Spring注解学习[email protected]注解

注解概括

Conditional注解

当满足一定条件是才向Spring容器中注册Bean。
该注解可以注释在配置类或者方法上，向其中传入实现了Condition接口的类变量。如果配置在方法上，则满足条件当前Bean方法生效。如果配置在类上，则满足条件当前类中的所有Bean方法全部生效。

Since Spring4.0

代码演示

先创建一个Bean对象
Subject.java

package cc.fireflyhut.selfstudy.bean;

public class Subject {

    public Subject() {}

    public Subject(String name, String element) {
        this.name = name;
        this.element = element;
    }

    private String name;

    private String element;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getElement() {
        return element;
    }

    public void setElement(String element) {
        this.element = element;
    }
}

创建两个实现Condition接口的类
ConditionEvenImpl.java

package cc.fireflyhut.selfstudy.bean.condition;

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

import java.util.Date;

public class ConditionEvenImpl implements Condition {

    @Override
    public boolean matches(ConditionContext conditionContext, AnnotatedTypeMetadata annotatedTypeMetadata) {
        Date now = new Date();
        int num = now.getSeconds();
        if (num % 2 == 0) {
            return true;
        }
        return false;
    }

}

package cc.fireflyhut.selfstudy.bean.condition;


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

import java.util.Date;

public class ConditionOddImpl implements Condition {

    @Override
    public boolean matches(ConditionContext conditionContext, AnnotatedTypeMetadata annotatedTypeMetadata) {
        Date now = new Date();
        int num = now.getSeconds();
        if (num % 2 != 0) {
            return true;
        }
        return false;
    }
}

再创建一个配置类
BeanConfig.java

package cc.fireflyhut.selfstudy.bean;

import cc.fireflyhut.selfstudy.bean.condition.ConditionEvenImpl;
import cc.fireflyhut.selfstudy.bean.condition.ConditionOddImpl;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Conditional;

public class BeanConfig {

    @Conditional(ConditionOddImpl.class)
    @Bean
    public Subject odd() {
        return new Subject("一只小对象", "奇数哦~");
    }

    @Conditional(ConditionEvenImpl.class)
    @Bean
    public Subject even() {
        return new Subject("一只大对象", "偶数！");
    }

}

开始在测试类中测试

package cc.fireflyhut.selfstudy.bean;

import org.junit.Test;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;

import java.text.SimpleDateFormat;
import java.util.Date;

public class BeanTest {

    ApplicationContext applicationContext = new AnnotationConfigApplicationContext(BeanConfig.class);

    @Test
    public void test() {
        String[] beanName = applicationContext.getBeanNamesForType(Subject.class);
        System.out.println(new SimpleDateFormat("HH:mm:ss").format(new Date()));
        for (String name : beanName) {
            System.out.println(name);
        }
    }
    
}

在秒数为奇数的时候可以看到名字为odd的bean被注册，秒数为偶数的时候名字为even的bean被注册到容器中。