应用服务器连接mysql，有时候会出现以下异常：
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145) [na:1.7.0_95]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615) [na:1.7.0_95]
at java.lang.Thread.run(Thread.java:745) [na:1.7.0_95]
Caused by: java.io.EOFException: Can not read response from server. Expected to read 4 bytes, read 0 bytes before connection was unexpectedly lost.
at com.mysql.jdbc.MysqlIO.readFully(MysqlIO.java:3161) ~[mysql-connector-java-5.1.31.jar:na]
at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:3615) ~[mysql-connector-java-5.1.31.jar:na]
... 43 common frames omitted
这个问题主要原因是应用服务器很长时间没有连接mysql，超过了mysql设置的最大超时时间，再连接mysql就会出现这个问题。mysql默认设置是8小时，一般网站白天都有人访问，从夜里到早上一般都会超过8小时，所以再来访问就会这个问题。
简单的解决办法就是修改最大超时时间，比如改为12小时或10小时，这样恰好避免了无人访问的时段，这里修改为10小时，方法如下：
mysql> show variables like '%timeout';
+----------------------------+-------+
| Variable_name | Value |
+----------------------------+-------+
| connect_timeout | 10 |
| delayed_insert_timeout | 300 |
| innodb_lock_wait_timeout | 50 |
| innodb_rollback_on_timeout | OFF |
| interactive_timeout | 28800 |
| net_read_timeout | 30 |
| net_write_timeout | 60 |
| slave_net_timeout | 3600 |
| table_lock_wait_timeout | 50 |
| wait_timeout | 28800 |
+----------------------------+-------+
10 rows in set (0.00 sec)
mysql> set wait_timeout = 36000;
Query OK, 0 rows affected (0.00 sec)
mysql> set interactive_timeout = 36000;
Query OK, 0 rows affected (0.00 sec)
mysql> show variables like '%timeout';
+----------------------------+-------+
| Variable_name | Value |
+----------------------------+-------+
| connect_timeout | 10 |
| delayed_insert_timeout | 300 |
| innodb_lock_wait_timeout | 50 |
| innodb_rollback_on_timeout | OFF |
| interactive_timeout | 36000 |
| net_read_timeout | 30 |
| net_write_timeout | 60 |
| slave_net_timeout | 3600 |
| table_lock_wait_timeout | 50 |
| wait_timeout | 36000 |
+----------------------------+-------+
10 rows in set (0.00 sec)