Java Hibernate/C3P0 错误：“无法获取连接元数据。客户端尝试签出连接已超时。”

Question

我正在尝试获取一些我传递并运行的代码。它似乎使用了Hibernate框架。我已经克服了大部分调整配置的错误，但这一个让我难住了。

它正在尝试连接到两个数据库：gameapp 和 gamelog。两者都存在。连接到游戏日志似乎有问题，但连接到游戏应用程序没有问题（稍后在初始化中，它连接到并加载其他数据库就好了）。下面，我粘贴了错误和异常堆栈转储。

我想象配置中还有其他内容，因此我还包含了该数据库的配置文件。我知道这很模糊，但我希望一些专业人士能够看到我错过的愚蠢错误。

<?xml version="1.0" encoding="GBK"?>
<!DOCTYPE hibernate-configuration PUBLIC
    "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
    "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">

<hibernate-configuration>
    <session-factory>
        <property name="dialect">org.hibernate.dialect.MySQLDialect</property>
        <property name="connection.driver_class">com.mysql.jdbc.Driver</property>
        <property name="connection.url">jdbc:mysql://127.0.0.1:3306/gamelog</property>
        <property name="connection.username">root</property>
        <property name="connection.password"></property>
        <property   name="connection.useUnicode">true</property>     
            <property   name="connection.characterEncoding">UTF-8</property>   
        <property name="hibernate.jdbc.batch_size">100</property>
        <property name="jdbc.fetch_size">1</property>
        <property name="hbm2ddl.auto">none</property><!-- update -->
        <property name="connection.useUnicode">true</property>
        <property name="show_sql">true</property>
        <!-- c3p0-configuration -->
        <property name="hibernate.connection.provider_class">org.hibernate.connection.C3P0ConnectionProvider</property> 
        <property name="hibernate.c3p0.min_size">5</property>
        <property name="hibernate.c3p0.max_size">10</property>
        <property name="hibernate.c3p0.timeout">30</property>
        <property name="hibernate.c3p0.idle_test_period">30</property>
        <property name="hibernate.c3p0.max_statements">0</property>
        <property name="hibernate.c3p0.acquire_increment">5</property>      
    </session-factory>
</hibernate-configuration>

异常和堆栈跟踪：

2010-04-30 17:50:00,411 WARN [org.hibernate.cfg.SettingsFactory] - Could not obtain connection metadata
java.sql.SQLException: An attempt by a client to checkout a Connection has timed out.
    at com.mchange.v2.sql.SqlUtils.toSQLException(SqlUtils.java:106)
    at com.mchange.v2.sql.SqlUtils.toSQLException(SqlUtils.java:65)
    at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool.checkoutPooledConnection(C3P0PooledConnectionPool.java:527)
    at com.mchange.v2.c3p0.impl.AbstractPoolBackedDataSource.getConnection(AbstractPoolBackedDataSource.java:128)
    at org.hibernate.connection.C3P0ConnectionProvider.getConnection(C3P0ConnectionProvider.java:35)
    at org.hibernate.cfg.SettingsFactory.buildSettings(SettingsFactory.java:76)
    at org.hibernate.cfg.Configuration.buildSettings(Configuration.java:1933)
    at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1216)
    at com.database.hibernate.util.HibernateFactory.<init>(Unknown Source)
    at com.database.hibernate.util.HibernateUtil.<clinit>(Unknown Source)
    at com.server.databaseop.goodOp.GoodOpImpl.initBreedGoods(Unknown Source)
    at com.server.databaseop.goodOp.GoodOpImpl.access$000(Unknown Source)
    at com.server.databaseop.goodOp.GoodOpImpl$1.run(Unknown Source)
    at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471)
    at java.util.concurrent.FutureTask$Sync.innerRunAndReset(FutureTask.java:351)
    at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:178)
    at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$201(ScheduledThreadPoolExecutor.java:165)
    at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:267)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
    at java.lang.Thread.run(Thread.java:636)
Caused by: com.mchange.v2.resourcepool.TimeoutException: A client timed out while waiting to acquire a resource from com.mchange.v2.resourcepool.BasicResourcePool@ca470 -- timeout at awaitAvailable()
    at com.mchange.v2.resourcepool.BasicResourcePool.awaitAvailable(BasicResourcePool.java:1317)
    at com.mchange.v2.resourcepool.BasicResourcePool.prelimCheckoutResource(BasicResourcePool.java:557)
    at com.mchange.v2.resourcepool.BasicResourcePool.checkoutResource(BasicResourcePool.java:477)
    at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool.checkoutPooledConnection(C3P0PooledConnectionPool.java:525)
    ... 18 more

Answer 1

如果您将 C3P0 的“checkoutTimeout”属性设置为 0 以外的值，您可能会超时得太快（这是我的问题，解决方案：将其从 500 毫秒增加到 2000 毫秒）。

或者，有一个解决此警告的方法：

将 hibernate.temp.use_jdbc_metadata_defaults 属性设置为 false。

在 http://www.docjar.com/ 中找到了这个html/api/org/hibernate/cfg/SettingsFactory.java.html，尽管不让 Hibernate 提取 JDBC 元数据默认值可能会产生副作用。

Answer 2

实际上，这甚至不是身份验证错误。 MySQL 是否正在运行或绑定到本地主机？

telnet 127.0.0.1 3306 可以吗？
如果是这样，请在盒子上安装 mysql 客户端并尝试

mysql --user=root --ip=127.0.0.1
看看会发生什么

Answer 3

检查是否可以使用 root 用户且无需密码（！）在命令行上连接到 gamelog mysql 数据库。作为旁注，我建议为 root 设置密码并使用不同的帐户从应用程序连接到数据库，但这是另一个故事。