在jdbc基础上进阶一小步的C3p0 连接池(DBCP 不能读xml配置文件,已淘汰) 和DBUtils 中两个主要类QueryRunner和ResultSetHandler的使用

Posted 2020-10-27 Advancing Swift

首先看C3p0这个连接池,最大优势可以自动读取默认的配置文件

<?xml version="1.0" encoding="UTF-8"?>
<c3p0-config>
    <default-config>
        <property name="driverClass">com.mysql.jdbc.Driver</property>
        <property name="jdbcUrl">jdbc:mysql://localhost:3306/swift_db
        </property>
        <property name="user">root</property>
        <property name="password">root</property>
        <property name="initialPoolSize">20</property>
        <property name="acquireIncrement">5</property>
        <property name="maxPoolSize">50</property>
        <property name="minPoolSize">5</property>
    </default-config>
</c3p0-config>

配置文件中有常规的4个主选项和一些其他配置

只需要使用C3p0中的实现javax.sql.DateSource接口的实现类ComboPooledDataSource 创建对象即可

private static ComboPooledDataSource dataSource = new ComboPooledDataSource();

这个是放成员变量那,只要new 空参就会自动调用xml配置文件,配置文件需要标签<default-config>

也可以调用命名的配置文件,需要配置文件<named-config>

<?xml version="1.0" encoding="UTF-8"?>
<c3p0-config>
    <named-config>
        <property name="driverClass">com.mysql.jdbc.Driver</property>
        <property name="jdbcUrl">jdbc:mysql://localhost:3306/swift_db
        </property>
        <property name="user">root</property>
        <property name="password">root</property>
        <property name="initialPoolSize">20</property>
        <property name="acquireIncrement">5</property>
        <property name="maxPoolSize">50</property>
        <property name="minPoolSize">5</property>
    </named-config>
</c3p0-config>

一般把C3p0做成工具类使用,方便调用

package com.swift.base;

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

import javax.sql.DataSource;

import com.mchange.v2.c3p0.ComboPooledDataSource;

public class C3p0Utils {

    // 数据源连接池c3p0作用不用每次建立连接,浪费资源与等待时间,把连接做好放在连接池中,需要时获取
    // c3p0连接池可以通过配置文件c3p0-config.xml文件自动读取相关属性
    // c3p0连接池是java中 javax.sql.DataSource的实现类,其中必须实现getConnection方法
    private static ComboPooledDataSource dataSource = new ComboPooledDataSource("swift");

    // 获得数据源(连接池)的方法
    public static DataSource getDataSource() {
        return dataSource;
    }

    // 从连接池中获得一个conn资源的
    public static Connection getConnection() throws Exception {
        dataSource.setDriverClass("com.mysql.jdbc.Driver");
        dataSource.setJdbcUrl("jdbc:mysql://localhost:3306/swift_db");
        dataSource.setUser("root");
        dataSource.setPassword("root");
        dataSource.setAcquireIncrement(5);
        dataSource.setInitialPoolSize(20);
        dataSource.setMinPoolSize(5);
        dataSource.setMaxPoolSize(50);

        Connection conn = dataSource.getConnection();
        return conn;
    }

    public static void close(Connection conn, Statement stmt, ResultSet rs) {
        if (rs != null) {
            try {
                rs.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        if (stmt != null) {
            try {
                stmt.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        if (conn != null) {
            try {
                conn.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }

}

这个已经调用了xml配置文件,每次又调用Connection都会来一遍属性配置,浪费资源,可以用静态代码块,只调用一次即可

package com.swift.jinji;

import java.beans.PropertyVetoException;
import java.sql.Connection;
import java.sql.SQLException;

import javax.sql.DataSource;

import com.mchange.v2.c3p0.ComboPooledDataSource;

/*使用C3P0获得10个连接对象
要求：不使用配置文件*/

public class C3p0_10con {

    private static ComboPooledDataSource dataSource = new ComboPooledDataSource();

    static {
        try {
            dataSource.setDriverClass("com.mysql.jdbc.Driver");
        } catch (PropertyVetoException e) {
            e.printStackTrace();
        }
        dataSource.setJdbcUrl("jdbc:mysql://localhost:3306/swift_db");
        dataSource.setUser("root");
        dataSource.setPassword("root");
        dataSource.setInitialPoolSize(20);
        dataSource.setAcquireIncrement(5);
        dataSource.setMaxPoolSize(50);
        dataSource.setMinPoolSize(5);
    }

    public static void main(String[] args) throws PropertyVetoException {

        for(int i=0;i<10;i++) {
            System.out.println(C3p0_10con.getConnection());
        }
    }

    public static DataSource getDataSource() {
        return dataSource;

    }

    public static Connection getConnection() {

        Connection con = null;
        try {
            con = dataSource.getConnection();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return con;

    }
    
    public static void close(Connection con) {
        if(con!=null) {
            try {
                con.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }

}

配合DBUtils的QureyRunner类和ResultSetHandler类使用,更加方便数据库增删改与查询

package com.swift.jinji;

import java.sql.SQLException;
import java.util.Arrays;
import java.util.List;
import java.util.Map;

import org.apache.commons.dbutils.QueryRunner;
import org.apache.commons.dbutils.ResultSetHandler;
import org.apache.commons.dbutils.handlers.ArrayHandler;
import org.apache.commons.dbutils.handlers.ArrayListHandler;
import org.apache.commons.dbutils.handlers.BeanHandler;
import org.apache.commons.dbutils.handlers.ColumnListHandler;
import org.apache.commons.dbutils.handlers.KeyedHandler;
import org.apache.commons.dbutils.handlers.MapHandler;
import org.apache.commons.dbutils.handlers.MapListHandler;
import org.apache.commons.dbutils.handlers.ScalarHandler;

import com.swift.base.C3p0Utils;
import com.swift.domain.Puppy;

/*查询用户表中的第一条数据。并将数据封装成对象数组。*/

public class Qurey_Puppy {

    public static void main(String[] args) {

        QueryRunner qr=new QueryRunner(C3p0Utils.getDataSource());
        String sql="select * from puppy;";
        ResultSetHandler<Puppy> rsh=new BeanHandler<Puppy>(Puppy.class);
        ResultSetHandler<Object[]> rsh1=new ArrayHandler();
        ResultSetHandler<List<Object[]>> rsh2=new ArrayListHandler();
        ResultSetHandler<Object> rsh3=new ScalarHandler("name");
        ResultSetHandler<Map<String, Object>> rsh4=new MapHandler();
        ResultSetHandler<List<Map<String, Object>>> rsh5=new MapListHandler();
        ResultSetHandler<List<Object>> rsh6=new ColumnListHandler("name");
        ResultSetHandler<Map<Object,Map<String,Object>>> rsh7=new KeyedHandler("id");
        
        try {
             Map<Object, Map<String, Object>> result = qr.query(sql, rsh7);
        /*    for(Object[] puppy:dog) {
                
                System.out.println(Arrays.toString(puppy));
            }*/
//            System.out.println(result);
             
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

}

ResultSetHandler有很多子类,可以放到各种容器中,从数据库取出数据后,将数据放到对象数组,数组集合,对象元素,Map集合,Map集合列表,对象列表,Map的Map中