注释Spring bootstrap类并在其他地方实现注释

Question

我想做如下事情：-

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
public @interface MyCustomAnnotation {
    public String field1();
    public String[] list1();
}

@SpringBootApplication
@MyCustomAnnotation(field1 = "value1", list1 = { "list value 1", "list value2" })
public class Application {
    public static void main(String[] args){
        SpringApplication.run(Application.class, args);
    }
}

public class AnnotationImplementationClass {
    // Inject field1 and list1 values from @MyCustomAnnotation into this class
    private String field1;
    private String[] list1;
}

我想将AnnotationImplementationClass与被注释的类隔离开来，这样我就可以打包和分发自定义注释及其实现，从而允许开发人员使用@MyCustomAnnotation注释他们自己的spring boot应用程序类。

限制条件是我不知道Spring Boot类（在本例中为Application.java）的类名，显然我无权访问该类来修改它。我必须在运行时以某种方式获得访问权限，以便使用反射来获取自定义注释中的值。

我已经研究了试图演示BeanPostProcess使用的示例，但当它应用于包含@SpringBootApplication的java类时，我无法找到@MyCustomAnnoation。

Answer 1

我终于自己解决了这个问题。以下是我的解决方案：-

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
@Import(AnnotationImplementationClass.class)
public @interface MyCustomAnnotation {
    public String field1();
    public String[] list1();
}


@SpringBootApplication
@MyCustomAnnotation(field1 = "field1 value", list1 = { "list1 value 1", "list1 value 2" })
public class Application
{
    public static void main(String[] args)
    {
        SpringApplication.run(Application.class, args);
    }
}

public class AnnotationImplementationClass implements ApplicationContextAware
{
    private String field1;
    private String[] list1;

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException
    {
        // Grab the beans from the app context that are annotated with my custom annotation
        Map<String, Object> beanMap = applicationContext.getBeansWithAnnotation(MyCustomAnnotation.class);
        Collection<Object> beans = beanMap.values();

        // There is a possibility that multiple beans are annotated with the annotation. I only annotated one bean
        // but I am using a "for" loop for illustration.
        for (Object bean : beans)
        {
            // Spring annotated classes are often proxied when Spring is initializing. I found that I was unable to get
            // the annotation and its parameter values from the proxy instance. I need to find the actual class that was
            // annotated using the the proxy as a start point. The following "if" clause illustrates the process.
            Class<? extends Object> annotatedClass = null;
            if (bean instanceof TargetClassAware)
            {
                annotatedClass = ((TargetClassAware) bean).getTargetClass();
            }
            else if (ClassUtils.isCglibProxy(bean))
            {
                annotatedClass = bean.getClass().getSuperclass();
            }
            else
            {
                annotatedClass = bean.getClass();
            }

            // Now I can get the annotation and its parameter values
            MyCustomAnnotation annotation = annotatedClass.getAnnotation(MyCustomAnnotation.class);
            field1 = annotation.field1();
            list1 = annotation.list1();

            // Since I only want one of the classes annotated by my custom annotation I break out of the loop
            break;
        }
    }
}

需要注意的几点：-

• 在自定义注释界面上使用@import。这允许我将实现类挂接到Spring上下文中。不确定这是否是@import的正确使用，但它是我最终解决方案的关键。
• 在实现类上使用"implements Application ContextAware"。这为我在Spring初始化期间进行控制提供了一个切入点。

希望这对其他人有帮助。

Answer 2

Spring Boot Starter类包含“public static void main（String[]args）”方法。您可以通过反射来引用容器类。

这也许会帮助你。我不知道你的目标如何实现。但是你的自定义注释应该以最高优先级扫描。