java - 修改 .csv 文件数据 JAVA 时遇到问题

Question

我在使用 Java AddressBook 时遇到问题，我正在尝试编辑和更新 .csv 文件中存储的一行数据中的值

我尝试运行代码并检查逻辑错误，但似乎无法找到引发 try catch 异常的原因。这确实在某一时刻起作用，但无法弄清楚是什么改变了它停止工作

    private class ammendActionListener implements ActionListener {

        public ammendActionListener() {
        }

        @Override
        public void actionPerformed(ActionEvent arg0) {
           String filePath = "Personal.csv";
           String editTerm = id.getText();
           String newID = id.getText();
           String newFName = fn.getText();
           String newLName = ln.getText();
           String newAddr = addr.getText(); 
           String newAddr2 = addr2.getText();
           String newPost = post.getText();
           String newCont = cont.getText();

           editRecord(filePath, editTerm, newID, newFName, newLName, newAddr, newAddr2, newPost, newCont);
        }
    }
    private Scanner x; 
    public void editRecord(String filePath, String editTerm, String newID, String newFName, String newLName, String newAddr, String newAddr2, String newPost, String newCont){
        String tempFile = "temp.csv"; 
        File oldFile = new File(filePath);
        File newFile = new File(tempFile);
        String ID = ""; String first = ""; String last = ""; String addr =""; String addr2=""; String post = ""; String cont = ""; 
        try{
            FileWriter fw = new FileWriter(tempFile, true);
            BufferedWriter bw = new BufferedWriter(fw);
            PrintWriter pw = new PrintWriter(bw);
            x = new Scanner(new File(filePath));
            x.useDelimiter("[,\n]");

            while(x.hasNext()){
                ID = x.next();
                first = x.next();
                last = x.next();
                addr = x.next();
                addr2 = x.next();
                post = x.next();
                cont = x.next();

                if(ID.equals(editTerm)){
                    pw.println(newID+","+newFName+","+newLName+","+newAddr+","+newAddr2+","+newPost+","+newCont);
                }else{
                    pw.println(ID+","+first+","+last+","+addr+","+addr2+","+post+","+cont);
                }
            }
            x.close();
            pw.flush();
            pw.close();
            oldFile.delete();
            File dump = new File(filePath);
            newFile.renameTo(dump);

        }catch(Exception e){
            JOptionPane.showMessageDialog(null, "ERROR");
        }

    }

}

我希望文件通过识别 ID 列重写和重命名 temp.csv 文件并删除原始 Presonal.csv 和更新的行来修改适当的数据。执行没有错误

<小时/>

取得成功

总时间:36.814 秒结束于:2019-07-15T11:07:47+01:00

最终内存:13M/47M

更新错误

java.util.NoSuchElementException
at java.base/java.util.Scanner.throwFor(Scanner.java:937)
at java.base/java.util.Scanner.next(Scanner.java:1478)
at com.mycompany.ppaddressbook.ammContact.editRecord(ammContact.java:174)
at
  com.mycompany.ppaddressbook.ammContact$ammendActionListener.actionPerformed(ammContact.java:154)
at java.desktop/javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1967)
at java.desktop/javax.swing.AbstractButton$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:2762)
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$4.run(EventQueue.java:715)
at java.base/java.security.AccessController.doPrivileged(AccessController.java:389)
at java.base/java.security.ProtectionDomain$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$5.run(EventQueue.java:743)
at java.base/java.security.AccessController.doPrivileged(AccessController.java:389)
at java.base/java.security.ProtectionDomain$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

我猜问题出在File#renameTo()。根据 Javadoc，此方法严重依赖平台库。

Many aspects of the behavior of this method are inherently platform-dependent: The rename operation might not be able to move a file from one filesystem to another, it might not be atomic, and it might not succeed if a file with the destination abstract pathname already exists. The return value should always be checked to make sure that the rename operation was successful.

您的代码可以在我的环境中运行，但要使其保存以在任何平台上使用，您应该使用 NIO-Library(新 IO)。这是一个快速代码，应该可以完成您想要做的事情。请注意，您不需要刷新或关闭读取器/写入器，因为 try-with-resources 会为您完成这些操作。

public class Test {
    public static void main(String[] args) {
        Test test = new Test();
        test.editRecord("C:/temp/test.csv", "2", "2", "foobar", "baz");
    }

    public void editRecord(String filePath, String editTerm, String newID, String newFName, String newLName){
        String tempFile = "temp.csv"; 
        Path oldPath = Paths.get(filePath);
        Path newPath = Paths.get(tempFile);
        
        try(BufferedReader reader = Files.newBufferedReader(oldPath); BufferedWriter writer = Files.newBufferedWriter(newPath)) {
            String read;
            while( (read = reader.readLine()) != null ) {
                String[] line = read.split(",");
                if(line[0].equals(editTerm)) {
                    line[0] = newID;
                    line[1] = newFName;
                    line[2] = newLName;
                }
                
                writer.append(String.join(",", line));
                writer.newLine();
            }
        } catch (IOException e) {
            JOptionPane.showMessageDialog(null, e.getMessage());
        }
        
        try {
            Files.move(newPath, oldPath, StandardCopyOption.REPLACE_EXISTING);
        } catch (IOException e) {
            JOptionPane.showMessageDialog(null, e.getMessage());
        }

    }

}

编辑:

考虑使用 Files.createTempFile("temp", ".csv"); 作为临时文件。

由于抛出 IOException 的可能性有很多，因此将 throws 添加到 editRecord(...) 中也许会更好。您可以捕获异常并将其显示在调用者上。