Spring5参考指南:Environment
Spring的Environment接口有两个关键的作用：1. Profile， 2.properties。可以看下该接口的定义：
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);
}
它继承了PropertyResolver：
public interface PropertyResolver {
/**
* Return whether the given property key is available for resolution,
* i.e. if the value for the given key is not {@code null}.
*/
boolean containsProperty(String key);
/**
* Return the property value associated with the given key,
* or {@code null} if the key cannot be resolved.
* @param key the property name to resolve
* @see #getProperty(String, String)
* @see #getProperty(String, Class)
* @see #getRequiredProperty(String)
*/
@Nullable
String getProperty(String key);
/**
* Return the property value associated with the given key, or
* {@code defaultValue} if the key cannot be resolved.
* @param key the property name to resolve
* @param defaultValue the default value to return if no value is found
* @see #getRequiredProperty(String)
* @see #getProperty(String, Class)
*/
String getProperty(String key, String defaultValue);
/**
* Return the property value associated with the given key,
* or {@code null} if the key cannot be resolved.
* @param key the property name to resolve
* @param targetType the expected type of the property value
* @see #getRequiredProperty(String, Class)
*/
@Nullable
<T> T getProperty(String key, Class<T> targetType);
/**
* Return the property value associated with the given key,
* or {@code defaultValue} if the key cannot be resolved.
* @param key the property name to resolve
* @param targetType the expected type of the property value
* @param defaultValue the default value to return if no value is found
* @see #getRequiredProperty(String, Class)
*/
<T> T getProperty(String key, Class<T> targetType, T defaultValue);
/**
* Return the property value associated with the given key (never {@code null}).
* @throws IllegalStateException if the key cannot be resolved
* @see #getRequiredProperty(String, Class)
*/
String getRequiredProperty(String key) throws IllegalStateException;
/**
* Return the property value associated with the given key, converted to the given
* targetType (never {@code null}).
* @throws IllegalStateException if the given key cannot be resolved
*/
<T> T getRequiredProperty(String key, Class<T> targetType) throws IllegalStateException;
/**
* Resolve ${...} placeholders in the given text, replacing them with corresponding
* property values as resolved by {@link #getProperty}. Unresolvable placeholders with
* no default value are ignored and passed through unchanged.
* @param text the String to resolve
* @return the resolved String (never {@code null})
* @throws IllegalArgumentException if given text is {@code null}
* @see #resolveRequiredPlaceholders
* @see org.springframework.util.SystemPropertyUtils#resolvePlaceholders(String)
*/
String resolvePlaceholders(String text);
/**
* Resolve ${...} placeholders in the given text, replacing them with corresponding
* property values as resolved by {@link #getProperty}. Unresolvable placeholders with
* no default value will cause an IllegalArgumentException to be thrown.
* @return the resolved String (never {@code null})
* @throws IllegalArgumentException if given text is {@code null}
* or if any placeholders are unresolvable
* @see org.springframework.util.SystemPropertyUtils#resolvePlaceholders(String, boolean)
*/
String resolveRequiredPlaceholders(String text) throws IllegalArgumentException;
}
Profile是一个Bean的逻辑分组，只有在给定的配置文件处于活动状态时，才会在容器中注册。
Properties主要用来从各种源：属性文件、JVM系统属性、系统环境变量、JNDI、servlet上下文参数、特殊属性对象、映射对象等读取属性的定义。
Profiles
在开发中，我们可以需要在不同的环境定义不同的配置，例如：
- 在开发中处理内存中的数据源，而不是在QA或生产中从JNDI中查找相同的数据源。
- 仅在将应用程序部署到性能环境中时注册监控基础结构。
- 为客户A和客户B部署注册定制的bean实现。
假如我们有两个数据源，一个是在测试环境使用，一个是在线上环境使用，则可以通过profile来指定不同的环境。如下所示：
@Configuration
@Profile("development")
public class StandaloneDataConfig {
@Bean
public DataSource dataSource() {
return new EmbeddedDatabaseBuilder()
.setType(EmbeddedDatabaseType.HSQL)
.addScript("classpath:com/bank/config/sql/schema.sql")
.addScript("classpath:com/bank/config/sql/test-data.sql")
.build();
}
}
@Configuration
@Profile("production")
public class JndiDataConfig {
@Bean(destroyMethod="")
public DataSource dataSource() throws Exception {
Context ctx = new InitialContext();
return (DataSource) ctx.lookup("java:comp/env/jdbc/datasource");
}
}
@Profile里面的表达式可以是简单的字符串，也可以支持运算符，如：
- ! 逻辑非
- & 逻辑与
- | 逻辑或
可以将@Profile用作元注解，以创建自定义组合注解。以下示例定义了一个自定义的@Production注解，您可以将其用作@Profile（“production”）的替换：
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Profile("production")
public @Interface Production {
}
@Profile也可以用在方法级别用来包含一个特殊的bean或者配置类。如下所示：
@Configuration
public class AppConfig {
@Bean("dataSource")
@Profile("development")
public DataSource standaloneDataSource() {
return new EmbeddedDatabaseBuilder()
.setType(EmbeddedDatabaseType.HSQL)
.addScript("classpath:com/bank/config/sql/schema.sql")
.addScript("classpath:com/bank/config/sql/test-data.sql")
.build();
}
@Bean("dataSource")
@Profile("production")
public DataSource jndiDataSource() throws Exception {
Context ctx = new InitialContext();
return (DataSource) ctx.lookup("java:comp/env/jdbc/datasource");
}
}
Profiles在XML中使用
可以在XML中使用profile属性，如下所示：
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:jdbc="http://www.springframework.org/schema/jdbc"
xmlns:jee="http://www.springframework.org/schema/jee"
xsi:schemaLocation="...">
<!-- other bean definitions -->
<beans profile="development">
<jdbc:embedded-database id="dataSource">
<jdbc:script location="classpath:com/bank/config/sql/schema.sql"/>
<jdbc:script location="classpath:com/bank/config/sql/test-data.sql"/>
</jdbc:embedded-database>
</beans>
<beans profile="production">
<jee:jndi-lookup id="dataSource" jndi-name="java:comp/env/jdbc/datasource"/>
</beans>
</beans>
激活Profile
上面我们定义好了Profile，但是怎么激活他们？
激活一个概要文件可以用几种方法完成，但最简单的方法是通过应用程序上下文提供的环境API以编程方式完成。以下示例显示了如何执行此操作：
public static void main(String[] args) {
AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext();
ctx.getEnvironment().setActiveProfiles("development");
ctx.register(AppConfig.class, StandaloneDataConfig.class, JndiDataConfig.class);
ctx.refresh();
}
此外，还可以通过spring.profiles.active属性声明性地激活概要文件，该属性可以通过系统环境变量、jvm系统属性、web.xml中的servlet上下文参数指定，甚至可以作为JNDI中的条目指定.
如下所示：
-Dspring.profiles.active=“profile1,profile2”
你也可以同时激活多个pofile
ctx.getEnvironment().setActiveProfiles(“profile1”, “profile2”);
默认Profile
默认的Profile表示该Profile默认被激活，如下所示：
@Configuration
@Profile("default")
public class DefaultDataConfig {
@Bean
public DataSource dataSource() {
return new EmbeddedDatabaseBuilder()
.setType(EmbeddedDatabaseType.HSQL)
.addScript("classpath:com/bank/config/sql/schema.sql")
.build();
}
}
如果没有Profile被激活，那么dataSource就会被创建，你可以看成创建bean的默认方式。如果其他的Profile被激活了，那么默认的Profile就不会被使用。
您可以在环境中使用SetDefaultProfiles（）更改默认profile的名称，或者声明性地使用spring.profiles.default属性更改默认概要文件的名称。
PropertySource
下面是使用PropertySource的例子：
public static void main(String[] args) {
ApplicationContext ctx = new GenericApplicationContext();
Environment env = ctx.getEnvironment();
boolean containsMyProperty = env.containsProperty("my-property");
System.out.println("Does my environment contain the 'my-property' property? " + containsMyProperty);
}
这里Spring查询是否定义了my-property属性，这里的StandardEnvironment定义了两组PropertySource对象进行查询，
/** System environment property source name: {@value}. */
public static final String SYSTEM_ENVIRONMENT_PROPERTY_SOURCE_NAME = "systemEnvironment";
/** JVM system properties property source name: {@value}. */
public static final String SYSTEM_PROPERTIES_PROPERTY_SOURCE_NAME = "systemProperties";
一个表示一组JVM系统属性（System.GetProperties（）），另一个表示一组系统环境变量（System.getEnv（））。
对于常见的StandardServletEnvironment，property的查询优先级如下：
- ServletConfig参数（如果适用-例如，对于DispatcherServlet上下文）
- ServletContext参数（web.xml context-param 项）
- JNDI环境变量（Java:COMP/Env/条目）
- JVM系统属性（-d命令行参数）
- JVM系统环境（操作系统环境变量）
使用@PropertySource
@PropertySource注解提供了方便和声明式的机制为Spring的添加PropertySource.
下面的@Configuration类使用@PropertySource 来调用testBean.getName() 返回 myTestBean：
@Configuration
@PropertySource("classpath:app.properties")
public class PropertiesConfig {
@Autowired
Environment env;
@Bean
public TestBean testBean() {
TestBean testBean = new TestBean();
testBean.setName(env.getProperty("testbean.name"));
return testBean;
}
}
@Propertysource资源位置中存在的任何$…占位符将根据已针对环境注册的属性源集进行解析，如下示例所示：
@PropertySource("classpath:/com/${my.placeholder:default/path}/app.properties")
假设my.placeholder存在于已注册的某个属性源中（例如，系统属性或环境变量），则将占位符解析为相应的值。如果不是，则default/path用作默认值。如果未指定默认值且无法解析属性，则将引发IllegalArgumentException。
本节的例子可以参考Environment
更多教程请参考flydean的博客
