SpringBoot自定义注解属性支持占位符${}

小半 • 2023年1月19日下午6:10 • 技术随笔 • 阅读 428

环境：SpringBoot2.3.8.RELEASE + JDK1.8

本文教你如何在SpringBoot环境下使得自定义的注解能够使用${xxx}表达式。

相关依赖

<dependency>
			<groupId>org.aspectj</groupId>
			<artifactId>aspectjrt</artifactId>
</dependency>
<dependency>
			<groupId>org.aspectj</groupId>
			<artifactId>aspectjweaver</artifactId>
			<scope>runtime</scope>
</dependency>

自定义注解

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
@Documented
public @interface Manufactur {
	String value() default "" ; // 厂商编号
}

需要AOP在方法执行器对方法上的注解进行解析处理，获取占位符对应的值

@Component
@Aspect
public class ManufacturAspect implements EnvironmentAware {
	
	private static final Logger logger = LoggerFactory.getLogger(ManufacturAspect.class) ;
	
	private Environment environment;
	
	@Pointcut("@annotation(com.pack.annotation.Manufactur)")
	private void info() {}
	
	@Before("info()")
	public void execBefore(JoinPoint jp) {
		MethodSignature sign = (MethodSignature) jp.getSignature() ;
		Method method = sign.getMethod() ;
		Manufactur manu = method.getAnnotation(Manufactur.class) ;
		String value = manu.value() ;
		logger.info("获取到注解值：{}", value) ;
		BusinessService.code.set(this.environment.resolvePlaceholders(value)) ;
	}

	@Override
	public void setEnvironment(Environment environment) {
		this.environment = environment ;
	}
	
}

该类实现了EnvironmentAware 用于获取Environment对象，该对象能够获取当前环境下的所有相关配置信息。同时通过该类的resolvePlaceholders方法能够解析占位符对应的内容值。

Service中使用

@Service
public class BusinessService {
	
	public static ThreadLocal<String> code = new ThreadLocal<String>() ;
	
	private static Logger logger = LoggerFactory.getLogger(BusinessService.class) ;
	
	@Manufactur("${manufactur.code}-#{1 + 3}")
	public String invoke(String id) {
		String sno = code.get() ;
		logger.info("自定义注解动态获取属性值：{}", sno) ;
		// todo
		return sno ;
	}
	
}

在AOP中将解析后的值已经存入到了ThreadLocal中。

测试

@RestController
@RequestMapping("/business")
public class BusinessController {
	
	@Resource
	private BusinessService bs ;
	
	@GetMapping("/{id}")
	public Object home(@PathVariable String id) {
		return bs.invoke(id) ;
	}
	
}