从 Java 中的文本文件替换字符串

Question

I've got a text file like this: https://i.stack.imgur.com/nL0Z4.png The first column represents the user ID and the last column represents balance. I want to iterate through the elements to find a specific user ID and then update their balance. I've managed to match the user ID and access the balance using the Scanner but I'm not sure how to update the balance in the text file with a new value. This is the code I've written so far: I tried to take the elements, modify the balances and put the updated values in an arraylist. Then put them into the text file using PrintWriter. But I keep getting an empty text file when I call this function.

File file = new File("UserInfo.txt");
Scanner sc = new Scanner(file);
ArrayList<String> items = new ArrayList<String>(); 
while(sc.hasNextLine()){
    String info = sc.nextLine();
    String data[] = info.split(" ");
    
    if(String.valueOf(currentUser.getAccountNumber()).equals(data[0])){
        data[3] = String.valueOf(currentUser.getBorrowBalance()); 
        //Updating the balance in ArrayList
    }else{
        continue;
    }
    for(int i=0; i<data.length; i++){
        items.add(data[i]);
    }
}
PrintWriter pw = new PrintWriter(file);
for(int j=0; j<items.size(); j++) {
    pw.printf("%s ", items.get(j));
    if(j%3==0) pw.println(); //Going to new line after writing 4 elements to text file
}
pw.close();
sc.close();

Answer 1

I would highly reccomend to use Serialization for this. I am assumming you already have a Customer class with balance,id etc. With Serialization things are just as simple as getting the customer you want,updating his balance,and then writing in your file.For example:

customer = getCustomerById(selectedId);
customer.setBalance(newBalance);
customer.write();

And the write method would look like this

public void write(String filename) {
        try {
            File temp = new File(filename);
            temp.createNewFile(); // create file if not present
            FileOutputStream fileOut = new FileOutputStream(filename);
            ObjectOutputStream objectOut = new ObjectOutputStream(fileOut);
            objectOut.writeObject(this);
            
        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }

More on Serialization here