JSP 中Hibernate实现映射枚举类型
问题：
Java BO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？
public enum Gender{ UNKNOWN("Unknown"), MALE("Male"), FEMALE("Female"); private String key; private Gender(final String key) { this.key = key; } public getGender(String key) { for (Gender gender : Gender.values()) { if (key.euqals(gender.getKey())) return gender; } throw new NoSuchElementException(key); } }
使用UserType：
public class GenderUserType implements UserType { private static int[] typeList = { Types.VARCHAR}; /* * Return the SQL type codes for the columns mapped by this type. * The codes are defined on <tt>java.sql.Types</tt>. */ /**设置和Gender类的sex属性对应的字段的SQL类型 */ public int[] sqlTypes() { return typeList; } /*The class returned by <tt>nullSafeGet()</tt>.*/ /** 设置GenderUserType所映射的Java类：Gender类 */ public Class returnedClass() { return Gender.class; } /** 指明Gender类是不可变类 */ public boolean isMutable() { return false; } /* * Return a deep copy of the persistent state, stopping at entities and at * collections. It is not necessary to copy immutable objects, or null * values, in which case it is safe to simply return the argument. */ /** 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 */ public Object deepCopy(Object value) { return (Gender)value; } /** 比较一个Gender对象是否和它的快照相同 */ public boolean equals(Object x, Object y) { //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); } public int hashCode(Object x){ return x.hashCode(); } /* * Retrieve an instance of the mapped class from a JDBC resultset. Implementors * should handle possibility of null values. */ /** 从JDBC ResultSet中读取key，然后返回相应的Gender实例 */ public Object nullSafeGet(ResultSet rs, String[] names, Object owner) throws HibernateException, SQLException{ //从ResultSet中读取key String sex = (String) Hibernate.STRING.nullSafeGet(rs, names[0]); if (sex == null) { return null; } //按照性别查找匹配的Gender实例 try { return Gender.getGender(sex); }catch (java.util.NoSuchElementException e) { throw new HibernateException("Bad Gender value: " + sex, e); } } /* * Write an instance of the mapped class to a prepared statement. Implementors * should handle possibility of null values. * A multi-column type should be written to parameters starting from <tt>index</tt>. */ /** 把Gender对象的key属性添加到JDBC PreparedStatement中 */ public void nullSafeSet(PreparedStatement st, Object value, int index) throws HibernateException, SQLException{ String sex = null; if (value != null) sex = ((Gender)value).getKey(); Hibernate.String.nullSafeSet(st, sex, index); } /* * Reconstruct an object from the cacheable representation. At the very least this * method should perform a deep copy if the type is mutable. (optional operation) */ public Object assemble(Serializable cached, Object owner){ return cached; } /* * Transform the object into its cacheable representation. At the very least this * method should perform a deep copy if the type is mutable. That may not be enough * for some implementations, however; for example, associations must be cached as * identifier values. (optional operation) */ public Serializable disassemble(Object value) { return (Serializable)value; } /* * During merge, replace the existing (target) value in the entity we are merging to * with a new (original) value from the detached entity we are merging. For immutable * objects, or null values, it is safe to simply return the first parameter. For * mutable objects, it is safe to return a copy of the first parameter. For objects * with component values, it might make sense to recursively replace component values. */ public Object replace(Object original, Object target, Object owner){ return original; } }
然后再hbm.xml中定义映射关系：
<hibernate-mapping package="" default-lazy="true" default-cascade="save-update,merge,persist"> <typedef> <property type="Gender"> <column not-null="true"> </column> </property>
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
public abstract class OrdinalEnumUserType<E extends Enum<E>> implements UserType { protected Class<E> clazz; protected OrdinalEnumUserType(Class<E> clazz) { this.clazz = clazz; } private static final int[] SQL_TYPES = {Types.NUMERIC}; public int[] sqlTypes() { return SQL_TYPES; } public Class<?> returnedClass() { return clazz; } public E nullSafeGet(ResultSet resultSet, String[] names, Object owner) throws HibernateException, SQLException { //Hibernate.STRING.nullSafeGet(rs, names[0]) int index = resultSet.getInt(names[0]); E result = null; if (!resultSet.wasNull()) { result = clazz.getEnumConstants()[index]; } return result; } public void nullSafeSet(PreparedStatement preparedStatement, Object value,int index) throws HibernateException, SQLException { if (null == value) { preparedStatement.setNull(index, Types.NUMERIC); } else { //Hibernate.String.nullSafeSet(st, sex, index); preparedStatement.setInt(index, ((E)value).ordinal()); } } public Object deepCopy(Object value) throws HibernateException{ return value; } public boolean isMutable() { return false; } public Object assemble(Serializable cached, Object owner) throws HibernateException { return cached; } public Serializable disassemble(Object value) throws HibernateException { return (Serializable)value; } public Object replace(Object original, Object target, Object owner) throws HibernateException { return original; } public int hashCode(Object x) throws HibernateException { return x.hashCode(); } public boolean equals(Object x, Object y) throws HibernateException { if (x == y) return true; if (null == x || null == y) return false; return x.equals(y); } }