java之SpringMVC+Hibernate :criteria. list() 返回空

Spring :版本 3.2.9 hibernate :版本 4.2.19

BaseDaoImpl.java

public class BaseDaoImpl<T> implements BaseDao<T> { 
 
    public SessionFactory sessionFactory; 
    protected Class<T> entityClass; 
 
    @Override 
    public SessionFactory getSessionFactory() { 
        return sessionFactory; 
    } 
 
    public Session getSession(){ 
        return sessionFactory.getCurrentSession(); 
    } 
 
    @SuppressWarnings({ "unchecked", "rawtypes" }) 
    public BaseDaoImpl() { 
        Class c = getClass(); 
        Type type = c.getGenericSuperclass(); 
        if (type instanceof ParameterizedType) { 
            Type[] parameterizedType = ((ParameterizedType) type).getActualTypeArguments(); 
            this.entityClass = (Class<T>) parameterizedType[0]; 
        } 
    } 
 
    @Resource(name="sessionFactory") 
    public void setSessionFactory(SessionFactory sessionFactory) { 
        this.sessionFactory = sessionFactory; 
    } 
 
 
    @Override 
    public boolean save(T entity) { 
        try { 
            getSession().save(entity); 
            return true; 
        } catch (Exception e) { 
            e.printStackTrace(); 
            return false; 
        } 
 
    } 
 
    @Override 
    public boolean delete(T entity) { 
        try { 
            getSession().delete(entity); 
            return true; 
        } catch (Exception e) { 
 
            e.printStackTrace(); 
            return false; 
        } 
 
    } 
 
    @Override 
    public boolean update(T entity) { 
 
        try { 
            getSession().update(entity); 
            return true; 
        } catch (Exception e) { 
            e.printStackTrace(); 
            return false; 
        } 
 
    } 
 
    @SuppressWarnings("unchecked") 
    @Override 
    public T get(Integer id) { 
        return (T) getSession().get(entityClass, id); 
    } 
 
    @SuppressWarnings("unchecked") 
    @Override 
    public List<T> findByIdSet(Integer[] ids) { 
        Criteria criteria=getSession().createCriteria(entityClass); 
        criteria.add(Restrictions.in("id", ids));        
        return (List<T>)criteria.list(); 
    } 
 
    @SuppressWarnings("unchecked") 
    @Override 
    public List<T> findAllList() { 
 
        return getSession().createCriteria(entityClass).list(); 
    } 
 
    @SuppressWarnings("unchecked") 
    @Override 
    public Pager findByPager(Pager pager) { 
        Criteria criteria=getSession().createCriteria(entityClass); 
 
 
        criteria.setProjection(Projections.rowCount()); 
        int totalCount = ((Long) criteria.uniqueResult()).intValue(); 
        pager.setTotalCount(totalCount); 
 
        criteria.setProjection(null); 
 
        pager.init(); 
 
 
        criteria.setFirstResult((pager.getPageIndex()-1)*pager.getPageSize());  
        criteria.setMaxResults(pager.getPageSize());     
        List<T> te =(List<T>)criteria.list(); 
        pager.setDatas((List<T>)criteria.list()); 
        return pager; 
    } 
 
 
} 

寻呼机

import java.util.List; 
    public class Pager { 
 
 
        private int pageSize; 
 
        private int pageIndex; 
 
        private int totalCount; 
 
        private int totalPage; 
 
        private List<?> datas; 
 
        private boolean hasNextPage; 
 
        private boolean hasPreviousPage; 
 
        public void init(){ 
            pageIndex=1; 
 
        } 
 
        public int getPageSize() { 
            return pageSize; 
        } 
 
        public void setPageSize(int pageSize) { 
            this.pageSize = pageSize; 
        } 
 
        public int getPageIndex() { 
            return pageIndex; 
        } 
 
        public void setPageIndex(int pageIndex) { 
            this.pageIndex = pageIndex; 
        } 
 
        public int getTotalCount() { 
            return totalCount; 
        } 
 
        public void setTotalCount(int totalCount) { 
            this.totalCount = totalCount; 
        } 
 
        public int getTotalPage() { 
            return totalPage; 
        } 
 
        public void setTotalPage(int totalPage) { 
            this.totalPage = totalPage; 
        } 
 
        public List<?> getDatas() { 
            return datas; 
        } 
 
        public void setDatas(List<?> datas) { 
            this.datas = datas; 
        } 
 
        public boolean isHasNextPage() { 
            return hasNextPage; 
        } 
 
        public void setHasNextPage(boolean hasNextPage) { 
            this.hasNextPage = hasNextPage; 
        } 
 
        public boolean isHasPreviousPage() { 
            return hasPreviousPage; 
        } 
 
        public void setHasPreviousPage(boolean hasPreviousPage) { 
            this.hasPreviousPage = hasPreviousPage; 
        } 
 
 
    } 

实体:Student.java

import java.util.Date; 
 
import javax.persistence.Column; 
import javax.persistence.Entity; 
import javax.persistence.GeneratedValue; 
import javax.persistence.GenerationType; 
import javax.persistence.Id; 
import javax.persistence.JoinColumn; 
import javax.persistence.ManyToOne; 
import javax.persistence.Table; 
import javax.persistence.Temporal; 
import javax.persistence.TemporalType; 
 
 
@Entity 
@Table(name="student") 
public class Student { 
 
    private int stu_id; 
    private String stu_name; 
    private String stu_password; 
    private Department department; 
    private Major major; 
    private String stu_sex; 
    private String stu_per_sig; 
    private String stu_head_img; 
    private Date stu_regist_time; 
    private String stu_attn_crs_ids; 
    private String stu_pw_question; 
    private String stu_pw_answer; 
 
 
    public Student() { 
 
    } 
 
    public Student(int stu_id, String stu_name, String stu_password, 
            Department department, Major major, String stu_sex, 
            String stu_per_sig, String stu_head_img, Date stu_regist_time, 
            String stu_attn_crs_ids, String stu_pw_question, 
            String stu_pw_answer) { 
        this.stu_id = stu_id; 
        this.stu_name = stu_name; 
        this.stu_password = stu_password; 
        this.department = department; 
        this.major = major; 
        this.stu_sex = stu_sex; 
        this.stu_per_sig = stu_per_sig; 
        this.stu_head_img = stu_head_img; 
        this.stu_regist_time = stu_regist_time; 
        this.stu_attn_crs_ids = stu_attn_crs_ids; 
        this.stu_pw_question = stu_pw_question; 
        this.stu_pw_answer = stu_pw_answer; 
    } 
 
 
    @Id 
    @GeneratedValue(strategy=GenerationType.AUTO) 
    public int getStu_id() { 
        return stu_id; 
    } 
    public void setStu_id(int stu_id) { 
        this.stu_id = stu_id; 
    } 
 
    @Column(length=20,nullable=false) 
    public String getStu_name() { 
        return stu_name; 
    } 
    public void setStu_name(String stu_name) { 
        this.stu_name = stu_name; 
    } 
 
    @Column(length=20,nullable=false) 
    public String getStu_password() { 
        return stu_password; 
    } 
    public void setStu_password(String stu_password) { 
        this.stu_password = stu_password; 
    } 
 
 
    @Column(length=2,nullable=false) 
    public String getStu_sex() { 
        return stu_sex; 
    } 
    public void setStu_sex(String stu_sex) { 
        this.stu_sex = stu_sex; 
    } 
 
    @Column(length=255,nullable=true) 
    public String getStu_per_sig() { 
        return stu_per_sig; 
    } 
    public void setStu_per_sig(String stu_per_sig) { 
        this.stu_per_sig = stu_per_sig; 
    } 
 
    @Column(length=255,nullable=false) 
    public String getStu_head_img() { 
        return stu_head_img; 
    } 
    public void setStu_head_img(String stu_head_img) { 
        this.stu_head_img = stu_head_img; 
    } 
 
    @Temporal(value=TemporalType.TIMESTAMP) 
    @Column(nullable=false) 
    public Date getStu_regist_time() { 
        return stu_regist_time; 
    } 
    public void setStu_regist_time(Date stu_regist_time) { 
        this.stu_regist_time = stu_regist_time; 
    } 
 
    @Column(length=255,nullable=true) 
    public String getStu_attn_crs_ids() { 
        return stu_attn_crs_ids; 
    } 
    public void setStu_attn_crs_ids(String stu_attn_crs_ids) { 
        this.stu_attn_crs_ids = stu_attn_crs_ids; 
    } 
 
    @Column(length=64,nullable=false) 
    public String getStu_pw_question() { 
        return stu_pw_question; 
    } 
    public void setStu_pw_question(String stu_pw_question) { 
        this.stu_pw_question = stu_pw_question; 
    } 
 
    @Column(length=64,nullable=false) 
    public String getStu_pw_answer() { 
        return stu_pw_answer; 
    } 
    public void setStu_pw_answer(String stu_pw_answer) { 
        this.stu_pw_answer = stu_pw_answer; 
    } 
 
 
    @ManyToOne() 
    @JoinColumn(name="stu_dept_id",nullable=false) 
    public Department getDepartment() { 
        return department; 
    } 
 
    public void setDepartment(Department department) { 
        this.department = department; 
    } 
 
    @ManyToOne() 
    @JoinColumn(name="stu_major_id",nullable=false) 
    public Major getMajor() { 
        return major; 
    } 
 
    public void setMajor(Major major) { 
        this.major = major; 
    } 
 
} 

我写 BaseDaoImpl.java实现interface BaseDao.java

当我调试项目时，我发现 te 的大小list是 0 。

在findByPager BaseDaoImpl.java的方法| . 为什么方法criteria.list()返回一个空的 list ？ 为什么不是 List<Student> list ?
困惑了我很久，我是新人，谁能帮我解决这个问题。

请您参考如下方法:

你的代码的问题是这一行:

Criteria criteria=getSession().createCriteria(entityClass); 

因为当您使用标准查询时，您是在针对特定持久类的引用构建查询，而您的变量 entityClass 不是。

protected Class<T> entityClass; 

构建条件查询的正确方法是:

Criteria criteria=getSession().createCriteria(Entity.class); 

然后您需要更改该行代码。您需要将 .class 添加到您的变量中:

   Criteria criteria=getSession().createCriteria(entityClass.class); 

我与您分享一些有关条件查询的链接。

https://docs.jboss.org/hibernate/orm/3.5/api/org/hibernate/Criteria.html

https://docs.jboss.org/hibernate/orm/3.3/reference/en/html/querycriteria.html

希望这些信息对您有所帮助。

祝你好运。