@ConditionalOnMissingBean 如何实现覆盖第三方组件中的 Bean

1. 自定义一个简单 spring-boot 组件

创建 olive-starter 项目

对应的 pom.xml文件如下

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>com.olive</groupId>
  <artifactId>olive-starter</artifactId>
  <version>0.0.1-SNAPSHOT</version>
  <parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>2.7.1</version>
    <relativePath/>
  </parent>
  <name>olive-starter</name>
  <description>olive starter for Spring Boot</description>
  <properties>
    <java.version>1.8</java.version>
  </properties>
  <dependencies>
    <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter</artifactId>
    </dependency>
  </dependencies>
</project>

注意这里不要引入 spring-boot 的插件，使用maven原生的，否则使用maven install的时，其他工程无法引入

定义一个加载路由的接口

package com.olive.service;
import java.util.List;
import com.olive.model.RouterDO;
​
public interface RouterService {
  public List<RouterDO> getRouters();
}

路由的实体类 DouterDO 与实现类如下

DouterDO.java 类

package com.olive.model;
​
import java.io.Serializable;
​
public class RouterDO implements Serializable{

  private String id;

  private String routerName;

  //TODO 省略getter  setter
}

DefaultRouterServiceImpl.java 类，默认的路由加载策略

package com.olive.service.impl;
​
import java.util.ArrayList;
import java.util.List;
import com.olive.model.RouterDO;
import com.olive.service.RouterService;
​
public class DefaultRouterServiceImpl implements RouterService{
​
  @Override
  public List<RouterDO> getRouters() {
    //TODO
     System.out.println("-------------DefaultRouterServiceImpl----------");
    return new ArrayList<RouterDO>();
  }
​
}

配置默认的路由加载 Bean

package com.olive.config;
​
import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import com.olive.service.RouterService;
import com.olive.service.impl.DefaultRouterServiceImpl;
​
@Configuration
public class RouterConfig {
​
  @Bean
    @ConditionalOnMissingBean
    public RouterService getRouterService(){
        return new DefaultRouterServiceImpl();
    }
​
}

创建 MATE-INF 文件夹，并在该文件下创建 spring.factories 文件；spring.factories 文件内容如下

org.springframework.boot.autoconfigure.EnableAutoConfiguration=com.olive.config.RouterConfig​

​整体项目结构如下：

2. 创建另外一个项目 olive-gateway，引用 olive-starter 工程

olive-gateway 的 pom.xml 文件如下
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>com.olive</groupId>
  <artifactId>olive-gateway</artifactId>
  <version>0.0.1-SNAPSHOT</version>
  <parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>2.7.1</version>
    <relativePath />
  </parent>
  <name>olive-starter</name>
  <description>olive starter for Spring Boot</description>
  <properties>
    <java.version>1.8</java.version>
  </properties>
  <dependencies>
    <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter</artifactId>
    </dependency>
    <dependency>
      <groupId>com.olive</groupId>
      <artifactId>olive-starter</artifactId>
      <version>0.0.1-SNAPSHOT</version>
    </dependency>
  </dependencies>
</project>

创建 springboot 启动引导类

package com.gateway;
​
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ApplicationContext;
import com.olive.service.RouterService;
​
@SpringBootApplication
public class GwApplication {
​
  public static void main(String[] args) {
    ApplicationContext ac = SpringApplication.run(GwApplication.class, args);
    RouterService routerService = ac.getBean(RouterService.class);
    routerService.getRouters();
  }

}

启动项目

观察日志，使用默认的路由加载类 DefaultRouterServiceImpl

再自定义一个路由加载类实现 RouterService 接口

package com.gateway.service.impl;
​
import java.util.ArrayList;
import java.util.List;
import org.springframework.stereotype.Service;
import com.olive.model.RouterDO;
import com.olive.service.RouterService;
​
​
@Service
public class CustomRouterServiceImpl implements RouterService {
  @Override
  public List<RouterDO> getRouters() {
    System.out.println("-------CustomRouterServiceImpl------");
    return new ArrayList<>();
  }
}

再次启动项目

观察日志，已经覆盖默认的路由加载类 DefaultRouterServiceImpl

​