mysql對emoji的支持

步驟：

1. 升級mysql數據庫到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;
   
    #修改表中類型爲varchar、char等類型的列，長度或字符個數視狀況而定。
    alter table TABLE_NAME change OLD_COLUMN_NAME NEW_COLUMN_NAME varchar(字符個數) 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. 從新啓動mysql數據庫

   service mysql restart；

5. 檢查mysql數據庫字符集

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

   檢查是否有以下輸出：

   | 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. 確認mysql-connector-java的版本，網上說只要大於5.1.13就能夠，通過測試5.1.26不能夠，可是最新版5.1.35（Mar 17, 2015版本）能夠，其它版本未測試

7. 檢查服務器端的mysql數據庫鏈接字符串，必定要包含charactorEncoding=utf八、useUnicode=true、autoReconnect=true等字段

   注：JDBC Connection String的具體配置可參見：http://dev.mysql.com/doc/connector-j/en/connector-j-reference-configuration-properties.html

8. 導出數據庫時，須要設置字符集爲utf8mb4

   mysqldump --default-character-set=utf8mb4 用戶名 密碼 數據庫名 > 文件名