Hibernate初探

开始看Hibernate reference,运行hibernate的test中的代码。
Environment是一个非常重要的类。它定义了很多常量，最重要的是hibernate的入口在这里。在Environemt类中有段static 代码：
static {
  //一些常量设置

  //导入hibernate.properties到GLOBAL_PROPERTIES
  InputStream stream = ConfigHelper.getResourceAsStream("/hibernate.properties");
  ... 
    GLOBAL_PROPERTIES.load(stream);
  ...  
    stream.close();
  ...
  //将系统属性放入全局属性GLOBAL_PROPERTIES中  
  try {
   GLOBAL_PROPERTIES.putAll( System.getProperties() );
  }
  catch (SecurityException se) {
   log.warn("could not copy system properties, system properties will be ignored");
  }
  //检查是否有属性废弃了或改名了
  verifyProperties(GLOBAL_PROPERTIES);

  //其他一些设置。。。
  
  //看db driver/JVM？ 是否支持产生key的方法
  boolean getGeneratedKeysSupport;
  try {
   Statement.class.getMethod("getGeneratedKeys", null);
   getGeneratedKeysSupport = true;
  }
  catch (NoSuchMethodException nsme) {
   getGeneratedKeysSupport = false;
  }
  JVM_SUPPORTS_GET_GENERATED_KEYS = getGeneratedKeysSupport;
  if (!JVM_SUPPORTS_GET_GENERATED_KEYS) log.info("JVM does not support Statement.getGeneratedKeys()");

  
  //查JDK是否有java.util.LinkedHashSet类
  //Timestamp似乎有点问题
  JVM_HAS_TIMESTAMP_BUG = new Timestamp(123456789).getTime() != 123456789;
  if (JVM_HAS_TIMESTAMP_BUG) log.info("using workaround for JVM bug in java.sql.Timestamp");
  Timestamp t = new Timestamp(0);
  t.setNanos(5 * 1000000);
  JVM_HAS_JDK14_TIMESTAMP = t.getTime() == 5;
  if (JVM_HAS_JDK14_TIMESTAMP) {
   log.info("using JDK 1.4 java.sql.Timestamp handling");
  }
  else {
   log.info("using pre JDK 1.4 java.sql.Timestamp handling");
  }
 }

然后正常的一个流程：
Configuration cfg = new Configuration();
//从配置文件中得到的各种属性设置
cfg.setProperty();
//得到所有mapping文件或mapping类
cfg.addResource(//mapping文件名);
或cfg.addClass(//类名)
//针对每个resource，有个HbmBinder来读xml文件，并产生配置时期模型类，就是在org.hibernate.mapping包中的各个类，
如Any,OneToMany,List,Join等。称为配置时期的模型configuration-time metamodel。
cfg.buildMappings(); //这里对复合查询进行，外键等进行处理

SessionFactory sessionFactory = cfg.buildSessionFactory();
 {//...
  return new SessionFactoryImpl(
    this,
    mapping,
    settings,
    getInitializedEventListeners()
   );
 }

Session s = sessionFactory.openSession(){
//org.hibernate.impl.SessionImpl
return new SessionImpl(
          connection,
          this,
          autoClose,
          timestamp,
          sessionLocalInterceptor == null ? interceptor : sessionLocalInterceptor,
          settings.getDefaultEntityMode(),
          settings.isFlushBeforeCompletionEnabled(),
          settings.isAutoCloseSessionEnabled(),
          settings.getConnectionReleaseMode()
   );
}
Transaction tx = s.beginTransaction();
....
tx.commit();
s.close();