Java: Annotaion

 

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/**  * 版权所有 2022 涂聚文有限公司  * 许可信息查看：  * 描述：  *  * 历史版本： JDK 17.01  * 2022-09-12 创建者 geovindu  * 2022-09-12 添加 Lambda  * 2022-09-12 修改：date  * 接口类  * 2022-09-12 修改者：Geovin Du  * 生成API帮助文档的指令：  *javadoc - -encoding Utf-8 -d apidoc DBField.java  * Interface  * Record  * Annotation  * Enum  * */       package CoreJava.twelfth;   import java.lang.annotation.Documented; import java.lang.annotation.ElementType; import java.lang.annotation.Inherited; import java.lang.annotation.Retention; import java.lang.annotation.RetentionPolicy; import java.lang.annotation.Target;     /**  *  *  * */ @Documented @Target(ElementType.FIELD) @Inherited @Retention(RetentionPolicy.RUNTIME) public @interface DBField {     /**      *      *      * */     String name();     /**      *      *      * */     Class< ?> type();     /**      *      *      * */     boolean isPrimaryKey() default false;     }

　　

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/**  * 版权所有 2022 涂聚文有限公司  * 许可信息查看：  * 描述：  *  * 历史版本： JDK 17.01  * 2022-09-12 创建者 geovindu  * 2022-09-12 添加 Lambda  * 2022-09-12 修改：date  * 接口类  * 2022-09-12 修改者：Geovin Du  * 生成API帮助文档的指令：  *javadoc - -encoding Utf-8 -d apidoc DuUser.java  * Interface  * Record  * Annotation  * Enum  * */     package CoreJava.twelfth; import java.util.Date;   /**  *  *  * */ public class DuUser {     /**      *      *      * */     @DBField(name = "id", isPrimaryKey = true, type = Long.class)     private long id;     /**      *      *      * */     @DBField(name = "name", type = String.class)     private String name;     /**      *      *      * */     @DBField(name = "email", type = String.class)     private String email;     /**      *      *      * */     @DBField(name = "createdtime", type = Date.class)     private Date created;     /**      *      *      * */     public long getId() {         return id;     }     /**      *      *      * */     public void setId(long id) {         this.id = id;     }     /**      *      *      * */     public String getName() {         return name;     }     /**      *      *      * */     public void setName(String name) {         this.name = name;     }     /**      *      *      * */     public String getEmail() {         return email;     }     /**      *      *      * */     public void setEmail(String email) {         this.email = email;     }     /**      *      *      * */     public Date getCreated() {         return created;     }     /**      *      *      * */     public void setCreated(Date created) {         this.created = created;     }   }

　　

调用：

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System.out.println("Java Custom Annotation Example");           System.out.println();             DuUser usr = new DuUser();           usr.setEmail("geovindu@dusystem.com");           usr.setName("Geovin Du");           usr.setId(112);           usr.setCreated(new Date());             for (Field field : usr.getClass().getDeclaredFields()) {               DBField dbField = field.getAnnotation(DBField.class);               System.out.println("field name: " + dbField.name());                 // changed the access to public               field.setAccessible(true);               Object value = field.get(usr);               System.out.println("field value: " + value);                 System.out.println("field type: " + dbField.type());               System.out.println("is primary: " + dbField.isPrimaryKey());               System.out.println();           }

　　

输出：

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Java Custom Annotation Example   field name: id field value: 112 field type: class java.lang.Long is primary: true   field name: name field value: Geovin Du field type: class java.lang.String is primary: false   field name: email field value: geovindu@dusystem.com field type: class java.lang.String is primary: false   field name: createdtime field value: Tue Nov 01 21:46:59 CST 2022 field type: class java.util.Date is primary: false