Java：创建文件或目录（如果不存在）

Question

My class gets a String containing a Path (dir1/dir2/abc.txt) or a file (def.txt) and I want to write/read into that file. If the file does not exist I want to create the directories (if there are any) and the file.

My class constructor so far("pfad" is a instance-variable):

public SerializedFahrzeugDAO(String path) {
    pfad=path;

    try{


        FileInputStream filein= new FileInputStream(pfad);
        ObjectInputStream in = new ObjectInputStream(filein);
        List<Fahrzeug> liste = (List<Fahrzeug>)in.readObject();
        in.close();
        FileOutputStream fileout = new FileOutputStream(pfad);
        ObjectOutputStream out = new ObjectOutputStream(fileout);

        out.writeObject(liste);
        out.close();

    }
    catch (Exception f){
        if(f instanceof FileNotFoundException){
            try{
                File ziel = new File(pfad);
                File dir= new File(ziel.getParentFile().getAbsolutePath());
                dir.mkdirs();
                FileOutputStream fileout = new FileOutputStream(pfad);
                ObjectOutputStream out = new ObjectOutputStream(fileout);
                List<Fahrzeug> newlist = new ArrayList<Fahrzeug>();
                out.writeObject(newlist);
                out.close();
            }
            catch(Exception y){System.out.println(y); }
        }

        else {System.out.println(f);}}

It works fine with paths like "dir/file.txt", but if I only enter a filename I get a NullPointerException .

Answer 1

Without having a stacktrace, I would assume, the exception happens here:

            File dir= new File(ziel.getParentFile().getAbsolutePath());

ziel doesn't have a parent, so ziel.getParentFile() is null .

You could first convert to absolute path then get the parent.

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Edit (1):

You should improve your error handling.

        catch(Exception y){System.out.println(y); }

Doesn't print the stacktrace. You should use y.printStackTrace() instead (or a proper logging framework).

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Edit (2):

Instead of catching a FileNotFoundException , you should check if the file exists using a method of java.io.File .