面試題- Spring IOC 條件加載Bean-註解Conditional

Spring IOC 條件加載Bean-註解Conditional

1)在配置文件中配置加載類

condition.impl=com.cdchen.study.service.impl.ConditionTestImpl1

2)編寫ConditionConfig

import org.springframework.context.annotation.Condition;
import org.springframework.context.annotation.ConditionContext;
import org.springframework.core.type.AnnotatedTypeMetadata;
import org.springframework.core.type.classreading.AnnotationMetadataReadingVisitor;

/**
 *
 * @description: ConditionConfig
 *
 * @author: cdchen
 *
 * @create: 2019-05-24 11:05
 **/
public class ConditionConfig implements Condition {

    @Override
    public boolean matches(ConditionContext conditionContext,
                           AnnotatedTypeMetadata annotatedTypeMetadata) {
        AnnotationMetadataReadingVisitor annotationMetadataReadingVisitor = (AnnotationMetadataReadingVisitor) annotatedTypeMetadata;
        // 獲取配置的實現類
        String impl = conditionContext.getEnvironment().getProperty("condition.impl");
        // 獲取 Conditional 註解的類的className
        String className = annotationMetadataReadingVisitor.getClassName();
        //判斷是否一致
        if(impl.equals(className)){
            return true;
        }else{
            return false;
        }
    }

3)編寫接口

public interface ConditionTest {
    public void test();
}

4)編寫實現類

import com.cdchen.study.service.ConditionTest;
import lombok.extern.slf4j.Slf4j;
import org.springframework.context.annotation.Conditional;
import org.springframework.stereotype.Component;

/**
 *
 * @description: ConditionTestImpl1
 *
 * @author: cdchen
 *
 * @create: 2019-05-24 11:03
 **/
@Slf4j
@Conditional({ ConditionConfig.class})
@Component
public class ConditionTestImpl1 implements ConditionTest {
    @Override
    public void test() {
        log.info("這是ConditionTestImpl1實現");
    }
}

import com.cdchen.study.service.ConditionTest;
import lombok.extern.slf4j.Slf4j;
import org.springframework.context.annotation.Conditional;
import org.springframework.stereotype.Component;

/**
 *
 * @description: ConditionTestImpl2
 *
 * @author: cdchen
 *
 * @create: 2019-05-24 11:04
 **/
@Slf4j
@Conditional({ ConditionConfig.class})
@Component
public class ConditionTestImpl2 implements ConditionTest {
    @Override
    public void test() {
        log.info("這是ConditionTestImpl2 實現");
    }
}

5)驗證

public static void main(String[] args) {
		SpringApplication.run(Application.class, args);
		ConditionTest conditionTest = SpringBeanUtil.getBean(ConditionTest.class);
		conditionTest.test();
	}

結果如下

15:58:49.283 [main] INFO  com.cdchen.study.Application - Started Application in 8.339 seconds (JVM running for 12.797)
15:58:49.284 [main] INFO  c.c.s.s.impl.ConditionTestImpl1 - 這是ConditionTestImpl1實現