译文篇：Retrofit源码之Call接口

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该接口来源于 Retrofit 源码，接口中定义了网络请求方法以及请求状态。

源码

package retrofit2;

import java.io.IOException;
import okhttp3.Request;

/**
 * An invocation of a Retrofit method that sends a request to a webserver and returns a response.
 * Each call yields its own HTTP request and response pair. Use {@link #clone} to make multiple
 * calls with the same parameters to the same webserver; this may be used to implement polling or
 * to retry a failed call.
 *
 * <p>Calls may be executed synchronously with {@link #execute}, or asynchronously with {@link
 * #enqueue}. In either case the call can be canceled at any time with {@link #cancel}. A call that
 * is busy writing its request or reading its response may receive a {@link IOException}; this is
 * working as designed.
 *
 * @param <T> Successful response body type.
 */
public interface Call<T> extends Cloneable {
  /**
   * Synchronously send the request and return its response.
   * @throws IOException if a problem occurred talking to the server.
   * @throws RuntimeException (and subclasses) if an unexpected error occurs creating the request
   * or decoding the response.
   */
  Response<T> execute() throws IOException;

  /**
   * Asynchronously send the request and notify {@code callback} of its response or if an error
   * occurred talking to the server, creating the request, or processing the response.
   */
  void enqueue(Callback<T> callback);

  /**
   * Returns true if this call has been either {@linkplain #execute() executed} or {@linkplain
   * #enqueue(Callback) enqueued}. It is an error to execute or enqueue a call more than once.
   */
  boolean isExecuted();

  /**
   * Cancel this call. An attempt will be made to cancel in-flight calls, and if the call has not
   * yet been executed it never will be.
   */
   
  void cancel();

  /** True if {@link #cancel()} was called. */
  boolean isCanceled();

  /**
   * Create a new, identical call to this one which can be enqueued or executed even if this call
   * has already been.
   */
  Call<T> clone();

  /** The original HTTP request. */
  Request request();
}

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译

• 一个retrofit方法的调用接口，通过这些方法可以向服务端发起请求并得到返回结果。 每一个回调都会对应请求和返回结果。可通过 execute 方法发起同步异步请求，或者 enqueue 发起异步请求，当然请求也可通过 cancel 方法随时取消。当请求过于频繁时可能报IO异常。

  <T> 表示 请求成功结果返回值类型

/**
 * An invocation of a Retrofit method that sends a request to a webserver and returns a response.
 * Each call yields its own HTTP request and response pair. Use {@link #clone} to make multiple
 * calls with the same parameters to the same webserver; this may be used to implement polling or
 * to retry a failed call.
 *
 * <p>Calls may be executed synchronously with {@link #execute}, or asynchronously with {@link
 * #enqueue}. In either case the call can be canceled at any time with {@link #cancel}. A call that
 * is busy writing its request or reading its response may receive a {@link IOException}; this is
 * working as designed.
 *
 * @param <T> Successful response body type.
 */
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• 同步请求方法

/**
   * Synchronously send the request and return its response.
   * 
   * @throws IOException if a problem occurred talking to the server.
   * @throws RuntimeException (and subclasses) if an unexpected error occurs creating the request
   * or decoding the response.
   */
  
  Response<T> execute() throws IOException;
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• 异步请求方法

/**
   * Asynchronously send the request and notify {@code callback} of its response or if an error
   * occurred talking to the server, creating the request, or processing the response.
   */
  void enqueue(Callback<T> callback);
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• 当调用同步或异步请求时，该值返回true

/**
   * Returns true if this call has been either {@linkplain #execute() executed} or {@linkplain
   * #enqueue(Callback) enqueued}. It is an error to execute or enqueue a call more than once.
   */
  boolean isExecuted();
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• 一个正在执行的请求可能被取消，但是如果请求没有被执行的话将无法取消。

/**
   * Cancel this call. An attempt will be made to cancel in-flight calls, and if the call has not
   * yet been executed it never will be.
   */
  void cancel();
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• 当cancel() 方法被回调时，该值为true

/** True if {@link #cancel()} was called. */
  boolean isCanceled();
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• 克隆一个回调

/**
   * Create a new, identical call to this one which can be enqueued or executed even if this call
   * has already been.
   */
  Call<T> clone();
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• 原始的Http请求

/** The original HTTP request. */
  Request request();
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