注解_Annotation_内置注解_自定义注解_反射机制读取注解JAVA208-210

来源：http://www.bjsxt.com/
一、S02E208_01注解_Annotation、内置注解

什么是注解

内置注解

二、S02E209_01自定义注解

元注解

package com.test.annotation;@MyAnnotation01public class Demo01 {    @MyAnnotation01(age=19,studentName="test",id=1001,            schools={"北大","浙大"})    public static void main(String[] args) {    }    @MyAnnotation02(value="aaa")//或者("aaa")    public void test(){    }}

package com.test.annotation;import java.lang.annotation.ElementType;import java.lang.annotation.Retention;import java.lang.annotation.RetentionPolicy;import java.lang.annotation.Target;@Target(value={ElementType.METHOD,ElementType.TYPE})@Retention(RetentionPolicy.RUNTIME)public @interface MyAnnotation01 {    String studentName() default "";    int age() default 0;    int id() default -1;    String[] schools() default{"清华","复旦"};}

package com.test.annotation;import java.lang.annotation.ElementType;import java.lang.annotation.Retention;import java.lang.annotation.RetentionPolicy;import java.lang.annotation.Target;@Target(value={ElementType.METHOD,ElementType.TYPE})@Retention(RetentionPolicy.RUNTIME)public @interface MyAnnotation02 {    String value();}

三、S02E210_01反射机制读取注解

注解作业

package com.test.annotation2;import java.lang.annotation.Annotation;import java.lang.reflect.Field;/** * 使用反射读取注解的信息，模拟处理注解信息的流程 */public class Demo {    public static void main(String[] args) {        try {            Class clazz = Class.forName("com.test.annotation2.SxtStudent");            //获取类的所有有效注解            Annotation[] annotations = clazz.getAnnotations();            for (Annotation a : annotations) {                System.out.println(a);            }            //获取类的指定的注解            SxtTable st = (SxtTable) clazz.getAnnotation(SxtTable.class);            System.out.println(st.value());            //获取类的属性的注解            Field f = clazz.getDeclaredField("sname");            SxtField sxtField = f.getAnnotation(SxtField.class);            System.out.println(sxtField.columnName()+"--"+sxtField.type()+"--"+sxtField.length());            //根据获取的表名和字段的信息，拼出DDL语句，然后，使用JDBC执行这个SQL，在数据库中生成相关的表        } catch (Exception e) {            e.printStackTrace();        }    }}

package com.test.annotation2;@SxtTable("tb_student")public class SxtStudent {    @SxtField(columnName="id",type="int",length=10)    private int id;    @SxtField(columnName="sname",type="varchar",length=10)    private String sname;    @SxtField(columnName="age",type="int",length=3)    private int age;    public int getId() {        return id;    }    public void setId(int id) {        this.id = id;    }    public String getStudentName() {        return sname;    }    public void setStudentName(String studentName) {        this.sname = studentName;    }    public int getAge() {        return age;    }    public void setAge(int age) {        this.age = age;    }}

package com.test.annotation2;import java.lang.annotation.ElementType;import java.lang.annotation.Retention;import java.lang.annotation.RetentionPolicy;import java.lang.annotation.Target;@Target(value={ElementType.TYPE})@Retention(RetentionPolicy.RUNTIME)public @interface SxtTable {    String value();}

package com.test.annotation2;import java.lang.annotation.ElementType;import java.lang.annotation.Retention;import java.lang.annotation.RetentionPolicy;import java.lang.annotation.Target;@Target(value={ElementType.FIELD})@Retention(RetentionPolicy.RUNTIME)public @interface SxtField {    String columnName();    String type();    int length();}

控制台输出

@com.test.annotation2.SxtTable(value=tb_student)tb_studentsname--varchar--10