Spring之Environment类详解

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)}*/@Deprecatedboolean 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();