上传图片到Mysql数据库，max_allowed_packet 过小导致失败

    项目中遇到要把图片保存到数据库中报错如下：

Caused by: com.mysql.jdbc.PacketTooBigException: Packet for query is too large (47233263 > 31457280). You can change this value on the server by setting the max_allowed_packet' variable.
	at com.mysql.jdbc.MysqlIO.send(MysqlIO.java:3592)
	at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:2417)
	at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2582)
	at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2530)
	at com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:1907)
	at com.mysql.jdbc.PreparedStatement.execute(PreparedStatement.java:1199)
	at com.alibaba.druid.filter.FilterChainImpl.preparedStatement_execute(FilterChainImpl.java:2931)
	at com.alibaba.druid.filter.FilterEventAdapter.preparedStatement_execute(FilterEventAdapter.java:440)
	at com.alibaba.druid.filter.FilterChainImpl.preparedStatement_execute(FilterChainImpl.java:2929)
	at com.alibaba.druid.proxy.jdbc.PreparedStatementProxyImpl.execute(PreparedStatementProxyImpl.java:131)
	at com.alibaba.druid.pool.DruidPooledPreparedStatement.execute(DruidPooledPreparedStatement.java:493)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.apache.ibatis.logging.jdbc.PreparedStatementLogger.invoke(PreparedStatementLogger.java:59)
	at com.sun.proxy.$Proxy27.execute(Unknown Source)
	at org.apache.ibatis.executor.statement.PreparedStatementHandler.update(PreparedStatementHandler.java:45)
	at org.apache.ibatis.executor.statement.RoutingStatementHandler.update(RoutingStatementHandler.java:73)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.apache.ibatis.plugin.Plugin.invoke(Plugin.java:63)
	at com.sun.proxy.$Proxy25.update(Unknown Source)
	at org.apache.ibatis.executor.ReuseExecutor.doUpdate(ReuseExecutor.java:51)
	at org.apache.ibatis.executor.BaseExecutor.update(BaseExecutor.java:115)
	at org.apache.ibatis.executor.CachingExecutor.update(CachingExecutor.java:75)
	at org.apache.ibatis.session.defaults.DefaultSqlSession.update(DefaultSqlSession.java:170)
	at org.apache.ibatis.session.defaults.DefaultSqlSession.insert(DefaultSqlSession.java:157)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.mybatis.spring.SqlSessionTemplate$SqlSessionInterceptor.invoke(SqlSessionTemplate.java:408)
	... 77 more

网上查询资料后发现，上传图片过大，保存到数据库的时候异常；因为mysql根据配置文件会限制server接受的数据包大小。有时候插入大的数据和更新会被max_allowed_packet 参数限制，而导致失败。

查看当前配置参数 ：show VARIABLES like '%max_allowed_packet%';    显示结果如下（我用的是SQLyog,已设置上传最大30M）：

修改方法：

1. 修改my.ini文件，,在[mysqld]段配置段进行修改；

max_allowed_packet = 30M

2.用命令修改：

SET GLOBAL max_allowed_packet = 3*1024*1024*10;

修改成功后查看max_allowed_packet，发现值没有改变，需要重新连接数据库；如果在mysql server运行命令行，需要退出重新登录在进行查看；