spring - 动态 Spring bean 创建

Question

我正在使用一个 API，它以 XXXLocalServiceUtil 类的形式公开服务，这些类是单例对象的静态包装器。我不想使用静态 XXXLocalServiceUtil 方法，而是想自己注入(inject) XXXLocalService 对象以直接在我的代码中使用它们，例如:

@Named
public class MyMailingService {        
    @Inject UserLocalService userService;

    public String mailUser(String email) {
       User user = userService.getUser(email);
       emailUser(user);
    }
}

然后像这样配置我的 applicationContext.xml:

<beans ...>
    <bean class="x.y.z.UserLocalServiceUtil" factory-method="getService"/>
    <bean class="x.y.z.CompanyLocalServiceUtil" factory-method="getService"/>
    ...
</beans>

这非常有效。现在，我正在谈论的这个 API 有大约 100 个这样的 XXXLocalServiceUtil 类，每个类都有自己的静态 getService 方法，该方法返回实际的服务。我不想在我的 applicationContext.xml 中列出所有这些服务，我想让 Spring 为我注入(inject)的每个 XXXLocalService 找到正确的 XXXLocalServiceUtil 类。所以我需要某种动态 bean 工厂，它可以为我完成工作，当然是在延迟加载的基础上。

有人知道如何轻松实现吗？

Answer 1

您可以使用 GenericApplicationContext 将 bean 与在 xml 中声明的其余 spring bean 一起动态加载到 applicationContext。这是一个使用 Reflections library 实现的示例...

private static final Pattern SERVICE_UTIL_PATTERN = Pattern.compile(".*LocalServiceUtil.*");

public static void main(String[] args) {
    ConfigurationBuilder builder = new ConfigurationBuilder().addUrls(
            ClasspathHelper.forPackage("x.y.z"))
            .setScanners(new SubTypesScanner(false));
    Reflections reflections = new Reflections(builder);
    GenericApplicationContext applicationContext = new GenericApplicationContext();
    Set<Class<? extends Object>> classes = reflections.getSubTypesOf(Object.class);

    for (Class<? extends Object> serviceUtilClass : classes) {
        String className = serviceUtilClass.getName();

        if (SERVICE_UTIL_PATTERN.matcher(className).matches()) {
            GenericBeanDefinition beanDefinition = new GenericBeanDefinition();
            beanDefinition.setBeanClassName(className);
            beanDefinition.setFactoryMethodName("getService");
            beanDefinition.setLazyInit(true);

            String beanName = StringUtils.uncapitalize(serviceClass.getSimpleName().replace("Util", ""));
            applicationContext.registerBeanDefinition(beanName, beanDefinition);
        }
    }

    XmlBeanDefinitionReader reader = new XmlBeanDefinitionReader(applicationContext);
    reader.loadBeanDefinitions("classpath:/applicationContext.xml");
    applicationContext.refresh();
}

更新:要在 Web 应用程序中使用它，您可以简单地扩展 Spring 的 XmlWebApplicationContext 并覆盖 initBeanDefinitionReader 方法，如下所示...

private static final Pattern SERVICE_UTIL_PATTERN = Pattern.compile(".*LocalServiceUtil.*");

@Override
protected void initBeanDefinitionReader(
        XmlBeanDefinitionReader beanDefinitionReader) {
    ConfigurationBuilder builder = new ConfigurationBuilder().addUrls(
            ClasspathHelper.forPackage("x.y.z"))
            .setScanners(new SubTypesScanner(false));
    Reflections reflections = new Reflections(builder);
    Set<Class<? extends Object>> classes = reflections.getSubTypesOf(Object.class);
    BeanDefinitionRegistry registry = beanDefinitionReader.getRegistry();

    for (Class<? extends Object> serviceClass : classes) {
        String className = serviceClass.getName();

        if (SERVICE_UTIL_PATTERN.matcher(className).matches()) {
            GenericBeanDefinition beanDefinition = new GenericBeanDefinition();
            beanDefinition.setBeanClassName(className);
            beanDefinition.setFactoryMethodName("getService");
            beanDefinition.setLazyInit(true);
            String beanName = StringUtils.uncapitalize(serviceClass
                    .getSimpleName().replace("Util", ""));
            registry.registerBeanDefinition(beanName, beanDefinition);
        }
    }
}

}

并将以下 context-param 添加到您的 web.xml...

<context-param>
  <param-name>contextClass</param-name>
  <param-value>x.y.z.MyXmlWebApplicationContext</param-value>
</context-param>