java - 我使用 Hibernate 创建了一个基本的 CRUD GUI，但我得到 "index out of bound exception"。可能是什么问题呢？

Question

这是我的应用程序的 GUI，其中包含索引超出范围的错误消息:

这是搜索算法的代码:

  private void searchButtonActionPerformed(java.awt.event.ActionEvent evt) {                                             
        try {
            String name = this.searchTextField.getText();
            if (name.equals("")) {
                FillData();
            }else{
            session=sessionFactory.openSession();
            transaction = session.beginTransaction();
            Criteria criteria = session.createCriteria(Items.class);
            Items list = (Items) criteria.add(Restrictions.eq("name", name).ignoreCase()).uniqueResult();
            transaction.commit();
            session.close();
            if (list.equals(null)) {
                    JOptionPane.showMessageDialog(null, "No results");
                }else{

                if (dtm.getColumnCount()==0) {
                dtm.addColumn("Name");
                dtm.addColumn("Category");
                dtm.addColumn("Quantity");
                dtm.addColumn("Net Price (per unit)");
                dtm.addColumn("Gross Pice (per unit)");
                dtm.addColumn("Net Price (total)");
                dtm.addColumn("Gross Price (total)");
                }
                Font f = new Font("Georgia", Font.BOLD, 16);      
                JTableHeader header = itemTable.getTableHeader();
                header.setFont(f);
                itemTable.setRowHeight(25);

                for (int i = 0; i < 1; i++) {
                    dtm.addRow(new Object[]{list.getName(), list.getCategory().getName(), getQuantity().get(i).getQuantity(), list.getNetPrice(), list.getNetPrice()*(list.getVatRate()+1), getQuantity().get(i).getQuantity()*list.getNetPrice(), list.getNetPrice()*(list.getVatRate()+1)*getQuantity().get(i).getQuantity()});
                }

                this.itemTable.setModel(dtm);}}} catch (Exception e) {
             JOptionPane.showMessageDialog(null, e.getMessage()); 
             e.printStackTrace();
        }
    }     

我还尝试了一种不同的算法，其中项目列表实际上是列表列表，但我意识到我只会得到单个结果。

任何解决方案的想法都将受到高度赞赏!

我正在尝试用此类写出必要的数据。注意“尝试”这个词。

     public List<ItemAndQuantity> getQuantity()
        {
        List<ItemAndQuantity> quantity = new ArrayList<ItemAndQuantity>();       
            try {
                session = sessionFactory.openSession();
                transaction = session.beginTransaction();
//  Query query = session.createQuery("select sum(t.Flow * a.In_Or_Out), i.Item_ID from TRANSACTIONS t, and i.Item_ID = t.Item_ID group by i.Item_ID");
                Query query = session.createQuery("select sum(t.flow * a.inOrOut) from Advicenote a join a.transactions t join t.item i group by i.itemId");
                //Query query = session.createQuery("select sum(t.flow * a.inOrOut) from Advicenote a join Transactions t join Items i group by i.itemId");
                quantity.addAll(query.list());
                transaction.commit();
            } 
        catch (HibernateException e) {
            if (transaction != null) {
                transaction.rollback();
            }
        }
        finally {
             session.close();}
             return quantity;
        }

这是我的异常(exception)情况:

java.lang.IndexOutOfBoundsException: Index 0 out of bounds for length 0 Hibernate: select items0_.ITEM_ID as ITEM_ID1_2_, items0_.NAME as NAME2_2_, items0_.NET_PRICE as NET_PRIC3_2_, items0_.VAT_RATE as VAT_RATE4_2_, items0_.CATEGORY_ID as CATEGORY5_2_ from APP.ITEMS items0_ Hibernate: select categories0_.CATEGORY_ID as CATEGORY1_1_0_, categories0_.NAME as NAME2_1_0_ from APP.CATEGORIES categories0_ where categories0_.CATEGORY_ID=? Hibernate: select items0_.CATEGORY_ID as CATEGORY5_2_0_, items0_.ITEM_ID as ITEM_ID1_2_0_, items0_.ITEM_ID as ITEM_ID1_2_1_, items0_.NAME as NAME2_2_1_, items0_.NET_PRICE as NET_PRIC3_2_1_, items0_.VAT_RATE as VAT_RATE4_2_1_, items0_.CATEGORY_ID as CATEGORY5_2_1_ from APP.ITEMS items0_ where items0_.CATEGORY_ID=? Hibernate: select items0_.ITEM_ID as ITEM_ID1_2_, items0_.NAME as NAME2_2_, items0_.NET_PRICE as NET_PRIC3_2_, items0_.VAT_RATE as VAT_RATE4_2_, items0_.CATEGORY_ID as CATEGORY5_2_ from APP.ITEMS items0_ Hibernate: select categories0_.CATEGORY_ID as CATEGORY1_1_0_, categories0_.NAME as NAME2_1_0_ from APP.CATEGORIES categories0_ where categories0_.CATEGORY_ID=? at java.base/jdk.internal.util.Preconditions.outOfBounds(Preconditions.java:64) at java.base/jdk.internal.util.Preconditions.outOfBoundsCheckIndex(Preconditions.java:70) at java.base/jdk.internal.util.Preconditions.checkIndex(Preconditions.java:248) at java.base/java.util.Objects.checkIndex(Objects.java:372) at java.base/java.util.ArrayList.get(ArrayList.java:458) at stock.view.StockView.searchButtonActionPerformed(StockView.java:479) at stock.view.StockView$FormListener.actionPerformed(StockView.java:359) at java.desktop/javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1967) at java.desktop/javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2308) at java.desktop/javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:405) at java.desktop/javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:262) at java.desktop/javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:279) at java.desktop/java.awt.Component.processMouseEvent(Component.java:6632) at java.desktop/javax.swing.JComponent.processMouseEvent(JComponent.java:3342) at java.desktop/java.awt.Component.processEvent(Component.java:6397) at java.desktop/java.awt.Container.processEvent(Container.java:2263) at java.desktop/java.awt.Component.dispatchEventImpl(Component.java:5008) at java.desktop/java.awt.Container.dispatchEventImpl(Container.java:2321) at java.desktop/java.awt.Component.dispatchEvent(Component.java:4840) at java.desktop/java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4918) at java.desktop/java.awt.LightweightDispatcher.processMouseEvent(Container.java:4547) at java.desktop/java.awt.LightweightDispatcher.dispatchEvent(Container.java:4488) at java.desktop/java.awt.Container.dispatchEventImpl(Container.java:2307) at java.desktop/java.awt.Window.dispatchEventImpl(Window.java:2772) at java.desktop/java.awt.Component.dispatchEvent(Component.java:4840) at java.desktop/java.awt.EventQueue.dispatchEventImpl(EventQueue.java:772) at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:721) at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:715) Hibernate: select items0_.CATEGORY_ID as CATEGORY5_2_0_, items0_.ITEM_ID as ITEM_ID1_2_0_, items0_.ITEM_ID as ITEM_ID1_2_1_, items0_.NAME as NAME2_2_1_, items0_.NET_PRICE as NET_PRIC3_2_1_, items0_.VAT_RATE as VAT_RATE4_2_1_, items0_.CATEGORY_ID as CATEGORY5_2_1_ from APP.ITEMS items0_ where items0_.CATEGORY_ID=? at java.base/java.security.AccessController.doPrivileged(Native Method) at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:85) at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:95) at java.desktop/java.awt.EventQueue$5.run(EventQueue.java:745) at java.desktop/java.awt.EventQueue$5.run(EventQueue.java:743) at java.base/java.security.AccessController.doPrivileged(Native Method) at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:85) at java.desktop/java.awt.EventQueue.dispatchEvent(EventQueue.java:742) at java.desktop/java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:203) at java.desktop/java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:124) at java.desktop/java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:113) at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:109) at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101) at java.desktop/java.awt.EventDispatchThread.run(EventDispatchThread.java:90)

Answer 1

当您的代码尝试从空列表中获取第一个元素时，会生成该错误。

不要测试 null:list.equals(null)，而是检查是否为空:list.isEmpty()。

null 和empty 是两个不同的概念。空列表是不指向任何内容的引用。空列表是对实现包含 0 个元素的 List 的现有对象的引用。

此外，list.equals(null) 永远不会工作，如果 list 为 null，则代码将导致 NullPointerException。实例方法(如 equals)需要在一个对象上执行，不能在空引用上执行实例方法。因此，如果您想检查 null ，则必须使用 list == null 代替。

这就是为什么您会看到检查非空、非空列表的代码，如下所示:

if (list != null && !list.isEmpty()) {

因为它会检查 nullness 和emptiness。这是安全的(避免取消引用 null)，因为它首先检查非空，并且当列表为空时 && 操作会短路。

可以安全地假设您不必检查 Hibernate 返回的列表是否为空。如果返回的列表为空，那么您的代码将会失败并出现 NPE。