C3P0配置以及详细用法

一：C3P0Utils：负责从连接池获取一个连接、放回一个连接。

在src目录下新建一个名叫 c3p0-config.xml 的文件，注意，必须是这个文件名。

<c3p0-config>
   
    <default-config>  
        <property name="initialPoolSize">10property>  
        <property name="maxIdleTime">30property>  
        <property name="maxPoolSize">100property>  
        <property name="minPoolSize">10property>  
        <property name="maxStatements">200property>  
    default-config>  

   
    <named-config name="mysql">  
        <property name="driverClass">com.mysql.jdbc.Driverproperty>  
        <property name="jdbcUrl">jdbc:mysql://localhost:3306/CoupleSpaceproperty>  
        <property name="user">rootproperty>  
        <property name="password">rootproperty>  
        <property name="initialPoolSize">10property>  
        <property name="maxIdleTime">30property>  
        <property name="maxPoolSize">100property>  
        <property name="minPoolSize">10property>  
        <property name="maxStatements">200property>  
    named-config>  

    
    ......
    
    ......
    
    ......
c3p0-config>

还可以配置其他属性

    <property name="acquireIncrement">3property>

    
    <property name="acquireRetryAttempts">30property>

    
    <property name="acquireRetryDelay">1000property>

    
    <property name="autoCommitOnClose">falseproperty>

    
    <property name="automaticTestTable">Testproperty>

    
    <property name="breakAfterAcquireFailure">falseproperty>

     
    <property name="checkoutTimeout">100property>

    
    <property name="connectionTesterClassName">property>

    
    <property name="factoryClassLocation">nullproperty>

     
    <property name="forceIgnoreUnresolvedTransactions">falseproperty>

     
    <property name="idleConnectionTestPeriod">60property>

     
    <property name="initialPoolSize">3property>

    
    <property name="maxIdleTime">60property>

    
    <property name="maxPoolSize">15property>

    
    <property name="maxStatements">100property>

    
    <property name="maxStatementsPerConnection">property>

     
    <property name="numHelperThreads">3property>

     
    <property name="overrideDefaultUser">rootproperty>

    
    <property name="overrideDefaultPassword">passwordproperty>

     
    <property name="password">property>

    
    <property name="preferredTestQuery">select id from test where id=1property>

     
    <property name="propertyCycle">300property>

    
    <property name="testConnectionOnCheckout">falseproperty>

    
    <property name="testConnectionOnCheckin">trueproperty>

    
    <property name="user">rootproperty>

    
    <property name="usesTraditionalReflectiveProxies">falseproperty>

创建工具类，定义获取connection、释放connection的方法

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

import com.mchange.v2.c3p0.ComboPooledDataSource;

public class C3p0Utils {

    //通过标识名来创建相应连接池
    static ComboPooledDataSource dataSource=new ComboPooledDataSource();
    //从连接池中取用一个连接
    public static Connection getConnection(){
        try {
            return dataSource.getConnection();

        } catch (Exception e) {
           throw new CustomException(ExceptionList.FAILURE);         
        }
    }    
    //释放连接回连接池
     public static void close(Connection conn,PreparedStatement pst,ResultSet rs){  
            if(rs!=null){  
                try {  
                    rs.close();  
                } catch (SQLException e) {  
                    throw new CustomException(ExceptionList.FAILURE);         
                }  
            }  
            if(pst!=null){  
                try {  
                    pst.close();  
                } catch (SQLException e) {  
                    throw new CustomException(ExceptionList.FAILURE);         
                }  
            }  

            if(conn!=null){  
                try {  
                    conn.close();  
                } catch (SQLException e) {  
                    throw new CustomException(ExceptionList.FAILURE);         

                }  
            }  
        }  
}

二：创建DBUtils_BO类来封装一次数据库操作

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;

public class DBUtil_BO {   
    public Connection conn = null;
    public PreparedStatement st = null;
    public ResultSet rs = null;
    public DBUtil_BO() {
        super();
    }    
}

三：创建DBUtils数据库操作类进行具体的数据库操作

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;


public class DBUtils {

    private static void realseSource(Connection _conn, PreparedStatement _st, ResultSet _rs) {
        C3p0Utils.close(_conn, _st, _rs);
    }

    public static void realseSource(DBUtil_BO _vo) {
        if (_vo != null) {
            realseSource(_vo.conn, _vo.st, _vo.rs);
        }
    }

    // 注意：查询操作完成后，因为还需提取结果集中信息，所以仍保持连接，在结果集使用完后才通过DBUtils.realseSource()手动释放连接
    public static ResultSet executeQuery(DBUtil_BO vo) {
        try {
            vo.rs = vo.st.executeQuery();
        } catch (SQLException e) {
            realseSource(vo);
            throw new CustomException(ExceptionList.FAILURE);
        }
        return vo.rs;
    }

    // 而update操作完成后就可以直接释放连接了，所以在方法末尾直接调用了realseSourse()
    public static void executeUpdate(DBUtil_BO vo) {

        Connection conn = vo.conn;
        PreparedStatement st = vo.st;
        try {
            st.executeUpdate();
        } catch (SQLException e) {
            realseSource(conn, st, null);
             throw new CustomException(ExceptionList.FAILURE); 
        }
        realseSource(conn, st, null);
    }
}

四：写DBhelper类，简化方法，重复调用。

import java.sql.ResultSet;
import java.sql.SQLException;

public class DBHelper {

    private static DBUtil_BO dbBo1;

    /**
     * 查询
     * 
     * @param sql
     * @param obj
     * @return
     * @throws SQLException
     */
    public static ResultSet select(String sql, Object... obj) throws Exception {
        if (null != dbBo1) {
            DBUtils.realseSource(dbBo1);
        }
        DBUtil_BO dbBo = new DBUtil_BO();
        dbBo.conn = C3p0Utils.getConnection();
        dbBo.st = dbBo.conn.prepareStatement(sql);
        for (int i = 0; i < obj.length; i++) {
            dbBo.st.setObject(i + 1, obj[i]);
        }
        ResultSet rs = DBUtils.executeQuery(dbBo);
        dbBo1 = dbBo;
        return rs;

    }

    /**
     * 修改
     * 
     * @param sql
     * @param obj
     * @return
     * @throws Exception
     */
    public static void update(String sql, Object... obj) throws Exception {

        DBUtil_BO dbBo = new DBUtil_BO();
        dbBo.conn = C3p0Utils.getConnection();
        dbBo.st = dbBo.conn.prepareStatement(sql);
        for (int i = 0; i < obj.length; i++) {
            dbBo.st.setObject(i + 1, obj[i]);
        }
        DBUtils.executeUpdate(dbBo);
    }

}

五：项目中的调用

String selectSql = "SELECT USER_ID_ FROM act_hi_comment WHERE TASK_ID_ = ( SELECT ID_ FROM act_hi_taskinst WHERE PROC_INST_ID_ = ? AND NAME_ = ? AND ASSIGNEE_ = ? )";
rs = DBHelper.select(selectSql, procInstId, sysRole.getRoleName(), sysUser.getId());
                            rs.next();

这样很简单的实现数据库连接池的管理。