一篇文章教你如何用Java自定义一个参数校验器

@Target({ElementType.FIELD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Constraint(validatedBy = {IsUniqueValidator.class}) // 指定自定义的校验器
public @interface IsUnique {
    // 提示信息
    String message() default "";
    // 不加这俩参数 error msg: contains Constraint annotation, but does not contain a groups parameter.
    // 必须包含这两个参数
    Class<?>[] groups() default {};
    Class<? extends Payload>[] payload() default {};
    // -----
}

public class IsUniqueValidator implements ConstraintValidator<IsUnique, String> {
    @Override
    public void initialize(IsUnique constraintAnnotation) {
    }
    
    @Override
    public boolean isValid(String value, ConstraintValidatorContext context) {
        // 模拟数据库判断是否存在改用户名
        return !"aaaa".equals(value);
    }
} 

@ControllerAdvice
@ResponseBody
public class ValidatorExceptionHandler {
    @ExceptionHandler(value = BindException.class)
    public Map<String, String> exceptionHandler(BindException e) {
        List<ObjectError> allErrors = e.getAllErrors();
        StringBuilder sb = new StringBuilder();
        for (ObjectError error : allErrors) {
            sb.append(error.getDefaultMessage());
            sb.append(", ");
        }
        String error = sb.toString();
        HashMap<String, String> resp = new HashMap<>();
        resp.put("1004", error.substring(0, error.lastIndexOf(",")));
        return resp;
    }
}

@Data
public class User {
    @NotNull(message = "name不为null")
    @IsUnique(message = "用户名是唯一的")
    private String name;
    @NotNull
    private String password;
}

    @PostMapping
    public String hello(@RequestBody @Valid User user) {
        return "hello" + user.getName();
    }