Spring Boot 环境变量读取和属性对象的绑定

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凡是被spring管理的类,实现接口 EnvironmentAware 重写方法 setEnvironment 可以在工程启动时,获取到系统环境变量和application配置文件中的变量。
如:

@Configuration
public class MyWebAppConfigurer implements EnvironmentAware
        {
    private static final Logger logger = LoggerFactory.getLogger(MyWebAppConfigurer.class);

    private RelaxedPropertyResolver propertyResolver;

    @Value("${spring.datasource.url}")
    private String myUrl;

    /**
     * 这个方法只是测试实现EnvironmentAware接口,读取环境变量的方法。
     */
    @Override
    public void setEnvironment(Environment env) {
        logger.info(env.getProperty("JAVA_HOME"));
        logger.info(myUrl);
        String str = env.getProperty("spring.datasource.url");
        logger.info(str);
        propertyResolver = new RelaxedPropertyResolver(env, "spring.datasource.");
        String url = propertyResolver.getProperty("url");
        logger.info(url);
    }
}

@Controller @Service 等被Spring管理的类都支持,注意重写的方法 setEnvironment 是在系统启动的时候被执行。
或者如下Controller:

@Controller
public class PageController implements EnvironmentAware{

    @Override
    public void setEnvironment(Environment environment) {
        String s = environment.getProperty("JAVA_HOME");
        System.out.println(s);
    }
}

我们还可以通过@ConfigurationProperties 读取application属性配置文件中的属性。

@Configuration
@ConditionalOnClass(Mongo.class)
@EnableConfigurationProperties(MongoProperties.class)
public class MongoAutoConfiguration {

    @Autowired
    private MongoProperties properties; 

}

@ConditionOnClass表明该@Configuration仅仅在一定条件下才会被加载,这里的条件是Mongo.class位于类路径上

  • @EnableConfigurationProperties将Spring Boot的配置文件(application.properties)中的spring.data.mongodb.*属性映射为MongoProperties并注入到MongoAutoConfiguration中。
  • @ConditionalOnMissingBean说明Spring Boot仅仅在当前上下文中不存在Mongo对象时,才会实例化一个Bean。这个逻辑也体现了Spring Boot的另外一个特性——自定义的Bean优先于框架的默认配置,我们如果显式的在业务代码中定义了一个Mongo对象,那么Spring Boot就不再创建。
@ConfigurationProperties(prefix = "spring.data.mongodb")
public class MongoProperties {

    private String host;
    private int port = DBPort.PORT;
    private String uri = "mongodb://localhost/test";
    private String database;

    // ... getters/ setters omitted
} 

它就是以spring.data.mongodb作为前缀的属性,然后通过名字直接映射为对象的属性,同时还包含了一些默认值。如果不配置,那么mongo.uri就是mongodb://localhost/test。

 

  • class不用继承任何东西,只需在类中添加属性
@Inject
private Environment env;
  • 调用

OTHER_DIR = env.getProperty("converter.sourcedir");

converter.sourcedir是yml中的配置,如下

converter:
    sourcedir: /a/b/c/d

继续深究,Environment的源码:

/*
 * Copyright 2002-2013 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

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 true if the given profile is <em>not</em> active.
     * For example, <pre class="code">env.acceptsProfiles("p1", "!p2")</pre> 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
     */
    boolean acceptsProfiles(String... profiles);

}

鉴于注释太多,抽出其中核心代码:

package org.springframework.core.env;

public interface Environment extends PropertyResolver {


    String[] getActiveProfiles();

    String[] getDefaultProfiles();

    boolean acceptsProfiles(String... profiles);

}

可以看到Environment 又extends PropertyResolver

/*
 * Copyright 2002-2013 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.core.env;

/**
 * Interface for resolving properties against any underlying source.
 *
 * @author Chris Beams
 * @since 3.1
 * @see Environment
 * @see PropertySourcesPropertyResolver
 */
public interface PropertyResolver {

    /**
     * Return whether the given property key is available for resolution, i.e.,
     * 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)
     */
    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)
     */
    <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);

    /**
     * Convert the property value associated with the given key to a {@code Class}
     * of type {@code T} or {@code null} if the key cannot be resolved.
     * @throws org.springframework.core.convert.ConversionException if class specified
     * by property value cannot be found  or loaded or if targetType is not assignable
     * from class specified by property value
     * @see #getProperty(String, Class)
     */
    <T> Class<T> getPropertyAsClass(String key, Class<T> targetType);

    /**
     * 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;

}

第三种方法(最简单)

    @Value("${a.b.c.d}")
    private String testValue;

a.b.c.d 是配置文件中的

就这样简单~~~



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