Spring Boot 中基于配置属性条件化创建 Bean 的实践指南

import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

// 模拟JMS相关的接口和类，以便示例代码能够独立运行
interface ConnectionFactory {}
class CachingConnectionFactory implements ConnectionFactory {
    public void setTargetConnectionFactory(ConnectionFactory cf) { /* ... */ }
    public void setReconnectOnException(boolean reconnect) { /* ... */ }
    public void setSessionCacheSize(int size) { /* ... */ }
}
class UserCredentialsConnectionFactoryAdapter implements ConnectionFactory {
    public void setUsername(String username) { /* ... */ }
    public void setPassword(String password) { /* ... */ }
    public void setTargetConnectionFactory(ConnectionFactory cf) { /* ... */ }
}
class AxonConnectionFactory implements ConnectionFactory {}
class MessagingJMSService {
    public ConnectionFactory getConnectionFactory(String name) { return new AxonConnectionFactory(); }
}

@Configuration
public class ConnectionStrategyConfig {

    // 假设 AxonConnectionFactory 是一个独立的 Bean 或通过其他方式提供
    @Bean
    public AxonConnectionFactory axonConnectionFactory() {
        return new AxonConnectionFactory();
    }

    // 假设 MessagingJMSService 是一个独立的 Bean
    @Bean
    public MessagingJMSService messagingJMSService() {
        return new MessagingJMSService();
    }

    /**
     * 根据属性 `app.connection.strategy.enable-user-credentials` 的值来条件性创建 CachingConnectionFactory Bean。
     * 当该属性为 `false` 或未配置时，此 Bean 将被创建。
     *
     * @param axonConnectionFactory 目标连接工厂
     * @return CachingConnectionFactory 实例
     */
    @Bean
    @ConditionalOnProperty(
        prefix = "app.connection.strategy",
        name = "enable-user-credentials",
        havingValue = "false", // 只有当属性值为 "false" 时匹配
        matchIfMissing = true  // 如果属性不存在，也匹配（即创建此Bean）
    )
    public CachingConnectionFactory cachingConnectionFactory(AxonConnectionFactory axonConnectionFactory) {
        System.out.println(">>> Creating CachingConnectionFactory Bean...");
        CachingConnectionFactory connectionFactory = new CachingConnectionFactory();
        connectionFactory.setTargetConnectionFactory(axonConnectionFactory);
        connectionFactory.setReconnectOnException(true);
        connectionFactory.setSessionCacheSize(10); // 示例值
        return connectionFactory;
    }

    /**
     * 根据属性 `app.connection.strategy.enable-user-credentials` 的值来条件性创建 UserCredentialsConnectionFactoryAdapter Bean。
     * 只有当该属性为 `true` 时，此 Bean 才会被创建。
     *
     * @param messagingJMSService 消息JMS服务，用于获取目标连接工厂
     * @return UserCredentialsConnectionFactoryAdapter 实例
     * @throws Exception 如果创建过程中发生错误
     */
    @Bean
    @ConditionalOnProperty(
        prefix = "app.connection.strategy",
        name = "enable-user-credentials",
        havingValue = "true" // 只有当属性值为 "true" 时匹配
    )
    public UserCredentialsConnectionFactoryAdapter userCredentialsConnectionFactoryAdapter(
            MessagingJMSService messagingJMSService) throws Exception {
        System.out.println(">>> Creating UserCredentialsConnectionFactoryAdapter Bean...");
        UserCredentialsConnectionFactoryAdapter connectionFactoryAdapter =
            new UserCredentialsConnectionFactoryAdapter();
        // 实际应用中，这些值通常也应从属性文件中读取
        connectionFactoryAdapter.setUsername("myUser");
        connectionFactoryAdapter.setPassword("myPass");
        connectionFactoryAdapter.setTargetConnectionFactory(
            messagingJMSService.getConnectionFactory("default")); // 使用注入的服务
        return connectionFactoryAdapter;
    }
}

app.connection.strategy.enable-user-credentials=true

app.connection.strategy.enable-user-credentials=false

# 不配置此属性，因为 CachingConnectionFactory 的 @ConditionalOnProperty 设置了 matchIfMissing = true