常用輪子之Okhttp基本使用及原理

jasonhww發表於2018-12-02

不忘初心砥礪前行, Tomorrow Is Another Day !

本文概要:

基本使用
基本原理

一. 基本使用

okhttp的請求和響應大多數採用建造者模式設計.

1. GET同步請求

public void syncGetRequest() {
        String url = "http://api.k780.com/?app=weather.future&weaid=1&&appkey=10003" +
                "&sign=b59bc3ef6191eb9f747dd4e83c99f2a4&format=json";
        final OkHttpClient okHttpClient = new OkHttpClient();
        final Request request = new Request.Builder()
                .get()
                .url(url)
                .build();
        new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    Response response = okHttpClient.newCall(request).execute();
                    Log.d(TAG, "syncGetRequest: " + response.body().string());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }).star
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2. GET非同步請求

public void asyncGetRequest() {
        String url = "http://api.k780.com/?app=weather.future&weaid=1&&appkey=10003" +
                "&sign=b59bc3ef6191eb9f747dd4e83c99f2a4&format=json";
        final OkHttpClient okHttpClient = new OkHttpClient();
        Request request = new Request.Builder()
                .get()
                .url(url)
                .build();
        okHttpClient.newCall(request).enqueue(new Callback() {
            @Override
            public void onFailure(Call call, IOException e) {

            }

            @Override
            public void onResponse(Call call, Response response) throws IOException {
                Log.d(TAG, "Callback-Thread: " + Thread.currentThread());
                String result = response.body().string();
                Log.d(TAG, "asyncGetRequest: " + result);
                //通過handler或者runOnUiThread方式切換執行緒.
                runOnUiThread(new Runnable() {
                    @Override
                    public void run() {
                        idtv.setText("jasonhww");
                    }
                });
                /*
                 *如果獲取的是檔案/圖片
                 */
                //方式一:通過獲取流
                //InputStream inputStream = response.body().byteStream();
                //方式二:通過獲取位元組陣列
                //byte[] bytes = response.body().bytes();
            }
        });
    }
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注意事項:

Callback的回撥方法是在子執行緒執行的,如需更新UI,可通過runjOnUiThread或者handler切換到主執行緒.

3. POST提交表單

可以使用FormBody.Builder構建一個表單請求體

  
    public void asyncPostForm(){
        String url = "http://api.k780.com/";
        final OkHttpClient okHttpClient = new OkHttpClient();
        //構建表單請求體
        RequestBody requestBody = new FormBody.Builder()
                .add("app","weather.future")
                .add("weaid","1")
                .add("appkey","10003")
                .add("sign","b59bc3ef6191eb9f747dd4e83c99f2a4")
                .add("format","json")
                .build();
        //建立POST請求
        Request request = new Request.Builder()
                .url(url)
                .post(requestBody)
                .build();
        okHttpClient.newCall(request).enqueue(new Callback() {
            @Override
            public void onFailure(Call call, IOException e) {

            }

            @Override
            public void onResponse(Call call, Response response) throws IOException {
                Log.d(TAG, "asyncPostForm: "+response.body().string());
            }
        });
    }
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4. POST提交JSON字串

指定請求體的媒體型別為"application/json"


    public void asyncJson() {
        String url = "http://api.k780.com/?app=weather.future&weaid=1&&appkey=10003" +
                "&sign=b59bc3ef6191eb9f747dd4e83c99f2a4&format=json";
        String json = "{code:1,result:null}";
        OkHttpClient okHttpClient = new OkHttpClient();
        //指定媒體型別
        MediaType mediaType = MediaType.parse("application/json,charset=utf-8");
        RequestBody requestBody = RequestBody.create(mediaType, json);
        Request request = new Request.Builder()
                .url(url)
                .post(requestBody)
                .build();
        okHttpClient.newCall(request).enqueue(new Callback() {
            @Override
            public void onFailure(Call call, IOException e) {

            }

            @Override
            public void onResponse(Call call, Response response) throws IOException {
                Log.d(TAG, "asyncJson: " + response.body().string());
            }
        });

    }

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5. 快取

快取使用相對比較簡單,只需指定一下快取目錄及大小即可.

 //虛擬碼
 Cache cache = new Cache(cacheDirectory,cacheSize);
 OkHttpClient okHttpClient = new OkHttpClient.Builder()
                      .cache(cache)
                      .build();
 
 
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6. 攔截器

通過攔截器我們可以很方便的去修改請求和響應的相關資訊,如修改請求頭,請求體等.

應用攔截器
攔截應用層與okhttp之間的請求和響應
網路攔截器
攔截okhttp與網路層之間的請求和響應,此時網路連線已經建立

public class LoggingInterceptor implements Interceptor {
    private static final String TAG = "LoggingInterceptor";

    @Override
    public Response intercept(Chain chain) throws IOException {
        //獲取請求
        Request request = chain.request();
        //列印url,連線狀態,請求頭
        Log.d(TAG, "LoggingInterceptor: url = " + request.url() +
                "\nconnectionStatus = " + chain.connection() +
                "\nrequestHeaderInfo = " + request.headers());
        //執行請求
        Response response = chain.proceed(request);
         //列印url,響應頭
        Log.d(TAG, "LoggingInterceptor: url = " + response.request() +
                "\nresponseHeaderInfo = " + response.headers());
        return response;
    }
}


public class NetInterceptor implements Interceptor {
    private static final String TAG = "LoggingInterceptor";

    @Override
    public Response intercept(Chain chain) throws IOException {
    
        Request request = chain.request();
        Response response = chain.proceed(request);
        //演示設定響應頭
        CacheControl.Builder builder = new CacheControl.Builder()  
        .maxAge(10,TimeUnit.MINUTES);
        return response.newBuilder()
                        .header("Cache-Control",builder.build().toString)
                        .build();
    }
}



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    public void asyncCacheInterceptor() {
        String url = "http://api.k780.com/?app=weather.future&weaid=1&&appkey=10003" +
                "&sign=b59bc3ef6191eb9f747dd4e83c99f2a4&format=json";
        OkHttpClient okHttpClient = new OkHttpClient.Builder()
                .addInterceptor(new LoggingInterceptor())//應用攔截
                .addNetworkInterceptor(new NetInterceptor())//網路攔截器
                .build();

        //通過攔截器修改請求頭
        Request request = new Request.Builder()
                .get()
                .header("user-Agent","Interceptor example")
                .url(url)
                .build();

        okHttpClient.newCall(request).enqueue(new Callback() {
            @Override
            public void onFailure(Call call, IOException e) {

            }

            @Override
            public void onResponse(Call call, Response response) throws IOException {
                Log.d(TAG, "asyncCacheInterceptor: " + response.body().string());
            }
        });
 
    }
    
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二. 基本原理

採用OkHttp原始碼版本為3.8.1

1. OkHttpClient的建立

OkHttpClient作為okhttp的入口,一般將OkHttpClient採用單例模式.
初始化兩種方式

採用直接"new"的方式
採用建造者模式

對應原始碼

//內部也是通過建造者進行初始化
OkHttpClient okhttpClient = new OkHttpClient();

OkHttpClient okhttpClient = new OkHttpClient.Builder()
                            .build();
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通過初始化okhttpclient,完成對許多成員變數的初始化工作.

對應原始碼

 OkHttpClient(Builder builder) {
    //分發器物件,記錄請求執行情況,內部維護一個執行緒池來執行非同步請求
    this.dispatcher = builder.dispatcher;
    this.proxy = builder.proxy;
    this.protocols = builder.protocols;
    this.connectionSpecs = builder.connectionSpecs;
    //應用攔截器集合
    this.interceptors = Util.immutableList(builder.interceptors);
    //網路攔截器集合
    this.networkInterceptors = Util.immutableList(builder.networkInterceptors);
    this.eventListenerFactory = builder.eventListenerFactory;
    this.proxySelector = builder.proxySelector;
    //Cookie瓶
    this.cookieJar = builder.cookieJar;
    //磁碟快取
    this.cache = builder.cache;
    this.internalCache = builder.internalCache;
    this.socketFactory = builder.socketFactory;
   
   //HTTPS相關成員變數初始化
    ......
    
    }
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2. Call的建立

當okhttpclient初始化後，再通過okHttpClient.newCall(request),建立一個Call物件,最終實際返回了一個RealCall物件.

對應原始碼

@Override public Call newCall(Request request) {
    
    return new RealCall(this, request, false /* for web socket */);
  }
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2.1 同步請求時

呼叫RealCall的execute方法

對應原始碼

  /**
   * 1. 首先看RealCall的execute方法.
   */
@Override public Response execute() throws IOException {
    synchronized (this) {
      if (executed) throw new IllegalStateException("Already Executed");
      executed = true;
    }
    captureCallStackTrace();
    try {
      //實際呼叫了分發器的executed方法,傳入RealCall物件.
      client.dispatcher().executed(this);
      //最終通過攔截器鏈獲取響應.
      //最終通過攔截器鏈獲取響應.
      //最終通過攔截器鏈獲取響應.
      //重要的話說三遍.
      Response result = getResponseWithInterceptorChain();
      if (result == null) throw new IOException("Canceled");
      return result;
    } finally {
      client.dispatcher().finished(this);
    }
  }
  
/**
 * 2. 接著看dispatcher的executed方法
 */
synchronized void executed(RealCall call) {
    //標識已經執行了請求
    runningSyncCalls.add(call);
  }
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2.1 非同步請求時

同樣呼叫RealCall的enqueue方法

對應原始碼

  /**
   * 1.首先看RealCall的enqueue方法.
   */
@Override public void enqueue(Callback responseCallback) {
    synchronized (this) {
      if (executed) throw new IllegalStateException("Already Executed");
      executed = true;
    }
    captureCallStackTrace();
    //實際呼叫了分發器的enqueue方法,傳入AsyncCall物件
    client.dispatcher().enqueue(new AsyncCall(responseCallback));
  }
  
  /**
   * 2.接著看dispatcher物件的enqueue方法.
   */
  synchronized void enqueue(AsyncCall call) {
    //檢測請求是否超過最大請求數和一個host對應最大的請求數
    if (runningAsyncCalls.size() < maxRequests && runningCallsForHost(call) < maxRequestsPerHost) {
      //標識已經執行了請求(這裡和同步方法一樣操作,可以對比上一點方法)
      runningAsyncCalls.add(call);
      //使用執行緒池執行請求
      executorService().execute(call);
    } else {
      readyAsyncCalls.add(call);
    }
  }
  
   /**
    * 3.最後我們看AsyncCall的實現.
    */
   //AsyncCall是RealCall的內部類,繼承自NamedRunnable
   //NamedRunnable的實現比較簡單就是修改執行緒名.提供一個execute方法在run用呼叫,這裡就不再曬出具體原始碼了.
   //AsyncCall的實現主是獲取響應,進行回撥.
   
   final class AsyncCall extends NamedRunnable {
    private final Callback responseCallback;

    //....省略部分程式碼
    
    @Override protected void execute() {
      boolean signalledCallback = false;
      try {
        //最終通過攔截器鏈獲取響應.
        //最終通過攔截器鏈獲取響應.
        //最終通過攔截器鏈獲取響應.
        //重要的話說三遍.
        Response response = getResponseWithInterceptorChain();
        if (retryAndFollowUpInterceptor.isCanceled()) {
          signalledCallback = true;
           //回撥失敗
          responseCallback.onFailure(RealCall.this, new IOException("Canceled"));
        } else {
          signalledCallback = true;
           //回撥成功
          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 {
         //回撥失敗
          responseCallback.onFailure(RealCall.this, e);
        }
      } finally {
        client.dispatcher().finished(this);
      }
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最後將Realcall對同步與非同步請求處理流程做個小結：

同步時.

呼叫RealCall的execute,實際呼叫了分發器的executed方法,傳入RealCall物件.

分發器的executed方法,僅僅標識已經執行了請求.

最終通過攔截器鏈獲取響應.

非同步時.

呼叫RealCall的enqueue,實際呼叫了分發器的enqueue方法,傳入AsyncCall物件.

分發器的executed方法,先檢查請求,滿足則標識已經執行了請求,最終使用執行緒池執行請求.不滿足則進人等待佇列

AsyncCall的實現

AsyncCall是一個NamedRunnable子類

通過攔截器鏈獲取響應,回撥成功與失敗.

3.攔截器鏈的構建與啟動

整個okhttp的核心設計之處

遵循單一原則,每個攔截器只做一項處理.
攔截器之間通過攔截器鏈(RealInterceptorChain)進行連線,構建出處理請求和響應的流水鏈.

請求通過層層攔截器處理，最後傳送出去,反之響應.

對應原始碼

 //通過攔截器鏈獲取響應
 Response getResponseWithInterceptorChain() throws IOException {
 
    /**
     * 初始化攔截器集合
     */
    List<Interceptor> interceptors = new ArrayList<>();
    //新增7種型別攔截器
    interceptors.addAll(client.interceptors());
    interceptors.add(retryAndFollowUpInterceptor);
    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));


    /**
     * 建立一個攔截器鏈
     /
    Interceptor.Chain chain = new 
    //第五個參數列示指向的攔截器位置,這裡指向了第一個.
    RealInterceptorChain(
        interceptors, null, null, null, 0, originalRequest);
    //啟動攔截器鏈
    return chain.proceed(originalRequest);
  }
  
  /**
   * 攔截器鏈的啟動
   */
    public Response proceed(Request request, StreamAllocation streamAllocation, HttpCodec httpCodec,
      RealConnection connection) throws IOException {
      
      //......省略部分程式碼
      
      
    // 建立一個新的攔截器鏈,攔截器位置指向將index+1.即下一個.
    
    RealInterceptorChain next = new RealInterceptorChain(
        interceptors, streamAllocation, httpCodec, connection, index + 1, request);
    
    //通過下標index獲取當前要執行的攔截器    
    Interceptor interceptor = interceptors.get(index);
    
    //執行攔截器intercept方法
    //如果當前攔截器執行完後,則呼叫傳入的next(新鏈物件)的proceed方法,執行下一個攔截器.依次類推.
    Response response = interceptor.intercept(next);

    
    if (httpCodec != null && index + 1 < interceptors.size() && next.calls != 1) {
      throw new IllegalStateException("network interceptor " + interceptor
          + " must call proceed() exactly once");
    }

   
    if (response == null) {
      throw new NullPointerException("interceptor " + interceptor + " returned null");
    }

    return response;
    }
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這7種攔截器執行順序為：

應用攔截器
retryAndFollowUpInterceptor
BridgeInterceptor
CacheInterceptor
ConnectInterceptor
網路攔截器
CallServerInterceptor

其中帶下劃線的攔截器，就是我們之前自定義的攔截器.接下來就依次講解7種攔截器的作用.

3.1 應用攔截器

不再講述

3.2 retryAndFollowUpInterceptor

處理錯誤重試和重定向

對應原始碼

@Override public Response intercept(Chain chain) throws IOException {
    Request request = chain.request();
    
    while (true) {
      if (canceled) {
        streamAllocation.release();
        throw new IOException("Canceled");
      }

      Response response = null;
      boolean releaseConnection = true;
      try {
        //執行下一個攔截器，獲取響應
        response = ((RealInterceptorChain) chain).proceed(request, streamAllocation, null, null);
        releaseConnection = false;
      } catch (RouteException e) {
        // The attempt to connect via a route failed. The request will not have been sent.
        if (!recover(e.getLastConnectException(), false, request)) {
          throw e.getLastConnectException();
        }
        releaseConnection = false;
        //滿足條件,則重試
        continue;
      } catch (IOException e) {
      // An attempt to communicate with a server failed. The request may have been sent.
        boolean requestSendStarted = !(e instanceof ConnectionShutdownException);
        if (!recover(e, requestSendStarted, request)) throw e;
        releaseConnection = false;
        //滿足條件,則重試
        continue;
      } finally {
        //出現異常釋放資源,continue在finally語句塊執行後才執行
        // We're throwing an unchecked exception. Release any resources.

        if (releaseConnection) {
          streamAllocation.streamFailed(null);
          streamAllocation.release();
        }
      }
      
     //檢測是否滿足定向的要求程式碼
     ......
     
      //重新賦值為重定向的請求
      request = followUp;
      priorResponse = response;
    }
  }
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3.3 BridgeInterceptor

橋接應用層和網路層

A. 將請求進行深加工,使其成為真正請求

對一些請求頭的設定

B. 並且也對網路響應做響應處理.

解壓縮,去掉不必要的響應頭

對應原始碼

@Override public Response intercept(Chain chain) throws IOException {
    //獲取請求
    Request userRequest = chain.request();
    Request.Builder requestBuilder = userRequest.newBuilder();
    //對一些請求頭的設定.
    RequestBody body = userRequest.body();
    if (body != null) {
      MediaType contentType = body.contentType();
      if (contentType != null) {
        requestBuilder.header("Content-Type", contentType.toString());
      }

      long contentLength = body.contentLength();
      if (contentLength != -1) {
        requestBuilder.header("Content-Length", Long.toString(contentLength));
        requestBuilder.removeHeader("Transfer-Encoding");
      } else {
        requestBuilder.header("Transfer-Encoding", "chunked");
        requestBuilder.removeHeader("Content-Length");
      }
    }

    if (userRequest.header("Host") == null) {
      requestBuilder.header("Host", hostHeader(userRequest.url(), false));
    }

    if (userRequest.header("Connection") == null) {
      requestBuilder.header("Connection", "Keep-Alive");
    }

    // If we add an "Accept-Encoding: gzip" header field we're responsible for also decompressing
    // the transfer stream.
    boolean transparentGzip = false;
    if (userRequest.header("Accept-Encoding") == null && userRequest.header("Range") == null) {
      transparentGzip = true;
      //如果沒有配置,預設配置gzip.獲取響應時需要解壓縮.
      requestBuilder.header("Accept-Encoding", "gzip");
    }

    List<Cookie> cookies = cookieJar.loadForRequest(userRequest.url());
    if (!cookies.isEmpty()) {
      requestBuilder.header("Cookie", cookieHeader(cookies));
    }

    if (userRequest.header("User-Agent") == null) {
      requestBuilder.header("User-Agent", Version.userAgent());
    }
    
    //執行下一個攔截器獲取響應
    Response networkResponse = chain.proceed(requestBuilder.build());

    HttpHeaders.receiveHeaders(cookieJar, userRequest.url(), networkResponse.headers());

    Response.Builder responseBuilder = networkResponse.newBuilder()
        .request(userRequest);

    if (transparentGzip
        && "gzip".equalsIgnoreCase(networkResponse.header("Content-Encoding"))
        && HttpHeaders.hasBody(networkResponse)) {
      //用於解壓縮
      GzipSource responseBody = new GzipSource(networkResponse.body().source());
      //返回應用層去掉不需要的響應頭
      Headers strippedHeaders = networkResponse.headers().newBuilder()
          .removeAll("Content-Encoding")
          .removeAll("Content-Length")
          .build();
      responseBuilder.headers(strippedHeaders);
      responseBuilder.body(new RealResponseBody(strippedHeaders, Okio.buffer(responseBody)));
    }

    return responseBuilder.build();
  }
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3.4 CacheInterceptor

承擔快取的查詢和儲存職責

A. 不需要網路請求,快取可用,直接返回

B. 快取不可用,執行下一個攔截器獲取響應;
如果使用者配置了需要快取,將響應寫入快取,並返回.

對應原始碼

 @Override
  public Response intercept(Chain chain) throws IOException {
    Response cacheCandidate = cache != null
        ? cache.get(chain.request())
        : null;

    long now = System.currentTimeMillis();
    //檢查快取策略
    CacheStrategy strategy = new CacheStrategy.Factory(now, chain.request(), cacheCandidate).get();
    //networkRequest不為空,需要傳送請求
    Request networkRequest = strategy.networkRequest;
    //cacheResponse不為空,則快取可用
    Response cacheResponse = strategy.cacheResponse;

   //......省略部分程式碼

    // If we don't need the network, we're done.
    //不需要網路請求,快取可用,直接返回
    if (networkRequest == null) {
      return cacheResponse.newBuilder()
          .cacheResponse(stripBody(cacheResponse))
          .build();
    }

    Response networkResponse = null;
    try {
      //快取不可用,執行下一個攔截器獲取響應
      networkResponse = chain.proceed(networkRequest);
    } finally {
      //......省略部分程式碼
    }
    //......省略部分程式碼
    
    //包裝網路響應
    Response response = networkResponse.newBuilder()
        .cacheResponse(stripBody(cacheResponse))
        .networkResponse(stripBody(networkResponse))
        .build();
    
    //使用者配置了快取
    if (cache != null) {
      //判斷條件
      if (HttpHeaders.hasBody(response) && CacheStrategy.isCacheable(response, networkRequest)) {
        // Offer this request to the cache.
        CacheRequest cacheRequest = cache.put(response);
        //網路響應寫入快取,並返回
        return cacheWritingResponse(cacheRequest, response);
      }

      if (HttpMethod.invalidatesCache(networkRequest.method())) {
        try {
          cache.remove(networkRequest);
        } catch (IOException ignored) {
          // The cache cannot be written.
        }
      }
    }

    return response;
  }
複製程式碼

3.5 ConnectInterceptor

給請求提供一個連線

TCP的連線,HTTPS的連線全部在此完成.

對應原始碼

 @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");
    //獲取HTTP編碼解碼器
    HttpCodec httpCodec = streamAllocation.newStream(client, doExtensiveHealthChecks);
    //獲取一個連結
    RealConnection connection = streamAllocation.connection();
    //執行下一個攔截器
    return realChain.proceed(request, streamAllocation, httpCodec, connection);
  }
複製程式碼

3.6 網路攔截器

不再講述

3.7 CallServerInterceptor

將請求傳送出去

對應原始碼

 @Override 
  public Response intercept(Chain chain) throws IOException {
   
    //.......省略部分程式碼
  
    //傳送網路請求,httpCodec則是在上一個ConnectInterceptor攔截器獲取到的
    httpCodec.finishRequest();

    if (responseBuilder == null) {
      responseBuilder = httpCodec.readResponseHeaders(false);
    }
    
    //構建網路響應物件
    Response response = responseBuilder
        .request(request)
        .handshake(streamAllocation.connection().handshake())
        .sentRequestAtMillis(sentRequestMillis)
        .receivedResponseAtMillis(System.currentTimeMillis())
        .build();

    int code = response.code();
    if (forWebSocket && code == 101) {
      // Connection is upgrading, but we need to ensure interceptors see a non-null response body.
      response = response.newBuilder()
          .body(Util.EMPTY_RESPONSE)
          .build();
    } else {
      //寫入響應體
      response = response.newBuilder()
          .body(httpCodec.openResponseBody(response))
          .build();
    }

    if ("close".equalsIgnoreCase(response.request().header("Connection"))
        || "close".equalsIgnoreCase(response.header("Connection"))) {
      streamAllocation.noNewStreams();
    }

    if ((code == 204 || code == 205) && response.body().contentLength() > 0) {
      throw new ProtocolException(
          "HTTP " + code + " had non-zero Content-Length: " + response.body().contentLength());
    }

    return response;
  }
複製程式碼

由於本人技術有限,如有錯誤的地方,麻煩大家給我提出來,本人不勝感激,大家一起學習進步.

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相關文章

一. 基本使用

1. GET同步請求

2. GET非同步請求

3. POST提交表單

4. POST提交JSON字串

5. 快取

6. 攔截器

二. 基本原理

1. OkHttpClient的建立

2. Call的建立

2.1 同步請求時

2.1 非同步請求時

3.攔截器鏈的構建與啟動

3.1 應用攔截器

3.2 retryAndFollowUpInterceptor

3.3 BridgeInterceptor

3.4 CacheInterceptor

3.5 ConnectInterceptor

3.6 網路攔截器

3.7 CallServerInterceptor

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