java - hibernate 时内存不足

Question

嗨，我在 hibernate 中创建了多对一关系。以下是相关代码。

B 表中有数千条记录，它链接到表 A 的单个记录。当我使用 getBList() 方法时，它将返回数千条记录，并且 JAVA 内存不足。那么我该如何解决这个问题。

@Entity
@Table(name = "A")
public class A {

    private int Id;
    private String aName;
    private List<MksReleaseInfo> bList;

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "id")
    public int getId() {
        return releaseId;
    }

    public void setId(final int Id) {
        this.Id = Id;
    }

    @Column(name = "aname", unique = true)
    public String getAName() {
        return aName;
    }

    public void setAName(final String aName) {
        this.aName = aName;
    }
    @OneToMany(mappedBy = "aName")
    public List<MksReleaseInfo> getBList() {
        return bList;
    }

    public void setBList(final List<B> bList) {
        this.bList = bList;
    }
}   


@Entity
@Table(name = "B")
public class B {

    private int bIndex;
    private int bpriority;
    private A aName;

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "id")
    protected int getBIndex() {
        return mksReleaseInfoIndex;
    }

    protected void setBIndex(final int bIndex) {
        this.bIndex = bIndex;
    }

    @Column(name = "priority")
    public int getBPriority() {
        return bpriority;
    }

    public void setBPriority(final int bpriority) {
        this.bpriority = bpriority;
    }

    @ManyToOne
    @JoinColumn(name = "Id")
    public A getAName() {
        return aName;
    }

    public void setAName(final A aName) {
        this.aName = aName;
    }
}

在所有评论之后我已经实现了以下代码。但它再次给出内存不足。我是否应该显式刷新内存以及如何刷新？

public List<B> getList(String name, int offset, int limit) throws DAOException {
        try {
            String hql = "from B where name = :name";
            begin();
            Query query = getSession().createQuery(hql);
            query.setString("name", name);

            if(offset > 0){
                query.setFirstResult(offset);
            }

            if(limit > 0){
                query.setMaxResults(limit);
                query.setFetchSize(limit);
            }
            commit();
            return query.list();
        } catch (HibernateException e) {
            rollback(); 
        }
    }

    public Long countB(String name) throws DAOException {
        try {
            String hql = "select count(*) from B where name = :name";
            begin();
            Query query = getSession().createQuery(hql);
            query.setString("name", name);
            commit();
            return (Long)query.uniqueResult();
        } catch (HibernateException e) {
            rollback();
        }
    }


    long count = countB(name);
    int counter = (int) (count / 200);
    if(count%200 > 0){
        counter++;
    }
    for(int j = 0;j<counter;j++){
        lists = getList(name, j*200, 200);

        for(B count1 : lists){
            System.out.println(count1);
        }
    }

Answer 1

您可以引入一个 DAO，以便以分页方式从给定 A 对象的 B 检索记录。

例如:

public interface BDao {

   Page findByA(A a, PageRequest pageRequest);

}

也许您可以从Spring Data中采取的方法中得到一些想法。