前言：手機app應用評論的時候，恢復表情符號，提示失敗。
1，查看tomcat後臺日誌，核心報錯信息如下：
Caused by: java.sql.SQLException: Incorrect string value: '\xF0\x9F\x98\x97\xF0\x9F...' for column 'CONTENT' 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.execute(PreparedStatement.java:1379)
at org.apache.commons.dbcp.DelegatingPreparedStatement.execute(DelegatingPreparedStatement.java:172)
at org.apache.commons.dbcp.DelegatingPreparedStatement.execute(DelegatingPreparedStatement.java:172)
at com.ibatis.sqlmap.engine.execution.SqlExecutor.executeUpdate(SqlExecutor.java:80)
at com.ibatis.sqlmap.engine.mapping.statement.MappedStatement.sqlExecuteUpdate(MappedStatement.java:216)
at com.ibatis.sqlmap.engine.mapping.statement.MappedStatement.executeUpdate(MappedStatement.java:94)
... 46 more
[root@mysqlvm2 ~]# mysql -root -p
mysql> use test;
Database changed
mysql> show tables;
Ignoring query to other database
mysql> Ctrl-C -- exit!
Aborted
忘記輸入-u參數了，沖洗你輸入，OK，如下所示：
[root@mysqlvm2 ~]# mysql -uroot -p
Enter password:
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 4
Server version: 5.6.12-log Source distribution
Copyright (c) 2000, 2011, Oracle and/or its affiliates. All rights reserved.
Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
mysql>
mysql> use test;
Database changed
mysql> show tables;
+------------------------+
| Tables_in_test |
+------------------------+
| c |
| lubin_test |
| test |
| tt |
+------------------------+
10 rows in set (0.00 sec)
這種輸入Incorrect string value: '\xF0\x9F\x98\x97\xF0\x9F...'的問題，多數都是字符集的，以前從latain改成gbk，從gbk改成utf8，而我的CONTENT字段已經utf8了，那麼比utf8更多的就只有utf8mb4了，所以去修改表字段的字符集吧。
mysql>
2，先去修改表字段字符集爲utf8mb4：
ALTER TABLE UGC_REVIEW_CONTENT MODIFY `CONTENT` TEXT CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci COMMENT '評論內容';
執行完後，再在手機端的app測試，依然報同樣的錯誤。
3，再去修改表字符集utf8mb4：
ALTER TABLE UGC_REVIEW_CONTENT CHARSET=utf8mb4 COMMENT='曬單/推薦的評論內容';
執行完後，再在手機端的app測試，依然報同樣的錯誤。
4，再去修改數據庫的字符集utf8mb4:
vim my.cnf
init-connect='SET NAMES utf8mb4'
character-set-server=utf8mb4
重啓mysql數據庫
[root@mysqlvm4 ~]# service mysql restart
Shutting down MySQL.... [確定]
Starting MySQL.............................................[確定]..
[root@mysqlvm4 ~]#
查看db的字符集
mysql> show variables like '%char%';
+--------------------------+----------------------------------+
| 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/local/mysql/share/charsets/ |
+--------------------------+----------------------------------+
8 rows in set (0.00 sec)
mysql>
在手機app端重新評論，輸入表情符號，點擊提交提示評論成功。
5，問題分析總結：
㈠ 原因
普通的字符串或者表情都是佔位3個字節，所以utf8足夠用了，但是移動端的表情符號佔位是4個字節，普通的utf8就不夠用了，爲了應對無線互聯網的機遇和挑戰、避免 emoji 表情符號帶來的問題、涉及無線相關的 MySQL 數據庫建議都提前採用 utf8mb4 字符集，這必須要作爲移動互聯網行業的一個技術選型的要點
㈡ 限制
需要 >= MySQL 5.5.3版本、從庫也必須是5.5的了、低版本不支持這個字符集、複製報錯。