死磕源码系列【AutoConfigurationImportFilter自动化配置过滤器详解】

偏执的太偏执、 2022-12-11 07:25 218阅读 0赞

/** * Filter that can be registered in {@code spring.factories} to limit the * auto-configuration classes considered. This interface is designed to allow fast removal * of auto-configuration classes before their bytecode is even read. * <p> * An {@link AutoConfigurationImportFilter} may implement any of the following * {@link org.springframework.beans.factory.Aware Aware} interfaces, and their respective * methods will be called prior to {@link #match}: * <ul> * <li>{@link EnvironmentAware}</li> * <li>{@link BeanFactoryAware}</li> * <li>{@link BeanClassLoaderAware}</li> * <li>{@link ResourceLoaderAware}</li> * </ul> * * @author Phillip Webb * @since 1.5.0 */
    @FunctionalInterface
    public interface AutoConfigurationImportFilter { 
    
    	/** * Apply the filter to the given auto-configuration class candidates. * @param autoConfigurationClasses the auto-configuration classes being considered. * This array may contain {@code null} elements. Implementations should not change the * values in this array. * @param autoConfigurationMetadata access to the meta-data generated by the * auto-configure annotation processor * @return a boolean array indicating which of the auto-configuration classes should * be imported. The returned array must be the same size as the incoming * {@code autoConfigurationClasses} parameter. Entries containing {@code false} will * not be imported. */
    	boolean[] match(String[] autoConfigurationClasses, AutoConfigurationMetadata autoConfigurationMetadata);
    
    }

AutoConfigurationImportFilter是一个过滤器接口，其实现类是被注册到spring.factories配置文件，被设计用来在自动化配置类字节码加载之前根据条件删除配置类；该接口实现类可以实现org.springframework.beans.factory.Aware接口，可以在match方法被调用之前执行，如：EnvironmentAware、BeanFactoryAware、BeanClassLoaderAware、ResourceLoaderAware

spring.factories配置的实现类如下：

# Auto Configuration Import Filters
    org.springframework.boot.autoconfigure.AutoConfigurationImportFilter=\
    org.springframework.boot.autoconfigure.condition.OnBeanCondition,\
    org.springframework.boot.autoconfigure.condition.OnClassCondition,\
    org.springframework.boot.autoconfigure.condition.OnWebApplicationCondition

从配置中可以看到AutoConfigurationImportFilter接口一共有三个实现类，且三个类都是通过FilteringSpringBootCondition抽象类间接实现AutoConfigurationImportFilter过滤器接口；FilteringSpringBootCondition抽象类是SpringBootCondition类的子类；SpringBootCondition类的作用是提供合理的日志记录以帮助用户诊断加载了哪些类，具体的比对由其子类来实现；

*  SpringBootCondition实现了Condition接口，将一些模板处理定义在该类中，声明了getMatchOutcome这么一个抽象方法，子类只需要实现该方法即可实现业务逻辑，matches方法用于判定其条件是否成立，如果不成立，则会组织该bean的注册

public abstract class SpringBootCondition implements Condition { 
    
    	private final Log logger = LogFactory.getLog(getClass());
    
    	@Override
    	public final boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) { 
    		//获取类名或者方法名（条件注解作用的类或方法上） 
        String classOrMethodName = getClassOrMethodName(metadata);
        //抽象方法，具体子类实现，返回值ConditionOutcome记录了匹配结果boolean和log信息
    		ConditionOutcome outcome = getMatchOutcome(context, metadata);
        //打印日志trace级别
    		logOutcome(classOrMethodName, outcome);
        //记录结果
    		recordEvaluation(context, classOrMethodName, outcome);
    		return outcome.isMatch();
    	}
      //抽象方法，由子类实现
    	public abstract ConditionOutcome getMatchOutcome(ConditionContext context, AnnotatedTypeMetadata metadata);
    		}

getClassOrMethodName方法：

//获取类名或者方法名，条件注解可以作用在类上或方法上
    private static String getClassOrMethodName(AnnotatedTypeMetadata metadata) { 
      //如果metadata是ClassMetadata实例，则返回类名，否则返回全类目#方法名
       if (metadata instanceof ClassMetadata) { 
          ClassMetadata classMetadata = (ClassMetadata) metadata;
          return classMetadata.getClassName();
       }
       MethodMetadata methodMetadata = (MethodMetadata) metadata;
       return methodMetadata.getDeclaringClassName() + "#" + methodMetadata.getMethodName();
    }

getMatchOutcome抽象方法，由子类实现

抽象类的返回结果是ConditionOutcome类型，是对结果boolean和log信息的封装

public class ConditionOutcome { 
    	//是否匹配
    	private final boolean match;
    	//消息封住对象，提供了一个流式构造风格
    	private final ConditionMessage message;
    }

logOutcome方法

//打印日志，trace级别
    	protected final void logOutcome(String classOrMethodName, ConditionOutcome outcome) { 
    		if (this.logger.isTraceEnabled()) { 
    			this.logger.trace(getLogMessage(classOrMethodName, outcome));
    		}
    	}

recordEvaluation方法：

//最终将结果记录到缓存之中 
    private void recordEvaluation(ConditionContext context, String classOrMethodName, ConditionOutcome outcome) { 
    		if (context.getBeanFactory() != null) { 
    			ConditionEvaluationReport.get(context.getBeanFactory()).recordConditionEvaluation(classOrMethodName, this,
    					outcome);
    		}
    	}

另外还提供了两个有用的方法供子类使用：

protected final boolean anyMatches(ConditionContext context, AnnotatedTypeMetadata metadata,
          Condition... conditions) { 
       for (Condition condition : conditions) { 
          if (matches(context, metadata, condition)) { 
             return true;
          }
       }
       return false;
    }

matches方法：

protected final boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata, Condition condition) { 
    		if (condition instanceof SpringBootCondition) { 
    			return ((SpringBootCondition) condition).getMatchOutcome(context, metadata).isMatch();
    		}
    		return condition.matches(context, metadata);
    	}

三个过滤器子类OnBeanCondition、OnClassCondition、OnWebApplicationCondition的实现方法都是通过父类中的match方法调用抽象实现方法getOutcomes进行判定是否符合条件；

GitHub地址：[https://github.com/mingyang66/spring-parent][https_github.com_mingyang66_spring-parent]

[https_github.com_mingyang66_spring-parent]: https://github.com/mingyang66/spring-parent