Hibernate SessionFactory创建新连接后，如何立即运行SQL查询？

Question

My server uses Hibernate in order to connect to a MySQL db. I'm also using c3p0 for connection pooling. I want to execute a specific sql query once on each connection when it is created, but since I'm using ComboPooledDataSource , there is no way to detect when a new session is created. I found out that I can run my query by enabling test connection on checkout and set the query that I want to run as preferred test query (but it can run more than once).

String query = "my query";
comboPooledDataSource.setTestConnectionOnCheckout(true);
comboPooledDataSource.setPreferredTestQuery(query);

Is there a more elegant way to accomplish this?

* Edit *

I'm trying to make my db accept utf8mb4 characters. The acceptable way to do it is by applying the following to the my.cnf file:

[mysqld]
character-set-server = utf8mb4
collation-server = utf8mb4_unicode_ci

The problem is that I don't have access to anything but my db, so my solution is to execute SET NAMES utf8mb4 COLLATE utf8mb4_unicode_ci; for each connection.

Answer 1

See c3p0's ConnectionCustomizer interface. Override the onAcquire(...) method of AbstractConnectionCustomizer . onAcquire(...) is called just once for each Connection, after it has been acquired from the database, before it is made available for check-out by clients.

Or, if you want you can just use c3p0's built-in example for just this sort of use case, com.mchange.v2.c3p0.example.InitSqlConnectionCustomizer

In c3p0.properties:

c3p0.connectionCustomizerClassName=com.mchange.v2.c3p0.example.InitSqlConnectionCustomizer
c3p0.extensions.initSql=SET NAMES utf8mb4 COLLATE utf8mb4_unicode_ci