自定义注解的定义和作用范围

• 自定义注解可以作用在类、方法、属性、参数、异常、字段或其他注解上。

如何创建自定义注解

创建注解接口

package hanshuhuan.test.anonotion;import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;/*** 实体检验自定义注解类，根据我们自定义的注解去检查实体各个字段是否在规定的值内* @author shuhu**/
@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
public @interface ValidateEntity {public boolean required() default false;//是否检验nullpublic boolean requiredLeng() default false;//是否检验长度public boolean requiredMaxValue() default false;//是否检验最大值public boolean requiredMinValue() default false;//是否检验最小值public int maxLength() default -1;//最大长度public int minLength() default -1;//最小长度public long maxValue() default -1;//最大值public long minValue() default -1;//最小值public String errorRequiredMsg() default "";//值为null时的错误提示信息public String errorMinLengthMsg() default "";//最小长度不满足时的提示信息public String errorMaxLengthMsg() default "";//最大长度不满足时的提示信息public String errorMinValueMsg() default "";//最小值不满足时的提示信息public String errorMaxValueMsg() default "";//最大值不满足时的提示信息
}

如何使用自定义注解进行数据验证

创建注解处理器

package hanshuhuan.test.util;import java.lang.reflect.Field;import hanshuhuan.test.anonotion.ValidateEntity;
import hanshuhuan.test.bean.CodeMsg;/*** 验证实体工具类* @author shuhu**/
public class ValidateEntityUtil {public static CodeMsg validate(Object object){Field[] declaredFields = object.getClass().getDeclaredFields();for(Field field : declaredFields){ValidateEntity annotation = field.getAnnotation(ValidateEntity.class);if(annotation != null){if(annotation.required()){//表示该字段是必填字段field.setAccessible(true);try {Object o = field.get(object);//首先判断是否为空if(o == null){CodeMsg codeMsg = CodeMsg.VALIDATE_ENTITY_ERROR;codeMsg.setMsg(annotation.errorRequiredMsg());return codeMsg;}//到这，说明该变量的值不是null//首先判断是不是String类型if(o instanceof String){//若是字符串类型，则检查其长度if(annotation.requiredLeng()){if(o.toString().length() < annotation.minLength()){CodeMsg codeMsg = CodeMsg.VALIDATE_ENTITY_ERROR;codeMsg.setMsg(annotation.errorMinLengthMsg());return codeMsg;}if(o.toString().length() > annotation.maxLength()){CodeMsg codeMsg = CodeMsg.VALIDATE_ENTITY_ERROR;codeMsg.setMsg(annotation.errorMaxLengthMsg());return codeMsg;}}}//其次来判断是否为数字if(isNumberObject(o)){//判断是否规定检查最小值if(annotation.requiredMinValue()){if(Double.valueOf(o.toString()) < annotation.minValue()){CodeMsg codeMsg = CodeMsg.VALIDATE_ENTITY_ERROR;codeMsg.setMsg(annotation.errorMinValueMsg());return codeMsg;}}//判断是否规定检查最大值if(annotation.requiredMaxValue()){if(Double.valueOf(o.toString()) > annotation.maxValue()){CodeMsg codeMsg = CodeMsg.VALIDATE_ENTITY_ERROR;codeMsg.setMsg(annotation.errorMaxValueMsg());return codeMsg;}}}} catch (IllegalArgumentException e) {// TODO Auto-generated catch blocke.printStackTrace();} catch (IllegalAccessException e) {// TODO Auto-generated catch blocke.printStackTrace();}}}}return CodeMsg.SUCCESS;}/*** 检查对象是否是数字类型* @param object* @return*/public static boolean isNumberObject(Object object){if(object instanceof Integer)return true;if(object instanceof Long)return true;if(object instanceof Float)return true;if(object instanceof Double)return true;return false;}
}

控制器中使用注解

@RequestMapping(value="/login",method=RequestMethod.POST)
@ResponseBody
public Result<Boolean> login(User user,String cpacha){if(user == null){return Result.error(CodeMsg.DATA_ERROR);}//用统一验证实体方法验证是否合法CodeMsg validate = ValidateEntityUtil.validate(user);if(validate.getCode() != CodeMsg.SUCCESS.getCode()){return Result.error(validate);}//表示实体信息合法，开始验证验证码是否为空if(StringUtils.isEmpty(cpacha)){return Result.error(CodeMsg.CPACHA_EMPTY);}log.info("ok"+user);return Result.success(true);
}

如何为字段添加注解

• 自定义注解的定义是通过@注解名的方式实现的。

@ValidateEntity(required=true,requiredLeng=true,minLength=4,maxLength=18,errorRequiredMsg="用户名不能为空!",errorMinLengthMsg="用户名长度需大于4!",errorMaxLengthMsg="用户名长度不能大于18!")
@Column(name="username",nullable=false,length=18)
private String username;//用户名@ValidateEntity(required=true,requiredLeng=true,minLength=4,maxLength=32,errorRequiredMsg="密码不能为空！",errorMinLengthMsg="密码长度需大于4!",errorMaxLengthMsg="密码长度不能大于32!")
@Column(name="password",nullable=false,length=32)
private String password;//密码