ClassCastException无法将数据源强制转换为javax.sql.ConnectionPoolDataSource [英] ClassCastException DataSource cannot be cast to javax.sql.ConnectionPoolDataSource

问题描述

我收到此异常：

java.lang.ClassCastException: org.apache.tomcat.jdbc.pool.DataSource cannot be cast to javax.sql.ConnectionPoolDataSource

当我尝试运行我的webapp时（在Tomcat6中）使用与Tomcat7无缝协作的tomcat jdbc池

When I try to run my webapp (in Tomcat6) that use tomcat jdbc pool that seamlessly work with Tomcat7

我已将这些jar包含在tomcat 6 lib文件夹中：

I have included these jars already in tomcat 6 lib folder:

tomcat-jdbc.jar
tomcat-juli.jar

可能是什么问题？

更新：

protected static Connection getConnection() throws NamingException, SQLException {
    InitialContext cxt = new InitialContext();
    String jndiName = "java:/comp/env/jdbc/MyDBHrd";
    ConnectionPoolDataSource dataSource = (ConnectionPoolDataSource) cxt.lookup(jndiName); // ClassCastException here....
    PooledConnection pooledConnection = dataSource.getPooledConnection();
    Connection conn = pooledConnection.getConnection();
    return conn; // Obtain connection from pool
} 

配置：

<Resource name="jdbc/MyDBHrd"
          auth="Container"
          type="javax.sql.DataSource"
          factory="org.apache.tomcat.jdbc.pool.DataSourceFactory"
          testWhileIdle="true"
          testOnBorrow="true"
          testOnReturn="false"
          validationQuery="SELECT 1"
          validationInterval="30000"
          timeBetweenEvictionRunsMillis="30000"
          maxActive="5000"
          minIdle="10"
          maxWait="10000"
          initialSize="20"
          removeAbandonedTimeout="120"
          removeAbandoned="true"
          logAbandoned="false"
          minEvictableIdleTimeMillis="30000"
          jmxEnabled="true"
          jdbcInterceptors="org.apache.tomcat.jdbc.pool.interceptor.ConnectionState;
            org.apache.tomcat.jdbc.pool.interceptor.StatementFinalizer"
          username="sa"
          password="password"
          driverClassName="net.sourceforge.jtds.jdbc.Driver"
          url="jdbc:jtds:sqlserver://192.168.114.130/MyDB"/>

当我更改类型时：

 type="javax.sql.ConnectionPoolDataSource"

I得到此警告：

WARNING: javax.sql.ConnectionPoolDataSource is not a valid class name/type for this JNDI factory.

导致 getConnection（）返回NULL 。

进口：

import java.io.IOException;
import java.sql.CallableStatement;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Timestamp;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Map;

import javax.naming.InitialContext;
import javax.naming.NamingException;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.sql.ConnectionPoolDataSource;
import javax.sql.PooledConnection;

import org.apache.commons.dbutils.DbUtils;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

推荐答案

作为最终用户，你永远不应该直接使用 ConnectionPoolDataSource 。它旨在作为物理连接的工厂（ PooledConnection ）。那个 PooledConnection 保存在连接池中。当您执行 DataSource.getConnection 时，数据源将从池中检出 PooledConnection ，并返回逻辑连接使用 PooledConnection.getConnection（）作为最终用户获得，并在逻辑连接已关闭。

As an end-user you should never ever have to use a ConnectionPoolDataSource directly. It is intended as a factory for physical connections (the PooledConnection). That PooledConnection is kept in the connectionpool. When you do a DataSource.getConnection, the datasource will check out a PooledConnection from the pool, and return the logical connection obtained using PooledConnection.getConnection() to you as the end-user, and returning the physical connection to the pool when that logical Connection is closed.

所以构造是

User -- uses --> DataSource (with connectionpooling) -- uses --> ConnectionPoolDataSource

或

ConnectionPoolDataSource --> creates PooledConnection --> DataSource --> returns Connection --> User

使用 DataSource 是独立的事实上，如果 DataSource 提供或不提供连接池（它应该对你透明）。

The use of a DataSource is independent of the fact if that DataSource provides connectionpooling or not (it should be transparent to you).

参见a以前对我的回答是另一个问题： https://stackoverflow.com/a/12651163/466862

See also a previous answer of mine to another question: https://stackoverflow.com/a/12651163/466862

换句话说，您的代码应更改为：

In other words your code should be changed to:

protected static Connection getConnection() throws NamingException, SQLException {
    InitialContext cxt = new InitialContext();
    String jndiName = "java:/comp/env/jdbc/MyDBHrd";
    DataSource dataSource = (DataSource) cxt.lookup(jndiName);
    Connection conn = dataSource.getConnection();
    return conn;
} 

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