Spring set注入jdbc url为null

Question

使用apacha的basicdatasource连接池，写了一个spring小程序，测试获得mySQL数据库连接，set注入数据库连接的基本参数后，提示错误

Exception in thread "main" java.sql.SQLException: Cannot create JDBC driver of class '' for connect URL 'null'
    at org.apache.commons.dbcp2.BasicDataSource.createConnectionFactory(BasicDataSource.java:2023)
    at org.apache.commons.dbcp2.BasicDataSource.createDataSource(BasicDataSource.java:1897)
    at org.apache.commons.dbcp2.BasicDataSource.getConnection(BasicDataSource.java:1413)
    at com.alex.util.MySQLDataSource.getConnection(MySQLDataSource.java:43)
    at com.alex.util.test.TestCase.main(TestCase.java:16)
Caused by: java.sql.SQLException: No suitable driver
    at java.sql.DriverManager.getDriver(Unknown Source)
    at org.apache.commons.dbcp2.BasicDataSource.createConnectionFactory(BasicDataSource.java:2007)
    ... 4 more 

后多次修改调试，发现问题出在

    public MySQLDataSource() {
        bds = new BasicDataSource();
        bds.setDriverClassName(driver);
        bds.setUrl(url);
        bds.setUsername(username);
        bds.setPassword(password);
    }

修改成

 public MySQLDataSource() {
        bds = new BasicDataSource();
    }

    @Override
    public Connection getConnection() throws SQLException{
        bds.setDriverClassName(driver);
        bds.setUrl(url);
        bds.setUsername(username);
        bds.setPassword(password);
        return bds.getConnection();
    }

提示可以获得链接，请问这是为什么啊，是注入顺序问题吗，我百度过之后，还是无解，本人小白，求指教。附所有源代码。

applicationContext.xml

 <?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:context="http://www.springframework.org/schema/context" xmlns:jdbc="http://www.springframework.org/schema/jdbc"  
    xmlns:jee="http://www.springframework.org/schema/jee" xmlns:tx="http://www.springframework.org/schema/tx"
    xmlns:jpa="http://www.springframework.org/schema/data/jpa" xmlns:util="http://www.springframework.org/schema/util"

    xsi:schemaLocation="
        http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.2.xsd
        http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.2.xsd
        http://www.springframework.org/schema/jdbc http://www.springframework.org/schema/jdbc/spring-jdbc-3.2.xsd
        http://www.springframework.org/schema/jee http://www.springframework.org/schema/jee/spring-jee-3.2.xsd
        http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-3.2.xsd
        http://www.springframework.org/schema/data/jpa http://www.springframework.org/schema/data/jpa/spring-jpa-1.3.xsd
        http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util-3.1.xsd
        ">

        <bean id="mydatasource" class="com.alex.util.MySQLDataSource">
            <property name="driver" value="com.mysql.jdbc.Driver"/>
            <property name="url" value="jdbc:mysql://localhost:3306/jsd1407?useUnicode=true&amp;characterEncoding=utf8"/>
            <property name="username" value="root"/>
            <property name="password" value="root"/>
        </bean>
</beans>

interface:

 package com.alex.util;

import java.sql.Connection;
import java.sql.SQLException;

public interface DataSource {

    public abstract Connection getConnection() throws SQLException;

    public abstract void closeConnection() throws SQLException;

}

MySQLDataSource:

 package com.alex.util;

import java.sql.Connection;
import java.sql.SQLException;

import org.apache.commons.dbcp2.BasicDataSource;

public class MySQLDataSource implements DataSource {

    private String driver;
    private String url;
    private String username;
    private String password;
    private BasicDataSource bds;

    public void setDriver(String driver) {
        this.driver = driver;
    }

    public void setUrl(String url) {
        this.url = url;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public MySQLDataSource() {
        bds = new BasicDataSource();
    }

    @Override
    public Connection getConnection() throws SQLException{
        bds.setDriverClassName(driver);
        bds.setUrl(url);
        bds.setUsername(username);
        bds.setPassword(password);
        return bds.getConnection();
    }

    @Override
    public void closeConnection() throws SQLException{
        bds.close();
    }
}