连接池Hibernate

Question

以下代码：

hibernate.cfg.xml：

<property name="hibernate.connection.provider_class">
org.hibernate.connection.C3P0ConnectionProvider
</property>
<property name="hibernate.c3p0.min_size">7</property>
<property name="hibernate.c3p0.max_size">53</property>
<property name="hibernate.c3p0.timeout">100</property>
<property name="hibernate.c3p0.max_statements">50</property>
<property name="hibernate.c3p0.idle_test_period">1000</property>
<property name="hibernate.c3p0.validate">true</property>

hibernateutil.java：

public final class HibernateUtil{  
     private static SessionFactory sessionFactory;  
        public static SessionFactory getSessionFactory()  throws MappingException  
        {  
            if(sessionFactory == null) {
                //sessionFactory = new AnnotationConfiguration().configure().buildSessionFactory();
                sessionFactory = new Configuration().configure().buildSessionFactory();
            }  
            return sessionFactory;  
        } 

        public static Session openSession()  
        {  
            return getSessionFactory().openSession();  
        }  

}

import java.math.BigInteger;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;
import org.hibernate.Criteria;
import org.hibernate.HibernateException;
import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.Transaction;
import org.hibernate.criterion.Restrictions;
import org.hibernate.transform.Transformers;
import org.hibernate.type.StandardBasicTypes;
import ConnectionHibernate.ConnectionHibernate;
import ConnectionHibernate.HibernateUtil;
import br.com.cuponero.bean.Cidades;

public class CidadesDao {
    private static final String TABLE = "Cidades";
    Session session;

    public CidadesDao() {
        this.session = HibernateUtil.getSessionFactory().openSession();
        this.session.beginTransaction();
    }

    /**
     * Select todos
     * @return 
     **/
    public List<Cidades> getTodos(){
          List<Cidades> lCit = null;

          try{
             Query q = session.createSQLQuery("SELECT * FROM "+TABLE)
                     .addScalar("id", StandardBasicTypes.BIG_INTEGER)
                     .addScalar("nome", StandardBasicTypes.STRING)
                     .addScalar("ddd", StandardBasicTypes.STRING)
                     .addScalar("estaoId", StandardBasicTypes.INTEGER)
                     .addScalar("ativo", StandardBasicTypes.INTEGER)

                     .setResultTransformer(Transformers.aliasToBean(Cidades.class));
             //System.out.println("list 0: "+q.list().get(0));

             lCit = q.list();
             //tx.commit();

          }catch (HibernateException e) {
             if (session!=null) session.beginTransaction().rollback();
             e.printStackTrace(); 
          }finally{
              //closeMyConnection();
              //mySessionClose();

              session.beginTransaction().commit();
          }

          return lCit;
    }

为了获得最好的帮助，当我尝试连接this Web服务时，请在Android Studio中查看my应用程序的日志：

org.hibernate.exception.internal.standardsqlexceptionconverter.convert（standardsqlexceptionconverter.java:47)org.hibernate.engine.jdbc.spi.sqlexceptionhelper.convert（sqlexceptionhelper.java:109)org.hibernate.engine.jdbc.spi.sqlexceptionhelper.convert（sqlexceptionhelper.java:95)ne.transaction.internal.transactionimpl.begin（transactionimpl.java：52）org.hibernate.internal.sessionimpl.begintransaction（sessionimpl.java：1454）br.com.cuponero.dao.cidadesdao. （cidadesdao.java：31）br.com.cuponero.actionsdaservlet.cidadesactionservlet.getjsonregiao（cidadesactionservlet.java：35）br.com.cuponero.servlet.cidadesservlet.doPost（

根本原因java.sql.sqlexception：无法从基础数据库获取连接！com.mchange.v2.sql.sqlutils.ToSqlexception(Sqlutils.java:118)com.mchange.v2.c3p0.impl.c3p0PooledConnectionPool.CheckoutPooledConnection(C3p0PooledConnectionPool.java:689)com.mchange.v2.c3p0.impl.abstractPoolbackedDatasource.GetConnection（AbstractPoolbackedDatasource.java:140)org.hibernate.c3p0.internal.c3p0ConnectionProvider..java:237)org.hibernate.resource.transaction.backend.jdbc.internal.jdbcresourceLocalTransactionCoordinatorImpl$TransactionDriverControllimpl.Begin(jdbcresourceLocalTransactionCoordinatorImpl.java:213)org.hibernate.engine。

看到这条日志行，她说问题出在这里：br.com.cuponero.dao.cidadesdao。<>；初始化>；(CidadesDAO.java:31)有这一行的是以下代码：

This.Session.BeginTransaction（）；

Answer 1

这是直接来自堆栈跟踪：

用户cupone_plinhares已有多个“MAX_USER_CONNECTIONS”活动连接

一个显而易见的尝试是为用户cupone_plinhares增加max_user_connection。

一个更好的想法是根本不使用session作为成员变量，而是使用类似于

Session session = null;
Transaction txn = null;
try {
  session = HibernateUtil.getSessionFactory().openSession();
  txn = session.beginTransaction();

  //do important stuff here

  txn.commit()
} catch ( Exception e ) {
  try { if (txn != null) txn.rollback() }
  catch (HibernateException he) { 
    he.printStackTrace(); 
    e.addSuppressed( he );
    throw e;
  }
} finally {
  try { if (session != null) session.close() }
  catch (SQLException sqle) { sqle.printStackTrace(); }
}

您可以以不同于打印到标准错误的方式记录事件，或者在txn.rollback()失败时，对传播哪个异常做出不同的决定。但是您需要开始/提交/回滚一个一致的事务,并且您应该根据需要创建会话并迅速销毁它们,而不是在生命周期不确定的成员变量中保持它们的打开状态。

连接池的意义在于使会话创建变得廉价，因此您不必处理管理持久会话的复杂性。