JSP 中Hibernate实现映射枚举类型

2024-02-26 19:46:04 139

JSP中Hibernate实现映射枚举类型

问题：

JavaBO类Gender是枚举类型，想在数据库中存成字符串格式，如何编写hbm.xml？

publicenumGender{
UNKNOWN("Unknown"),
MALE("Male"),
FEMALE("Female");

privateStringkey;
privateGender(finalStringkey){
this.key=key;
}
publicgetGender(Stringkey){
for(Gendergender:Gender.values()){
if(key.euqals(gender.getKey()))
returngender;
}
thrownewNoSuchElementException(key);
}
}

使用UserType：

publicclassGenderUserTypeimplementsUserType{

privatestaticint[]typeList={Types.VARCHAR};

/*
*ReturntheSQLtypecodesforthecolumnsmappedbythistype.
*Thecodesaredefinedonjava.sql.Types.*/
/**设置和Gender类的sex属性对应的字段的SQL类型*/
publicint[]sqlTypes(){
returntypeList;
}

/*TheclassreturnedbynullSafeGet().*/
/**设置GenderUserType所映射的Java类：Gender类*/
publicClassreturnedClass(){
returnGender.class;
}

/**指明Gender类是不可变类*/
publicbooleanisMutable(){
returnfalse;
}

/*
*Returnadeepcopyofthepersistentstate,stoppingatentitiesandat
*collections.Itisnotnecessarytocopyimmutableobjects,ornull
*values,inwhichcaseitissafetosimplyreturntheargument.
*/
/**返回Gender对象的快照，由于Gender类是不可变类，因此直接将参数代表的Gender对象返回*/
publicObjectdeepCopy(Objectvalue){
return(Gender)value;
}

/**比较一个Gender对象是否和它的快照相同*/
publicbooleanequals(Objectx,Objecty){
//由于内存中只可能有两个静态常量Gender实例，
//因此可以直接按内存地址比较
return(x==y);
}
publicinthashCode(Objectx){
returnx.hashCode();
}

/*
*RetrieveaninstanceofthemappedclassfromaJDBCresultset.Implementors
*shouldhandlepossibilityofnullvalues.
*/
/**从JDBCResultSet中读取key，然后返回相应的Gender实例*/
publicObjectnullSafeGet(ResultSetrs,String[]names,Objectowner)
throwsHibernateException,SQLException{
//从ResultSet中读取key
Stringsex=(String)Hibernate.STRING.nullSafeGet(rs,names[0]);
if(sex==null){returnnull;}
//按照性别查找匹配的Gender实例
try{
returnGender.getGender(sex);
}catch(java.util.NoSuchElementExceptione){
thrownewHibernateException("BadGendervalue:"+sex,e);
}
}

/*
*Writeaninstanceofthemappedclasstoapreparedstatement.Implementors
*shouldhandlepossibilityofnullvalues.
*Amulti-columntypeshouldbewrittentoparametersstartingfromindex.
*/
/**把Gender对象的key属性添加到JDBCPreparedStatement中*/
publicvoidnullSafeSet(PreparedStatementst,Objectvalue,intindex)
throwsHibernateException,SQLException{
Stringsex=null;
if(value!=null)
sex=((Gender)value).getKey();
Hibernate.String.nullSafeSet(st,sex,index);
}

/*
*Reconstructanobjectfromthecacheablerepresentation.Attheveryleastthis
*methodshouldperformadeepcopyifthetypeismutable.(optionaloperation)
*/
publicObjectassemble(Serializablecached,Objectowner){
returncached;
}

/*
*Transformtheobjectintoitscacheablerepresentation.Attheveryleastthis
*methodshouldperformadeepcopyifthetypeismutable.Thatmaynotbeenough
*forsomeimplementations,however;forexample,associationsmustbecachedas
*identifiervalues.(optionaloperation)
*/
publicSerializabledisassemble(Objectvalue){
return(Serializable)value;
}

/*
*Duringmerge,replacetheexisting(target)valueintheentitywearemergingto
*withanew(original)valuefromthedetachedentitywearemerging.Forimmutable
*objects,ornullvalues,itissafetosimplyreturnthefirstparameter.For
*mutableobjects,itissafetoreturnacopyofthefirstparameter.Forobjects
*withcomponentvalues,itmightmakesensetorecursivelyreplacecomponentvalues.
*/
publicObjectreplace(Objectoriginal,Objecttarget,Objectowner){
returnoriginal;
}
}

然后再hbm.xml中定义映射关系：

延伸：

为每个枚举类型定义一个UserType是比较麻烦的，可以定义一个抽象类。

例如扩展下例即可适用于所有保存为index的枚举类型

publicabstractclassOrdinalEnumUserType>implementsUserType{

protectedClassclazz;

protectedOrdinalEnumUserType(Classclazz){
this.clazz=clazz;
}

privatestaticfinalint[]SQL_TYPES={Types.NUMERIC};
publicint[]sqlTypes(){
returnSQL_TYPES;
}

publicClassreturnedClass(){
returnclazz;
}

publicEnullSafeGet(ResultSetresultSet,String[]names,Objectowner)
throwsHibernateException,SQLException{

//Hibernate.STRING.nullSafeGet(rs,names[0])
intindex=resultSet.getInt(names[0]);
Eresult=null;
if(!resultSet.wasNull()){
result=clazz.getEnumConstants()[index];
}
returnresult;
}

publicvoidnullSafeSet(PreparedStatementpreparedStatement,
Objectvalue,intindex)throwsHibernateException,SQLException{
if(null==value){
preparedStatement.setNull(index,Types.NUMERIC);
}else{
//Hibernate.String.nullSafeSet(st,sex,index);
preparedStatement.setInt(index,((E)value).ordinal());
}
}

publicObjectdeepCopy(Objectvalue)throwsHibernateException{
returnvalue;
}

publicbooleanisMutable(){
returnfalse;
}

publicObjectassemble(Serializablecached,Objectowner)
throwsHibernateException{
returncached;
}

publicSerializabledisassemble(Objectvalue)throwsHibernateException{
return(Serializable)value;
}

publicObjectreplace(Objectoriginal,Objecttarget,Objectowner)
throwsHibernateException{
returnoriginal;
}
publicinthashCode(Objectx)throwsHibernateException{
returnx.hashCode();
}
publicbooleanequals(Objectx,Objecty)throwsHibernateException{
if(x==y)
returntrue;
if(null==x||null==y)
returnfalse;
returnx.equals(y);
}
}

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JSP 中Hibernate实现映射枚举类型

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