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This article will explain in detail how to customize annotations in Java. The quality of the article is high, so Xiaobian shares it with you as a reference. I hope you have a certain understanding of relevant knowledge after reading this article.

Java basics, annotations and custom annotations

Java annotation is an annotation mechanism introduced by JDK 5.0.

I. Self-explanatory

Before we learn about custom annotations, let's look at Java's internally defined set of annotations: there are seven of them, three in java.lang, and four in java. lang. annotation.

Acting on a class or method:

@Override Checks if the method is an override method. Compile errors are reported if the method is not found in its parent class, or in the referenced interface.@ Deprecated tag obsolete method. It is not recommended to use @SuppressWarnings to instruct the compiler to ignore warnings declared in annotations

Works on other comments

@Retention identifies how the annotation is saved, whether it is only in code, codified in a class file, or accessible via reflection at runtime.@ Documented flag Whether these annotations are included in the user documentation @Target flag What Java member should this annotation be @Inherited flag What annotation class does this annotation inherit from (default annotation does not inherit from any subclass)

Three additional comments added:

@SafeVarargs Java 7 supports ignoring any warnings generated by method or constructor calls that use generic variables as arguments.@ FunctionalInterface Java 8 supports identifying an anonymous function or functional interface.@ Repeatable Java 8 began to support, indicating that an annotation can be used multiple times on the same declaration. II. Annotations Structure

Annotation有三个重要的主干类，分别为：Annotation、ElememtType、RetentionPolicy

1、Annotation:public interface Annotation { boolean equals(Object obj); int hashCode(); String toString(); Class paramsMap = (Map) ServletUtils.getRequest().getAttribute(HandlerMapping.URI_TEMPLATE_VARIABLES_ATTRIBUTE); operLog.setOperParam(StringUtils.substring(paramsMap.toString(), 0, 2000)); } } /** * 是否存在注解，如果存在就获取 */ private Log getAnnotationLog(JoinPoint joinPoint) throws Exception { Signature signature = joinPoint.getSignature(); MethodSignature methodSignature = (MethodSignature) signature; Method method = methodSignature.getMethod(); if (method != null) { return method.getAnnotation(Log.class); } return null; } /** * 参数拼装 */ private String argsArrayToString(Object[] paramsArray) { String params = ""; if (paramsArray != null && paramsArray.length > 0) { for (int i = 0; i < paramsArray.length; i++) { if (!isFilterObject(paramsArray[i])) { Object jsonObj = JSON.toJSON(paramsArray[i]); params += jsonObj.toString() + " "; } } } return params.trim(); } /** * 判断是否需要过滤的对象。 * * @param o 对象信息。 * @return 如果是需要过滤的对象，则返回true;否则返回false。 */ public boolean isFilterObject(final Object o) { return o instanceof MultipartFile || o instanceof HttpServletRequest || o instanceof HttpServletResponse; }}3.4、注解的使用/** * 修改推荐位 */@Log(title = "推荐位", businessType = BusinessType.UPDATE)@PutMapping("/edit")public AjaxResult edit(@RequestBody GsRecommPosition gsRecommPosition){ Long gsRecommPositionId = gsRecommPosition.getGsRecommPositionId(); boolean condition = recommPositionHasCategory(gsRecommPositionId); return toAjax(gsRecommPositionService.updateGsRecommPosition(gsRecommPosition));}/** * 删除推荐位 */@Log(title = "推荐位", businessType = BusinessType.DELETE)@DeleteMapping("delete/{gsRecommPositionId}")public AjaxResult remove(@PathVariable Long gsRecommPositionId){ boolean condition = recommPositionHasCategory(gsRecommPositionId); return toAjax(gsRecommPositionService.deleteGsRecommPositionById(gsRecommPositionId));}四、JoinPoint解析1、JoinPoint

对象封装了SpringAop切面方法中的信息

方法名功能Signature getSignature();获取封装了署名信息的对象,在该对象中可以获取到目标方法名,所属类的Class等信息Object[] getArgs();获取传入目标方法的参数对象Object getTarget();获取被代理的对象Object getThis();获取代理对象joinPoint.getSignature().getName(); // 获取目标方法名joinPoint.getSignature().getDeclaringType().getSimpleName(); // 获取目标方法所属类的简单类名joinPoint.getSignature().getDeclaringTypeName(); // 获取目标方法所属类的类名joinPoint.getSignature().getModifiers(); // 获取目标方法声明类型(public、private、protected)Object[] args = joinPoint.getArgs(); // 获取传入目标方法的参数，返回一个数组joinPoint.getTarget(); // 获取被代理的对象joinPoint.getThis(); // 获取代理对象自己//获取自定义注解的信息MethodSignature methodSignature = (MethodSignature) joinPoint.getSignature();Method method = methodSignature.getMethod();CustomLog customLog = methodSignature.getMethod().getAnnotation(CustomLog.class);2、ProceedingJoinPoint

ProceedingJoinPoint对象是JoinPoint的子接口,该对象只用在@Around的切面方法中

Object proceed() throws Throwable //执行目标方法 Object proceed(Object[] var1) throws Throwable //传入的新的参数去执行目标方法关于Java中怎么自定义注解就分享到这里了，希望以上内容可以对大家有一定的帮助，可以学到更多知识。如果觉得文章不错，可以把它分享出去让更多的人看到。

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