spring @Conditional的使用与扩展源码分析

目录

• @Conditional的使用
• WindowsCondition
• LinuxCondition
• Conditional的扩展
• ConditionalOnBean
• ConditionalOnProperty
• 源码分析

@Conditional的使用

@Conditional可以根据条件来判断是否注入某些Bean。

package com.morris.spring.config;

import com.morris.spring.condition.LinuxCondition;
import com.morris.spring.condition.WindowsCondition;
import com.morris.spring.entity.User;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Conditional;
import org.springframework.context.annotation.Configuration;
@Configuration
public class ConditionalConfig {
	// 如果是windows系统就注入bill
	@Conditional(WindowsCondition.class)
	@Bean(name = "user")
	public User bill() {
		return new User("bill", 22);
	}
	// 如果是linux系统就注入linus
	@Conditional(LinuxCondition.class)
	public User linus() {
		return new User("linus", 20);
}

WindowsCondition和LinuxCondition都需要实现Condition接口。

WindowsCondition

package com.morris.spring.condition;

import org.springframework.context.annotation.Condition;
import org.springframework.context.annotation.ConditionContext;
import org.springframework.core.type.AnnotatedTypeMetadata;
public class WindowsCondition implements Condition {
    /**
     * 根据条件判断是否注入对应的Bean
     * @param conditionContext 应用上下文
     * @param annotatedTypeMetadata 加了@Conditional注解的方法的元数据信息
     * @return
     */
    @Override
    public boolean matches(ConditionContext conditionContext, AnnotatedTypeMetadata annotatedTypeMetadata) {
        String osName = conditionContext.getEnvironment().getProperty("os.name");
        if(osName.contains("Windows")) {
            return true;
        }
        return false;
    }
}

LinuxCondition

package com.morris.spring.condition;

import org.springframework.context.annotation.Condition;
import org.springframework.context.annotation.ConditionContext;
import org.springframework.core.type.AnnotatedTypeMetadata;
public class LinuxCondition implements Condition {
    @Override
    public boolean matches(ConditionContext conditionContext, AnnotatedTypeMetadata annotatedTypeMetadata) {
        String osName = conditionContext.getEnvironment().getProperty("os.name");
        if(osName.contains("linux")) {
            return true;
        }
        return false;
    }
}

如果要测试LinuxCondition并不需要再linux系统下运行，只需要的启动时设置环境参数：-Dos.name=linux。

Conditional的扩展

ConditionalOnBean

ConditionalOnBeanc.java

package com.morris.spring.condition;

import org.springframework.context.annotation.Conditional;
import java.lang.annotation.*;
@Target({ElementType.TYPE, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Conditional(OnBeanCondition.class)
public @interface ConditionalOnBean {
	Class<?>[] value() default {};
}

OnBeanCondition.java

package com.morris.spring.condition;

import org.springframework.context.annotation.Condition;
import org.springframework.context.annotation.ConditionContext;
import org.springframework.core.type.AnnotatedTypeMetadata;
import java.util.Map;
public class OnBeanCondition implements Condition {
	@Override
	public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
		Map<String, Object> annotationAttributes = metadata.getAnnotationAttributes(ConditionalOnBean.class.getName());
		Class<?>[] clazz = (Class<?>[]) annotationAttributes.get("value");
		for (Class<?> aClass : clazz) {
			Map<String, ?> beans = context.getBeanFactory().getBeansOfType(aClass);
			if(beans.isEmpty()) {
				return false;
			}
		}
		return true;
	}
}

ConditionalOnProperty

ConditionalOnProperty.java

package com.morris.spring.condition;

import org.springframework.context.annotation.Conditional;
import java.lang.annotation.*;
@Target({ElementType.TYPE, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Conditional(OnPropertyCondition.class)
public @interface ConditionalOnProperty {
	String[] value() default {};
}

OnPropertyCondition.java

package com.morris.spring.condition;

import org.springframework.context.annotation.Condition;
import org.springframework.context.annotation.ConditionContext;
import org.springframework.core.type.AnnotatedTypeMetadata;
import java.util.Map;
public class OnPropertyCondition implements Condition {
	@Override
	public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
		Map<String, Object> annotationAttributes = metadata.getAnnotationAttributes(ConditionalOnProperty.class.getName());
		String[] propertyArray = (String[]) annotationAttributes.get("value");
		for (String property : propertyArray) {
			if(!context.getEnvironment().containsProperty(property)) {
				return false;
			}
		}
		return true;
	}
}

源码分析

如果Condition返回的是false，那么spirng就不会对方法或类进行解析。

org.springframework.context.annotation.ConditionEvaluator#shouldSkip

public boolean shouldSkip(@Nullable AnnotatedTypeMetadata metadata, @Nullable ConfigurationPhase phase) {
	// 判断类或方法上面是否有@Conditional注解
	if (metadata == null || !metadata.isAnnotated(Conditional.class.getName())) {
		return false;
	}
	if (phase == null) {
		if (metadata instanceof AnnotationMetadata &&
				ConfigurationClassUtils.isConfigurationCandidate((AnnotationMetadata) metadata)) {
			return shouldSkip(metadata, ConfigurationPhase.PARSE_CONFIGURATION);
		}
		return shouldSkip(metadata, ConfigurationPhase.REGISTER_BEAN);
	List<Condition> conditions = new ArrayList<>();
	for (String[] conditionClasses : getConditionClasses(metadata)) {
		for (String conditionClass : conditionClasses) {
			Condition condition = getCondition(conditionClass, this.context.getClassLoader());
			conditions.add(condition);
	AnnotationAwareOrderComparator.sort(conditions);
	for (Condition condition : conditions) {
		ConfigurationPhase requiredPhase = null;
		if (condition instanceof ConfigurationCondition) {
			requiredPhase = ((ConfigurationCondition) condition).getConfigurationPhase();
		// 调用condition.matches方法
		if ((requiredPhase == null || requiredPhase == phase) && !condition.matches(this.context, metadata)) {
			return true;
	return false;
}