Question

我想在读取模式下在jTextPane中打开一个文件。但它给了一些例外...... 我该怎么办？我应该写ActionListner吗？我是java新手..所以帮帮我朋友.. 我的代码在下面给出..

try {
        // TODO add your handling code here:
        BufferedReader input=null;
        File file=new JFileChooser().getSelectedFile();
        /* Line no 524 */input = new BufferedReader(new InputStreamReader(new  FileInputStream(file)));
        jTextPane1.read(input, "READING FILE :-)");
    } catch (IOException ex) {
        Logger.getLogger(ExcelSheet.class.getName()).log(Level.SEVERE, null, ex);
    }

这些是例外

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at java.io.FileInputStream.<init>(FileInputStream.java:103)
at cvparser.ExcelSheet.jButton2ActionPerformed(ExcelSheet.java:524)
at cvparser.ExcelSheet.access$300(ExcelSheet.java:36)
at cvparser.ExcelSheet$4.actionPerformed(ExcelSheet.java:207)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1995)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2318)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:387)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:236)
at java.awt.Component.processMouseEvent(Component.java:6263)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3267)
at java.awt.Component.processEvent(Component.java:6028)
at java.awt.Container.processEvent(Container.java:2041)
at java.awt.Component.dispatchEventImpl(Component.java:4630)
at java.awt.Container.dispatchEventImpl(Container.java:2099)
at java.awt.Component.dispatchEvent(Component.java:4460)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4574)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4238)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4168)
at java.awt.Container.dispatchEventImpl(Container.java:2085)
at java.awt.Window.dispatchEventImpl(Window.java:2475)
at java.awt.Component.dispatchEvent(Component.java:4460)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:599)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)

Answer 1

这是问题所在：

File file=new JFileChooser().getSelectedFile();

您正在创建新的JFileChooser，但从未向用户显示，因此没有选定的文件。 file变量将具有空值，FileInputStream构造函数的参数不允许使用该值。

您需要向用户显示选择器然后获取所选文件...检查他们在使用之前确实选择了一个文件。有关示例，请参阅JFileChooser documentation。

Answer 2

执行此操作File file=new JFileChooser().getSelectedFile();只是创建JFileChooser的实例，并要求它传回代表所选文件的内容。但是看到没有选择任何文件，它将返回null ...

尝试更像......

JFileChooser fc = new JFileChooser();
switch (fc.showOpenDialog(null)) {
    case JFileChooser.APPROVE_OPTION:
        File file= fc.getSelectedFile();
        break;
}

请查看How to use file choosers了解详情。

更新了文件阅读示例

JFileChooser fc = new JFileChooser();
switch (fc.showOpenDialog(null)) {
    case JFileChooser.APPROVE_OPTION:
        File file= fc.getSelectedFile();
        BufferedReader br = null;
        try {
            input = new BufferedReader(new FileReader(file));
            jTextPane1.read(input, "READING FILE :-)");
        } catch (IOException exp) {
            exp.printStackTrace();
        } finally {
            try {
                br.close();
            } catch (Exception exp) {
            }
        }
        break;
}

线程“AWT-EventQueue-0”中的异常java.lang.NullPointerExceptionn

2 个答案: