java - 异常没有被捕获

Question

我有一个程序，您可以在其中输入姓名、ID 并将它们导出到文本文件。可以使用 load 方法将文件导回。加载方法的问题是，如果您按下加载按钮但未选择文件，则会出现错误列表。我需要为这些错误创建异常(exception)，以便用户收到“请选择文件”警告。所以我创建了一个自定义异常:

    public class CancelException extends Exception {

    public CancelException() {
    }

    public CancelException(String message) {
        super(message);
    }

}

然后我尝试将其放入load方法中:

public static Person loadcons() throws IOException, CancelException {
    Person loadcons = null;
    try {
        JFileChooser chooser = new JFileChooser();
        int chooserOption = chooser.showSaveDialog(null);
        chooserOption = JFileChooser.APPROVE_OPTION;

        File file = new File(chooser.getSelectedFile().getAbsolutePath());
        ObjectInputStream input = new ObjectInputStream(new FileInputStream(file));

        loadcons = (Person) input.readObject();
        input.close();
        return loadcons;

    } catch (IOException ex) {
        System.out.println(ex.getMessage());
    } catch (ClassNotFoundException ex) {
        System.out.println(ex.getMessage());
    } catch (Exception ex) {
        throw new CancelException("Please select a file");
    }
    return null;

}

private String toString(String PersonID) {
    throw new UnsupportedOperationException("Not supported yet."); //To change body of generated methods, choose Tools | Templates.
}

问题是异常未被识别，并且它仍然给我异常堆栈跟踪而不是警告。

错误列表如下:

    Aug 17, 2015 12:41:50 PM ryan_assignment_sit2.CreateConsultant    jButton3ActionPerformed
   SEVERE: null
    ryan_assignment_sit2.CancelException: Please select a file
    at ryan_assignment_sit2.Person.loadcons(Person.java:105)
    at ryan_assignment_sit2.CreateConsultant.jButton3ActionPerformed(CreateConsultant.java:218)
    at ryan_assignment_sit2.CreateConsultant.access$300(CreateConsultant.java:29)
    at ryan_assignment_sit2.CreateConsultant$4.actionPerformed(CreateConsultant.java:87)
    at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2022)
    at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2346)
    at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
    at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
    at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252)
    at java.awt.Component.processMouseEvent(Component.java:6525)
    at javax.swing.JComponent.processMouseEvent(JComponent.java:3324)
    at java.awt.Component.processEvent(Component.java:6290)
    at java.awt.Container.processEvent(Container.java:2234)
    at java.awt.Component.dispatchEventImpl(Component.java:4881)
    at java.awt.Container.dispatchEventImpl(Container.java:2292)
    at java.awt.Component.dispatchEvent(Component.java:4703)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4898)
    at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4533)
    at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4462)
    at java.awt.Container.dispatchEventImpl(Container.java:2278)
    at java.awt.Window.dispatchEventImpl(Window.java:2750)
    at java.awt.Component.dispatchEvent(Component.java:4703)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:758)
    at java.awt.EventQueue.access$500(EventQueue.java:97)
    at java.awt.EventQueue$3.run(EventQueue.java:709)
    at java.awt.EventQueue$3.run(EventQueue.java:703)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:75)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:86)
    at java.awt.EventQueue$4.run(EventQueue.java:731)
    at java.awt.EventQueue$4.run(EventQueue.java:729)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:75)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:728)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)

Answer 1

您可以通过添加以下条件来检查文件是否被选择:

if (chooser.getSelectedFile() == null)
{
     JOptionPane.showMessageDialog(null, "Please select a file", "No file selected", JOptionPane.WARNING_MESSAGE);
}