Spring源码分析（1）- Environment环境获取与路径解析

主函数

public class App {
    public static void main(String[] args) {
        ApplicationContext ac = new
                ClassPathXmlApplicationContext("applicationContext.xml");
        Student student = (Student) ac.getBean("student");
        System.out.println(student);
    }
}

执行构造方法

public ClassPathXmlApplicationContext(String[] configLocations, boolean refresh, ApplicationContext parent)
			throws BeansException {
	super(parent);
	setConfigLocations(configLocations);
	if (refresh) {
		refresh();
	}
}

其中setConfigLocations(configLocations);代码块执行配置文件地址的解析，以及环境的初始化，代码块如下所示：

public void setConfigLocations(String... locations) {
	if (locations != null) {
		Assert.noNullElements(locations, "Config locations must not be null");
		this.configLocations = new String[locations.length];
		for (int i = 0; i < locations.length; i++) {
			this.configLocations[i] = resolvePath(locations[i]).trim();
		}
	}
	else {
		this.configLocations = null;
	}
}

其中this.configLocations[i] = resolvePath(locations[i]).trim();代码块进行配置文件地址解析，实现如下：

protected String resolvePath(String path) {
	return getEnvironment().resolveRequiredPlaceholders(path);
}

其中getEnvironment()用于获取相关环境，包括JVM配置的相关环境和计算机系统所配置的环境变量。具体实现会new一个StandardEnvironment对象，StandardEnvironment对象的具体实现如下所示。在生成StandardEnvironment对象时会首先调用其父类AbstractEnvironment的构造方法，在AbstractEnvironment的构造方法中会调用customizePropertySources方法来获取相关的环境变量。

public class StandardEnvironment extends AbstractEnvironment {
    public static final String SYSTEM_ENVIRONMENT_PROPERTY_SOURCE_NAME = "systemEnvironment";
    public static final String SYSTEM_PROPERTIES_PROPERTY_SOURCE_NAME = "systemProperties";

    public StandardEnvironment() {
    }

    protected void customizePropertySources(MutablePropertySources propertySources) {
        propertySources.addLast(new MapPropertySource("systemProperties", this.getSystemProperties()));
        propertySources.addLast(new SystemEnvironmentPropertySource("systemEnvironment", this.getSystemEnvironment()));
    }
}

如上所示，其中this.getSystemProperties()的实现主要是调用System.getProperties()方法来获取JVM环境变量。
this.getSystemEnvironment()的实现主要是调用System.getenv()来获取本机所配置的环境变量。
在获取了StandardEnvironment对象后，就是进行配置文件路径的解析了，调用resolveRequiredPlaceholders(path) 将路径中含有${XXX}的字符串做相应的替换，然后进行返回。