Spring读源码系列番外篇---03---PropertyResolver的结构体系剖析---下-6ren

Spring读源码系列番外篇---03---PropertyResolver的结构体系剖析---下

转载作者：知者更新时间：2024-03-13 02:51:22

书接上文:

Spring读源码系列番外篇—02—PropertyResolver的结构体系剖析—上

Environment接口

和Environment相关的接口可以有那么多:

See Also:
PropertyResolver, 
EnvironmentCapable, 
ConfigurableEnvironment, 
AbstractEnvironment, 
StandardEnvironment, 
org.springframework.context.EnvironmentAware, 
org.springframework.context.ConfigurableApplicationContext.getEnvironment, 
org.springframework.context.ConfigurableApplicationContext.setEnvironment, 
org.springframework.context.support.AbstractApplicationContext.createEnvironment

可以看出该接口的发展潜力之大

个人认为这里英文注释有些讲的更加详细，所以我就不翻译了，不然翻译了反而读不懂了

public interface Environment extends PropertyResolver {

	/**
	   获取当前激活的环境
	 */
	String[] getActiveProfiles();

	/**
	 * Return the set of profiles to be active by default when no active profiles have
	 * been set explicitly.
	 */
	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 not active. 
For example, 
env.acceptsProfiles("p1", "!p2") will return true if profile 'p1' is active or 'p2' is not active.
	 */
	@Deprecated
	boolean acceptsProfiles(String... profiles);

	/**
Return whether the active profiles match the given Profiles predicate.
	 */
	boolean acceptsProfiles(Profiles profiles);

}

Environment顶层接口,主要暴露出来的接口主要功能是获取当前激活环境和默认环境，以及判断传入的环境是否被激活

ConfigurableEnvironment—可配置环境

public interface ConfigurableEnvironment extends Environment, ConfigurablePropertyResolver {
	void setActiveProfiles(String... profiles);
	void addActiveProfile(String profile);
	void setDefaultProfiles(String... profiles);

	/**
	    MutablePropertySources也是拥有一组属性源的集合
	    mutable是可变的意思，意味我们可以自己对返回的属性源进行CRUD
	 */
	MutablePropertySources getPropertySources();

   //System.getProperty()
	Map<String, Object> getSystemProperties();
   
   //System.getenv()
	Map<String, Object> getSystemEnvironment();

    //合并两个环境
	void merge(ConfigurableEnvironment parent);

}

可配置意味可以修改—通常里面会暴露出大量set接口

AbstractEnvironment----大部分接口的实现，少部分留给子类实现

public abstract class AbstractEnvironment implements ConfigurableEnvironment {

	public static final String IGNORE_GETENV_PROPERTY_NAME = "spring.getenv.ignore";
	public static final String ACTIVE_PROFILES_PROPERTY_NAME = "spring.profiles.active";
	public static final String DEFAULT_PROFILES_PROPERTY_NAME = "spring.profiles.default";
	protected static final String RESERVED_DEFAULT_PROFILE_NAME = "default";

	protected final Log logger = LogFactory.getLog(getClass());

	private final Set<String> activeProfiles = new LinkedHashSet<>();

	private final Set<String> defaultProfiles = new LinkedHashSet<>(getReservedDefaultProfiles());
    
    //可变的属性源集合
	private final MutablePropertySources propertySources;
     //可配置的属性解析器
	private final ConfigurablePropertyResolver propertyResolver;

	public AbstractEnvironment() {
	//如果构造函数没有传入一个属性源集合,那么默认创建一个空的可变的属性源集合
		this(new MutablePropertySources());
	}

	protected AbstractEnvironment(MutablePropertySources propertySources) {
		this.propertySources = propertySources;
		//返回的是PropertySourcesPropertyResolver
		this.propertyResolver = createPropertyResolver(propertySources);
		//从名字看是自定义属性源---->说明我们可以尝试去自定义集合中的属性源
		customizePropertySources(propertySources);
	}

	protected ConfigurablePropertyResolver createPropertyResolver(MutablePropertySources propertySources) {
	//PropertySourcesPropertyResolver讲解过了----PropertyResolver下面的一个具体实现子类
	//它负责从这些属性源中寻找key--->value
		return new PropertySourcesPropertyResolver(propertySources);
	}

	protected final ConfigurablePropertyResolver getPropertyResolver() {
		return this.propertyResolver;
	}

	//子类通过重新该方法完成对属性源的自定义修改操作---可以进行CRUD  
	protected void customizePropertySources(MutablePropertySources propertySources) {
	}
	
	protected Set<String> getReservedDefaultProfiles() {
		return Collections.singleton(RESERVED_DEFAULT_PROFILE_NAME);
	}

	//---------------------------------------------------------------------
	// Implementation of ConfigurableEnvironment interface
	//---------------------------------------------------------------------

	@Override
	public String[] getActiveProfiles() {
		return StringUtils.toStringArray(doGetActiveProfiles());
	}

//获取激活的
	protected Set<String> doGetActiveProfiles() {
		synchronized (this.activeProfiles) {
		//activeProfiles集合不为空,就直接返回该集合即可
			if (this.activeProfiles.isEmpty()) {
			//否则调用doGetActiveProfilesProperty获取激活的环境
				String profiles = doGetActiveProfilesProperty();
				if (StringUtils.hasText(profiles)) {
				//缓存获取到的激活环境
					setActiveProfiles(StringUtils.commaDelimitedListToStringArray(
							StringUtils.trimAllWhitespace(profiles)));
				}
			}
			return this.activeProfiles;
		}
	}

	/**
	 * Return the property value for the active profiles.
	 * @since 5.3.4
	 * @see #ACTIVE_PROFILES_PROPERTY_NAME
	 */
	@Nullable
	protected String doGetActiveProfilesProperty() {
	//尝试从属性源中获取激活的环境
		return getProperty(ACTIVE_PROFILES_PROPERTY_NAME);
	}

	@Override
	public void setActiveProfiles(String... profiles) {
		Assert.notNull(profiles, "Profile array must not be null");
		if (logger.isDebugEnabled()) {
			logger.debug("Activating profiles " + Arrays.asList(profiles));
		}
		synchronized (this.activeProfiles) {
		//清除之前保留的激活环境集合
			this.activeProfiles.clear();
			//缓存找到的激活环境
			for (String profile : profiles) {
				validateProfile(profile);
				this.activeProfiles.add(profile);
			}
		}
	}

	@Override
	public void addActiveProfile(String profile) {
		if (logger.isDebugEnabled()) {
			logger.debug("Activating profile '" + profile + "'");
		}
		validateProfile(profile);
		//每次添加新的激活环境前,会调用doGetActiveProfiles方法
		//这里是顺便将属性源中规定的激活环境也添加进来，顺便清除之前的缓存
		doGetActiveProfiles();
		synchronized (this.activeProfiles) {
			this.activeProfiles.add(profile);
		}
	}

//和上面获取激活环境套路类似
	@Override
	public String[] getDefaultProfiles() {
		return StringUtils.toStringArray(doGetDefaultProfiles());
	}

	protected Set<String> doGetDefaultProfiles() {
		synchronized (this.defaultProfiles) {
			if (this.defaultProfiles.equals(getReservedDefaultProfiles())) {
				String profiles = doGetDefaultProfilesProperty();
				if (StringUtils.hasText(profiles)) {
					setDefaultProfiles(StringUtils.commaDelimitedListToStringArray(
							StringUtils.trimAllWhitespace(profiles)));
				}
			}
			return this.defaultProfiles;
		}
	}

	@Nullable
	protected String doGetDefaultProfilesProperty() {
		return getProperty(DEFAULT_PROFILES_PROPERTY_NAME);
	}

	@Override
	public void setDefaultProfiles(String... profiles) {
		Assert.notNull(profiles, "Profile array must not be null");
		synchronized (this.defaultProfiles) {
			this.defaultProfiles.clear();
			for (String profile : profiles) {
				validateProfile(profile);
				this.defaultProfiles.add(profile);
			}
		}
	}

//!profile表示当前环境没被激活才算有效
	@Override
	@Deprecated
	public boolean acceptsProfiles(String... profiles) {
		Assert.notEmpty(profiles, "Must specify at least one profile");
		for (String profile : profiles) {
			if (StringUtils.hasLength(profile) && profile.charAt(0) == '!') {
				if (!isProfileActive(profile.substring(1))) {
					return true;
				}
			}
			else if (isProfileActive(profile)) {
				return true;
			}
		}
		return false;
	}

	@Override
	public boolean acceptsProfiles(Profiles profiles) {
		Assert.notNull(profiles, "Profiles must not be null");
		return profiles.matches(this::isProfileActive);
	}

	protected boolean isProfileActive(String profile) {
		validateProfile(profile);
		Set<String> currentActiveProfiles = doGetActiveProfiles();
		return (currentActiveProfiles.contains(profile) ||
				(currentActiveProfiles.isEmpty() && doGetDefaultProfiles().contains(profile)));
	}

	protected void validateProfile(String profile) {
		if (!StringUtils.hasText(profile)) {
			throw new IllegalArgumentException("Invalid profile [" + profile + "]: must contain text");
		}
		if (profile.charAt(0) == '!') {
			throw new IllegalArgumentException("Invalid profile [" + profile + "]: must not begin with ! operator");
		}
	}

	@Override
	public MutablePropertySources getPropertySources() {
		return this.propertySources;
	}

	@Override
	@SuppressWarnings({"rawtypes", "unchecked"})
	public Map<String, Object> getSystemProperties() {
		try {
			return (Map) System.getProperties();
		}
		catch (AccessControlException ex) {
			return (Map) new ReadOnlySystemAttributesMap() {
				@Override
				@Nullable
				protected String getSystemAttribute(String attributeName) {
					try {
						return System.getProperty(attributeName);
					}
					catch (AccessControlException ex) {
						if (logger.isInfoEnabled()) {
							logger.info("Caught AccessControlException when accessing system property '" +
									attributeName + "'; its value will be returned [null]. Reason: " + ex.getMessage());
						}
						return null;
					}
				}
			};
		}
	}

	@Override
	@SuppressWarnings({"rawtypes", "unchecked"})
	public Map<String, Object> getSystemEnvironment() {
		if (suppressGetenvAccess()) {
			return Collections.emptyMap();
		}
		try {
			return (Map) System.getenv();
		}
		catch (AccessControlException ex) {
			return (Map) new ReadOnlySystemAttributesMap() {
				@Override
				@Nullable
				protected String getSystemAttribute(String attributeName) {
					try {
						return System.getenv(attributeName);
					}
					catch (AccessControlException ex) {
						if (logger.isInfoEnabled()) {
							logger.info("Caught AccessControlException when accessing system environment variable '" +
									attributeName + "'; its value will be returned [null]. Reason: " + ex.getMessage());
						}
						return null;
					}
				}
			};
		}
	}
	
	protected boolean suppressGetenvAccess() {
		return SpringProperties.getFlag(IGNORE_GETENV_PROPERTY_NAME);
	}

	@Override
	public void merge(ConfigurableEnvironment parent) {
		for (PropertySource<?> ps : parent.getPropertySources()) {
			if (!this.propertySources.contains(ps.getName())) {
				this.propertySources.addLast(ps);
			}
		}
		String[] parentActiveProfiles = parent.getActiveProfiles();
		if (!ObjectUtils.isEmpty(parentActiveProfiles)) {
			synchronized (this.activeProfiles) {
				Collections.addAll(this.activeProfiles, parentActiveProfiles);
			}
		}
		String[] parentDefaultProfiles = parent.getDefaultProfiles();
		if (!ObjectUtils.isEmpty(parentDefaultProfiles)) {
			synchronized (this.defaultProfiles) {
				this.defaultProfiles.remove(RESERVED_DEFAULT_PROFILE_NAME);
				Collections.addAll(this.defaultProfiles, parentDefaultProfiles);
			}
		}
	}

	//---------------------------------------------------------------------
	// Implementation of ConfigurablePropertyResolver interface
	//---------------------------------------------------------------------

	@Override
	public ConfigurableConversionService getConversionService() {
		return this.propertyResolver.getConversionService();
	}

	@Override
	public void setConversionService(ConfigurableConversionService conversionService) {
		this.propertyResolver.setConversionService(conversionService);
	}

	@Override
	public void setPlaceholderPrefix(String placeholderPrefix) {
		this.propertyResolver.setPlaceholderPrefix(placeholderPrefix);
	}

	@Override
	public void setPlaceholderSuffix(String placeholderSuffix) {
		this.propertyResolver.setPlaceholderSuffix(placeholderSuffix);
	}

	@Override
	public void setValueSeparator(@Nullable String valueSeparator) {
		this.propertyResolver.setValueSeparator(valueSeparator);
	}

	@Override
	public void setIgnoreUnresolvableNestedPlaceholders(boolean ignoreUnresolvableNestedPlaceholders) {
		this.propertyResolver.setIgnoreUnresolvableNestedPlaceholders(ignoreUnresolvableNestedPlaceholders);
	}

	@Override
	public void setRequiredProperties(String... requiredProperties) {
		this.propertyResolver.setRequiredProperties(requiredProperties);
	}

	@Override
	public void validateRequiredProperties() throws MissingRequiredPropertiesException {
		this.propertyResolver.validateRequiredProperties();
	}

	//---------------------------------------------------------------------
	// Implementation of PropertyResolver interface
	//---------------------------------------------------------------------

	@Override
	public boolean containsProperty(String key) {
		return this.propertyResolver.containsProperty(key);
	}

	@Override
	@Nullable
	public String getProperty(String key) {
		return this.propertyResolver.getProperty(key);
	}

	@Override
	public String getProperty(String key, String defaultValue) {
		return this.propertyResolver.getProperty(key, defaultValue);
	}

	@Override
	@Nullable
	public <T> T getProperty(String key, Class<T> targetType) {
		return this.propertyResolver.getProperty(key, targetType);
	}

	@Override
	public <T> T getProperty(String key, Class<T> targetType, T defaultValue) {
		return this.propertyResolver.getProperty(key, targetType, defaultValue);
	}

	@Override
	public String getRequiredProperty(String key) throws IllegalStateException {
		return this.propertyResolver.getRequiredProperty(key);
	}

	@Override
	public <T> T getRequiredProperty(String key, Class<T> targetType) throws IllegalStateException {
		return this.propertyResolver.getRequiredProperty(key, targetType);
	}

	@Override
	public String resolvePlaceholders(String text) {
		return this.propertyResolver.resolvePlaceholders(text);
	}

	@Override
	public String resolveRequiredPlaceholders(String text) throws IllegalArgumentException {
		return this.propertyResolver.resolveRequiredPlaceholders(text);
	}

	@Override
	public String toString() {
		return getClass().getSimpleName() + " {activeProfiles=" + this.activeProfiles +
				", defaultProfiles=" + this.defaultProfiles + ", propertySources=" + this.propertySources + "}";
	}

}

该抽象类源码比较多，但是很好理解，这里不展开套路了，主要是对profile的处理

StandardEnvironment—标准环境实现类

public class StandardEnvironment extends AbstractEnvironment {
     // 这两个值定义就是在@Value注解要使用它们时的key~~~~~
	public static final String SYSTEM_ENVIRONMENT_PROPERTY_SOURCE_NAME = "systemEnvironment";
	public static final String SYSTEM_PROPERTIES_PROPERTY_SOURCE_NAME = "systemProperties";

	public StandardEnvironment() {
	}

	protected StandardEnvironment(MutablePropertySources propertySources) {
		super(propertySources);
	}

   //往属性源集合中添加两个属性源---》System.getProperties()和System.getenv()
	@Override
	protected void customizePropertySources(MutablePropertySources propertySources) {
		propertySources.addLast(
				new PropertiesPropertySource(SYSTEM_PROPERTIES_PROPERTY_SOURCE_NAME, getSystemProperties()));
		propertySources.addLast(
				new SystemEnvironmentPropertySource(SYSTEM_ENVIRONMENT_PROPERTY_SOURCE_NAME, getSystemEnvironment()));
	}

}

EnvironmentCapable

//当前组件包含并且会对外暴露一个当前环境对象的引用
//所有 Spring 应用程序上下文都是 EnvironmentCapable，
//并且该接口主要用于在框架方法中执行 instanceof 检查，
//这些方法接受 BeanFactory 实例，这些实例可能实际上是也可能不是 
//ApplicationContext 实例，以便与环境交互（如果确实可用）

//如前所述，ApplicationContext 扩展了 EnvironmentCapable，因此公开了一个 getEnvironment() 方法；
//但是，ConfigurableApplicationContext 重新定义了 getEnvironment() 并缩小了签名以返回 ConfigurableEnvironment。
//效果是 Environment 对象在从 ConfigurableApplicationContext 访问之前是“只读的”，此时它也可以被配置。
public interface EnvironmentCapable {
	Environment getEnvironment();
}

EnvironmentAware

在bean的生命周期初始化过程中,会去判断当前bean是否实现了相关aware接口，以便给其注入相关类，这里同理

public interface EnvironmentAware extends Aware {
	void setEnvironment(Environment environment);
}

StringValueResolver

//用于解析字符串值的简单策略接口。由ConfigurableBeanFactory 使用。
// @since 2.5  该接口非常简单，就是个函数式接口~
@FunctionalInterface
public interface StringValueResolver {
	@Nullable
	String resolveStringValue(String strVal);
}

EmbeddedValueResolver

帮助ConfigurableBeanFactory处理placeholders占位符的。

ConfigurableBeanFactory#resolveEmbeddedValue处理占位符真正干活的间接的就是它~~

// @since 4.3  这个类出现得还是蛮晚的   因为之前都是用内部类的方式实现的~~~~这个实现类是最为强大的  只是SpEL
public class EmbeddedValueResolver implements StringValueResolver {

	// BeanExpressionResolver 它支持的是SpEL  可以说非常的强大
	// 并且它有BeanExpressionContext就能拿到BeanFactory工厂，就能使用它的`resolveEmbeddedValue`来处理占位符~~~~
	// 双重功能都有了~~~拥有了和@Value一样的能力，非常强大~~~
	private final BeanExpressionContext exprContext;
	@Nullable
	private final BeanExpressionResolver exprResolver;

	public EmbeddedValueResolver(ConfigurableBeanFactory beanFactory) {
		this.exprContext = new BeanExpressionContext(beanFactory, null);
		this.exprResolver = beanFactory.getBeanExpressionResolver();
	}

	@Override
	@Nullable
	public String resolveStringValue(String strVal) {
		
		// 先使用Bean工厂处理占位符resolveEmbeddedValue
		String value = this.exprContext.getBeanFactory().resolveEmbeddedValue(strVal);
		// 再使用el表达式参与计算~~~~
		if (this.exprResolver != null && value != null) {
			Object evaluated = this.exprResolver.evaluate(value, this.exprContext);
			value = (evaluated != null ? evaluated.toString() : null);
		}
		return value;
	}

}

关于Bean工厂resolveEmbeddedValue的实现，我们这里也顺带看看：

AbstractBeanFactory :
	@Override
	@Nullable
	public String resolveEmbeddedValue(@Nullable String value) {
		if (value == null) {
			return null;
		}
		String result = value;
		for (StringValueResolver resolver : this.embeddedValueResolvers) {
			result = resolver.resolveStringValue(result);
			if (result == null) {
				return null;
			}
		}
		return result;
	}

EmbeddedValueResolverAware

public interface EmbeddedValueResolverAware extends Aware {

	/**
	 * Set the StringValueResolver to use for resolving embedded definition values.
	 */
	void setEmbeddedValueResolver(StringValueResolver resolver);

}

继承该接口的bean，可以在初始化阶段得到一个内嵌的值解析器