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发表时间：2007-10-07
Hibernate可以说伴随着我的整个Java历程。从我一开始工作，我就在一次意外的机会认识了它。以前，在使用语言上我是非常激进的。因为公司不采用Hibernate，我辞去了两份工作。可今天我们搞门户网站的时候，我却第一个反对使用Hibernate。总之，Hibernate让我彻夜难眠。 刚开始接触Hibernate时，自然就要接触Hibernate配置文件，众所周知，Hibernate有两种配置模式：一个采用属性文件，一个采用XML配置文件。一般在早期Hibernate2时，大家都喜欢采用属性文件，现在大家都喜欢用XML配置文件。现在不妨贴一段基本XML配置给大家看看： java 代码
上面这段代码，在一般的Hibernate使用者来说再也普通不过了。但如果从本质上去看待这些文件，能够看到很多内容。
（2）大家要注意的是，作为一个配置文件开始的第一个标签是不动的。同样对于以上的配置文件来说，<hibernate-configuration>元素是全局元素。 先吃饭去了，过会儿再继续 声明：ITeye文章版权属于作者，受法律保护。没有作者书面许可不得转载。
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发表时间：2007-10-08
你吃了一天了?
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发表时间：2007-10-08
幸亏楼上的老兄提醒。这才发现自己吃了一天了，终于，吃饱了，喝足了。接着说。哈哈！
续：如果发现开始元素不唯一，建议拆分成多个文件。 (3)通过观察环境dtd文件你会发现，<session-factory>元素是唯一的。这就表明一个配置文件可以创建一个sessionFacotry,也同时表示一个配置环境中可以连接一个的数据库。如果不放心，可以去看org.hibernate.cfg.Configuration下的 public SessionFactory buildSessionFactory() throws HibernateException {
log.debug( "Preparing to build session factory with filters : " + filterDefinitions );
secondPassCompile();
validate();
Environment.verifyProperties( properties );
Properties copy = new Properties();
copy.putAll( properties );
PropertiesHelper.resolvePlaceHolders( copy );
Settings settings = buildSettings( copy );
return new SessionFactoryImpl(
this,
mapping,
settings,
getInitializedEventListeners()
);
}
这个方法在配置文件下，不带参数创建SessionFactory,肯定表明是唯一性。 |
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发表时间：2007-10-08
把你前后对hibernate的态度的巨大变化讲一下，是啥让你变了心。
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发表时间：2007-10-08
secondPassCompile(); 这句话啥意思，我看源码时没找到出处。 |
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发表时间：2007-10-08
（4）SessionFacotry相信大家都用过。在配置时，往往因找不到下面的属性配置，而在网络上东找西找。其实非常简单，只需要打开源码下的\etc\hibernate.properties，真是要啥有啥。而且肯定不用怀疑是否准确。同时Hibernate支持多少种数据库也尽收眼底。
（5）介绍一个重要的属性-dialect。做数据库语句查询时，大家都知道dialect是数据库的方言，但是，当不知道一个Hibernate的HQL函数而抓耳挠腮时，却不知道打开Hibernate方言看看。打开Hibernate所对用的方言。会发现里面挂满了Hibernate所能支持函数的全部。不相信看看如下的Mysql的方言。 public MySQLDialect() {
super();
registerColumnType( Types.BIT, "bit" );
registerColumnType( Types.BIGINT, "bigint" );
registerColumnType( Types.SMALLINT, "smallint" );
registerColumnType( Types.TINYINT, "tinyint" );
registerColumnType( Types.INTEGER, "integer" );
registerColumnType( Types.CHAR, "char(1)" );
registerColumnType( Types.FLOAT, "float" );
registerColumnType( Types.DOUBLE, "double precision" );
registerColumnType( Types.DATE, "date" );
registerColumnType( Types.TIME, "time" );
registerColumnType( Types.TIMESTAMP, "datetime" );
registerColumnType( Types.VARBINARY, "longblob" );
registerColumnType( Types.VARBINARY, 16777215, "mediumblob" );
registerColumnType( Types.VARBINARY, 65535, "blob" );
registerColumnType( Types.VARBINARY, 255, "tinyblob" );
registerColumnType( Types.NUMERIC, "numeric($p,$s)" );
registerColumnType( Types.BLOB, "longblob" );
registerColumnType( Types.BLOB, 16777215, "mediumblob" );
registerColumnType( Types.BLOB, 65535, "blob" );
registerColumnType( Types.CLOB, "longtext" );
registerColumnType( Types.CLOB, 16777215, "mediumtext" );
registerColumnType( Types.CLOB, 65535, "text" );
registerVarcharTypes();
registerFunction("ascii", new StandardSQLFunction("ascii", Hibernate.INTEGER) );
registerFunction("bin", new StandardSQLFunction("bin", Hibernate.STRING) );
registerFunction("char_length", new StandardSQLFunction("char_length", Hibernate.LONG) );
registerFunction("character_length", new StandardSQLFunction("character_length", Hibernate.LONG) );
registerFunction("lcase", new StandardSQLFunction("lcase") );
registerFunction("lower", new StandardSQLFunction("lower") );
registerFunction("length", new StandardSQLFunction("length", Hibernate.LONG) );
registerFunction("ltrim", new StandardSQLFunction("ltrim") );
registerFunction("ord", new StandardSQLFunction("ord", Hibernate.INTEGER) );
registerFunction("quote", new StandardSQLFunction("quote") );
registerFunction("reverse", new StandardSQLFunction("reverse") );
registerFunction("rtrim", new StandardSQLFunction("rtrim") );
registerFunction("soundex", new StandardSQLFunction("soundex") );
registerFunction("space", new StandardSQLFunction("space", Hibernate.STRING) );
registerFunction("ucase", new StandardSQLFunction("ucase") );
registerFunction("upper", new StandardSQLFunction("upper") );
registerFunction("unhex", new StandardSQLFunction("unhex", Hibernate.STRING) );
registerFunction("abs", new StandardSQLFunction("abs") );
registerFunction("sign", new StandardSQLFunction("sign", Hibernate.INTEGER) );
registerFunction("acos", new StandardSQLFunction("acos", Hibernate.DOUBLE) );
registerFunction("asin", new StandardSQLFunction("asin", Hibernate.DOUBLE) );
registerFunction("atan", new StandardSQLFunction("atan", Hibernate.DOUBLE) );
registerFunction("cos", new StandardSQLFunction("cos", Hibernate.DOUBLE) );
registerFunction("cot", new StandardSQLFunction("cot", Hibernate.DOUBLE) );
registerFunction("crc32", new StandardSQLFunction("crc32", Hibernate.LONG) );
registerFunction("exp", new StandardSQLFunction("exp", Hibernate.DOUBLE) );
registerFunction("ln", new StandardSQLFunction("ln", Hibernate.DOUBLE) );
registerFunction("log", new StandardSQLFunction("log", Hibernate.DOUBLE) );
registerFunction("log2", new StandardSQLFunction("log2", Hibernate.DOUBLE) );
registerFunction("log10", new StandardSQLFunction("log10", Hibernate.DOUBLE) );
registerFunction("pi", new NoArgSQLFunction("pi", Hibernate.DOUBLE) );
registerFunction("rand", new NoArgSQLFunction("rand", Hibernate.DOUBLE) );
registerFunction("sin", new StandardSQLFunction("sin", Hibernate.DOUBLE) );
registerFunction("sqrt", new StandardSQLFunction("sqrt", Hibernate.DOUBLE) );
registerFunction("tan", new StandardSQLFunction("tan", Hibernate.DOUBLE) );
registerFunction("radians", new StandardSQLFunction("radians", Hibernate.DOUBLE) );
registerFunction("degrees", new StandardSQLFunction("degrees", Hibernate.DOUBLE) );
registerFunction("ceiling", new StandardSQLFunction("ceiling", Hibernate.INTEGER) );
registerFunction("ceil", new StandardSQLFunction("ceil", Hibernate.INTEGER) );
registerFunction("floor", new StandardSQLFunction("floor", Hibernate.INTEGER) );
registerFunction("round", new StandardSQLFunction("round", Hibernate.INTEGER) );
registerFunction("datediff", new StandardSQLFunction("datediff", Hibernate.INTEGER) );
registerFunction("timediff", new StandardSQLFunction("timediff", Hibernate.TIME) );
registerFunction("date_format", new StandardSQLFunction("date_format", Hibernate.STRING) );
registerFunction("curdate", new NoArgSQLFunction("curdate", Hibernate.DATE) );
registerFunction("curtime", new NoArgSQLFunction("curtime", Hibernate.TIME) );
registerFunction("current_date", new NoArgSQLFunction("current_date", Hibernate.DATE, false) );
registerFunction("current_time", new NoArgSQLFunction("current_time", Hibernate.TIME, false) );
registerFunction("current_timestamp", new NoArgSQLFunction("current_timestamp", Hibernate.TIMESTAMP, false) );
registerFunction("date", new StandardSQLFunction("date", Hibernate.DATE) );
registerFunction("day", new StandardSQLFunction("day", Hibernate.INTEGER) );
registerFunction("dayofmonth", new StandardSQLFunction("dayofmonth", Hibernate.INTEGER) );
registerFunction("dayname", new StandardSQLFunction("dayname", Hibernate.STRING) );
registerFunction("dayofweek", new StandardSQLFunction("dayofweek", Hibernate.INTEGER) );
registerFunction("dayofyear", new StandardSQLFunction("dayofyear", Hibernate.INTEGER) );
registerFunction("from_days", new StandardSQLFunction("from_days", Hibernate.DATE) );
registerFunction("from_unixtime", new StandardSQLFunction("from_unixtime", Hibernate.TIMESTAMP) );
registerFunction("hour", new StandardSQLFunction("hour", Hibernate.INTEGER) );
registerFunction("last_day", new StandardSQLFunction("last_day", Hibernate.DATE) );
registerFunction("localtime", new NoArgSQLFunction("localtime", Hibernate.TIMESTAMP) );
registerFunction("localtimestamp", new NoArgSQLFunction("localtimestamp", Hibernate.TIMESTAMP) );
registerFunction("microseconds", new StandardSQLFunction("microseconds", Hibernate.INTEGER) );
registerFunction("minute", new StandardSQLFunction("minute", Hibernate.INTEGER) );
registerFunction("month", new StandardSQLFunction("month", Hibernate.INTEGER) );
registerFunction("monthname", new StandardSQLFunction("monthname", Hibernate.STRING) );
registerFunction("now", new NoArgSQLFunction("now", Hibernate.TIMESTAMP) );
registerFunction("quarter", new StandardSQLFunction("quarter", Hibernate.INTEGER) );
registerFunction("second", new StandardSQLFunction("second", Hibernate.INTEGER) );
registerFunction("sec_to_time", new StandardSQLFunction("sec_to_time", Hibernate.TIME) );
registerFunction("sysdate", new NoArgSQLFunction("sysdate", Hibernate.TIMESTAMP) );
registerFunction("time", new StandardSQLFunction("time", Hibernate.TIME) );
registerFunction("timestamp", new StandardSQLFunction("timestamp", Hibernate.TIMESTAMP) );
registerFunction("time_to_sec", new StandardSQLFunction("time_to_sec", Hibernate.INTEGER) );
registerFunction("to_days", new StandardSQLFunction("to_days", Hibernate.LONG) );
registerFunction("unix_timestamp", new StandardSQLFunction("unix_timestamp", Hibernate.LONG) );
registerFunction("utc_date", new NoArgSQLFunction("utc_date", Hibernate.STRING) );
registerFunction("utc_time", new NoArgSQLFunction("utc_time", Hibernate.STRING) );
registerFunction("utc_timestamp", new NoArgSQLFunction("utc_timestamp", Hibernate.STRING) );
registerFunction("week", new StandardSQLFunction("week", Hibernate.INTEGER) );
registerFunction("weekday", new StandardSQLFunction("weekday", Hibernate.INTEGER) );
registerFunction("weekofyear", new StandardSQLFunction("weekofyear", Hibernate.INTEGER) );
registerFunction("year", new StandardSQLFunction("year", Hibernate.INTEGER) );
registerFunction("yearweek", new StandardSQLFunction("yearweek", Hibernate.INTEGER) );
registerFunction("hex", new StandardSQLFunction("hex", Hibernate.STRING) );
registerFunction("oct", new StandardSQLFunction("oct", Hibernate.STRING) );
registerFunction("octet_length", new StandardSQLFunction("octet_length", Hibernate.LONG) );
registerFunction("bit_length", new StandardSQLFunction("bit_length", Hibernate.LONG) );
registerFunction("bit_count", new StandardSQLFunction("bit_count", Hibernate.LONG) );
registerFunction("encrypt", new StandardSQLFunction("encrypt", Hibernate.STRING) );
registerFunction("md5", new StandardSQLFunction("md5", Hibernate.STRING) );
registerFunction("sha1", new StandardSQLFunction("sha1", Hibernate.STRING) );
registerFunction("sha", new StandardSQLFunction("sha", Hibernate.STRING) );
registerFunction( "concat", new StandardSQLFunction( "concat", Hibernate.STRING ) );
getDefaultProperties().setProperty(Environment.MAX_FETCH_DEPTH, "2");
getDefaultProperties().setProperty(Environment.STATEMENT_BATCH_SIZE, DEFAULT_BATCH_SIZE);
}
看到这些，如果你不是很笨，应该明白是怎么一回事了吧。 |
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发表时间：2007-10-08
（6）打开org.hibernate.Dialect目录还有一件让人兴奋的事情。Hibernate对Mysql的数据库作了区分，如MySQL5Dialect、MySQLDialect、MySQLInnoDBDialect等等。打开MySQL5Dialect代码
public class MySQL5Dialect extends MySQLDialect {
protected void registerVarcharTypes() {
registerColumnType( Types.VARCHAR, "longtext" );
registerColumnType( Types.VARCHAR, 16777215, "mediumtext" );
registerColumnType( Types.VARCHAR, 65535, "varchar($l)" );
}
}
从以上代码，你可以知道，MySQL4和MySQL5之间有什么区别。更重要的它告诉了你，Hibernate Dialect是可以扩展的。只要你继承自己所需要的方言就可以扩展自己的函数，或者Mysql方言没有注册的MySQL函数。 |
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发表时间：2007-10-08
让我再去吃点东西吧，领导老瞄着我的屏幕。哈哈
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发表时间：2007-10-08
javachs 写道 secondPassCompile(); 这句话啥意思，我看源码时没找到出处。 我用的是版本3.2，源码是这样 protected void secondPassCompile() throws MappingException {
log.debug( "processing extends queue" );
processExtendsQueue();
log.debug( "processing collection mappings" );
Iterator iter = secondPasses.iterator();
while ( iter.hasNext() ) {
SecondPass sp = (SecondPass) iter.next();
if ( ! (sp instanceof QuerySecondPass) ) {
sp.doSecondPass( classes );
iter.remove();
}
}
log.debug( "processing native query and ResultSetMapping mappings" );
iter = secondPasses.iterator();
while ( iter.hasNext() ) {
SecondPass sp = (SecondPass) iter.next();
sp.doSecondPass( classes );
iter.remove();
}
log.debug( "processing association property references" );
iter = propertyReferences.iterator();
while ( iter.hasNext() ) {
Mappings.PropertyReference upr = (Mappings.PropertyReference) iter.next();
PersistentClass clazz = getClassMapping( upr.referencedClass );
if ( clazz == null ) {
throw new MappingException(
"property-ref to unmapped class: " +
upr.referencedClass
);
}
Property prop = clazz.getReferencedProperty( upr.propertyName );
if ( upr.unique ) {
( (SimpleValue) prop.getValue() ).setAlternateUniqueKey( true );
}
}
//TODO: Somehow add the newly created foreign keys to the internal collection
log.debug( "processing foreign key constraints" );
iter = getTableMappings();
Set done = new HashSet();
while ( iter.hasNext() ) {
secondPassCompileForeignKeys( (Table) iter.next(), done );
}
}
意图非常的明显，重新加载各种属性，在源码中被多次用到。 |
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发表时间：2007-10-08
感谢你讲了一些一般人不会注意而实际上很有用的东西，但大家最关心的是你为什么反对在门户网站使用Hibernate。
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