我已将我们的服务器 MySQL 数据库更改为使用 utf8mb4，因为我们需要支持表情。我已按照Mathias Bynens的How to support full Unicode in MySQL databases文章中的说明进行操作。唯一的区别是我没有从 utf8 更改。
这是配置：
[client]
default-character-set = utf8mb4
[mysql]
default-character-set = utf8mb4
[mysqld]
character-set-client-handshake = FALSE
init-connect = 'SET NAMES utf8mb4'
character-set-server = utf8mb4
collation-server = utf8mb4_unicode_ci
这是 MySQLSHOW VARIABLES输出：
mysql> SHOW VARIABLES WHERE Variable_name LIKE 'character\_set\_%' OR Variable_name LIKE 'collation%';
+--------------------------+--------------------+
| 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 |
| collation_connection | utf8mb4_unicode_ci |
| collation_database | utf8mb4_unicode_ci |
| collation_server | utf8mb4_unicode_ci |
+--------------------------+--------------------+
10 rows in set (0.00 sec)
在我重新启动 MySQL 和我的应用程序后，控制台打印了如下错误日志：
2014-08-05 17:33:49,022 [com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread-#2] WARN com.mchange.v2.resourcepool.BasicResourcePool - com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask@6ae03500 -- Acquisition Attempt Failed!!! Clearing pending acquires. While trying to acquire a needed new resource, we failed to succeed more than the maximum number of allowed acquisition attempts (30). Last acquisition attempt exception:
java.sql.SQLException: Unknown character set index for field '224' received from server.
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:910)
at com.mysql.jdbc.Connection.getCharsetNameForIndex(Connection.java:3556)
at com.mysql.jdbc.Field.<init>(Field.java:192)
at com.mysql.jdbc.MysqlIO.unpackField(MysqlIO.java:731)
at com.mysql.jdbc.MysqlIO.getResultSet(MysqlIO.java:387)
at com.mysql.jdbc.MysqlIO.readResultsForQueryOrUpdate(MysqlIO.java:2076)
at com.mysql.jdbc.MysqlIO.readAllResults(MysqlIO.java:1451)
at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:1787)
at com.mysql.jdbc.Connection.execSQL(Connection.java:3277)
at com.mysql.jdbc.Connection.execSQL(Connection.java:3206)
at com.mysql.jdbc.Statement.executeQuery(Statement.java:1232)
at com.mysql.jdbc.Connection.loadServerVariables(Connection.java:4478)
at com.mysql.jdbc.Connection.initializePropsFromServer(Connection.java:4062)
at com.mysql.jdbc.Connection.createNewIO(Connection.java:2789)
at com.mysql.jdbc.Connection.<init>(Connection.java:1555)
at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:285)
at com.mchange.v2.c3p0.DriverManagerDataSource.getConnection(DriverManagerDataSource.java:134)
at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:182)
at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:171)
at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.acquireResource(C3P0PooledConnectionPool.java:137)
at com.mchange.v2.resourcepool.BasicResourcePool.doAcquire(BasicResourcePool.java:1014)
at com.mchange.v2.resourcepool.BasicResourcePool.access$800(BasicResourcePool.java:32)
at com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask.run(BasicResourcePool.java:1810)
at com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:547)
Aug 5, 2014 5:33:49 PM org.hibernate.util.JDBCExceptionReporter logExceptions
WARNING: SQL Error: 0, SQLState: null
Aug 5, 2014 5:33:49 PM org.hibernate.util.JDBCExceptionReporter logExceptions
SEVERE: Connections could not be acquired from the underlying database!
Aug 5, 2014 5:33:49 PM org.hibernate.util.JDBCExceptionReporter logExceptions
WARNING: SQL Error: 0, SQLState: null
Aug 5, 2014 5:33:49 PM org.hibernate.util.JDBCExceptionReporter logExceptions
SEVERE: Connections could not be acquired from the underlying database!
登录到我的 CMS 或 API 调用都不起作用。它给了我上面的错误，我无法用谷歌搜索任何解决方案。
为了修复错误，下一步该怎么做？