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SpringBoot的条件装配原理

news 2025/8/26 7:25:51

一.前言

SpringBoot的条件装配是基于@Conditional注解实现的。下面我们使用原生的@Conditional注解模拟实现类的条件装配。

二.实现思路

1.实现Condition接口

写一个类实现Condition接口并重写matches方法，matches方法返回的布尔值决MyConditional1是否生效。下面我们模拟DruidDataSource类存在则返回真。

static class MyConditional1 implements Condition {@Overridepublic boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {return ClassUtils.isPresent("com.alibaba.druid.pool.DruidDataSource", null);}}

同上，但是条件刚好相反，模拟DruidDataSource类不存在则返回真。

 static class MyConditional2 implements Condition {@Overridepublic boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {return !ClassUtils.isPresent("com.alibaba.druid.pool.DruidDataSource", null);}}

2.使用注解@Conditional条件装配自动配置类

自动配置类生效与否取决于自我实现的MyConditional1、MyConditional2类中match方法的返回值。

    @Configuration@Conditional(MyConditional1.class)static class AutoConfiguration1{@Beanpublic Bean1 Bean1(){return new Bean1();}}@Configuration@Conditional(MyConditional2.class)static class AutoConfiguration2{@Beanpublic Bean2 Bean2(){return new Bean2();}}static class Bean1{}static class Bean2{}

3.测试代码如下

package com.example.springdemo.demos.a08;
import org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryAutoConfiguration;
import org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext;
import org.springframework.context.annotation.*;
import org.springframework.core.type.AnnotatedTypeMetadata;
import org.springframework.core.type.AnnotationMetadata;
import org.springframework.util.ClassUtils;/*** @author zhou* @version 1.0* @description TODO* @date 2025/8/24 16:11*/
public class TestMyConditional {public static void main(String[] args) {AnnotationConfigServletWebServerApplicationContext context = new AnnotationConfigServletWebServerApplicationContext();context.registerBean("config", Config.class);context.refresh();for(String name : context.getBeanDefinitionNames()){String resource = context.getBeanDefinition(name).getResourceDescription();if(resource != null){System.out.println(name + "来源："+resource);}}context.close();}@Configuration@Import(MyImportSelector.class)static  class Config{}static class MyImportSelector implements DeferredImportSelector{@Overridepublic String[] selectImports(AnnotationMetadata importingClassMetadata) {return new String[]{AutoConfiguration1.class.getName(),AutoConfiguration2.class.getName(), ServletWebServerFactoryAutoConfiguration.class.getName()};}}static class MyConditional1 implements Condition {@Overridepublic boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {return ClassUtils.isPresent("com.alibaba.druid.pool.DruidDataSource", null);}}static class MyConditional2 implements Condition {@Overridepublic boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {return !ClassUtils.isPresent("com.alibaba.druid.pool.DruidDataSource", null);}}@Configuration@Conditional(MyConditional1.class)static class AutoConfiguration1{@Beanpublic Bean1 Bean1(){return new Bean1();}}@Configuration@Conditional(MyConditional2.class)static class AutoConfiguration2{@Beanpublic Bean2 Bean2(){return new Bean2();}}static class Bean1{}static class Bean2{}}

4.测试结果

由于我的代码中不存在com.alibaba.druid.pool.DruidDataSource类，所以AutoConfiguration1类配置的Bean1没有生效，所以输出Bean1。现在我们换一个存在的类，代码中的一个类com.example.springdemo.demos.a08.TestMyConditional.AutoConfiguration1，由于该类存在，所以AutoConfiguration1类上的配置生效，AutoConfiguration2类上刚好需要相反的条件，所以不成立。最后打印了Bean1类。