使用C3P0连接池时TimeoutException的解决方法

梦里梦外; 2024-04-17 14:09 40阅读 0赞

## 使用C3P0连接池时报TimeoutException错的解决方法 ##

最近在跟着黑马程序员的Java就业班教程学习数据库连接池的配置和使用时，遇到了一个棘手的问题，就是在使用C3P0连接池连接本机的lzm数据库时无法获取连接，测试代码如下：

C3P0Demo1.java

package cn.itcast.datasource.c3p0;
    
    import com.mchange.v2.c3p0.ComboPooledDataSource;
    
    import javax.sql.DataSource;
    import java.sql.Connection;
    import java.sql.SQLException;
    
    public class C3P0Demo1 {
        public static void main(String[] args) throws SQLException {
            //1.创建数据库连接池对象
            DataSource dataSource =new ComboPooledDataSource();
            //2.获取连接对象
            Connection connection=dataSource.getConnection();
            //3.打印
            System.out.println(connection);
        }
    }

c3p0-config.xml配置信息如下：

<?xml version="1.0" encoding="utf-8"?>
    <c3p0-config>
      <default-config>
        <property name="driverClass">com.mysql.cj.jdbc.Driver</property>
        <property name="jdbcUrl">jdbc:mysql://localhost:3306/lzm</property>
        <property name="user">root</property>
        <property name="password">root</property>
        
        
        <property name="initialPoolSize">5</property>
        
        <property name="maxPoolSize">10</property>
        
        <property name="checkoutTimeout">3000</property>
      </default-config>
      <named-config name="otherc3p0">
        <property name="driverClass">com.mysql.cj.jdbc.Driver</property>
        <property name="jdbcUrl">jdbc:mysql://localhost:3306/lzm</property>
        <property name="user">root</property>
        <property name="password">root</property>
        
        
        <property name="initialPoolSize">5</property>
        
        <property name="maxPoolSize">10</property>
        
        <property name="checkoutTimeout">3000</property>
      </named-config>
    </c3p0-config>

IDEA报了以下错误：

Exception in thread "main" java.sql.SQLException: An attempt by a client to checkout a Connection has timed out.
    	at com.mchange.v2.sql.SqlUtils.toSQLException(SqlUtils.java:118)
    	at com.mchange.v2.sql.SqlUtils.toSQLException(SqlUtils.java:77)
    	at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool.checkoutPooledConnection(C3P0PooledConnectionPool.java:690)
    	at com.mchange.v2.c3p0.impl.AbstractPoolBackedDataSource.getConnection(AbstractPoolBackedDataSource.java:140)
    	at cn.itcast.datasource.c3p0.C3P0Demo1.main(C3P0Demo1.java:14)
    Caused by: com.mchange.v2.resourcepool.TimeoutException: A client timed out while waiting to acquire a resource from com.mchange.v2.resourcepool.BasicResourcePool@19bb089b -- timeout at awaitAvailable()
    	at com.mchange.v2.resourcepool.BasicResourcePool.awaitAvailable(BasicResourcePool.java:1467)
    	at com.mchange.v2.resourcepool.BasicResourcePool.prelimCheckoutResource(BasicResourcePool.java:644)
    	at com.mchange.v2.resourcepool.BasicResourcePool.checkoutResource(BasicResourcePool.java:554)
    	at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool.checkoutAndMarkConnectionInUse(C3P0PooledConnectionPool.java:758)
    	at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool.checkoutPooledConnection(C3P0PooledConnectionPool.java:685)
    	... 2 more

在各种网站上都搜索不到解决的方法，在即将陷入绝望时，突发灵感，检查开发环境  
我的开发环境是 Java8+MySQL5.7，使用的Jar包是mysql-connector-java-8.0.17.jar，c3p0-0.9.5.2.jar，mchange-commons-java-0.2.12.jar  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MzM5NTkxMQ_size_16_color_FFFFFF_t_70]  
而视频教程中使用的数据库驱动包是mysql-connector-java-5.1.48.jar，于是我将libs目录下的mysql-connector-java-8.0.17.jar删除，导入mysql-connector-java-5.1.48.jar

把c3p0-config.xml配置信息中的`<property name="driverClass">com.mysql.cj.jdbc.Driver</property>`代码都修改成`<property name="driverClass">com.mysql.jdbc.Driver</property>`

再次运行C3P0Demo1.java后，问题解决，控制台打印的消息如下：  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MzM5NTkxMQ_size_16_color_FFFFFF_t_70 1]问题解决！原来这个问题的根本原因是mysql-connector-java-8.0.17.jar与c3p0-0.9.5.2.jar，mchange-commons-java-0.2.12.jar这两个包不匹配或不兼容所导致的，像mysql-connector-java-8.0.17.jar是最新版的Jar包，c3p0-0.9.5.2.jar，mchange-commons-java-0.2.12.jar是较老的Jar包，显然会出现不能适配的情况了，所以开发不做最新版，这句话还是很有道理的啦！

#### 总结 ####

解决的这个问题给了我一个很大的警示，就是在做Java开发的过程中选择正确的开发环境很重要，一定要选择好版本相匹配的开发环境和Jar包，配置合适的文件信息，才能让程序正常地运行，才不会产生让人焦头烂额的各种异常信息。今后，要引以为戒！

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[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MzM5NTkxMQ_size_16_color_FFFFFF_t_70 1]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/17/d61450334f6d415db9d3e0c55192cd81.png