Mysql JDBC驱动源码分析(加载驱动)一
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
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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
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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 that they can be instantiated. * It may be the case that the driver class may not be there * i.e. there may be a packaged driver with the service class * as implementation of java.sql.Driver but the actual class * may be missing. In that case a sun.misc.ServiceConfigurationError * will be thrown at runtime by the VM trying to locate * and load the service. * * Adding a try catch block to catch those runtime errors * if driver not available in classpath but it's * packaged as service and that service is there in classpath. */try { while (ps.hasNext()) { ps.next();//遍历所有的驱动 } // end while} catch(Throwable t) { // Do nothing} return null; } //end run} ?
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//找到所有的拥有权限的java.sql.Driver的实现java.security.AccessController.doPrivileged(ds);?
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