jdbc.sql.Driver d = (Driver)Class.forName("sun.jdbc.odbc.JdbcOdbcDriver"); jdbc.sql.Connection con = DriverManager.getConnection("jdbc:odbc:pubs","sa","");
以上的语句您已经很熟了吧 但 到底是怎么连上数据库的?:-)
java.sql包中的 java.sql.Driver, jdbc.sql.Connection等提供给程序开发人员统一的开发接口,数据库提供商提供相应的实现,对程序开发人员来讲只要知道这些接口都有哪些方法就可以了,但我们可以深入一些 看看到底这里面都做了那些事, 同时也可以学习其中的编程模式(如Interface模式等)
1 Class.forName(String classname) 的源码为: public final class Class implements java.io.Serializable { ... public static Class forName(String className) throws ClassNotFoundException { return forName0(className, true, ClassLoader.getCallerClassLoader()); }
... } 关于forName0 请自己查看jdk source.
目的是把指定的Class装载到JVM中来。(注意class的装载、初始化过程) 在装载过程中将执行被装载类的static块(如下)
2 sun的JdbcOdbcDriver 源码: public class JdbcOdbcDriver extends JdbcOdbcObject implements JdbcOdbcDriverInterface { ... /** * connect to DB */ public synchronized Connection connect(String s, Properties properties) throws SQLException { if(JdbcOdbcObject.isTracing()) JdbcOdbcObject.trace("*Driver.connect (" + s + ")"); if(!acceptsURL(s)) return null; if(hDbc != 0) { disconnect(hDbc); closeConnection(hDbc); hDbc = 0; } if(!initialize()) { return null; } else { JdbcOdbcConnection jdbcodbcconnection = new JdbcOdbcConnection(OdbcApi, hEnv, this); jdbcodbcconnection.initialize(getSubName(s), properties, DriverManager.getLoginTimeout()); jdbcodbcconnection.setURL(s); return jdbcodbcconnection; } } static { if(JdbcOdbcObject.isTracing()) JdbcOdbcObject.trace("JdbcOdbcDriver class loaded"); JdbcOdbcDriver jdbcodbcdriver = new JdbcOdbcDriver(); try { DriverManager.registerDriver(jdbcodbcdriver); } catch(SQLException sqlexception) { if(JdbcOdbcObject.isTracing()) JdbcOdbcObject.trace("Unable to register driver"); } } }
public interface JdbcOdbcDriverInterface extends Driver { ... }
3 连接过程 jdbc.sql.Connection con = DriverManager.getConnection("jdbc:odbc:pubs","sa","");
public class DriverManager { public static synchronized Connection getConnection(String url, String user, String password) throws SQLException { java.util.Properties info = new java.util.Properties();
// Gets the classloader of the code that called this method, may // be null. ClassLoader callerCL = DriverManager.getCallerClassLoader();
if (user != null) { info.put("user", user); } if (password != null) { info.put("password", password); }
return (getConnection(url, info, callerCL)); } private static synchronized Connection getConnection( String url, java.util.Properties info, ClassLoader callerCL) throws SQLException { ... Connection result = di.driver.connect(url, info); ... } } 4 结构图: 请点击查看 结构图 http://jdeveloper.myrice.com/doc/jdbc/images/howjdbc.jpg
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