Java注解demo
# 为了熟悉了解注解,写的一个小demo
# demo的主要功能是扫描一个class中的包含我们自定义注解的方法,然后把他们的返回值放到一个map中
public class QQ { public static void main(String[] args) throws IllegalAccessException, IllegalArgumentException, InvocationTargetException, InstantiationException { Map<String, Object> map = new HashMap<>(); Class<Test> clazz = Test.class; Method[] mtds = clazz.getMethods(); for (Method method : mtds) { // 判断方法上有没有注解 boolean hasAnno = method.isAnnotationPresent(CacheInMap.class); Object result = null; // 忽略不含注解的方法 if (!hasAnno) { continue; } // 获取方法参数个数 int paramCount = method.getParameterCount(); if (paramCount == 0) { result = method.invoke(clazz.newInstance()); } else if (paramCount == 1) { result = method.invoke(clazz.newInstance(), ""); } // 获取注解 CacheInMap anno = method.getAnnotation(CacheInMap.class); if ("".equals(anno.key())) { String methodName = method.getName(); map.put(methodName, result); } else { map.put(anno.key(), result); } } printMap(map); } public static void printMap(Map<String, Object> map) { for (Map.Entry<String, Object> entry : map.entrySet()) { System.out.println(String.format("key:%s, value:%s", entry.getKey(), entry.getValue())); } } } @Documented @Retention(RetentionPolicy.RUNTIME) @Target({ ElementType.METHOD, ElementType.ANNOTATION_TYPE }) @interface CacheInMap { String key() default ""; } class Test { @CacheInMap(key = "qwer") public String method1(String str) { return "This is Method1"; } @CacheInMap public int method2() { return 1024; } public double method3() { return 3.141592653; } }
# 上面代码的输出结果为:
key:method2, value:1024
key:qwer, value:This is Method1