在后端开发中，对于键唯一值的判断很常见，但是每判断一个键就要几行if判断，很啰嗦，怎么才能让我们开发的效率更高呢。

(你肯定也写过像以下这种代码)

重复的判断浪费了太多时间，使用其实在数据库中使用unique进行约束即可

sql
create table sys_user
(
    id          mediumtext        null,
    username    varchar(256)      null,
    password    varchar(128)      null,
    nickname    varchar(256)      null,
    role        tinyint default 0 not null comment '角色 ''用户|管理员'' 0 1',
    phone       varchar(20)       null,
    email       varchar(128)      null,
    create_time datetime          null,
    deleted     tinyint default 0 not null comment '逻辑删除',
    constraint sys_user_pk
        unique (username),
    constraint sys_user_pk2
        unique (phone),
    constraint sys_user_pk3
        unique (email)
)
    row_format = DYNAMIC;

当然如果插入报错，报错信息可能是这样的

### Error updating database.  Cause: java.sql.SQLIntegrityConstraintViolationException: Duplicate entry 'admin' for key 'sys_user.sys_user_pk'
### The error may exist in cn/pepedd/mapper/UserMapper.java (best guess)
### The error may involve cn.pepedd.mapper.UserMapper.insert-Inline
### The error occurred while setting parameters
### SQL: INSERT INTO sys_user  ( id, username, nickname, password, role,  email, create_time )  VALUES  ( ?, ?, ?, ?, ?,  ?, ? )
### Cause: java.sql.SQLIntegrityConstraintViolationException: Duplicate entry 'admin' for key 'sys_user.sys_user_pk'
; Duplicate entry 'admin' for key 'sys_user.sys_user_pk'; nested exception is java.sql.SQLIntegrityConstraintViolationException: Duplicate entry 'admin' for key 'sys_user.sys_user_pk'

不能直接在接口显示，于是我们使用异常处理器处理这个错误即可

• 不返回重复的键名

java
/**
* 处理键重复异常
*/
@ExceptionHandler(DuplicateKeyException.class)
public R handleDuplicateKeyException(DuplicateKeyException e) {
    return R.error(ErrorCode.PARAMS_ERROR, "数据重复，请检查后提交");
}

• 返回重复的键名

java
/**
* 处理键重复异常
*/
@ExceptionHandler(DuplicateKeyException.class)
public R handleDuplicateKeyException(DuplicateKeyException e) {
    String errorMessage = e.getMessage();
    String duplicateEntry = null;

    // 从错误消息中提取字段名
    Pattern pattern = Pattern.compile("Duplicate entry '(.*?)' for key '.*'");
    Matcher matcher = pattern.matcher(errorMessage);
    if (matcher.find()) {
      duplicateEntry = matcher.group(1);
    }

    String message = "数据重复，请检查后提交";
    if (duplicateEntry != null) {
      message += "。重复的值是：" + duplicateEntry;
    }

    return R.error(ErrorCode.PARAMS_ERROR, message);
}

就像这样