前言

在上文Hibernate使用中曾经提到过Hibernate是JPA实现的一个超集，但当时使用的都是原生Hibernate，在本文中我们将拥抱JPA规范，重构持久化层。

JPA+HIbernate配置

下面是ApplicationContxt文件

XML
            
             
             
                 
              
             
                 
                      
       
        update
                       
       
        org.hibernate.dialect.MySQLDialect
                       
       
        true
                   
              
         
        
            
         
        
        
              
              
          
    

JPA动态查询

javaCriteriaBuilder cb=entityManager.getCriteriaBuilder();CriteriaQuery
    
      query=cb.createQuery(clazz);//clazz是你想要转换的类型，就是你的Entity.claa，如果你查的是count,就是Long.claaRoot
     
       root=query.from(clazz);query.select(root);//选取实体//选择的条件List
      
        predicates=new ArrayList
       
        ();predicates.add(cb.equal(..));predicates.add(..);...query.where(cb.and(predicates.toArray(new Predicate[predicates.size()])));
       
      
     
    

上面通过数组来组合与条件，还有一种方式：

javaPredicate predicate=cb.conjunction();//交集predicate=cb.and(predicate,cb.equal(root.get("sex"),condition.get("sex")));Predicate predicate=cb.disjunction();//并集predicate=cb.or(predicate,cb.equal(root.get("sex"),condition.get("sex")));

JPA里面对类型控制比较严格，如下所示：

java//比较大小cb.gt(root.
    
     get("degree"),(Integer) condition.get("degree"));//likecb.like(root.get("user").
     
       get("nickName"),keyword)//in 条件root.get("tags").in(condition.get("tag"))
     
    

对于关联映射，如果是ToOne，你可以连写get

root.get("user").get("account");

对于ToMany的，你可以使用Join

javaCriteriaQuery
    
      criteria = cb.createQuery((Class
     
      ) Parent.class);Root
      
        parent = criteria.from(Parent.class);criteria.select((Selection
       
        ) parent);SetJoin
        
          children = parent.joinSet("children", JoinType.LEFT);Predicate sexPredicate = cb.equal(children.get("sex"), "MALE");parent.fetch(children);//parent.fetch("children");//try also thiscriteria.where(sexPredicate);
        
       
      
     
    

JPA分页

取分页内容

javaTypedQuery
    
      typedQuery=entityManager.createQuery(query);typedQuery.setFirstResult((pageNum-1)*PAGE_SIZE);typedQuery.setMaxResults(PAGE_SIZE);
    

取查询数目

javaCriteriaBuilder cb=entityManager.getCriteriaBuilder();CriteriaQuery
    
      query=cb.createQuery(Long.class);query.select(cb.count(query.from(clazz)));//选取实体return entityManager.createQuery(query).getSingleResult();
    

JPA 动态更新

javaCriteriaBuilder cb=entityManager.getCriteriaBuilder();CriteriaUpdate
    
      op=cb.createCriteriaUpdate(clazz);Root
     
       root=op.from(clazz);op.set(fieldName, value);op.where(cb.equal(root.get(keyName), delta.get(keyName)));entityManager.createQuery(op).executeUpdate();
     
    

JPQL

JPA的JPQL语句和Hibernate的HQL语句十分类似

javaQuery query=entityManager.createQuery("SELECT r FROM Resume r WHERE r.user.id=:userId");query.setParameter("id", userId);return (Resume) query.getSingleResult();

JPA CRUD

javapublic interface GenericDAO
    
      {    public void insert(T t);    public void update(T t);    public void simpleUpdate(Map
     
       delta);    public void delete(T t);    public T load(Long id);    public void refresh(T t);    public List
      
        list(int pageNum);    public Long count();    public List
       
         findByCondition(Map
        
          condition);    public Long countByCondition(Map
         
           condition);}@SuppressWarnings("unchecked")public class GenericDAOImpl
          
            implements GenericDAO
           
             { private Class
            
              clazz; @PersistenceContext protected EntityManager entityManager; protected Session getCurrentSession() { return entityManager.unwrap(Session.class); } public GenericDAOImpl(){ //取得T的类型变量 ParameterizedType type = (ParameterizedType) this.getClass().getGenericSuperclass(); clazz = (Class
             
              ) type.getActualTypeArguments()[0]; } public void insert(T t) { entityManager.persist(t); } public void update(T t) { entityManager.merge(t); } public void simpleUpdate(Map
              
                delta) { Field[] fields=clazz.getDeclaredFields(); CriteriaBuilder cb=entityManager.getCriteriaBuilder(); CriteriaUpdate
               
                 op=cb.createCriteriaUpdate(clazz); Root
                
                  root=op.from(clazz); String keyName="id";//默认选择基准为Id //调整选择域 if(delta.containsKey("keyName")) keyName=(String) delta.get("keyName"); for(Field field:fields){ String fieldName=field.getName(); if(fieldName==keyName) continue; if(delta.containsKey(fieldName)){ op.set(fieldName, delta.get(fieldName)); } } op.where(cb.equal(root.get(keyName), delta.get(keyName))); entityManager.createQuery(op).executeUpdate(); } public void delete(T t) { entityManager.remove(t); } public T load(Long id) { return (T) entityManager.find(clazz, id); } public List
                 
                   list(int pageNum) { CriteriaBuilder cb=entityManager.getCriteriaBuilder(); CriteriaQuery
                  
                    query=cb.createQuery(clazz); Root
                   
                     root=query.from(clazz); query.select(root);//选取实体 query.orderBy(cb.desc(root.get("created")));//排序 TypedQuery
                    
                      typedQuery=entityManager.createQuery(query); if(pageNum>0){ typedQuery.setFirstResult((pageNum-1)*SbeatConfig.PAGE_SIZE); typedQuery.setMaxResults(SbeatConfig.PAGE_SIZE); } return typedQuery.getResultList(); } public void refresh(T t) { entityManager.refresh(t); } public Long count() { //返回数目 CriteriaBuilder cb=entityManager.getCriteriaBuilder(); CriteriaQuery
                     
                       query=cb.createQuery(Long.class); query.select(cb.count(query.from(clazz)));//选取实体 return entityManager.createQuery(query).getSingleResult(); } public List
                      
                        findByCondition( Map
                       
                         condition) { Field[] fields=clazz.getDeclaredFields(); CriteriaBuilder cb=entityManager.getCriteriaBuilder(); CriteriaQuery
                        
                          query=cb.createQuery(clazz); Root
                         
                           root=query.from(clazz); query.select(root);//选取实体 //选择的条件 List
                          
                            predicates=new ArrayList
                           
                            (); for(Field field:fields){ String fieldName=field.getName(); if(condition.containsKey(fieldName)){ predicates.add(cb.equal(root.get(fieldName), condition.get(fieldName))); } } query.where(cb.and(predicates.toArray(new Predicate[predicates.size()]))); query.orderBy(cb.desc(root.get("created"))); TypedQuery
                            
                              typedQuery=entityManager.createQuery(query); Integer pageNum=0; if(condition.containsKey(pageNum)){ pageNum=(Integer) condition.get("pageNum"); } if(pageNum>0){ typedQuery.setFirstResult((pageNum-1)*SbeatConfig.PAGE_SIZE); typedQuery.setMaxResults(SbeatConfig.PAGE_SIZE); } return typedQuery.getResultList(); } public Long countByCondition(Map
                             
                               condition) { Field[] fields=clazz.getDeclaredFields(); CriteriaBuilder cb=entityManager.getCriteriaBuilder(); CriteriaQuery
                              
                                query=cb.createQuery(Long.class); Root
                               
                                 root=query.from(clazz); query.select(cb.count(root));//选取实体 List
                                
                                  predicates=new ArrayList
                                 
                                  (); for(Field field:fields){ String fieldName=field.getName(); if(condition.containsKey(fieldName)){ predicates.add(cb.equal(root.get(fieldName), condition.get(fieldName))); } } query.where(cb.and(predicates.toArray(new Predicate[predicates.size()]))); return entityManager.createQuery(query).getSingleResult(); }}