使用 PrintStream 附加到文本文件 [英] Append to text file using PrintStream

问题描述

我无法将文本附加到文本文件中，它只会覆盖之前的文本.我的代码:

I cant append text to a text file, it only overwrites the previous text. My code:

//using JFileChooser to select where to save file
PrintStream outputStream = MyFrame.ShowSaveDialog();
    if(outputStream!=null){
        outputStream.append(input);
        outputStream.close();
    } 

ShowSaveDialog 返回一个 PrintStream.这是该方法的代码:

Edited: The ShowSaveDialog returns a PrintStream. Here is the code for that method:

public static PrintStream ShowSaveDialog(){
    JFileChooser chooser = new JFileChooser();
    FileNameExtensionFilter filter = new FileNameExtensionFilter(
            "Tekst filer", "txt");
    chooser.setFileFilter(filter);

    int returnVal = chooser.showSaveDialog(null);
    try{
        if(returnVal == JFileChooser.APPROVE_OPTION){

            return new PrintStream(chooser.getSelectedFile());              
        }
        else{
            return null;
        } 
    }
    catch(FileNotFoundException e){
        JOptionPane.showMessageDialog(null, "Ugyldig Fil!",
                   "error", JOptionPane.ERROR_MESSAGE);
    }
    return null;

}

推荐答案

MyFrame.ShowSaveDialog(); 返回什么?关键是使用适当的构造函数创建一个 FileOutputStream(第二个参数应该是布尔值 true)，这将使它成为一个附加的 FileOutputStream，然后使用这个 FileOutputStream 对象构造你的 PrintStream.

What does MyFrame.ShowSaveDialog(); return? The key is to create a FileOutputStream with the appropriate constructor (the second parameter should be the boolean true) which will make it an appending FileOutputStream, and then construct your PrintStream using this FileOutputStream object.

例如，如果 showSaveDialog()(注意方法和变量名称应以小写字母开头)返回文件或 File 对象的名称，您可以执行以下操作:

For instance, if showSaveDialog() (note that method and variable names should begin with lower case letters) returns the name of a file or a File object, you could do something like so:

try {
  File file = myFrame.showSaveDialog(); // if this method returns a File!!!!!
  FileOutputStream fos = new FileOutputStream(file, true);
  PrintStream printStream = new PrintStream(fos);
  //.... etc
} catch(....) {
  // ....
}

要将其应用于上面发布的代码，请执行以下操作:

To apply this to your posted code above, do something like so:

   public static PrintStream showSaveDialog() {
      JFileChooser chooser = new JFileChooser();
      FileNameExtensionFilter filter = new FileNameExtensionFilter(
            "Tekst filer", "txt");
      chooser.setFileFilter(filter);

      int returnVal = chooser.showSaveDialog(null);
      try {
         if (returnVal == JFileChooser.APPROVE_OPTION) {

            //  ******* note changes below *****
            File file = chooser.getSelectedFile();

            FileOutputStream fos = new FileOutputStream(file, true);
            return new PrintStream(fos);
         } else {
            return null;
         }
      } catch (FileNotFoundException e) {
         JOptionPane.showMessageDialog(null, "Ugyldig Fil!", "error",
               JOptionPane.ERROR_MESSAGE);
      }
      return null;

   }

关键是这里的这些行:

            File file = chooser.getSelectedFile();
            FileOutputStream fos = new FileOutputStream(file, true);
            return new PrintStream(fos);

FileOutputStream 构造函数中的 true 会创建一个附加到现有文件的 FileOutputStream.有关详细信息，请查看 FileOutputStream API.

The true in the FileOutputStream constructor creates a FileOutputStream that appends to the existing file. Please check out the FileOutputStream API for the details on this.

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