Spring之Environment类详解

Posted 2021-09-05 敲代码的小小酥

一、Environment接口

先上源码:

package org.springframework.core.env;

/**
 * Interface representing the environment in which the current application is running.
 * Models two key aspects of the application environment: <em>profiles</em> and
 * <em>properties</em>. Methods related to property access are exposed via the
 * {@link PropertyResolver} superinterface.
 *
 * <p>A <em>profile</em> is a named, logical group of bean definitions to be registered
 * with the container only if the given profile is <em>active</em>. Beans may be assigned
 * to a profile whether defined in XML or via annotations; see the spring-beans 3.1 schema
 * or the {@link org.springframework.context.annotation.Profile @Profile} annotation for
 * syntax details. The role of the {@code Environment} object with relation to profiles is
 * in determining which profiles (if any) are currently {@linkplain #getActiveProfiles
 * active}, and which profiles (if any) should be {@linkplain #getDefaultProfiles active
 * by default}.
 *
 * <p><em>Properties</em> play an important role in almost all applications, and may
 * originate from a variety of sources: properties files, JVM system properties, system
 * environment variables, JNDI, servlet context parameters, ad-hoc Properties objects,
 * Maps, and so on. The role of the environment object with relation to properties is to
 * provide the user with a convenient service interface for configuring property sources
 * and resolving properties from them.
 *
 * <p>Beans managed within an {@code ApplicationContext} may register to be {@link
 * org.springframework.context.EnvironmentAware EnvironmentAware} or {@code @Inject} the
 * {@code Environment} in order to query profile state or resolve properties directly.
 *
 * <p>In most cases, however, application-level beans should not need to interact with the
 * {@code Environment} directly but instead may have to have {@code ${...}} property
 * values replaced by a property placeholder configurer such as
 * {@link org.springframework.context.support.PropertySourcesPlaceholderConfigurer
 * PropertySourcesPlaceholderConfigurer}, which itself is {@code EnvironmentAware} and
 * as of Spring 3.1 is registered by default when using
 * {@code <context:property-placeholder/>}.
 *
 * <p>Configuration of the environment object must be done through the
 * {@code ConfigurableEnvironment} interface, returned from all
 * {@code AbstractApplicationContext} subclass {@code getEnvironment()} methods. See
 * {@link ConfigurableEnvironment} Javadoc for usage examples demonstrating manipulation
 * of property sources prior to application context {@code refresh()}.
 *
 * @author Chris Beams
 * @since 3.1
 * @see PropertyResolver
 * @see EnvironmentCapable
 * @see ConfigurableEnvironment
 * @see AbstractEnvironment
 * @see StandardEnvironment
 * @see org.springframework.context.EnvironmentAware
 * @see org.springframework.context.ConfigurableApplicationContext#getEnvironment
 * @see org.springframework.context.ConfigurableApplicationContext#setEnvironment
 * @see org.springframework.context.support.AbstractApplicationContext#createEnvironment
 */
public interface Environment extends PropertyResolver {

	/**
	 * Return the set of profiles explicitly made active for this environment. Profiles
	 * are used for creating logical groupings of bean definitions to be registered
	 * conditionally, for example based on deployment environment. Profiles can be
	 * activated by setting {@linkplain AbstractEnvironment#ACTIVE_PROFILES_PROPERTY_NAME
	 * "spring.profiles.active"} as a system property or by calling
	 * {@link ConfigurableEnvironment#setActiveProfiles(String...)}.
	 * <p>If no profiles have explicitly been specified as active, then any
	 * {@linkplain #getDefaultProfiles() default profiles} will automatically be activated.
	 * @see #getDefaultProfiles
	 * @see ConfigurableEnvironment#setActiveProfiles
	 * @see AbstractEnvironment#ACTIVE_PROFILES_PROPERTY_NAME
	 */
	String[] getActiveProfiles();

	/**
	 * Return the set of profiles to be active by default when no active profiles have
	 * been set explicitly.
	 * @see #getActiveProfiles
	 * @see ConfigurableEnvironment#setDefaultProfiles
	 * @see AbstractEnvironment#DEFAULT_PROFILES_PROPERTY_NAME
	 */
	String[] getDefaultProfiles();

	/**
	 * Return whether one or more of the given profiles is active or, in the case of no
	 * explicit active profiles, whether one or more of the given profiles is included in
	 * the set of default profiles. If a profile begins with '!' the logic is inverted,
	 * i.e. the method will return {@code true} if the given profile is <em>not</em> active.
	 * For example, {@code env.acceptsProfiles("p1", "!p2")} will return {@code true} if
	 * profile 'p1' is active or 'p2' is not active.
	 * @throws IllegalArgumentException if called with zero arguments
	 * or if any profile is {@code null}, empty, or whitespace only
	 * @see #getActiveProfiles
	 * @see #getDefaultProfiles
	 * @see #acceptsProfiles(Profiles)
	 * @deprecated as of 5.1 in favor of {@link #acceptsProfiles(Profiles)}
	 */
	@Deprecated
	boolean acceptsProfiles(String... profiles);

	/**
	 * Return whether the {@linkplain #getActiveProfiles() active profiles}
	 * match the given {@link Profiles} predicate.
	 */
	boolean acceptsProfiles(Profiles profiles);

}

然后，进行讲解:

Enviroment包括两方面内容:profiles和properties。

• profiles

关于profiles的作用，需要先研究@Profile注解的用法。Evnironment与profiles的关系是Environment存储着哪些profiles是激活状态的，以及哪些profiles应该被默认激活。

其定义的前两个方法我们可以看到上面两点作用:

String[] getActiveProfiles();

String[] getDefaultProfiles();

由此可知，Environment是用于获取和管理profiles的一个类。

• properties
  properties包括了如下几个方面:
  properties配置文件；
  JVM系统属性；
  系统环境变量；
  servlet context参数；
  … …

一切参数类数据，都有Environment管理。Envrionment为用户提供了便捷的接口服务，来配置和解析properties相关的内容。

可以通过实现EnvironmentAware接口，来直接查询配置文件状态或解析属性。
大多数情况下，我们不会直接和Enviornment进行交互，而是通过${…}占位符，来设定相应的属性，然后通过PropertySourcesPlaceholderConfigurer来进行解析，PropertySourcesPlaceholderConfigurer类实现了EnvironmentAware接口，将解析后的数据，塞入Environment中去。

二、ConfigurableEnvironment接口

该接口更为全面，我们看其定义的方法;

• 设置profiles:

void setActiveProfiles(String... profiles);

• 添加profiles:

void addActiveProfile(String profile);

• 设置默认profiles:

void setDefaultProfiles(String... profiles);

• 获取MutablePropertySources：

MutablePropertySources getPropertySources();

• 获取系统属性:

Map<String, Object> getSystemProperties();

• 获取系统环境变量:

Map<String, Object> getSystemEnvironment();