设计模式课程 设计模式精讲 4-3 简单工厂源码解析

1　　　　源码解析

1.1　　Calendar源码解析

1.2　　DriverManager源码解析

1　　　　源码解析

1.1　　Calendar源码解析

  /**
     * Gets a calendar using the specified time zone and default locale.
     * The <code>Calendar</code> returned is based on the current time
     * in the given time zone with the default locale. 
     *
     * @param zone the time zone to use
     * @return a Calendar.
     */
    public static Calendar getInstance(TimeZone zone)
    {
        return createCalendar(zone, Locale.getDefault());
    }

private static Calendar createCalendar(TimeZone zone, Locale aLocale)
    {
    // If the specified locale is a Thai locale, returns a BuddhistCalendar
    // instance.
    if ("th".equals(aLocale.getLanguage())
        && ("TH".equals(aLocale.getCountry()))) {
        return new sun.util.BuddhistCalendar(zone, aLocale);
    } else if ("JP".equals(aLocale.getVariant())
           && "JP".equals(aLocale.getCountry())
           && "ja".equals(aLocale.getLanguage())) {
        return new JapaneseImperialCalendar(zone, aLocale);
    }        

    // else create the default calendar
        return new GregorianCalendar(zone, aLocale);    
    ｝

1.2　　DriverManager源码解析（通过classForName获取）

    public static Connection getConnection(String url, 
    java.util.Properties info) throws SQLException {
  
        // Gets the classloader of the code that called this method, may 
    // be null.
    ClassLoader callerCL = DriverManager.getCallerClassLoader();

        return (getConnection(url, info, callerCL));
    }

//  Worker method called by the public getConnection() methods.
    private static Connection getConnection(
    String url, java.util.Properties info, ClassLoader callerCL) throws SQLException {
    java.util.Vector drivers = null;
        /*
     * When callerCl is null, we should check the application's
     * (which is invoking this class indirectly)
     * classloader, so that the JDBC driver class outside rt.jar
     * can be loaded from here.
     */
    synchronized(DriverManager.class) {     
      // synchronize loading of the correct classloader.
      if(callerCL == null) {
          callerCL = Thread.currentThread().getContextClassLoader();
       }    
    } 
     
    if(url == null) {
        throw new SQLException("The url cannot be null", "08001");
    }
    
    println("DriverManager.getConnection("" + url + "")");
    
    if (!initialized) {
        initialize();
    }

    synchronized (DriverManager.class){ 
            // use the readcopy of drivers
        drivers = readDrivers;  
        }

    // Walk through the loaded drivers attempting to make a connection.
    // Remember the first exception that gets raised so we can reraise it.
    SQLException reason = null;
    for (int i = 0; i < drivers.size(); i++) {
        DriverInfo di = (DriverInfo)drivers.elementAt(i);
      
        // If the caller does not have permission to load the driver then 
        // skip it.
        if ( getCallerClass(callerCL, di.driverClassName ) != di.driverClass ) {
        println("    skipping: " + di);
        continue;
        }
        try {
        println("    trying " + di);
        Connection result = di.driver.connect(url, info);
        if (result != null) {
            // Success!
            println("getConnection returning " + di);
            return (result);
        }
        } catch (SQLException ex) {
        if (reason == null) {
            reason = ex;
        }
        }
    }
    
    // if we got here nobody could connect.
    if (reason != null)    {
        println("getConnection failed: " + reason);
        throw reason;
    }
    
    println("getConnection: no suitable driver found for "+ url);
    throw new SQLException("No suitable driver found for "+ url, "08001");
    }