Java Annoration小解 Java

【Java Annoration小解】注：本文均是在Spring项目下编写及测试（自带validation）
注解声明（简单，不定时更新）

// 一般注解 @Target(ElementType.FIELD) @Retention(RetentionPolicy.RUNTIME) public @interface AnnorationName {}

注解分类（一般关联Java反射）

一般注解

@Target(ElementType.FIELD) @Retention(RetentionPolicy.RUNTIME) public @interface AnnorationName {}

验证注解（依赖validation）

// 继承已有注解（@Pattern），注解可以被继承，但必须包含message，groups， payload @Pattern(regexp = "1313897830", message = "继承的格式错误") @Target(ElementType.FIELD) @Retention(RetentionPolicy.RUNTIME) @Constraint(validatedBy = {}) @Documented public @interface Phone2 { String message() default ""; Class[] groups() default { }; Class[] payload() default { }; }// 无继承，通过Constraint指定对应的注解处理器（可以实现ConstraintValidator接口） @Target(ElementType.FIELD) @Retention(RetentionPolicy.RUNTIME) @Constraint(validatedBy = PhoneValidate.class) @Documented public @interface Phone { // 不可为空 boolean nullAble() default true; // 长度必须为11位 int length() default 11; String message() default "手机号码错误"; Class[] groups() default { }; Class[] payload() default { }; }

重复注解（jdk1.8之后变化）

1.8 before

// 声明 @Target(ElementType.FIELD) @Retention(RetentionPolicy.RUNTIME) public @interface SimpleAnnoration { String value() default "hi"; }// 声明重复注解 @Target(ElementType.FIELD) @Retention(RetentionPolicy.RUNTIME) public @interface SimpleAnnorations { SimpleAnnoration[] value(); }// 使用 public class User { @SimpleAnnorations(value = https://www.it610.com/article/{@SimpleAnnoration("w"), @SimpleAnnoration("l"), @SimpleAnnoration("z") }) private String name; }

1.8 after

// 声明 @Target(ElementType.FIELD) @Retention(RetentionPolicy.RUNTIME) @Repeatable(SimpleAnnorations.class) public @interface SimpleAnnoration { String value() default "hi"; }// 声明重复注解 @Target(ElementType.FIELD) @Retention(RetentionPolicy.RUNTIME) public @interface SimpleAnnorations { SimpleAnnoration[] value(); }// 使用 public class User { @SimpleAnnoration("J") @SimpleAnnoration("a") @SimpleAnnoration("s") private Integer age; }

// 测试 @Test public void duplicationTest() throws Exception { Class clazz = User.class; Field[] fields = clazz.getDeclaredFields(); // Java 8 之前的重复注解做法 SimpleAnnorations simpleAnnorations = clazz.getDeclaredField("name").getAnnotation(SimpleAnnorations.class); if (simpleAnnorations != null) { for (SimpleAnnoration annoration : simpleAnnorations.value()) { System.out.println("tag.value: " + annoration.value()); } }Annotation[] annotations1 = clazz.getDeclaredField("age").getAnnotationsByType(SimpleAnnoration.class); for (Annotation annotation : annotations1) { SimpleAnnoration annoration2 = (SimpleAnnoration) annotation; System.out.println("tag.value: " + annoration2.value()); } } // 结果 tag.value: w tag.value: l tag.value: ztag.value: J tag.value: a tag.value: s