Java連結數據庫內幕
Java.sql包中的 java.sql.Driver, jdbc.sql.Connection等提供給程序開發人員統一的開發接口，數據庫提供商提供相應的實現，對程序開發人員來講只要知道這些接口都有哪些方法就可以了。但我們可以深入一些看看到底這里面都做了那些事， 同時也可以學習其中的編程模式(如Interface模式等)。
1、 Class.forName(String classname) 的源碼為：
| public final class Class implements java.io.Serializable { ... public static Class forName(String className) throws ClassNotFoundException { return forName0(className, true, ClassLoader.getCallerClassLoader()); } ... } |
關于forName0 請自己查看jdk source.
的是把指定的Class裝載到JVM中來。（注意class的裝載、初始化過程）在裝載過程中將執行被裝載類的static塊(如下)
2 sun的JdbcOdbcDriver 源碼：
| 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 連接過程
| 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 結構圖：
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