server.getUrl();
RequestBuilder requestBuilder = new RequestBuilder(serverUrl, methodInfo, converter);
requestBuilder.setArguments(args);
requestInterceptor.intercept(requestBuilder); //在网络访问之前,执行拦截器的方法. 保证拦截器是最后起作用的.
Request request = requestBuilder.build();
url = request.getUrl();
if (!methodInfo.isSynchronous) {
// If we are executing asynchronously then update the current thread with a useful name.
int substrEnd = url.indexOf("?", serverUrl.length());
if (substrEnd == -1) {
substrEnd = url.length();
}
Thread.currentThread().setName(THREAD_PREFIX
+ url.substring(serverUrl.length(), substrEnd));
}
if (logLevel.log()) {
// Log the request data.
request = logAndReplaceRequest("HTTP", request, args);
}
Object profilerObject = null;
if (profiler != null) {
profilerObject = profiler.beforeCall();
}
long start = System.nanoTime();
Response response = clientProvider.get().execute(request); //调用okHttp或者其他Client进行网络访问.并把返回的数据封装进retrofit的Response中.
long elapsedTime = TimeUnit.NANOSECONDS.toMillis(System.nanoTime() - start);
int statusCode = response.getStatus(); //返回码
if (profiler != null) {
RequestInformation requestInfo = getRequestInfo(serverUrl, methodInfo, request);
//noinspection unchecked
profiler.afterCall(requestInfo, elapsedTime, statusCode, profilerObject);
}
if (logLevel.log()) {
// Log the response data.
response = logAndReplaceResponse(url, response, elapsedTime);
}
Type type = methodInfo.responseObjectType;
if (statusCode >= 200 && statusCode < 300) { // 2XX == successful request //返回码在200到300之间认为是一次成功的网络访问.
// Caller requested the raw Response object directly.
if (type.equals(Response.class)) { //如果方法的返回值类型(封装在responseObjectType)是retrofit的Response的话. 那就不用converter转换.
if (!methodInfo.isStreaming) {
// Read the entire stream and replace with one backed by a byte[].
response = Utils.readBodyToBytesIfNecessary(response);
}
if (methodInfo.isSynchronous) { //同步方式
return response;
}
return new ResponseWrapper(response, response); //异步的时候返回的是这个.
}
TypedInput body = response.getBody();
if (body == null) {
if (methodInfo.isSynchronous) { //① 结合下面的② ,返回值类型不同是因为invokeRequest()分别由2个不同的方法调用. ①是由 invoke()调用的.
return null;
}
return new ResponseWrapper(response, null); //② 的情况是异步的. 是由callBack模式中的obtainResponse()中调用的. 下面和上面的返回值类型不同的情况皆是如此
}
ExceptionCatchingTypedInput wrapped = new ExceptionCatchingTypedInput(body);
try {
Object convert = converter.fromBody(wrapped, type); //方法的返回值是非Response. 那么由Converter把Response转换成对应的类型.
logResponseBody(body, convert);
if (methodInfo.isSynchronous) {
return convert;
}
return new ResponseWrapper(response, convert);
} catch (ConversionException e) {
// If the underlying input stream threw an exception, propagate that rather than
// indicating that it was a conversion exception.
if (wrapped.threwException()) {
throw wrapped.getThrownException();
}
// The response body was partially read by the converter. Replace it with null.
response = Utils.replaceResponseBody(response, null);
throw RetrofitError.conversionError(url, response, converter, type, e);
}
}
response = Utils.readBodyToBytesIfNecessary(response);
throw RetrofitError.httpError(url, response, converter, type);
} catch (RetrofitError e) {
throw e; // Pass through our own errors.
} catch (IOException e) {
if (logLevel.log()) {
logException(e, url);
}
throw RetrofitError.networkError(url, e);
} catch (Throwable t) {
if (logLevel.log()) {
logException(t, url);
}
throw RetrofitError.unexpectedError(url, t);
} finally {
if (!methodInfo.isSynchronous) {
Thread.currentThread().setName(IDLE_THREAD_NAME);
}
}
}
}
对于上面的getMethodInfo()方法, 是把method信息提取出来,封装到RestMethodInfo中. 包括访问方式.Headers,path,参数,返回值等.
static RestMethodInfo getMethodInfo(Map<Method, RestMethodInfo> cache, Method method) {
synchronized (cache) {
RestMethodInfo methodInfo = cache.get(method);
if (methodInfo == null) { //经典的逻辑,如果缓存中有就从缓存中拿,如果没有,就生成一个新的,并且放到缓存中.
methodInfo = new RestMethodInfo(method);
cache.put(method, methodInfo);
}
return methodInfo;
}
}
RestMethodInfo
final class RestMethodInfo {
final Method method;
boolean loaded = false; //方法是否已经load过(解析过)
// Method-level details
final ResponseType responseType;
final boolean isSynchronous; //方法是同步还是异步.
final boolean isObservable;
Type responseObjectType;
RequestType requestType = RequestType.SIMPLE;
String requestMethod;
boolean requestHasBody;
String requestUrl;
Set<String> requestUrlParamNames;
String requestQuery;
List<retrofit.client.Header> headers;
String contentTypeHeader;
boolean isStreaming;
private enum ResponseType { //方法的返回值是什么类型
VOID, //void代表没有返回值,-->异步的方式
OBSERVABLE, //rxjava
OBJECT //方法的返回值是对象--->同步的方式
}
RestMethodInfo(Method method) {
this.method = method;
responseType = parseResponseType();
isSynchronous = (responseType == ResponseType.OBJECT);
isObservable = (responseType == ResponseType.OBSERVABLE);
}
private ResponseType parseResponseType() {
// Synchronous methods have a non-void return type. //同步的方法有一个非void的返回值
// Observable methods have a return type of Observable. //Observable的方法 返回值类型应该是Observable
Type returnType = method.getGenericReturnType();
// Asynchronous methods should have a Callback type as the last argument. //异步的方法最后一个方法的参数类型应该是Callback.
Type lastArgType = nul
Class<?> lastArgClass = null;
Type[] parameterTypes = method.getGenericParameterTypes();
if (parameterTypes.length > 0) {
Type typeToCheck = parameterTypes[parameterTypes.length - 1];
lastArgType = typeToCheck;
if (typeToCheck instanceof ParameterizedType) {
typeToCheck = ((ParameterizedType) typeToCheck).getRawType();
}
if (typeToCheck instanceof Class) {
lastArgClass = (Class<?>) typeToCheck;
}
}
boolean hasReturnType = returnType != void.class;
boolean hasCallback = lastArgClass != null && Callback.class.isAssignableFrom(lastArgClass); //如果有CallBack, CallBack只能是最后一个参数.
// Check for invalid configurations.
if (hasReturnType && hasCallback) { //返回值是非void类型和方法有CallBack参数有且只能有一个满足.
throw methodError("Must have return type or Callback as last argument, not both.");
}
if (!hasReturnType && !hasCallback) {
throw methodError("Must have either a return type or Callback as last argument.");
}
if (hasReturnType) {
if (Platform.HAS_RX_JAVA) {
Class rawReturnType = Types.getRawType(returnType);
if (RxSupport.isObservable(rawReturnType)) {
returnType = RxSupport.getObservableType(returnType, rawReturnType);
responseObjectType = getParameterUpperBound((ParameterizedType) returnType);
return ResponseType.OBSERVABLE;
}
}
responseObjectType = returnType;
return ResponseType.OBJECT;
}
lastArgType = Types.getSupertype(lastArgType, Types.getRawType(lastArgType), Callback.class);
if (lastArgType instanceof ParameterizedType) {
responseObjectType = getParameterUpperBound((ParameterizedType) lastArgType);
return ResponseType.VOID;
}
throw methodError("Last parameter must be of type Callback<X> or Callback<? super X>.");
}
private void parsePath(String path) { //解析路径 如GET(string),注意这里会对string进行判断,必须以"/"开头. 所以不能是空字符串,如""
...........
}
List<retrofit.client.Header> parseHeaders(String[] headers) { //解析Headers注解.
.....
}
private void parseParameters() { //解析方法参数,如方法参数的@Header, @Query等.
.......
}
private void parseMethodAnnotations() { //解析http方式.如GET(),POST()
.......
}
}
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