Hibernate中3种结果转换的详细说明(转)
Hibernate中3种结果转换的详细说明
在hibernate使用的过程中.我们通常需要对结果进行解释.
Hibernate为我们提供了以下3种解释方法:
Transformers.ALIAS_TO_ENTITY_MAP //把输出结果转换成map
Transformers.TO_LIST //把结果按顺序排进List
ransformers.aliasToBean(target) //把结果通过setter方法注入到指定的对像属性中
在Hibernate中Transformers的所有转换都是需要实现ResultTransformer接口
详解ALIAS_TO_ENTITY_MAP ,太简单了就是把key和值直接转换到Map当中
/** * {@inheritDoc} */ //aliases key //tuple value public Object transformTuple(Object[] tuple, String[] aliases) { Map result = new HashMap(tuple.length); for ( int i=0; i<tuple.length; i++ ) { String alias = aliases[i]; if ( alias!=null ) { result.put( alias, tuple[i] ); } } return result; }
详解TO_LIST,转换过程很简单,就是把value转换成List对像
/** * {@inheritDoc} */ //aliases key //tuple value public Object transformTuple(Object[] tuple, String[] aliases) { return Arrays.asList( tuple ); }
详解aliasToBean,转换过程就是通过读取查询后的字段.然后通过使用setter方法注入到目标对像中
public AliasToBeanResultTransformer(Class resultClass) { if ( resultClass == null ) { throw new IllegalArgumentException( "resultClass cannot be null" ); } this.resultClass = resultClass; //定义属性访问器. propertyAccessor = new ChainedPropertyAccessor( new PropertyAccessor[] { PropertyAccessorFactory.getPropertyAccessor( resultClass, null ), PropertyAccessorFactory.getPropertyAccessor( "field" ) } ); } public Object transformTuple(Object[] tuple, String[] aliases) { Object result; try { if ( setters == null ) { setters = new Setter[aliases.length]; for ( int i = 0; i < aliases.length; i++ ) { String alias = aliases[i]; if ( alias != null ) { //初始指定的setter方法 setters[i] = propertyAccessor.getSetter( resultClass, alias ); } } } //实例实体对像 result = resultClass.newInstance(); for ( int i = 0; i < aliases.length; i++ ) { if ( setters[i] != null ) { //向setter方法中指定的属性注入值 setters[i].set( result, tuple[i], null ); } } } catch ( InstantiationException e ) { throw new HibernateException( "Could not instantiate resultclass: " + resultClass.getName() ); } catch ( IllegalAccessException e ) { throw new HibernateException( "Could not instantiate resultclass: " + resultClass.getName() ); } return result; }