Spring-以编程方式生成一组bean

Z时代
2024-01-10
分类：问答

我有一个Dropwizard应用程序，需要为配置列表中的每个配置生成十几个bean。

像这样：

@Component
class MyModule {
    @Inject
    private MyConfiguration configuration;
    @Bean
    @Lazy
    public QuartzModule quartzModule() {
        return new QuartzModule(quartzConfiguration());
    }
    @Bean
    @Lazy
    public QuartzConfiguration quartzConfiguration() {
        return this.configuration.getQuartzConfiguration();
    }
    @Bean
    @Lazy
    public HealthCheck healthCheck() throws SchedulerException {
        return this.quartzModule().quartzHealthCheck();
    }
}

我有多个MyConfiguration实例，都需要这样的bean。现在，我必须复制并粘贴这些定义，并为每个新配置重命名它们。

我可以以某种方式遍历我的配置类并为每个配置类生成一组bean定义吗？

我可以使用子类解决方案或任何类型安全的东西，而无需每次添加新服务时都复制并粘贴相同的代码并重命名方法。

编辑：我应该补充一点，我还有其他依赖于这些bean的组件（Collection<HealthCheck>例如，它们注入）。

回答：

你需要即时声明新bean并将它们注入Spring的应用程序上下文中，就像它们只是普通bean一样，这意味着它们必须经受代理，后处理等操作，即它们必须经受Spring bean生命周期的约束。。

请参阅BeanDefinitionRegistryPostProcessor.postProcessBeanDefinitionRegistry()方法 javadocs。这正是你所需要的，因为它使你可以在装入常规bean定义之后但实例化任何单个bean之前修改Spring的应用程序上下文。

@Configuration
public class ConfigLoader implements BeanDefinitionRegistryPostProcessor {
    private final List<String> configurations;
    public ConfigLoader() {
        this.configurations = new LinkedList<>();
        // TODO Get names of different configurations, just the names!
        // i.e. You could manually read from some config file
        // or scan classpath by yourself to find classes 
        // that implement MyConfiguration interface.
        // (You can even hardcode config names to start seeing how this works)
        // Important: you can't autowire anything yet, 
        // because Spring has not instantiated any bean so far!
        for (String readConfigurationName : readConfigurationNames) {
            this.configurations.add(readConfigurationName);
        }
    }
    public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {
        // iterate over your configurations and create the beans definitions it needs
        for (String configName : this.configurations) {
            this.quartzConfiguration(configName, registry);
            this.quartzModule(configName, registry);
            this.healthCheck(configName, registry);
            // etc.
        }
    }
    private void quartzConfiguration(String configName, BeanDefinitionRegistry registry) throws BeansException {
        String beanName = configName + "_QuartzConfiguration";
        BeanDefinitionBuilder builder = BeanDefinitionBuilder.genericBeanDefinition(QuartzConfiguration.class).setLazyInit(true); 
        // TODO Add what the bean needs to be properly initialized
        // i.e. constructor arguments, properties, shutdown methods, etc
        // BeanDefinitionBuilder let's you add whatever you need
        // Now add the bean definition with given bean name
        registry.registerBeanDefinition(beanName, builder.getBeanDefinition());
    }
    private void quartzModule(String configName, BeanDefinitionRegistry registry) throws BeansException {
        String beanName = configName + "_QuartzModule";
        BeanDefinitionBuilder builder = BeanDefinitionBuilder.genericBeanDefinition(QuartzModule.class).setLazyInit(true); 
        builder.addConstructorArgReference(configName + "_QuartzConfiguration"); // quartz configuration bean as constructor argument
        // Now add the bean definition with given bean name
        registry.registerBeanDefinition(beanName, builder.getBeanDefinition());
    }
    private void healthCheck(String configName, BeanDefinitionRegistry registry) throws BeansException {
        String beanName = configName + "_HealthCheck";
        BeanDefinitionBuilder builder = BeanDefinitionBuilder.genericBeanDefinition(HealthCheck.class).setLazyInit(true); 
        // TODO Add what the bean needs to be properly initialized
        // i.e. constructor arguments, properties, shutdown methods, etc
        // BeanDefinitionBuilder let's you add whatever you need
        // Now add the bean definition with given bean name
        registry.registerBeanDefinition(beanName, builder.getBeanDefinition());
    }
    // And so on for other beans...
}

这有效地声明了你需要的bean，并将它们注入Spring的应用程序上下文中，每种配置都有一组bean。你必须依靠某种命名模式，然后在需要的地方通过名称自动连接bean：

@Service
public class MyService {
    @Resource(name="config1_QuartzConfiguration")
    private QuartzConfiguration config1_QuartzConfiguration;
    @Resource(name="config1_QuartzModule")
    private QuartzModule config1_QuartzModule;
    @Resource(name="config1_HealthCheck")
    private HealthCheck config1_HealthCheck;
    ...
}

笔记：