我想在我的tomcat webapplication中使用JPA。因此，我创建了自己的Filter（在web.xml中提到）。
过滤器有三种方法：
init方法创建EntityManagerFactory并将其存储在实例字段中（在部署应用程序时执行）doFilter方法使用存储的EntityManagerFactory创建一个entityManager，在要处理的请求之后启动一个事务并关闭事务（和entityManager）destroy方法关闭存储的EntityManagerFactory 此机制运行良好且速度非常快 - 但一旦数据库连接丢失，应用程序无法恢复。
如何刷新EntityManagerFactory，以便创建新的数据库连接？或者我应该销毁并重新创建EntityManagerFactory？我是否必须运行数据库查询，以检查连接是否处于活动状态？
我当前的过滤器实现如下：
package entityManagerTest;
import java.io.IOException;
import javax.persistence.*;
import javax.servlet.*;
import javax.servlet.annotation.WebFilter;
@WebFilter(urlPatterns = { "/JpaServlet" })
public class JpaFilter implements Filter {
private EntityManagerFactory entityManagerFactory;
@Override
public void init(FilterConfig config) throws ServletException {
entityManagerFactory = Persistence.createEntityManagerFactory("test");
}
@Override
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
EntityManager entityManager = entityManagerFactory .createEntityManager();
try {
EntityTransaction transaction = entityManager.getTransaction();
transaction.begin();
try {
request.setAttribute("entityManager", entityManager);
chain.doFilter(request, response);
} finally {
transaction.commit();
}
} finally {
entityManager.close();
}
}
@Override
public void destroy() {
entityManagerFactory.close();
}
}
servlet看起来像这样：
package entityManagerTest;
import java.io.*;
import javax.persistence.*;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.*;
@WebServlet(urlPatterns={"/JpaServlet"})
public class JpaServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
EntityManager entityManager = (EntityManager) req.getAttribute("entityManager");
Query query = entityManager.createNativeQuery("SELECT 42");
Object singleResult = query.getSingleResult();
PrintWriter writer = resp.getWriter();
writer.write("DB:"+singleResult);
writer.close();
}
}
我的persistence.xml：
<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.0" xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd">
<persistence-unit name="test">
<provider>org.hibernate.jpa.HibernatePersistenceProvider</provider>
<properties>
<property name="javax.persistence.jdbc.driver" value="com.microsoft.sqlserver.jdbc.SQLServerDriver" />
<property name="javax.persistence.jdbc.url" value="jdbc:sqlserver:..." />
<property name="javax.persistence.jdbc.user" value="x" />
<property name="javax.persistence.jdbc.password" value="y" />
</properties>
</persistence-unit>
</persistence>
我尝试添加 validationQuery ，但没有看到任何行为更改：
<property name="hibernate.connection.validationQuery" value="select 1"/>
<property name="connection.validationQuery" value="select 1"/>
当连接丢失时，我收到了一个回滚异常（并不令人惊讶）：
Aug 18, 2015 11:41:30 AM org.hibernate.engine.jdbc.spi.SqlExceptionHelper logExceptions
WARN: SQL Error: 0, SQLState: 08S01
Aug 18, 2015 11:41:30 AM org.hibernate.engine.jdbc.spi.SqlExceptionHelper logExceptions
ERROR: Software caused connection abort: recv failed
Aug 18, 2015 11:41:30 AM org.apache.catalina.core.StandardWrapperValve invoke
SCHWERWIEGEND: Servlet.service() for servlet [entityManagerTest.JpaServlet] in context with path [/EntityManagerTests] threw exception
org.hibernate.TransactionException: rollback failed
at org.hibernate.engine.transaction.spi.AbstractTransactionImpl.rollback(AbstractTransactionImpl.java:217)
at org.hibernate.jpa.internal.TransactionImpl.commit(TransactionImpl.java:73)
at entityManagerTest.JpaFilter.doFilter(JpaFilter.java:29)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:219)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:142)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:610)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:518)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1091)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:668)
at org.apache.coyote.http11.Http11NioProtocol$Http11ConnectionHandler.process(Http11NioProtocol.java:223)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1517)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1474)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:745)
Caused by: org.hibernate.TransactionException: unable to rollback against JDBC connection
at org.hibernate.engine.transaction.internal.jdbc.JdbcTransaction.doRollback(JdbcTransaction.java:167)
at org.hibernate.engine.transaction.spi.AbstractTransactionImpl.rollback(AbstractTransactionImpl.java:211)
... 21 more
Caused by: com.microsoft.sqlserver.jdbc.SQLServerException: Die Verbindung wurde geschlossen.
at com.microsoft.sqlserver.jdbc.SQLServerException.makeFromDriverError(SQLServerException.java:190)
at com.microsoft.sqlserver.jdbc.SQLServerConnection.checkClosed(SQLServerConnection.java:389)
at com.microsoft.sqlserver.jdbc.SQLServerConnection.rollback(SQLServerConnection.java:1955)
at org.hibernate.engine.transaction.internal.jdbc.JdbcTransaction.doRollback(JdbcTransaction.java:163)
... 22 more
但是在网络连接再次返回后，代码仍然失败并出现异常（即使连接现在可以恢复）：
Aug 18, 2015 11:42:54 AM org.apache.catalina.core.StandardWrapperValve invoke
SCHWERWIEGEND: Servlet.service() for servlet [entityManagerTest.JpaServlet] in context with path [/EntityManagerTests] threw exception
javax.persistence.PersistenceException: org.hibernate.TransactionException: JDBC begin transaction failed:
at org.hibernate.jpa.spi.AbstractEntityManagerImpl.convert(AbstractEntityManagerImpl.java:1763)
at org.hibernate.jpa.spi.AbstractEntityManagerImpl.convert(AbstractEntityManagerImpl.java:1677)
at org.hibernate.jpa.spi.AbstractEntityManagerImpl.throwPersistenceException(AbstractEntityManagerImpl.java:1771)
at org.hibernate.jpa.internal.TransactionImpl.begin(TransactionImpl.java:64)
at entityManagerTest.JpaFilter.doFilter(JpaFilter.java:24)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:219)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:142)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:610)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:518)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1091)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:668)
at org.apache.coyote.http11.Http11NioProtocol$Http11ConnectionHandler.process(Http11NioProtocol.java:223)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1517)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1474)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:745)
Caused by: org.hibernate.TransactionException: JDBC begin transaction failed:
at org.hibernate.engine.transaction.internal.jdbc.JdbcTransaction.doBegin(JdbcTransaction.java:76)
at org.hibernate.engine.transaction.spi.AbstractTransactionImpl.begin(AbstractTransactionImpl.java:162)
at org.hibernate.internal.SessionImpl.beginTransaction(SessionImpl.java:1471)
at org.hibernate.jpa.internal.TransactionImpl.begin(TransactionImpl.java:61)
... 20 more
Caused by: com.microsoft.sqlserver.jdbc.SQLServerException: Die Verbindung wurde geschlossen.
at com.microsoft.sqlserver.jdbc.SQLServerException.makeFromDriverError(SQLServerException.java:190)
at com.microsoft.sqlserver.jdbc.SQLServerConnection.checkClosed(SQLServerConnection.java:389)
at com.microsoft.sqlserver.jdbc.SQLServerConnection.getAutoCommit(SQLServerConnection.java:1910)
at org.hibernate.engine.transaction.internal.jdbc.JdbcTransaction.doBegin(JdbcTransaction.java:68)
... 23 more
答案 0 :(得分：4)
摘自the official hibernate documentation：
然而，Hibernate自己的连接池算法是相当的 简陋。它旨在帮助您入门，并且不是 打算用于生产系统，甚至用于性能 测试。 [...]例如，您可能想使用c3p0。
您必须指定连接池数据源。连接池通常在使用之前检查连接的有效性。以下是用于连接池的C3P0（连接池数据源）和Hibernate配置的示例。我希望它对你有用。
<?xml version="1.0" encoding="UTF-8"?>
<persistence xmlns="http://java.sun.com/xml/ns/persistence"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd"
version="2.0">
<persistence-unit name="test" transaction-type="RESOURCE_LOCAL">
<provider>org.hibernate.jpa.HibernatePersistenceProvider</provider>
<properties>
<property name="hibernate.dialect" value="org.hibernate.dialect.SQLServerDialect" />
<property name="hibernate.show_sql" value="true" />
<property name="hibernate.format_sql" value="true" />
<property name="hibernate.hbm2ddl.auto" value="update"/>
<!-- I am not exactly sure that which one is correct -->
<!-- javax.persistence.* or hibernate.connection.* properties -->
<property name="hibernate.connection.driver_class" value="com.microsoft.sqlserver.jdbc.SQLServerDriver"/>
<property name="hibernate.connection.url" value="jdbc:sqlserver:..."/>
<property name="hibernate.connection.username" value="x"/>
<property name="hibernate.connection.password" value="y"/>
<!-- Connection Pooling settings -->
<property name="hibernate.connection.provider_class" value="org.hibernate.service.jdbc.connections.internal.C3P0ConnectionProvider" />
<property name="hibernate.c3p0.max_size" value="100" />
<property name="hibernate.c3p0.min_size" value="0" />
<property name="hibernate.c3p0.acquire_increment" value="1" />
<property name="hibernate.c3p0.idle_test_period" value="300" />
<property name="hibernate.c3p0.max_statements" value="0" />
<property name="hibernate.c3p0.timeout" value="100" />
<property name="hibernate.c3p0.preferredTestQuery">SELECT 1;</property>
</properties>
</persistence-unit>
</persistence>
此外，您还需要将hibernate-c3p0添加到类路径中。
<dependency>
<groupId>org.hibernate</groupId>
<artifactId>hibernate-c3p0</artifactId>
<version>${hibernate.version}</version>
</dependency>