Question

我正在使用带有C3P0连接池的Hibernate处理Java EE JSF应用程序。我试图搜索任何可能的和不可能的东西并尝试了很多东西，但无法解决这个问题。

问题是处理数据库连接失败，例如当数据库关闭时。我找不到如何捕获ecfeption的方法，我可以使用它来显示用户界面上的错误状态。我唯一能做的就是在控制台中看到一些例外：

com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: Could not create connection to database server. Attempted reconnect 3 times. Giving up.
    at sun.reflect.GeneratedConstructorAccessor408.newInstance(Unknown Source)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:526)
    at com.mysql.jdbc.Util.handleNewInstance(Util.java:411)
    at com.mysql.jdbc.Util.getInstance(Util.java:386)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1015)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:989)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:975)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:920)
    at com.mysql.jdbc.ConnectionImpl.connectWithRetries(ConnectionImpl.java:2404)
    at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2325)
    at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:834)
    at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:46)
    at sun.reflect.GeneratedConstructorAccessor407.newInstance(Unknown Source)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:526)
    at com.mysql.jdbc.Util.handleNewInstance(Util.java:411)
    at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:416)
    at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:347)
    at com.mchange.v2.c3p0.DriverManagerDataSource.getConnection(DriverManagerDataSource.java:146)
    at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:195)
    at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:184)
    at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.acquireResource(C3P0PooledConnectionPool.java:200)
    at com.mchange.v2.resourcepool.BasicResourcePool.doAcquire(BasicResourcePool.java:1086)
    at com.mchange.v2.resourcepool.BasicResourcePool.doAcquireAndDecrementPendingAcquiresWithinLockOnSuccess(BasicResourcePool.java:1073)
    at com.mchange.v2.resourcepool.BasicResourcePool.access$800(BasicResourcePool.java:44)
    at com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask.run(BasicResourcePool.java:1810)
    at com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:648)
Caused by: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure
The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server.
    at sun.reflect.GeneratedConstructorAccessor404.newInstance(Unknown Source)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:526)
    at com.mysql.jdbc.Util.handleNewInstance(Util.java:411)
    at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:1129)
    at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:358)
    at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2498)
    at com.mysql.jdbc.ConnectionImpl.connectWithRetries(ConnectionImpl.java:2343)
    ... 18 more
Caused by: java.net.ConnectException: Connection timed out: connect
    at java.net.DualStackPlainSocketImpl.connect0(Native Method)
    at java.net.DualStackPlainSocketImpl.socketConnect(DualStackPlainSocketImpl.java:79)
    at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:339)
    at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:200)
    at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:182)
    at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:172)
    at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)
    at java.net.Socket.connect(Socket.java:579)
    at java.net.Socket.connect(Socket.java:528)
    at java.net.Socket.<init>(Socket.java:425)
    at java.net.Socket.<init>(Socket.java:241)
    at com.mysql.jdbc.StandardSocketFactory.connect(StandardSocketFactory.java:256)
    at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:308)
    ... 20 more
]]

但我无法理解这一点，它只是在控制台上，它甚至没有打印在Web浏览器响应中（客户端线程没有收到任何异常，它只是在尝试加载无限的页面时挂起）。

这是我的C3P0配置：

c3p0.testConnectionOnCheckout=true
c3p0.idleConnectionTestPeriod=60
c3p0.acquireIncrement=1
c3p0.preferredTestQuery=SELECT 1
c3p0.acquireRetryAttempts=1

我的问题是：如何以用户友好的方式处理数据库连接失败的情况？

Answer 1

您可以使用Omnifaces FullAjaxExceptionHandler来显示异常所需的内容。请参阅以下文档链接：

http://showcase.omnifaces.org/exceptionhandlers/FullAjaxExceptionHandler

Answer 2

好的，经过几天的工作，我已经构建了一个解决方案。

问题是，在没有数据库连接的情况下使用它时，典型的Hibernate会话没有抛出任何异常。但是，当数据库未连接时，这段代码会引发异常（因此它可以用作测试）：

Properties p = hibernateConnection.getCfg().getProperties();

String url = p.getProperty("hibernate.connection.url");
String user = p.getProperty("hibernate.connection.username");
String password = p.getProperty("hibernate.connection.password");

DriverManager.getConnection(url, user, password).close();

因此，可以使用简单的try-catch。如果发现异常，则连接已失效。

我用它来定期检查数据库连接。在应用程序部署时，TimerTask计划每分钟运行一次。当它捕获异常时，它将静态变量dbAvailable设置为false（否则为true）。正在对每个HTTP客户端请求检查此变量，如果为真，则会回复错误503。

为了安排我使用ServletContextListener的计时器。问题中提到的C3P0配置。

如何在Java EE上使用Hibernate，C3P0处理数据库连接失败？

2 个答案: