?? ?Hibernate提供客戶化映射類型接口，使用戶能以編程方式創(chuàng)建自定義的映射類型來將持久化類任意類型的屬性映射到數(shù)據(jù)庫中。使用客戶化映射類型，需要實現(xiàn)org.hibernate.usertype.UserType接口。這是個強大的功能，也是Hibernate的最佳實踐之一。我們經(jīng)常提到ORM中很困難的一點便是O的屬性和R的屬性不能一一映射，而Hibernate提供的UserType無疑給出了一個很好的解決方案。本文給出使用客戶化映射類型的兩個例子，算是對Hibernate初學者的拋磚。
?? ?第一個例子是使用UserType映射枚舉類型。假設Account表中含有一sex列，類型為tinyint（當前其0代表男，1代表女，將來可能出現(xiàn)2等代表其他性別類型）；我們當然可以在對應的Account類中添加int類型的sex屬性，但這種數(shù)字化無顯示意義且類型不安全的枚舉不是很好的解決方式，這里就采用了java5的enum來作為Account類的性別屬性（如果不熟悉java5的enum，也可采用《effective java》中提到的經(jīng)典的類型安全的枚舉方案）。在Account添加enum Gender：
public?class?Account?extends?AbstractDomain<Long>{
????
????public?enum?Gender{
????????Male("male",0),
????????Female("female",1);
????????
????????private?String?name;
????????private?int?value;
????????
????????public?String?getName()?{
????????????return?name;
????????}
????????public?int?getValue()?{
????????????return?value;
????????}
????????
????????private?Gender(String?name,int?value){
????????????this.name?=?name;
????????????this.value?=?value;
????????}
????????
????????public?static?Gender?getGender(int?value){
????????????if(0?==?value)return?Male;
????????????else?if(1?==?value)return?Female;
????????????else?throw?new?RuntimeException();
????????}
????????
????}
????
????private?Gender?gender;
????public?Gender?getGender()?{
????????return?gender;
????}
????public?void?setGender(Gender?gender)?{
????????this.gender?=?gender;
????}
???????//省略其他????
}
?? ?接下來定義實現(xiàn)UserType接口的GenderUserType：
public?class?GenderUserType?implements?UserType{
????public?Object?assemble(Serializable?arg0,?Object?arg1)?throws?HibernateException?{
????????return?null;
????}
????/*
?????*??這是用于Hibernate緩存生成的快照，由于Gender是不可變的，直接返回就好了。
?????*/
????public?Object?deepCopy(Object?arg0)?throws?HibernateException?{
????????return?arg0;
????}
????public?Serializable?disassemble(Object?arg0)?throws?HibernateException?{
????????return?null;
????}
????/*
?????*?由于Gender是不可變的，因此直接==了，這個方法將在insert、update時用到。
?????*/
????public?boolean?equals(Object?x,?Object?y)?throws?HibernateException?{
????????return?x?==?y;
????}
????public?int?hashCode(Object?o)?throws?HibernateException?{
????????return?o.hashCode();
????}
????/*
?????*?表明Gender是不是可變類（很重要的概念哦），這里的Gender由于是枚舉所以是不可變的
?????*/
????public?boolean?isMutable()?{
????????return?false;
????}
????/*
?????*??從ResultSet讀取sex并返回Gender實例，這個方法是在從數(shù)據(jù)庫查詢數(shù)據(jù)時用到。
?????*/
????public?Object?nullSafeGet(ResultSet?rs,?String[]?names,?Object?owner)?throws?HibernateException,?SQLException?{
????????int?value?=?rs.getInt(names[0]);
????????return?Account.Gender.getGender(value);
????}
????/*
?????*??將Gender的value設置到PreparedStatement。
?????*/
????public?void?nullSafeSet(PreparedStatement?ps,?Object?value,?int?index)?throws?HibernateException,?SQLException?{
??????? if(value == null){
??? ??? ??? ps.setInt(index,Account.Gender.Male.getValue());
??? ??? }else{
??? ??? ??? ps.setInt(index,((Account.Gender)value).getValue());
??? ??? }
????}
????public?Object?replace(Object?arg0,?Object?arg1,?Object?arg2)?throws?HibernateException?{
????????return?null;
????}
????/*
?????*?設置映射的Gender類
?????*/
????public?Class?returnedClass()?{
????????return?Account.Gender.class;
????}
????/*
?????*??設置Gender枚舉中的value屬性對應的Account表中的sex列的SQL類型
?????*/
????public?int[]?sqlTypes()?{
????????int[]?typeList?=?{Types.TINYINT};
????????return?typeList;
????}
}
?? ?最后在Account的配置文件中配置gender屬性就好了：
<property name="gender" type="org.prague.domain.util.GenderUserType" column="sex"></property>
?? ?除了可以使用 UserType映射枚舉類型，也可以使用Hibernate的PersistentEnum來實現(xiàn)同樣的功能，感興趣的朋友可以參考文章http://www.hibernate.org/203.html。
?? ?
?? ?第二個例子是關于email的。假設Account表中email是一個varchar型的字段，而Account中的Email是如下的類：
public?class?Email?{
????String?username;
????String?domain;
????public?Email()?{
????}
????public?Email(String?username,?String?domain)?{
????????this.username?=?username;
????????this.domain?=?domain;
????}
????public?String?getUsername()?{
????????return?username;
????}
????public?String?getDomain()?{
????????return?domain;
????}
????
????public?void?setDomain(String?domain)?{
????????this.domain?=?domain;
????}
????public?void?setUsername(String?username)?{
????????this.username?=?username;
????}
????public?String?toString()?{
????????return?username?+?'@'?+?domain;
????}
????public?static?Email?parse(String?email)?{
????????Email?e?=?new?Email();
????????int?at?=?email.indexOf('@');
????????if?(at?==?-1)?{
????????????throw?new?IllegalArgumentException("Invalid?email?address");
????????}
????????e.username?=?email.substring(0,?at);
????????e.domain?=?email.substring(at?+?1);
????????return?e;
????}
????@Override
????public?int?hashCode()?{
????????final?int?PRIME?=?31;
????????int?result?=?1;
????????result?=?PRIME?*?result?+?((domain?==?null)???0?:?domain.hashCode());
????????result?=?PRIME?*?result?+?((username?==?null)???0?:?username.hashCode());
????????return?result;
????}
????@Override
????public?boolean?equals(Object?obj)?{
????????if?(this?==?obj)????return?true;
??????if(null?==?obj)return?false;
????????if?(getClass()?!=?obj.getClass())
????????????return?false;
????????final?Email?other?=?(Email)?obj;
????????if?(domain?==?null)?{
????????????if?(other.domain?!=?null)
????????????????return?false;
????????}?else?if?(!domain.equals(other.domain))
????????????return?false;
????????if?(username?==?null)?{
????????????if?(other.username?!=?null)
????????????????return?false;
????????}?else?if?(!username.equals(other.username))
????????????return?false;
????????return?true;
????}
}
????email是Account類的一個屬性：
public?class?Account?extends?AbstractDomain<Long>{
????
????private?Email?email;
????public?Email?getEmail()?{
????????return?email;
????}
????public?void?setEmail(Email?email)?{
????????this.email?=?email;
????}
????//省略其他????
}
?? ?這樣的情況下，需要將email的username + '@' + domain映射到Account表的email列，定義一個EmailUserType如下：
?
???public?class?EmailUserType?implements?UserType{
????public?Object?assemble(Serializable?arg0,?Object?arg1)?throws?HibernateException?{
????????return?null;
????}
????public?Object?deepCopy(Object?o)?throws?HibernateException?{
????????if(null?==?o)return?null;
????????Email?e?=?(Email)o;
????????return?new?Email(e.getUsername(),e.getDomain());
????}
????public?Serializable?disassemble(Object?arg0)?throws?HibernateException?{
????????return?null;
????}
????public?boolean?equals(Object?x,?Object?y)?throws?HibernateException?{
????????if(x?==?y)return?true;
????????if(x?==?null?||?y?==?null)return?false;
????????boolean??f?=?x.equals(y);
????????return?f;
????}
????public?int?hashCode(Object?o)?throws?HibernateException?{
????????return?o.hashCode();
????}
????public?boolean?isMutable()?{
????????return?true;
????}
????public?Object?nullSafeGet(ResultSet?rs,?String[]?names,?Object?o)?throws?HibernateException,?SQLException?{
????????String?email?=?rs.getString(names[0]);
????????if(email?==?null)return?null;
????????int?index?=?email.indexOf("@");
????????if(index?<?0)throw?new?RuntimeException();
????????return?new?Email(email.substring(0,index),email.substring(index+1));
????}
????public?void?nullSafeSet(PreparedStatement?ps,?Object?o,?int?index)?throws?HibernateException,?SQLException?{
????????if(o?==?null?)ps.setNull(index,?Types.VARCHAR);
????????else{
????????????Email?e?=?(Email)o;
????????????if(e.getDomain()?==?null?||?e.getUsername()?==?null)ps.setNull(index,?Types.VARCHAR);
????????????else{
????????????????String?email?=?e.getUsername()?+?"@"?+?e.getDomain();
????????????????ps.setString(index,?email);
????????????}
????????}
????????
????}
????public?Object?replace(Object?arg0,?Object?arg1,?Object?arg2)?throws?HibernateException?{
????????return?null;
????}
????public?Class?returnedClass()?{
????????return?Email.class;
????}
????public?int[]?sqlTypes()?{
????????int[]?typeList?=?{Types.VARCHAR};
????????return?typeList;
????}
}
?? ?最后配置下 email 屬性：
<property name="email" type="org.prague.domain.util.EmailUserType" column="email"></property>
?? ?相比于Gedner，Email是一個可變類（如果想將其變?yōu)椴豢勺冾悾恍枰サ魧傩缘膕et方法），因此EmailUserType中的equals要用到Email的equals（hashCode()）方法，而deepCopy(Object o) 要做到是深拷貝，否則即便Email屬性內(nèi)容改變，由于Hibernate緩存中的快照指向的對象不變，在update時可能不起作用（在指定了dynamic-update屬性的清況下）。
?? ?