面对以下问题：服务器连接一切正常，直到我决定使用c3p0进行连接池。现在（有时）我得到一个SQLNontransientConnectionException，因为在30次采集尝试后无法获取新资源。这种行为是非常随机的，因为我经常在本地重启服务器时拒绝构建，因为没有找到连接。这可能与我实例化我的EntityManagerFactory的方式有关吗？ 我会对任何类型的帮助感到高兴
`WARNUNG: com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask@4ff43e8a -- Acquisition Attempt Failed!!! Clearing pending acquires. While trying to acquire a needed new resource, we failed to succeed more than the maximum number of allowed acquisition attempts (30).
Last acquisition attempt exception:java.sql.SQLNonTransientConnectionException: Could not create connection to database server.
at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:550)
at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:537)
at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:527)
at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:512)
at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:480)
at com.mysql.cj.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:1807)
at com.mysql.cj.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:1624)
at com.mysql.cj.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:637)
at com.mysql.cj.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:351)
at com.mysql.cj.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:224)
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: java.lang.ArrayIndexOutOfBoundsException`
的persistence.xml
<property name="hibernate.c3p0.min_size" value="5"/>
<property name="hibernate.c3p0.max_size" value="20"/>
<property name="hibernate.c3p0.timeout" value="3000"/>
<property name="hibernate.c3p0.max_statements" value="100"/>
<property name="hibernate.c3p0.idle_test_period" value="300"/>
<property name="hibernate.c3p0.numHelperThreads" value="8"/>
<property name="hibernate.c3p0.testConnectionOnCheckout" value="true"/>
编辑1：这是完整的堆栈跟踪
java.sql.SQLNonTransientConnectionException: Could not create connection to database server.
at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:550)
at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:537)
at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:527)
at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:512)
at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:480)
at com.mysql.cj.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:1807)
at com.mysql.cj.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:1624)
at com.mysql.cj.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:637)
at com.mysql.cj.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:351)
at com.mysql.cj.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:224)
at com.mchange.v2.c3p0.DriverManagerDataSource.getConnection(DriverManagerDataSource.java:175)
at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:220)
at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:206)
at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.acquireResource(C3P0PooledConnectionPool.java:203)
at com.mchange.v2.resourcepool.BasicResourcePool.doAcquire(BasicResourcePool.java:1138)
at com.mchange.v2.resourcepool.BasicResourcePool.doAcquireAndDecrementPendingAcquiresWithinLockOnSuccess(BasicResourcePool.java:1125)
at com.mchange.v2.resourcepool.BasicResourcePool.access$700(BasicResourcePool.java:44)
at com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask.run(BasicResourcePool.java:1870)
at com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:696)
Caused by: java.lang.ArrayIndexOutOfBoundsException: 24
at com.mysql.cj.mysqla.io.Buffer.readInteger(Buffer.java:271)
at com.mysql.cj.mysqla.io.MysqlaCapabilities.setInitialHandshakePacket(MysqlaCapabilities.java:62)
at com.mysql.cj.mysqla.io.MysqlaProtocol.readServerCapabilities(MysqlaProtocol.java:434)
at com.mysql.cj.mysqla.io.MysqlaProtocol.beforeHandshake(MysqlaProtocol.java:359)
at com.mysql.cj.mysqla.io.MysqlaProtocol.connect(MysqlaProtocol.java:1359)
at com.mysql.cj.mysqla.MysqlaSession.connect(MysqlaSession.java:132)
at com.mysql.cj.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:1754)
... 13 more
[C3P0PooledConnectionPoolManager[identityToken->1hge1tv9nk20xsdnfi9dv|6f911326]-HelperThread-#0] WARN com.mchange.v2.resourcepool.BasicResourcePool - Having failed to acquire a resource, com.mchange.v2.resourcepool.BasicResourcePool@55d58825 is interrupting all Threads waiting on a resource to check out. Will try again in response to new client requests.
编辑2：将配置从persistence.xml移至c3p0-config.xml
<c3p0-config>
<default-config>
<property name="automaticTestTable">con_test</property>
<property name="checkoutTimeout">30000</property>
<property name="idleConnectionTestPeriod">30</property>
<property name="initialPoolSize">10</property>
<property name="maxIdleTime">30</property>
<property name="maxPoolSize">100</property>
<property name="initialPoolSize">20</property>
<property name="minPoolSize">10</property>
<property name="maxStatements">200</property>
<user-overrides user="test-user">
<property name="maxPoolSize">10</property>
<property name="minPoolSize">1</property>
<property name="maxStatements">0</property>
</user-overrides>
</default-config>