我有一个使用MySQL的Tomcat应用程序，以及用于ORM的Hibernate。我们的应用程序的性质要求我们必须从NoSQL存储中为每个请求提取和聚合大量分析数据，因此我们将每个请求的提取和聚合分成几个任务，并将这些数据委托给线程池执行服务。
当每个线程执行任务时，它需要查询/更新MySQL有关某些事情，所以它借用了C3P0（我们用于连接池）的Hibernate会话。
基本配置：
<property name="current_session_context_class">thread</property>
<property name="connection.provider_class">org.hibernate.connection.C3P0ConnectionProvider</property>
<property name="hibernate.connection.shutdown">true</property>
<property name="hibernate.use_sql_comments">false</property>
<!-- C3p0 Performance Improvements -->
<property name="hibernate.c3p0.acquire_increment">1</property>
<property name="hibernate.c3p0.idle_test_period">300</property>
<property name="hibernate.c3p0.maxConnectionAge">3600</property>
<property name="hibernate.c3p0.timeout">120</property>
<property name="hibernate.c3p0.max_size">300</property>
<property name="hibernate.c3p0.min_size">1</property>
<property name="hibernate.c3p0.max_statements">100</property>
<property name="hibernate.c3p0.preferredTestQuery">select 1;</property>
问题是Hibernate请求在8小时后导致MySQL / JDBC连接超时错误（我们配置的MySQL的wait_timeout参数值是默认值，即8小时）。我通过将wait_timeout设置为11分钟来复制这个，但是8小时wait_timeout的结果也相同：
2013-01-27 20:08:00,088 ERROR [Thread-0] (JDBCExceptionReporter.java:234) - Communications link failure
The last packet successfully received from the server was 665,943 milliseconds ago. The last packet sent successfully to the server was 6 milliseconds ago.
org.hibernate.exception.JDBCConnectionException: could not execute query
at org.hibernate.exception.SQLStateConverter.convert(SQLStateConverter.java:99)
at org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:66)
at org.hibernate.loader.Loader.doList(Loader.java:2536)
at org.hibernate.loader.Loader.listIgnoreQueryCache(Loader.java:2276)
at org.hibernate.loader.Loader.list(Loader.java:2271)
at org.hibernate.loader.criteria.CriteriaLoader.list(CriteriaLoader.java:119)
at org.hibernate.impl.SessionImpl.list(SessionImpl.java:1716)
at org.hibernate.impl.CriteriaImpl.list(CriteriaImpl.java:347)
.....
Caused by: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure
The last packet successfully received from the server was 665,943 milliseconds ago. The last packet sent successfully to the server was 6 milliseconds ago.
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
at java.lang.reflect.Constructor.newInstance(Unknown Source)
at com.mysql.jdbc.Util.handleNewInstance(Util.java:411)
at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:1116)
at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:3102)
at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:2991)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3532)
at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:2002)
at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2163)
at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2624)
at com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:2127)
at com.mysql.jdbc.PreparedStatement.executeQuery(PreparedStatement.java:2293)
at com.mchange.v2.c3p0.impl.NewProxyPreparedStatement.executeQuery(NewProxyPreparedStatement.java:76)
at org.hibernate.jdbc.AbstractBatcher.getResultSet(AbstractBatcher.java:208)
at org.hibernate.loader.Loader.getResultSet(Loader.java:1953)
at org.hibernate.loader.Loader.doQuery(Loader.java:802)
at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:274)
at org.hibernate.loader.Loader.doList(Loader.java:2533)
... 9 more
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:2552)
at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:3002)
... 22 more
2013-01-27 20:19:00,179 WARN [Thread-0] (NewPooledConnection.java:487) - [c3p0] Another error has occurred [ com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: The last packet successfully received from the server was 1,326,037 milliseconds ago. The last packet sent successfully to the server was 660,100 milliseconds ago. is longer than the server configured value of 'wait_timeout'. You should consider either expiring and/or testing connection validity before use in your application, increasing the server configured values for client timeouts, or using the Connector/J connection property 'autoReconnect=true' to avoid this problem. ] which will not be reported to listeners!
com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: The last packet successfully received from the server was 1,326,037 milliseconds ago. The last packet sent successfully to the server was 660,100 milliseconds ago. is longer than the server configured value of 'wait_timeout'. You should consider either expiring and/or testing connection validity before use in your application, increasing the server configured values for client timeouts, or using the Connector/J connection property 'autoReconnect=true' to avoid this problem.
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
at java.lang.reflect.Constructor.newInstance(Unknown Source)
at com.mysql.jdbc.Util.handleNewInstance(Util.java:411)
at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:1116)
at com.mysql.jdbc.MysqlIO.send(MysqlIO.java:3364)
at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:1983)
at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2163)
at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2624)
at com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:2127)
at com.mysql.jdbc.PreparedStatement.executeQuery(PreparedStatement.java:2293)
at com.mchange.v2.c3p0.impl.NewProxyPreparedStatement.executeQuery(NewProxyPreparedStatement.java:76)
at org.hibernate.jdbc.AbstractBatcher.getResultSet(AbstractBatcher.java:208)
at org.hibernate.loader.Loader.getResultSet(Loader.java:1953)
at org.hibernate.loader.Loader.doQuery(Loader.java:802)
at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:274)
at org.hibernate.loader.Loader.doList(Loader.java:2533)
at org.hibernate.loader.Loader.listIgnoreQueryCache(Loader.java:2276)
at org.hibernate.loader.Loader.list(Loader.java:2271)
at org.hibernate.loader.criteria.CriteriaLoader.list(CriteriaLoader.java:119)
at org.hibernate.impl.SessionImpl.list(SessionImpl.java:1716)
at org.hibernate.impl.CriteriaImpl.list(CriteriaImpl.java:347)
....
Caused by: java.net.SocketException: Broken pipe
at java.net.SocketOutputStream.socketWrite0(Native Method)
at java.net.SocketOutputStream.socketWrite(Unknown Source)
at java.net.SocketOutputStream.write(Unknown Source)
at java.io.BufferedOutputStream.flushBuffer(Unknown Source)
at java.io.BufferedOutputStream.flush(Unknown Source)
at com.mysql.jdbc.MysqlIO.send(MysqlIO.java:3345)
... 20 more
我认为C3P0并没有足够频繁地驱逐过时的连接，因此在重载期间，连接将返回到池中，过时并在驱逐之前再次借用。所以我创建了一个c3p0.properties文件并将“c3p0.testConnectionsOnCheckout”设置为true，这样就不会从池中借用过时的连接。我又遇到了同样的错误。
我认为由于我的hibernate会话配置了会话上下文“线程”，因此在提交或回滚事务[http://docs.jboss.org/hibernate/orm/3.6/javadocs/org/hibernate/context/ThreadLocalSessionContext.html]之前，线程使用的会话不会被释放。所以我唯一的解释就是执行程序线程在没有提交的情况下进行只读DB调用，一旦任务完成，线程就会返回池，并与之保持会话。
我该怎么办？我们的应用程序在Data-Access-Object类中有一个hibernate查询代码，每个bean都有一个。我希望避免必须更改那些进行只读数据库调用的类中的每个方法，以便让它们不必要地“提交”。我还希望尽量减少对应用程序业务逻辑的更改。
有没有办法可以在每次声明/使用Data-Access-Object时检查sessionFactory.getCurrentSession（）返回的会话的新鲜度（所有Data-Access-Object类都从一个继承了一些东西）基类，所以我可以改变基类构造函数中的东西），并可能将过时的会话返回到池中？或者有更好的方法吗？
感谢。
答案 0 :(得分：0)
注意：以下内容基于Oracle示例，但可以针对MySQL进行修改。
我通过使用Tomcat管理的数据库连接解决了连接断开的问题。这可以通过在META-INF目录中创建context.xml文件来完成，如下所示：
<Context crossContext="true" docBase="myBase" path="/myBase" reloadable="false" useHttpOnly="true">
<ResourceLink global="jdbc/dbOne" name="jdbc/dbOne" type="javax.sql.DataSource" />
<!-- Need another DB? -->
<!-- <ResourceLink global="jdbc/dbTwo" name="jdbc/dbTwo" type="javax.sql.DataSource" /> -->
</Context>
要创建连接，还必须更新Tomcat server.xml文件。以下内容基于Tomcat 6.0.26。：
<!-- Global JNDI resources
Documentation at /docs/jndi-resources-howto.html
-->
<GlobalNamingResources>
<!-- Editable user database that can also be used by
UserDatabaseRealm to authenticate users
-->
<Resource name="UserDatabase" auth="Container"
type="org.apache.catalina.UserDatabase"
description="User database that can be updated and saved"
factory="org.apache.catalina.users.MemoryUserDatabaseFactory"
pathname="conf/tomcat-users.xml" />
<!-- START MY MODS -->
<!-- Add the db connection(s)! The rest is standard in the server.xml file.-->
<Resource auth="Container" driverClassName="oracle.jdbc.driver.OracleDriver" initialSize="2" logAbandoned="true" maxActive="5" maxIdle="2" maxWait="120000" minEvictableIdleTimeMillis="1800000" minIdle="1" name="jdbc/dbOne" numTestsPerEvictionRun="3" password="openPlease" removeAbandoned="true" removeAbandonedTimeout="60" testOnBorrow="true" testOnReturn="true" testWhileIdle="true" timeBetweenEvictionRunsMillis="900000" type="javax.sql.DataSource" url="jdbc:oracle:thin:@servername:portnumber:schema" username="myUser" validationQuery="select sysdate from dual"/>
<!-- Need another connection? Copy and past the above making the required changes. -->
<!-- END MY MODS -->
然后在我的hibernate.cfg.xml文件中指定了：
<!-- Connection handling -->
<property name="connection.datasource">java:/comp/env/jdbc/dbOne</property>
<property name="dialect">org.hibernate.dialect.Oracle10gDialect</property>
<property name="connection.autoReconnect">true</property>
<property name="connection.autoReconnectForPools">true</property>
<property name="connection.is-connection-validation-required">true</property>
<property name="current_session_context_class">thread</property>
话虽如此，以下使用C3P0的配置也适用于我，但我现在更喜欢Tomcat托管连接，因为它们可以在我的Tomcat服务器上的应用程序之间共享，这在我的情况下是可取的。
<?xml version="1.0" encoding="UTF-8"?>
<!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="hibernate.connection.driver_class">oracle.jdbc.driver.OracleDriver</property>
<property name="hibernate.connection.password">@dbPassword@</property>
<property name="hibernate.connection.url">@dbURL@</property>
<property name="hibernate.connection.username">someUser</property>
<property name="dialect">org.hibernate.dialect.Oracle10gDialect</property>
<property name="show_sql">false</property>
<property name="format_sql">false</property>
<property name="current_session_context_class">thread</property>
<!-- Connection handling -->
<property name="connection.autoReconnect">true</property>
<property name="connection.autoReconnectForPools">true</property>
<property name="connection.is-connection-validation-required">true</property>
<property name="current_session_context_class">thread</property>
<property name="max_fetch_depth">1</property>
<property name="hibernate.connection.provider_class">org.hibernate.connection.C3P0ConnectionProvider</property>
<property name="hibernate.c3p0.breakAfterAcquireFailure">false</property>
<property name="hibernate.c3p0.acquireRetryAttempts">-1</property>
<property name="hibernate.c3p0.acquireRetryDelay">3000</property>
<property name="hibernate.c3p0.automaticTestTable">C3P0_TEST</property> <!-- c3p0 uses this table for testing connection. -->
<property name="hibernate.c3p0.initialPoolSize">2</property> <!-- 3 is c3p0 default. -->
<property name="hibernate.c3p0.minPoolSize">2</property> <!-- 1 is Hibernate default. -->
<property name="hibernate.c3p0.maxPoolSize">6</property> <!-- 100 is Hibernate default. -->
<property name="hibernate.c3p0.acquireIncrement">2</property> <!-- 3 is c3p0 default. -->
<property name="hibernate.c3p0.maxIdleTimeExcessConnections">600</property> <!-- 0 seconds is c3p0 default and means do not check. This is the num of seconds a connections in excess of minPoolSize are permitted to remain idle in the pool before being culled. -->
<property name="hibernate.c3p0.idleConnectionTestPeriod">30</property> <!-- 0 seconds is the c3p0 default and means do not check. (i.e. never test). Using only this provides the best performance even if individuals may occasionally receive an error message due to a connection being dropped. -->
<!-- Cache setup -->
<property name="hibernate.cache.use_second_level_cache">true</property>
<property name="hibernate.cache.use_query_cache">true</property>
<property name="hibernate.cache.region.factory_class">net.sf.ehcache.hibernate.EhCacheRegionFactory</property>
<!-- <property name="hibernate.cache.provider_class">net.sf.ehcache.hibernate.SingletonEhCacheProvider</property> -->
<property name="cache.use_minimal_puts">true</property>
<property name="hibernate.generate_statistics">true</property>
<property name="hibernate.cache.use_structured_entries">true</property>
<!-- Mapping files -->
...
</session-factory>
</hibernate-configuration>