006-Spring Boot自动配置-Condition、Conditional

一、接口Condition、Conditional（原理）

主要提供一下方法

boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata);

true：表示装配

false：表示不装配

注解：Conditional() 参数是数组，数组内的都是true才装配

package com.lhx.spring.springboot_auto_config;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Condition;
import org.springframework.context.annotation.Conditional;

@SpringBootApplication
public class App2 {

public static void main(String[] args) {
ConfigurableApplicationContext context = SpringApplication.run(App2.class, args);
System.out.println(context.getBeansOfType(Runnable.class));
context.close();
}
}

View Code
默认是不能装配的

可以再application.properties中添加runnable.enable=true即可装配

或者@ConditionalOnProperty(name = "runnable.enable", havingValue = "true")增加

matchIfMissing=true，表示配置没有的时候也生效

示例二：ConditionalOnClass classpath有某个类才装配

增加或删除maven，查看效果

<dependency>
<groupId>com.google.code.gson</groupId>
<artifactId>gson</artifactId>
<version>2.8.2</version>
</dependency>

使用代码

@Bean
@ConditionalOnClass(name="com.google.gson.Gson")
public Runnable createGsonRunnable() {
return () -> {
};
}

示例三、ConditionalOnBean：根据容器中是否存在某个Bean进行装配

@Bean
@ConditionalOnBean(name="user")
public Runnable createOnBeanRunnable() {
return () -> {
};
}