import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@interface Table {
	String value();
}



import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Target({ElementType.FIELD})
@Retention(RetentionPolicy.RUNTIME)
@interface FieldInfo {
	String column();
}


@Table("t_user")
public class User{

	@FieldInfo(column="user_id")
    private int id;
	@FieldInfo(column="user_name")
	private String name;
	@FieldInfo(column="user_age")
	private int age = 0;



import java.lang.annotation.Annotation;
import java.lang.reflect.Field;

public class Hello {

    public static void main(String[] args) throws Exception {
        Class clazz = Class.forName("dyyx.User");

        Annotation[] annotations = clazz.getAnnotations();
        for (Annotation annotation : annotations) {
            System.out.println(annotation);
        }

        Table table = (Table) clazz.getAnnotation(Table.class);
        String value = table.value();
        System.out.println("table=" + value);

        String[] fieldNames = new String[]{"id", "name", "age"};
        for (String fieldName : fieldNames) {
            Field field = clazz.getDeclaredField(fieldName);
            FieldInfo anno = field.getAnnotation(FieldInfo.class);
            System.out.println(fieldName + "=" + anno.column());
        }
    }
}


字段上没有注解时  返回null

Field field = clazz.getDeclaredField("info");
FieldInfo anno = field.getAnnotation(FieldInfo.class);
// null
System.out.println(anno);




https://gitee.com/dyyx/hellocode/tree/master/demo/annotationdemo/