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发送简单请求

了解如何使用 Cronet 库在您的 Android 应用。Cronet 是作为库提供的 Chromium 网络堆栈供您在应用中使用如需详细了解库功能请参阅使用 Cronet。

在您的项目中设置库

要在您的项目中为 Cronet 库添加依赖项，请按以下步骤操作：

验证 Android Studio 是否包含对 Google Maven 制品库的引用在项目的 settings.gradle 文件中，如下所示示例：

Groovy

dependencyResolutionManagement {
   ...
   repositories {
       ...
       google()
   }
}

Kotlin

dependencyResolutionManagement {
   ...
   repositories {
       ...
       google()
   }
}

添加对适用于 Cronet 的 Google Play 服务客户端库的引用在应用模块的 build.gradle 文件的 dependencies 部分中，如下所示：如以下示例中所示：
Groovy
```
dependencies {
   implementation 'com.google.android.gms:play-services-cronet:18.0.1'
}
```
Kotlin
```
dependencies {
   implementation("com.google.android.gms:play-services-cronet:18.0.1")
}
```

创建过 CronetEngine 个对象依赖项时，将使用从 Google Play 服务加载的 Cronet。致电 CronetProviderInstaller.installProvider(Context) 然后再创建 CronetEngine 对象以防止意外异常因设备等错误而在 CronetEngine 创建期间抛出需要更新版本的 Google Play 服务。

如果无法从 Google Play 服务加载 Cronet，可以使用的 Cronet API 实现性能较差。要使用此后备实现，依赖于 org.chromium.net:cronet-fallback 然后调用 new JavaCronetProvider(context).createBuilder()。

创建网络请求

本部分介绍如何使用 Cronet 创建和发送网络请求影视库。发送网络请求后，您的应用应处理网络响应。

创建并配置 CronetEngine 的实例

该库提供了 CronetEngine.Builder 类您可以用它来创建 CronetEngine。以下示例展示了如何创建 CronetEngine 对象：

Kotlin

val myBuilder = CronetEngine.Builder(context)
val cronetEngine: CronetEngine = myBuilder.build()

Java

CronetEngine.Builder myBuilder = new CronetEngine.Builder(context);
CronetEngine cronetEngine = myBuilder.build();

您可以使用 Builder 类来配置 CronetEngine 对象，例如提供缓存和数据压缩等选项如需了解详情，请参阅 CronetEngine.Builder。

提供请求回调的实现

要提供回调的实现，请创建 UrlRequest.Callback和实现所需的抽象方法，如以下示例所示：

Kotlin

private const val TAG = "MyUrlRequestCallback"

class MyUrlRequestCallback : UrlRequest.Callback() {
    override fun onRedirectReceived(request: UrlRequest?, info: UrlResponseInfo?, newLocationUrl: String?) {
        Log.i(TAG, "onRedirectReceived method called.")
        // You should call the request.followRedirect() method to continue
        // processing the request.
        request?.followRedirect()
    }

    override fun onResponseStarted(request: UrlRequest?, info: UrlResponseInfo?) {
        Log.i(TAG, "onResponseStarted method called.")
        // You should call the request.read() method before the request can be
        // further processed. The following instruction provides a ByteBuffer object
        // with a capacity of 102400 bytes for the read() method. The same buffer
        // with data is passed to the onReadCompleted() method.
        request?.read(ByteBuffer.allocateDirect(102400))
    }

    override fun onReadCompleted(request: UrlRequest?, info: UrlResponseInfo?, byteBuffer: ByteBuffer?) {
        Log.i(TAG, "onReadCompleted method called.")
        // You should keep reading the request until there's no more data.
        byteBuffer.clear()
        request?.read(byteBuffer)
    }

    override fun onSucceeded(request: UrlRequest?, info: UrlResponseInfo?) {
        Log.i(TAG, "onSucceeded method called.")
    }
}

Java

class MyUrlRequestCallback extends UrlRequest.Callback {
  private static final String TAG = "MyUrlRequestCallback";

  @Override
  public void onRedirectReceived(UrlRequest request, UrlResponseInfo info, String newLocationUrl) {
    Log.i(TAG, "onRedirectReceived method called.");
    // You should call the request.followRedirect() method to continue
    // processing the request.
    request.followRedirect();
  }

  @Override
  public void onResponseStarted(UrlRequest request, UrlResponseInfo info) {
    Log.i(TAG, "onResponseStarted method called.");
    // You should call the request.read() method before the request can be
    // further processed. The following instruction provides a ByteBuffer object
    // with a capacity of 102400 bytes for the read() method. The same buffer
    // with data is passed to the onReadCompleted() method.
    request.read(ByteBuffer.allocateDirect(102400));
  }

  @Override
  public void onReadCompleted(UrlRequest request, UrlResponseInfo info, ByteBuffer byteBuffer) {
    Log.i(TAG, "onReadCompleted method called.");
    // You should keep reading the request until there's no more data.
    byteBuffer.clear();
    request.read(byteBuffer);
  }

  @Override
  public void onSucceeded(UrlRequest request, UrlResponseInfo info) {
    Log.i(TAG, "onSucceeded method called.");
  }
}

创建一个 Executor 对象来管理网络任务

您可以使用 Executor 类来执行网络任务。如需获取 Executor 的实例，请使用以下任一返回 Executors 类的静态方法 Executor 对象。以下示例展示了如何创建 Executor 对象（使用 newSingleThreadExecutor()）方法：

Kotlin

val executor: Executor = Executors.newSingleThreadExecutor()

Java

Executor executor = Executors.newSingleThreadExecutor();

创建并配置 UrlRequest 对象

要创建网络请求，请调用 newUrlRequestBuilder() CronetEngine 的相应方法，用于传递目标网址、回调类的实例以及执行器对象。 newUrlRequestBuilder() 方法会返回一个 UrlRequest.Builder 对象，可用于创建 UrlRequest，对象，如以下示例所示：

Kotlin

val requestBuilder = cronetEngine.newUrlRequestBuilder(
        "https://www.example.com",
        MyUrlRequestCallback(),
        executor
)

val request: UrlRequest = requestBuilder.build()

Java

UrlRequest.Builder requestBuilder = cronetEngine.newUrlRequestBuilder(
        "https://www.example.com", new MyUrlRequestCallback(), executor);

UrlRequest request = requestBuilder.build();

您可以使用 Builder 类执行以下操作：配置 UrlRequest 的实例。对于例如，您可以指定优先级或 HTTP 动词如需了解详情，请参阅 UrlRequest.Builder。

要启动网络任务，请调用 start() 方法：

Kotlin

request.start()

Java

request.start();

您可以按照本部分中的说明创建和发送网络使用 Cronet 请求。不过，为简单起见，此示例实施只有 UrlRequest.Callback 可打印向日志发送一条消息。以下部分介绍了如何提供回调一种更实用的实现方式，响应并检测请求失败的情况。

处理网络响应

调用 start() 之后，方法，便会启动 Cronet 请求生命周期。您的应用应管理请求。如需详细了解请参阅 Cronet 请求生命周期。您可以指定通过创建 UrlRequest.Callback和实现以下方法：

onRedirectReceived()

在服务器发出 HTTP 重定向代码以响应原始请求。要按照重定向到达新的目的地，请使用 followRedirect() 方法。否则，请使用 cancel() 方法。以下示例展示了如何实现该方法：

Kotlin

override fun onRedirectReceived(request: UrlRequest?, info: UrlResponseInfo?, newLocationUrl: String?) {
  // Determine whether you want to follow the redirect.
  ...

  if (shouldFollow) {
      request?.followRedirect()
  } else {
      request?.cancel()
  }
}

Java

@Override
public void onRedirectReceived(UrlRequest request, UrlResponseInfo info, String newLocationUrl) {
  // Determine whether you want to follow the redirect.
  …

  if (shouldFollow) {
    request.followRedirect();
  } else {
    request.cancel();
  }
}

onResponseStarted()

在收到最后一组标头时调用。onResponseStarted() 方法仅在遵循所有重定向后调用。以下代码显示了该方法的示例实现：

Kotlin

override fun onResponseStarted(request: UrlRequest?, info: UrlResponseInfo?) {
  val httpStatusCode = info?.httpStatusCode
  if (httpStatusCode == 200) {
    // The request was fulfilled. Start reading the response.
    request?.read(myBuffer)
  } else if (httpStatusCode == 503) {
    // The service is unavailable. You should still check if the request
    // contains some data.
    request?.read(myBuffer)
  }
  responseHeaders = info?.allHeaders
}

Java

@Override
public void onResponseStarted(UrlRequest request, UrlResponseInfo info) {
  int httpStatusCode = info.getHttpStatusCode();
  if (httpStatusCode == 200) {
    // The request was fulfilled. Start reading the response.
    request.read(myBuffer);
  } else if (httpStatusCode == 503) {
    // The service is unavailable. You should still check if the request
    // contains some data.
    request.read(myBuffer);
  }
  responseHeaders = info.getAllHeaders();
}

onReadCompleted()

在读取部分响应正文后调用。以下代码示例显示了如何实现方法并提取响应正文：

Kotlin

override fun onReadCompleted(request: UrlRequest?, info: UrlResponseInfo?, byteBuffer: ByteBuffer?) {
  // The response body is available, process byteBuffer.
  ...

  // Continue reading the response body by reusing the same buffer
  // until the response has been completed.
  byteBuffer?.clear()
  request?.read(myBuffer)
}

Java

@Override
public void onReadCompleted(UrlRequest request, UrlResponseInfo info, ByteBuffer byteBuffer) {
  // The response body is available, process byteBuffer.
  …

  // Continue reading the response body by reusing the same buffer
  // until the response has been completed.
  byteBuffer.clear();
  request.read(myBuffer);
}

onSucceeded()

在网络请求成功完成后调用。以下示例显示了如何实现该方法：

Kotlin

override fun onSucceeded(request: UrlRequest?, info: UrlResponseInfo?) {
    // The request has completed successfully.
}

Java

@Override
public void onSucceeded(UrlRequest request, UrlResponseInfo info) {
  // The request has completed successfully.
}

onFailed()

如果请求由于在调用了 start() 方法。通过以下示例展示了如何实现该方法并获取错误：

Kotlin

override fun onFailed(request: UrlRequest?, info: UrlResponseInfo?, error: CronetException?) {
    // The request has failed. If possible, handle the error.
    Log.e(TAG, "The request failed.", error)
}

Java

@Override
public void onFailed(UrlRequest request, UrlResponseInfo info, CronetException error) {
  // The request has failed. If possible, handle the error.
  Log.e(TAG, "The request failed.", error);
}

onCanceled()

如果使用 cancel() 方法。调用之后，不会其他方法 UrlRequest.Callback 类调用。您可以使用此方法释放分配给处理请求。以下示例展示了如何实现该方法：

Kotlin

override fun onCanceled(request: UrlRequest?, info: UrlResponseInfo?) {
    // Free resources allocated to process this request.
    ...
}

Java

@Override
public void onCanceled(UrlRequest request, UrlResponseInfo info) {
  // Free resources allocated to process this request.
  …
}