jdbc连接驱动器的注册加载
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一,jdbc连接驱动器的注册加载
- Class.forName("com.mysql.jdbc.Driver");
当以上类被装载时执行以下程序
- 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()
- }
- }
进入java.sql.DriverManager.registerDirver(new Driver());中的功能实现
- 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();
- span style="white-space: pre;"> </span>//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<em>快速失败的</em>
- }
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 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
- }
- //找到所有的拥有权限的java.sql.Driver的实现
- java.security.AccessController.doPrivileged(ds);
转自http://wuquanyin1011.iteye.com/blog/1409455
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