10分钟完成MySQL对emoji的支持
公司有新要求，ios客户端要上线评论中可以使用emoji表情的功能，在mysql 5.5 之前，UTF-8编码只支持1-3个字节；从MySQL 5.5开始，可以支持4个字节UTF编码 utf8mb4 ，一个字符能够支持更多的字符集，也能够支持更多表情符号。
utf8mb4兼容utf8，且比utf8能表示更多的字符，是utf8字符集的超集。所以现在一些新的业务，比如IOS中的emoji表情，会将MySQL数据库的字符集设置为utf8mb4。
先看问题：
Caused by: java.sql.SQLException: Incorrect string value: '\xF6\x9D\x98\x84' for column 'comment' at row 1
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1074)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:4096)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:4028)
at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:2490)
at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2651)
at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2734)
at com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:2155)
at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:2458)
如果我们将列comment设置为varchar(100)，用于存储评论信息，现在上线新功能存储emoji表情，插入emoji表情就会报出上述错误，UTF-8编码有可能是两个、三个、四个字节。Emoji表情是4个字节，而Mysql的utf8编码最多3个字节，所以数据插不进去。utf8mb4兼容utf8，且比utf8能表示更多的字符。
解决方案：将Mysql的编码从utf8转换成utf8mb4。
网上的文章各执一词，本文就生产环境中真实可用的参数进行记录
整体操作流程其实并不难
一：首先我们修改my.cnf参数
<span style="color:#333333"><span style="color:black"><code class="language-bash"><span style="color:#999999">[</span>client<span style="color:#999999">]</span>
default-character-set<span style="color:#9a6e3a">=</span>utf8mb4
<span style="color:#999999">[</span>mysql<span style="color:#999999">]</span>
default-character-set<span style="color:#9a6e3a">=</span>utf8mb4
<span style="color:#999999">[</span>mysqld<span style="color:#999999">]</span>
character-set-server <span style="color:#9a6e3a">=</span> utf8mb4
collation-server <span style="color:#9a6e3a">=</span> utf8mb4_unicode_ci
init_connect <span style="color:#9a6e3a">=</span> <span style="color:#669900">'SET NAMES utf8mb4'</span>
character-set-client-handshake <span style="color:#9a6e3a">=</span> <span style="color:#990055">false</span></code></span></span>
二：对数据库相关的表进行字符集修改
将数据库转换为utf8mb4
<span style="color:#333333"><span style="color:black"><code class="language-sql">mysql<span style="color:#9a6e3a">></span> <span style="color:#0077aa">ALTER</span> <span style="color:#0077aa">DATABASE</span> erp <span style="color:#0077aa">CHARACTER</span> <span style="color:#0077aa">SET</span> utf8mb4 <span style="color:#0077aa">COLLATE</span> utf8mb4_unicode_ci<span style="color:#999999">;</span></code></span></span>
将已经建好的表也转换成utf8mb4
<span style="color:#333333"><span style="color:black"><code class="language-sql">mysql<span style="color:#9a6e3a">></span><span style="color:#0077aa">ALTER</span> <span style="color:#0077aa">TABLE</span> <span style="color:#999999">`</span>erp_comment<span style="color:#999999">`</span> <span style="color:#0077aa">CONVERT</span> <span style="color:#0077aa">TO</span> <span style="color:#0077aa">CHARACTER</span> <span style="color:#0077aa">SET</span> utf8mb4 <span style="color:#0077aa">COLLATE</span> utf8mb4_unicode_ci<span style="color:#999999">;</span></code></span></span>将需要使用emoji的字段设置类型为：
<span style="color:#333333"><span style="color:black"><code class="language-sql">mysql<span style="color:#9a6e3a">></span><span style="color:#0077aa">ALTER</span> <span style="color:#0077aa">TABLE</span> <span style="color:#999999">`</span>erp_comment<span style="color:#999999">`</span> <span style="color:#0077aa">MODIFY</span> <span style="color:#0077aa">COLUMN</span> <span style="color:#999999">`</span><span style="color:#0077aa">comment</span><span style="color:#999999">`</span> <span style="color:#0077aa">varchar</span><span style="color:#999999">(</span><span style="color:#990055">100</span><span style="color:#999999">)</span> <span style="color:#0077aa">CHARACTER</span> <span style="color:#0077aa">SET</span> utf8mb4 <span style="color:#0077aa">COLLATE</span> utf8mb4_unicode_ci<span style="color:#999999">;</span></code></span></span>
三：重启数据库服务器使之生效
<span style="color:#333333"><span style="color:black"><code class="language-bash"><span style="color:#999999">[</span>root@HE3 ~<span style="color:#999999">]</span><span style="color:slategray"># /etc/init.d/mysqld restart</span>
Shutting down MySQL<span style="color:#999999">..</span> SUCCESS<span style="color:#9a6e3a">!</span>
Starting MySQL<span style="color:#999999">..</span><span style="color:#999999">..</span> SUCCESS<span style="color:#9a6e3a">!</span></code></span></span>四：登录数据库检查是否如下：
<span style="color:#333333"><span style="color:black"><code class="language-sql">mysql<span style="color:#9a6e3a">></span> <span style="color:#0077aa">SHOW</span> VARIABLES <span style="color:#0077aa">WHERE</span> Variable_name <span style="color:#9a6e3a">LIKE</span> <span style="color:#669900">'character%'</span> <span style="color:#9a6e3a">OR</span> Variable_name <span style="color:#9a6e3a">LIKE</span> <span style="color:#669900">'collation%'</span><span style="color:#999999">;</span>
<span style="color:#9a6e3a">+</span><span style="color:slategray">--------------------------+--------------------+</span>
<span style="color:#9a6e3a">|</span> Variable_name <span style="color:#9a6e3a">|</span> <span style="color:#0077aa">Value</span> <span style="color:#9a6e3a">|</span>
<span style="color:#9a6e3a">+</span><span style="color:slategray">--------------------------+--------------------+</span>
<span style="color:#9a6e3a">|</span> character_set_client <span style="color:#9a6e3a">|</span> utf8mb4 <span style="color:#9a6e3a">|</span>
<span style="color:#9a6e3a">|</span> character_set_connection <span style="color:#9a6e3a">|</span> utf8mb4 <span style="color:#9a6e3a">|</span>
<span style="color:#9a6e3a">|</span> character_set_database <span style="color:#9a6e3a">|</span> utf8mb4 <span style="color:#9a6e3a">|</span>
<span style="color:#9a6e3a">|</span> character_set_filesystem <span style="color:#9a6e3a">|</span> <span style="color:#0077aa">binary</span> <span style="color:#9a6e3a">|</span>
<span style="color:#9a6e3a">|</span> character_set_results <span style="color:#9a6e3a">|</span> utf8mb4 <span style="color:#9a6e3a">|</span>
<span style="color:#9a6e3a">|</span> character_set_server <span style="color:#9a6e3a">|</span> utf8mb4 <span style="color:#9a6e3a">|</span>
<span style="color:#9a6e3a">|</span> character_set_system <span style="color:#9a6e3a">|</span> utf8 <span style="color:#9a6e3a">|</span>
<span style="color:#9a6e3a">|</span> collation_connection <span style="color:#9a6e3a">|</span> utf8mb4_unicode_ci <span style="color:#9a6e3a">|</span>
<span style="color:#9a6e3a">|</span> collation_database <span style="color:#9a6e3a">|</span> utf8mb4_unicode_ci <span style="color:#9a6e3a">|</span>
<span style="color:#9a6e3a">|</span> collation_server <span style="color:#9a6e3a">|</span> utf8mb4_unicode_ci <span style="color:#9a6e3a">|</span>
<span style="color:#9a6e3a">+</span><span style="color:slategray">--------------------------+--------------------+</span>
<span style="color:#0077aa">rows</span> <span style="color:#9a6e3a">in</span> <span style="color:#0077aa">set</span> <span style="color:#999999">(</span><span style="color:#990055">0.00</span> sec<span style="color:#999999">)</span></code></span></span>特别说明下：collation_connection/collation_database/collation_server如果是utf8mb4_general_ci，没有关系。但必须保证character_set_client/character_set_connection/character_set_database/character_set_results/character_set_server为utf8mb4。
五：让开发那边的pom配置中，去掉characterEncoding参数，并重新编译一下
如果你用的是java服务器，升级或确保你的mysql connector版本高于5.1.13，否则仍然无法使用utf8mb4
最后再让前端应用插入emoji表情，就可以了。
一些小知识点:
其中character-set-server 和 collation-server 这些设置为utf8mb4字符集是比较容易理解的，就是将MySQL数据库相关的字符集都设置为utf8mb4；
但为了实现客户端utf8连接到MySQL后，使用的也是utf8mb4字符集，就在 mysqld配置中配置了 init_connect='SET NAMES utf8mb4' 表示初始化连接都设置为utf8mb4字符集，再配置一个 skip-character-set-client-handshake = true 忽略客户端字符集设置，不论客户端是何种字符集，都按照init_connect中的设置进行使用，这样就满足了应用的需求。
参考：Emoji对照表：
http://punchdrunker.github.io/iOSEmoji/table_html/bell.html