小编bkb*_*bkb的帖子

我正在尝试使用这种代码动态加载JDBC驱动程序:

        try{
        URL[] url={new URL("file:libs/mysql-connector-java-5.1.21.jar")};
        URLClassLoader loader = new URLClassLoader(url, System.class.getClassLoader());
        loader.loadClass(drivername);
        Enumeration<Driver> drivers = DriverManager.getDrivers();
        while(drivers.hasMoreElements()){
            Driver driver = drivers.nextElement();
            System.out.println("driver:"+driver);
        }
        Class.forName(drivername, true, loader);
        drivers = DriverManager.getDrivers();
        while(drivers.hasMoreElements()){
            Driver driver = drivers.nextElement();
            System.out.println("driver:"+driver);
        }
        Connection connect = DriverManager.getConnection(jdbcurl, user,
                password);

        return connect;
    }
    catch (MalformedURLException e){
        e.printStackTrace();
        return null;
    }

第一个while循环显示类路径的驱动程序:

driver:sun.jdbc.odbc.JdbcOdbcDriver@35712651
driver:oracle.jdbc.OracleDriver@58df0438
driver:com.ibm.db2.jcc.DB2Driver@525c7734
driver:SQLServerDriver:1

第二个循环显示相同的驱动程序,但没有MySQL驱动程序.

我的问题是为什么？我错过了什么？

我在JavaDoc中DriverManager读到,如果驱动程序已加载,则每个驱动程序都会尝试通过drivermanager注册自己.在我的代码中,这应该是loader.loadClass(drivername);.我认为这段代码应该调用静态部分,例如:

static {
  try {
      java.sql.DriverManager.registerDriver(new Driver());
  } catch (SQLException E) {
      throw new RuntimeException("Can't register …