一，jdbc连接驱动器的注册加载

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Class.forName("com.mysql.jdbc.Driver");

? ? ?当以上类被装载时执行以下程序

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package com.mysql.jdbc;

import java.sql.SQLException;
public class Driver extends NonRegisteringDriver implements java.sql.Driver {
	
       //执行这个静态代码块
	static {
		try {//注册mysql实现的驱动类
			java.sql.DriverManager.registerDriver(new Driver());
		} catch (SQLException E) {
			throw new RuntimeException("Can't register driver!");
		}
	}

	public Driver() throws SQLException {
		// Required for Class.forName().newInstance()
	}
}

?

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进入java.sql.DriverManager.registerDirver(new Driver());中的功能实现

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    public static synchronized void registerDriver(java.sql.Driver driver)
	throws SQLException {
	if (!initialized) {
            //初始化动作在下面作详解
	    initialize();
	}
        //用来存储驱动器信息
	DriverInfo di = new DriverInfo();

	di.driver = driver;
	di.driverClass = driver.getClass();
	di.driverClassName = di.driverClass.getName();

	// Not Required -- drivers.addElement(di);
        //用于加入驱动的集合
	writeDrivers.addElement(di); 
	println("registerDriver: " + di);
	
	/* 用于读取驱动的集合 */
	readDrivers = (java.util.Vector) writeDrivers.clone();
	//用以上两个集合达到读写分离的状态，由 Vector 的 iterator 和 listIterator 方法所返回的迭代器是快速失败的
    }

? ?二，驱动器的初始化操作

?

    static void initialize() {
        if (initialized) {
            return;
        }
       //private static boolean initialized = false;静态全局变量，只初始化一次
        initialized = true;
        loadInitialDrivers();
        println("JDBC DriverManager initialized");
    }

?实现初始化操作

private static void loadInitialDrivers() {
        String drivers;
	
        try {//得到系统属性jdbc.drivers对应驱动的驱动名称，使用了JAVA的安全许可
	    drivers = (String) java.security.AccessController.doPrivileged(
		new sun.security.action.GetPropertyAction("jdbc.drivers"));
        } catch (Exception ex) {
            drivers = null;
        }
        
        // If the driver is packaged as a Service Provider,
        // load it.
        
        // Get all the drivers through the classloader 
        // exposed as a java.sql.Driver.class service.
	
	 DriverService ds = new DriverService();

	 // Have all the privileges to get all the 
	 // implementation of java.sql.Driver
	 java.security.AccessController.doPrivileged(ds);		
	        
         println("DriverManager.initialize: jdbc.drivers = " + drivers);
        if (drivers == null) {
            return;
        }
        while (drivers.length() != 0) {
            int x = drivers.indexOf(':');
            String driver;
            if (x < 0) {
                driver = drivers;
                drivers = "";
            } else {
                driver = drivers.substring(0, x);
                drivers = drivers.substring(x+1);
            }
            if (driver.length() == 0) {
                continue;
            }
            try {
                println("DriverManager.Initialize: loading " + driver);
                Class.forName(driver, true,
			      ClassLoader.getSystemClassLoader());
            } catch (Exception ex) {
                println("DriverManager.Initialize: load failed: " + ex);
            }
        }
    }

?以上初始化代码分析

? 内部类对象，创建此对象时，它会从系统服务中加载驱动

?

 DriverService ds = new DriverService();

? ?代码如下：

? ?class DriverService implements java.security.PrivilegedAction {

        Iterator ps = null;
	public DriverService() {};
        public Object run() {

       //从系统服务中加载驱动
	ps = Service.providers(java.sql.Driver.class);

	/* Load these drivers, so