okhttp系列-拦截器的执行顺序

1.将拦截器添加到ArrayList

final class RealCall implements Call {
    Response getResponseWithInterceptorChain() throws IOException {
        //将Interceptor添加到ArrayList
        List interceptors = new ArrayList<>();
        interceptors.addAll(client.interceptors());
        interceptors.add(new RetryAndFollowUpInterceptor(client));
        interceptors.add(new BridgeInterceptor(client.cookieJar()));
        interceptors.add(new CacheInterceptor(client.internalCache()));
        interceptors.add(new ConnectInterceptor(client));
        if (!forWebSocket) {
            interceptors.addAll(client.networkInterceptors());
        }
        interceptors.add(new CallServerInterceptor(forWebSocket));

        //第一次的index为0
        Interceptor.Chain chain = new RealInterceptorChain(interceptors, transmitter, null, 
        0, originalRequest, this, client.connectTimeoutMillis(),
        client.readTimeoutMillis(), client.writeTimeoutMillis());

        //执行请求后，得到结果
        Response response = chain.proceed(originalRequest);
        return response;
    }
}

2.拦截器的执行-责任链模式

public final class RealInterceptorChain implements Interceptor.Chain {
    private final int index; //当前运行的Interceptor在ArrayList的索引

    public Response proceed(Request request, Transmitter transmitter, 
             @Nullable Exchange exchange)
      throws IOException {
        //每次index都基于上次的index +1，这样每次取得的就是下一个拦截器
        RealInterceptorChain next = new RealInterceptorChain(interceptors, transmitter, 
         exchange, index + 1, request, call, connectTimeout, readTimeout, writeTimeout);
        Interceptor interceptor = interceptors.get(index);
        //执行拦截器的方法的时候，携带了RealInterceptorChain作为参数，这样可以
        //调用这个chain的proceed
        Response response = interceptor.intercept(next);
        return response;
    }
}

3.总结

按照责任链模式执行拦截器

拦截器的执行顺序：

RetryAndFollowUpInterceptor：执行下一个拦截器，针对结果或者处理过程中的异常来进行重试或者重定向；

BridgeInterceptor：补充headers；执行下一个拦截器；处理返回的response；

CacheInterceptor：结果缓存，如果能用就返回缓存；如果不能用就执行下一个拦截器；

ConnectInterceptor：

CallServerInterceptor