okHttp3源码简要分析

首先看一下使用，

public static void main(String[] args) throws IOException {
	    OkHttpClient client = new OkHttpClient();  //创建client
        Request request = new Request.Builder().url("http://www.xxx.com")  
                .get().build();  //构建请求体
        Call call = client.newCall(request);//产生一个请求call  
         //同步请求
        Response response=call.execute();  
        System.out.println("result=:"+response.body().string());  
        //异步请求，enqueue方式  
        Call call2 = client.newCall(request);  
        call2.enqueue(new Callback() {            
			@Override
			public void onFailure(Call call, IOException e) {
				// TODO Auto-generated method stub
				
			}

			@Override
			public void onResponse(Call call, Response response)
					throws IOException {
				// TODO Auto-generated method stub
				
			}
        });  
	}

这里主要分为一下几个步骤：

Call对象分析：
从client.newCall(request)开始，client根据request创建请求Call，这个Call为一接口对象，真正实现的是RealCall

/**
   * Prepares the {@code request} to be executed at some point in the future.
   */
  @Override public Call newCall(Request request) {
    return new RealCall(this, request, false /* for web socket */);
  }

final class RealCall implements Call {
  final OkHttpClient client;
  final RetryAndFollowUpInterceptor retryAndFollowUpInterceptor;

  /** The application's original request unadulterated by redirects or auth headers. */
  final Request originalRequest;
  final boolean forWebSocket;

  // Guarded by this.
  private boolean executed;

  RealCall(OkHttpClient client, Request originalRequest, boolean forWebSocket) {
    this.client = client;
    this.originalRequest = originalRequest;
    this.forWebSocket = forWebSocket;
    this.retryAndFollowUpInterceptor = new RetryAndFollowUpInterceptor(client, forWebSocket);
  }
......

继续看一下excute实现，

 @Override public Response execute() throws IOException {
    synchronized (this) {//判断call是否执行过，可以看出每个Call对象只能使用一次原则
      if (executed) throw new IllegalStateException("Already Executed");
      executed = true;
    }
    captureCallStackTrace();
    try {
      client.dispatcher().executed(this);//把请求任务加入dispatcher任务调度器等待队列
      Response result = getResponseWithInterceptorChain();//使用拦截器处理response
      if (result == null) throw new IOException("Canceled");//调用cancel时，response为null
      return result;
    } finally {
      client.dispatcher().finished(this);
    }
  }

Dispatcher负责Request调度处理，我们看一下这个类实现

public final class Dispatcher {
  private int maxRequests = 64;
  private int maxRequestsPerHost = 5;
  private Runnable idleCallback;

  /** Executes calls. Created lazily. */
  private ExecutorService executorService;

  /** Ready async calls in the order they'll be run. */ //双端队列维护异步中等待执行任务
  private final Deque<AsyncCall> readyAsyncCalls = new ArrayDeque<>();

  /** Running asynchronous calls. Includes canceled calls that haven't finished yet. */
  private final Deque<AsyncCall> runningAsyncCalls = new ArrayDeque<>();//双端队列维护异步中正在运行中的任务

  /** Running synchronous calls. Includes canceled calls that haven't finished yet. */
  private final Deque<RealCall> runningSyncCalls = new ArrayDeque<>();//同步等待执行任务

  public Dispatcher(ExecutorService executorService) {//可以更换自定义的线程池
    this.executorService = executorService;
  }

  public Dispatcher() {
  }

  public synchronized ExecutorService executorService() {
    if (executorService == null) {//异步请求线程池，无上限，自动回收限制60s的线程，不对任务线程数量限制
      executorService = new ThreadPoolExecutor(0, Integer.MAX_VALUE, 60, TimeUnit.SECONDS,
          new SynchronousQueue<Runnable>(), Util.threadFactory("OkHttp Dispatcher", false));
    }
    return executorService;
  }
  
   /** Used by {@code Call#execute} to signal it is in-flight. */
  synchronized void executed(RealCall call) {//加入同步请求队列
    runningSyncCalls.add(call);
  }
  
   synchronized void enqueue(AsyncCall call) {//加入异步请求队列，最多64个请求，相同host请求为5个
    if (runningAsyncCalls.size() < maxRequests && runningCallsForHost(call) < maxRequestsPerHost) {
      runningAsyncCalls.add(call);
      executorService().execute(call);
    } else {//超过最大同时请求数量，则加入等待队列
      readyAsyncCalls.add(call);
    }
  }
  
   private <T> void finished(Deque<T> calls, T call, boolean promoteCalls) {
    ...
    synchronized (this) {//异步任务执行完成后，移除已经完成Call,调用加入等待执行任务到运行中的队列
      if (!calls.remove(call)) throw new AssertionError("Call wasn't in-flight!");
      if (promoteCalls) promoteCalls();
      runningCallsCount = runningCallsCount();
      idleCallback = this.idleCallback;
    }
...
  }
  
    private void promoteCalls() {//将等待执行的队列任务，放入执行的任务队列中，限制执行任务数量
    if (runningAsyncCalls.size() >= maxRequests) return; // Already running max capacity.
    if (readyAsyncCalls.isEmpty()) return; // No ready calls to promote.

    for (Iterator<AsyncCall> i = readyAsyncCalls.iterator(); i.hasNext(); ) {
      AsyncCall call = i.next();

      if (runningCallsForHost(call) < maxRequestsPerHost) {//相同host最多请求数量，可优化
        i.remove();
        runningAsyncCalls.add(call);
        executorService().execute(call);
      }

      if (runningAsyncCalls.size() >= maxRequests) return; // Reached max capacity.
    }
  }

AcyncCal为RealCall内部类，实现NamedRunnable，NamedRunnable为Runable实现，定义excute方法由run调用

final class AsyncCall extends NamedRunnable {
    ......
public abstract class NamedRunnable implements Runnable {
  protected final String name;

  public NamedRunnable(String format, Object... args) {
    this.name = Util.format(format, args);
  }

  @Override public final void run() {
    String oldName = Thread.currentThread().getName();
    Thread.currentThread().setName(name);
    try {
      execute();
    } finally {
      Thread.currentThread().setName(oldName);
    }
  }

  protected abstract void execute();

AsyncCal的excute实现：

@Override protected void execute() {
      boolean signalledCallback = false;
      try {
        Response response = getResponseWithInterceptorChain();//response拦截器实现，通过拦截器处理Response
        if (retryAndFollowUpInterceptor.isCanceled()) {//取消的任务调用onnfail
          signalledCallback = true;
          responseCallback.onFailure(RealCall.this, new IOException("Canceled"));
        } else {
          signalledCallback = true;
          responseCallback.onResponse(RealCall.this, response);
        }
      } catch (IOException e) {
        if (signalledCallback) {
          // Do not signal the callback twice!
          Platform.get().log(INFO, "Callback failure for " + toLoggableString(), e);
        } else {
          responseCallback.onFailure(RealCall.this, e);
        }
      } finally {
        client.dispatcher().finished(this);
      }
    }

因为excute在run里调用，所以这里的callback方法是在线程里回调的！！

Dispatcher处理流程：

强大的Interceptor：okhttp内部设计了Interceptor，使其设计更加灵活，使得每个request,response对其进行相关拦截与修改,

上面分析看出其实对网络处理是以Interceptor处理，那我们看一下Response result = getResponseWithInterceptorChain();

Response getResponseWithInterceptorChain() throws IOException {
    // Build a full stack of interceptors.
    List<Interceptor> interceptors = new ArrayList<>();
    interceptors.addAll(client.interceptors());
    interceptors.add(retryAndFollowUpInterceptor);//RetryAndFollowUpInterceptor 处理连接错误，重定向
    interceptors.add(new BridgeInterceptor(client.cookieJar()));//桥接应用层，网络层（请求头，cookie，encode）gzip处理
    interceptors.add(new CacheInterceptor(client.internalCache()));//Etag,Last-Modified请求头，缓存请求结果
    interceptors.add(new ConnectInterceptor(client));//打开网络连接处理
    if (!forWebSocket) {
      interceptors.addAll(client.networkInterceptors());
    }
    interceptors.add(new CallServerInterceptor(forWebSocket));//访问远端服务器 write read处理

    Interceptor.Chain chain = new RealInterceptorChain(
        interceptors, null, null, null, 0, originalRequest);
    return chain.proceed(originalRequest);
  }

由此可以看出OKHttp本身很多功能也是采用Interceptor按功能划分来处理
这里面涉及到设计模式FilterChain（责任链）过滤器来处理，整个请求过程通过递归调用由RealInterceptorChain的process()来完成，在每个Interceptor递归下一个Interceptor 直到最后返回RealInterceptorChain interceptor完成整个流程响应处理

public Response proceed(Request request, StreamAllocation streamAllocation, HttpCodec httpCodec,
      Connection connection) throws IOException {
    if (index >= interceptors.size()) throw new AssertionError();

    ......

    // Call the next interceptor in the chain.//每个Intercepter都是通过RealInterceptorChain封装后在进行调用下一个interceptor
    RealInterceptorChain next = new RealInterceptorChain(
        interceptors, streamAllocation, httpCodec, connection, index + 1, request);
    Interceptor interceptor = interceptors.get(index);
    Response response = interceptor.intercept(next);
    ......

    return response;
  }

 
Http connect连接处理 ，ConnectInterceptor负责处理server连接。

public final class ConnectInterceptor implements Interceptor {
 ...

  @Override public Response intercept(Chain chain) throws IOException {
    RealInterceptorChain realChain = (RealInterceptorChain) chain;
    Request request = realChain.request();
    StreamAllocation streamAllocation = realChain.streamAllocation();

    // We need the network to satisfy this request. Possibly for validating a conditional GET.
    boolean doExtensiveHealthChecks = !request.method().equals("GET");
//HttpCodechttp request编码，response解码处理
    HttpCodec httpCodec = streamAllocation.newStream(client, doExtensiveHealthChecks);
//一个请求连接
    RealConnection connection = streamAllocation.connection();

    return realChain.proceed(request, streamAllocation, httpCodec, connection);
  }
}

 StreamAllocation负责维护：连接(Connection)创建，取消，释放（Connection）内部使用ConnectionPool方式存取Connection

 ConnectionPool处理维护连接复用

public final class ConnectionPool {

  private static final Executor executor = new ThreadPoolExecutor(0 /* corePoolSize */,
      Integer.MAX_VALUE /* maximumPoolSize */, 60L /* keepAliveTime */, TimeUnit.SECONDS,
      new SynchronousQueue<Runnable>(), Util.threadFactory("OkHttp ConnectionPool", true));

  //最大连接数量
  private final int maxIdleConnections;
 //清理资源间隔
  private final long keepAliveDurationNs;
//清理资源执行任务
  private final Runnable cleanupRunnable = new Runnable() {
    @Override public void run() {
      while (true) {
        long waitNanos = cleanup(System.nanoTime());
        if (waitNanos == -1) return;
        if (waitNanos > 0) {
          long waitMillis = waitNanos / 1000000L;
          waitNanos -= (waitMillis * 1000000L);
          synchronized (ConnectionPool.this) {
            try {
              ConnectionPool.this.wait(waitMillis, (int) waitNanos);
            } catch (InterruptedException ignored) {
            }
          }
        }
      }
    }
  };

//双端队列存储connection
  private final Deque<RealConnection> connections = new ArrayDeque<>();
  final RouteDatabase routeDatabase = new RouteDatabase();
  boolean cleanupRunning;

 //默认为最多5个connection,每5min定时清理无用的连接资源
  public ConnectionPool() {
    this(5, 5, TimeUnit.MINUTES);
  }

  public ConnectionPool(int maxIdleConnections, long keepAliveDuration, TimeUnit timeUnit) {
    this.maxIdleConnections = maxIdleConnections;
    this.keepAliveDurationNs = timeUnit.toNanos(keepAliveDuration);

    // Put a floor on the keep alive duration, otherwise cleanup will spin loop.
    if (keepAliveDuration <= 0) {
      throw new IllegalArgumentException("keepAliveDuration <= 0: " + keepAliveDuration);
    }
  }

拦截器应用，看一下官方例子

OkHttpClient client = new OkHttpClient.Builder()
    .addInterceptor(new LoggingInterceptor())
    .build();
Request request = new Request.Builder()
    .url("http://www.publicobject.com/helloworld.txt")
    .header("User-Agent", "OkHttp Example")
    .build();

Response response = client.newCall(request).execute();

 class LoggingInterceptor implements Interceptor {
          @Override public Response intercept(Interceptor.Chain chain) throws IOException {
             //get request instance detail modify or add header and so on
            Request request = chain.request();

            long t1 = System.nanoTime();
            logger.info(String.format("Sending request %s on %s%n%s",
                request.url(), chain.connection(), request.headers()));

            //get response instance detail modify body and so on
            Response response = chain.proceed(request);

            long t2 = System.nanoTime();
            logger.info(String.format("Received response for %s in %.1fms%n%s",
                response.request().url(), (t2 - t1) / 1e6d, response.headers()));

            return response;
          }
        }

INFO: Sending request http://www.publicobject.com/helloworld.txt on null
User-Agent: OkHttp Example

INFO: Received response for https://publicobject.com/helloworld.txt in 1179.7ms
Server: nginx/1.4.6 (Ubuntu)
Content-Type: text/plain
Content-Length: 1759
Connection: keep-alive

通过一个拦截器很容易实现网络每个请求日志记录使用，可以看到拦截器可以对同一个request操作，也可以对Response进行处理既支持双向处理。

再来一个自己的实现

class MyIntercepter implements Interceptor {
		@Override
		public Response intercept(Chain chain) throws IOException {
			Response response = null;
			//指定debug下拦截指定的url 的response
			if (BuildConfig.DEBUG
					&& chain.request().url().uri().getPath()
							.equals("/api/id")) {
				// 这里读取我们需要返回的 Json 字符串
				String responseString = "{...}";
				//构建新的response
				response = new Response.Builder()
						.code(200)
						.message(responseString)
						.request(chain.request())
						.protocol(Protocol.HTTP_1_0)
						.body(ResponseBody.create(
								MediaType.parse("application/json"),
								responseString.getBytes()))
						.addHeader("content-type", "application/json").build();
			} else {
				response = chain.proceed(chain.request());
			}

			return response;
		}
	}

 
从例子可以看出拦截器强大与灵活。

okhttp中分为两种拦截方式，
1，Application Interceptors
2，Network Interceptors

 

上一个例子是Application Interceptors,修改为Network Interceptors后再看

OkHttpClient client = new OkHttpClient.Builder()
	    //.addInterceptor(new LoggingInterceptor())
	    .addNetworkInterceptor(new LoggingInterceptor())
	    .build();

INFO: Sending request http://www.publicobject.com/helloworld.txt on Connection{www.publicobject.com:80, proxy=DIRECT hostAddress=54.187.32.157 cipherSuite=none protocol=http/1.1}
User-Agent: OkHttp Example
Host: www.publicobject.com
Connection: Keep-Alive
Accept-Encoding: gzip

INFO: Received response for http://www.publicobject.com/helloworld.txt in 115.6ms
Server: nginx/1.4.6 (Ubuntu)
Content-Type: text/html
Content-Length: 193
Connection: keep-alive
Location: https://publicobject.com/helloworld.txt

INFO: Sending request https://publicobject.com/helloworld.txt on Connection{publicobject.com:443, proxy=DIRECT hostAddress=54.187.32.157 cipherSuite=TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA protocol=http/1.1}
User-Agent: OkHttp Example
Host: publicobject.com
Connection: Keep-Alive
Accept-Encoding: gzip

INFO: Received response for https://publicobject.com/helloworld.txt in 80.9ms
Server: nginx/1.4.6 (Ubuntu)
Content-Type: text/plain
Content-Length: 1759
Connection: keep-alive

这个是链接发生重定向日志结果，变为Network Interceptors时信息更全，网络中的具体情况redirect,retries等都会调用process(即多次执行process)

而Application Interceptors只会调用一次。

应用场景；通过intercepter我们可以更加方便灵活的方式实现不同方式，

修改header参数：

Request request = new Request.Builder()
    .url("https://api.github.com/repos/square/okhttp/issues")
    .header("User-Agent", "OkHttp Headers.java")
    .addHeader("Accept", "application/json; q=0.5")
    .addHeader("Accept", "application/vnd.github.v3+json")
    .build();

 
通过intercepter实现

public Response intercept(Interceptor.Chain chain) throws IOException {
        Request request = chain.request();
        Request newRequest;

        newRequest = request.newBuilder()
                .addHeader(HeadersContract.HEADER_AUTHONRIZATION, O_AUTH_AUTHENTICATION)
                .addHeader(HeadersContract.HEADER_X_CLIENT_ID, CLIENT_ID)
                .build();
        return chain.proceed(newRequest);
    }

 
可以看出intercepterer大大增加程序可扩展性，像插件一样可以方便特性，强大的组合功能

小结：

1，通过Intercepter实现实现功能划分处理，可扩展，自定义配置十分灵活

2，使用connectionPool实现连接复用，提高连接资源使用率

3，Dispatcher实现Request分发，维护请求队列，控制并行度

okhttp3结合okio request response读写操作，

private boolean bodyHasUnsupportedEncoding(Headers headers) {
        String contentEncoding = headers.get("Content-Encoding");
        return contentEncoding != null &&
                !contentEncoding.equalsIgnoreCase("identity") &&
                !contentEncoding.equalsIgnoreCase("gzip");
    }

    private boolean bodyGzipped(Headers headers) {
        String contentEncoding = headers.get("Content-Encoding");
        return "gzip".equalsIgnoreCase(contentEncoding);
    }

    private String readFromBuffer(Buffer buffer, Charset charset) {
        long bufferSize = buffer.size();
        long maxBytes = Math.min(bufferSize, maxContentLength);
        String body = "";
        try {
            body = buffer.readString(maxBytes, charset);
        } catch (EOFException e) {
            body += context.getString(R.string.chuck_body_unexpected_eof);
        }
        if (bufferSize > maxContentLength) {
            body += context.getString(R.string.chuck_body_content_truncated);
        }
        return body;
    }

    private BufferedSource getNativeSource(BufferedSource input, boolean isGzipped) {
        if (isGzipped) {
            GzipSource source = new GzipSource(input);
            return Okio.buffer(source);
        } else {
            return input;
        }
    }

    private BufferedSource getNativeSource(Response response) throws IOException {
        if (bodyGzipped(response.headers())) {
            BufferedSource source = response.peekBody(maxContentLength).source();
            if (source.buffer().size() < maxContentLength) {
                return getNativeSource(source, true);
            } else {
                Log.w(LOG_TAG, "gzip encoded response was too long");
            }
        }
        return response.body().source();
    }

 private static final Charset UTF8 = Charset.forName("UTF-8");
private long maxContentLength = 250000L;

/**
     * Returns true if the body in question probably contains human readable text. Uses a small sample
     * of code points to detect unicode control characters commonly used in binary file signatures.
     */
    private boolean isPlaintext(Buffer buffer) {
        try {
            Buffer prefix = new Buffer();
            long byteCount = buffer.size() < 64 ? buffer.size() : 64;
            buffer.copyTo(prefix, 0, byteCount);
            for (int i = 0; i < 16; i++) {
                if (prefix.exhausted()) {
                    break;
                }
                int codePoint = prefix.readUtf8CodePoint();
                if (Character.isISOControl(codePoint) && !Character.isWhitespace(codePoint)) {
                    return false;
                }
            }
            return true;
        } catch (EOFException e) {
            return false; // Truncated UTF-8 sequence.
        }
    }


ResponseBody responseBody = response.body();

        transaction.setRequestHeaders(response.request().headers()); // includes headers added later in the chain
        transaction.setResponseDate(new Date());
        transaction.setProtocol(response.protocol().toString());
        transaction.setResponseCode(response.code());
        transaction.setResponseMessage(response.message());

        transaction.setResponseContentLength(responseBody.contentLength());
        if (responseBody.contentType() != null) {
            transaction.setResponseContentType(responseBody.contentType().toString());
        }
        transaction.setResponseHeaders(response.headers());

        transaction.setResponseBodyIsPlainText(!bodyHasUnsupportedEncoding(response.headers()));
        if (HttpHeaders.hasBody(response) && transaction.responseBodyIsPlainText()) {
            BufferedSource source = getNativeSource(response);
            source.request(Long.MAX_VALUE);
            Buffer buffer = source.buffer();
            Charset charset = UTF8;
            MediaType contentType = responseBody.contentType();
            if (contentType != null) {
                try {
                    charset = contentType.charset(UTF8);
                } catch (UnsupportedCharsetException e) {
                    update(transaction, transactionUri);
                    return response;
                }
            }
            if (isPlaintext(buffer)) {
                transaction.setResponseBody(readFromBuffer(buffer.clone(), charset));
            } else {
                transaction.setResponseBodyIsPlainText(false);
            }
            transaction.setResponseContentLength(buffer.size());
        }