1.如何自定义注解?
package com.dudu.lizhen.customannotations
;
import java.lang.annotation.ElementType
;
import java.lang.annotation.
Retention;
import java.lang.annotation.RetentionPolicy
;
import java.lang.annotation.
Target;
/**
* 自定义注解
* ---@Target 标识可以允许在什么地方使用 (比如 :方法或者类什么的)
* --@Retention 标识 允许什么方式获取信息 (比如类似例子:就是可以通过java反射机制获取信息)
* Created by lizhen on 2018/1/29.
*/
@Target(
value = ElementType.
METHOD)
@Retention(RetentionPolicy.
RUNTIME)
public @
interface CustomAnnotations {
String
value()
default "";
int classId()
default 0;
String[]
arrAr()
;
}
/**
* 使用自定义注解的例子
*/
class AnnDemo{
private String
name;
@CustomAnnotations(
value =
"lizhen",classId =
175,arrAr = {
"11","22"})
public void add(){
}
}
2.利用自定义注解实现ORM
package com.dudu.lizhen.customannotations
;
import java.lang.annotation.
Retention;
import java.lang.annotation.RetentionPolicy
;
/**
* 实体类的注解
* 目的:通过自定义注解实现实体类与表的对应 select user_name ,user_age from user_table
* Created by lizhen on 2018/1/30.
*/
@Retention(RetentionPolicy.
RUNTIME)
public @
interface SetTable {
String
name()
;
}
package com.dudu.lizhen.customannotations
;
import java.lang.annotation.
Retention;
import java.lang.annotation.RetentionPolicy
;
/**
* 属性注解
* 目的:通过自定义注解实现实体类与表的对应 select user_name ,user_age from user_table
* Created by lizhen on 2018/1/30.
*/
@Retention(RetentionPolicy.
RUNTIME)
public @
interface SetProperty {
String
name()
;
int length()
;
}
package com.dudu.lizhen.customannotations
;
/**
* java实体类
* 目的 :通过自定义注解实现实体类与表的对应 select user_name ,user_age from user_table
* Created by lizhen on 2018/1/30.
*/
@SetTable(
name =
"user_table")
public class UserEntry {
/**
* 姓名
*/
@SetProperty(
name =
"user_name", length =
10 )
private String
name;
/**
* 年龄
*/
@SetProperty(
name =
"user_age" , length =
10 )
private Integer
age;
public String
getName() {
return name;
}
public void setName(String name) {
this.
name = name
;
}
public Integer
getAge() {
return age;
}
public void setAge(Integer age) {
this.
age = age
;
}
@Override
public String
toString() {
return "UserEntry{" +
"name='" +
name +
'\'' +
", age=" +
age +
'}';
}
}
package com.dudu.lizhen.customannotations
;
import java.lang.reflect.Field
;
/**
* 实体类与表的映射测试
* 目的 :通过自定义注解实现实体类与表的对应 select user_name ,user_age from user_table
* Created by lizhen on 2018/1/30.
*/
public class UserEntryTest {
public static void main(String[] args) {
try {
//项目使用注解肯定会用到java反射,java反射的应用场景 Spring IOC ,jdbc ,自定义注解的实现
Class<?> aClass = Class.
forName(
"com.dudu.lizhen.customannotations.UserEntry")
;
//getAnnotations 获取该类上使用了那些注解
// Annotation[] annotations = aClass.getAnnotations();
// for (Annotation annotation:annotations){
// System.out.println(annotation);
// }
StringBuffer stringBuffer =
new StringBuffer()
;
stringBuffer.append(
" select ")
;
Field[] declaredFields = aClass.getDeclaredFields()
;
for (
int i=
0;i<declaredFields.
length;i++){
SetProperty annotation = declaredFields[i].getAnnotation(
SetProperty.
class)
;
String name = annotation.name()
;
stringBuffer.append(name)
;
if (i == declaredFields.
length-
1){
stringBuffer.append(
" from ")
;
}
else{
stringBuffer.append(
" , ")
;
}
}
//获取某个注解对象
SetTable annotation = aClass.getAnnotation(
SetTable.
class)
;
String name = annotation.name()
;
stringBuffer.append(name)
;
System.
out.println(stringBuffer.toString())
;
}
catch (ClassNotFoundException e) {
e.printStackTrace()
;
}
}
}
查看效果:
