Spring5参考指南:Environment

文章目录

Profiles
PropertySource
使用@PropertySource

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)}*/@Deprecatedboolean 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)*/@NullableString 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 {@Beanpublic 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 {@Beanpublic 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 {@AutowiredEnvironment env;@Beanpublic 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

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