mysql对emoji的支持

步骤：

1. 升级mysql数据库到5.5.3+

2. 修改database、table和column字符集

   alter database DATABASE_NAME character set = utf8mb4 collate = utf8mb4_unicode_ci;
    alter table TABLE_NAME convert to character set utf8mb4 collate utf8mb4_unicode_ci;
   
    #修改表中类型为varchar、char等类型的列，长度或字符个数视状况而定。
    alter table TABLE_NAME change OLD_COLUMN_NAME NEW_COLUMN_NAME varchar(字符个数) character set utf8mb4 collate utf8mb4_unicode_ci;

3. 修改mysql的配置文件my.cnf

   [client]
    default-character-set = utf8mb4
   
    [mysql]
    default-character-set = utf8mb4
   
    [mysqld]
    character-set-client-handshake = FALSE
    character-set-server = utf8mb4
    collation-server = utf8mb4_unicode_ci
    init_connect='SET NAMES utf8mb4'

4. 从新启动mysql数据库

   service mysql restart；

5. 检查mysql数据库字符集

   show variables where variable_name like 'character_set_%' or variable_name like 'collation%';

   检查是否有以下输出：

   | Variable_name                 | Value                             |
    |-----------------------------------------|-----------------------------------------|
    | character_set_client          | utf8mb4                           |
    | character_set_connection  | utf8mb4                           |
    | character_set_database    | utf8mb4                           |
    | character_set_filesystem  | binary                            |
    | character_set_results     | utf8mb4                           |
    | character_set_server      | utf8mb4                           |
    | character_set_system      | utf8                              |
    | character_sets_dir            | /usr/share/mysql/charsets/    |
    | collation_connection      | utf8mb4_unicode_ci            |
    | collation_database        | utf8mb4_unicode_ci            |
    | collation_server              | utf8mb4_unicode_ci            |

6. 确认mysql-connector-java的版本，网上说只要大于5.1.13就能够，通过测试5.1.26不能够，可是最新版5.1.35（Mar 17, 2015版本）能够，其它版本未测试

7. 检查服务器端的mysql数据库链接字符串，必定要包含charactorEncoding=utf八、useUnicode=true、autoReconnect=true等字段

   注：JDBC Connection String的具体配置可参见：http://dev.mysql.com/doc/connector-j/en/connector-j-reference-configuration-properties.html

8. 导出数据库时，须要设置字符集为utf8mb4

   mysqldump --default-character-set=utf8mb4 用户名 密码 数据库名 > 文件名