flink深入研究(02) flink运行环境的获取(上)

// 获取运行环境
StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();

这行代码会返回一个可用的执行环境，是flink程序执行的上下文，记录了相关配，如并行度等，并提供了一系列方法，如输入流的读入方法，运行整个程序的execute方法等，对于分步式流处理程序来说，flatMap，keyBy等等操作，都可以理解为一种声明，告诉整个程序采用了什么样的算子(这段文字参考自https://www.cnblogs.com/bethunebtj/p/9168274.html)，接下来我们开始进入到代码内部，看看运行环境的获取过程。

代码讲解

我们开始看代码：

/**
	 * Creates an execution environment that represents the context in which the
	 * program is currently executed. If the program is invoked standalone, this
	 * method returns a local execution environment, as returned by
	 * {@link #createLocalEnvironment()}.
	 *
	 * @return The execution environment of the context in which the program is
	 * executed.
	 */
	public static StreamExecutionEnvironment getExecutionEnvironment() {
		return Utils.resolveFactory(threadLocalContextEnvironmentFactory, contextEnvironmentFactory)
			.map(StreamExecutionEnvironmentFactory::createExecutionEnvironment)
			.orElseGet(StreamExecutionEnvironment::createStreamExecutionEnvironment);
	}

其中threadLocalContextEnvironmentFactory的定义如下：

/** The ThreadLocal used to store {@link StreamExecutionEnviro