Java自学-注解与反射(4)
2021/9/4 22:05:55
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Java自学-注解与反射(4)
1、获取注解信息
package lesson01; import java.lang.annotation.*; import java.lang.reflect.Field; /** * Author: Gu Jiakai * Date: 2021/9/4 21:19 * FileName: Test12 * Description: */ //练习反射操作注解 public class Test12 { public static void main(String[] args) throws ClassNotFoundException, NoSuchFieldException { Class c1 = Class.forName("lesson01.Student2"); //通过反射获得注解 Annotation[] annotations = c1.getAnnotations(); for (Annotation annotation : annotations) { System.out.println(annotation); } //获得注解的value的值。 TableKai annotation = (TableKai)c1.getAnnotation(TableKai.class); String value = annotation.value(); System.out.println(value); //获得类指定的注解 Field f = c1.getDeclaredField("name"); FieldKai annotation1 = f.getAnnotation(FieldKai.class); System.out.println(annotation1.columnName()); System.out.println(annotation1.type()); System.out.println(annotation1.length()); } } @TableKai("db_student") class Student2{ @FieldKai(columnName = "db_id",type = "int",length = 10) private int id; @FieldKai(columnName = "db_age",type = "int",length = 10) private int age; @FieldKai(columnName = "db_name",type = "varchar",length = 3) private String name; public Student2() { } public Student2(int id, int age, String name) { this.id = id; this.age = age; this.name = name; } public int getId() { return id; } public void setId(int id) { this.id = id; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } public String getName() { return name; } public void setName(String name) { this.name = name; } @Override public String toString() { return "Student2{" + "id=" + id + ", age=" + age + ", name='" + name + '\'' + '}'; } } //类名的注解。 @Target(ElementType.TYPE) @Retention(RetentionPolicy.RUNTIME) @interface TableKai{ String value(); } //属性的注解 @Target(ElementType.FIELD) @Retention(RetentionPolicy.RUNTIME) @interface FieldKai{ String columnName(); String type(); int length(); }
2、本章小结
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