发送简单的请求

了解如何使用 Cronet 库在您的 Android 应用中执行网络操作。Cronet 是作为库提供的 Chromium 网络堆栈，可在您的应用中使用。要详细了解该库的功能，请参阅使用 Cronet 执行网络操作。

在您的项目中设置库

按照以下步骤在您的项目中添加 Cronet 库的依赖项

验证 Android Studio 是否在您的项目 settings.gradle 文件中包含了 Google Maven 仓库的引用，如以下示例所示

Groovy

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

Kotlin

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

在您的应用模块 build.gradle 文件的 dependencies 部分中包含对适用于 Cronet 的 Google Play 服务客户端库的引用，如以下示例所示

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")
}

添加此依赖项后创建的 CronetEngine 对象将使用从 Google Play 服务加载的 Cronet。在创建 CronetEngine 对象之前调用 CronetProviderInstaller.installProvider(Context)，以防止由于设备需要更新版本的 Google Play 服务等错误导致在 CronetEngine 创建期间抛出意外异常。

如果无法从 Google Play 服务加载 Cronet，可以使用性能较低的 Cronet API 实现。要使用此备用实现，请依赖于 org.chromium.net:cronet-fallback 并调用 new JavaCronetProvider(context).createBuilder()。

创建网络请求

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

创建并配置 CronetEngine 实例

该库提供了一个 CronetEngine.Builder 类，您可以使用它来创建 CronetEngine 实例。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 类配置 CronetEngine 对象，例如，您可以提供缓存和数据压缩等选项。要详细了解，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 的子类并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 类执行网络任务。要获取 Executor 实例，请使用 Executors 类中返回 Executor 对象的静态方法之一。以下示例展示了如何使用 newSingleThreadExecutor() 方法创建 Executor 对象

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 CronetEngine 的 newUrlRequestBuilder() 方法，并传入目标 URL、您的回调类实例和 executor 对象。newUrlRequestBuilder() 方法返回一个 UrlRequest.Builder 对象，您可以使用该对象创建 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 类配置 UrlRequest 实例。例如，您可以指定优先级或 HTTP 谓词。要详细了解，请参阅 UrlRequest.Builder。

要启动网络任务，请调用请求的 start() 方法

Kotlin

request.start()

Java

request.start();

按照本部分的说明，您可以使用 Cronet 创建和发送网络请求。但是，为简单起见，UrlRequest.Callback 的示例实现仅向日志输出一条消息。下一部分将展示如何提供支持更实用场景的回调实现，例如从响应中提取数据和检测请求失败。

处理网络响应

调用 start() 方法后，Cronet 请求生命周期即被启动。您的应用应通过指定回调来在生命周期期间管理请求。要详细了解生命周期，请参阅 Cronet 请求生命周期。您可以通过创建 UrlRequest.Callback 的子类并实现以下方法来指定回调

onRedirectReceived()

在服务器针对原始请求发出 HTTP 重定向代码时调用。要跟踪重定向到新目标，请使用 followRedirect() 方法。否则使用 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()

在收到最终标头集时调用。onResponseStarted() 方法仅在跟踪完所有重定向后调用。以下代码展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()

每当读取了部分响应体时调用。以下代码示例展示了如何实现该方法并提取响应体

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时调用。以下示例展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()

如果在调用 start() 方法后请求因任何原因失败时调用。以下示例展示了如何实现该方法并获取有关错误的信息

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() 方法取消了请求时调用。调用后，将不再调用 UrlRequest.Callback 类的其他方法。您可以使用此方法释放为处理请求分配的资源。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.
  …
}

发送简单的请求 使用收藏整理内容 根据您的偏好保存和分类内容。

在您的项目中设置库

Groovy

Kotlin

Groovy

Kotlin

创建网络请求

创建并配置 CronetEngine 实例

Kotlin

Java

提供请求回调的实现

Kotlin

Java

创建一个 Executor 对象来管理网络任务

Kotlin

Java

创建并配置 UrlRequest 对象

Kotlin

Java

Kotlin

Java

处理网络响应

Kotlin

Java

Kotlin

Java

Kotlin

Java

Kotlin

Java

Kotlin

Java

Kotlin

Java

发送简单的请求