I/O / Streams :: Appending To Existing File Instead Of Overwriting It
Jul 24, 2014
I do most of my file I/O with {Scanner} for input and {PrintWriter} for output. I've got lots of places in my code that looks like:
Scanner source = new Scanner( new File( sourceName));
PrintWriter dstntn = new PrintWriter( new BufferedWriter( new FileWriter( dstntnName)));
But when I call the constructor for {PrintWriter} up above, it overwrites whatever the original contents of the file designated by {dstntnName} were, doesn't it? Is there a way to call the constructor so that any future writes to it simply append to the original contents, instead of overwriting them?
class CreateFile implements ActionListener{ // MailOrderCreateFile.java @Override public void actionPerformed(ActionEvent ae){ String getDestination = txtDestination.getText(); file = new File(getDestination); // needed for Creating and Displaying the file currentTime = txtCurrentTime.getText(); try { FileWriter fw = new FileWriter(file);
[Code]...
What I wanted to do is that every time I press the button that will activate this part of the code, it will write to a .txt file defined in my txtDestination var (a JTextField). After the first time the file was created, it must append a new line every succeeding presses. However, everytime I do this, it just simply overwrites the contents of the .txt file. The example output would have been like this:
First time.
O R D E R D E T A I L S: Time ordered: 01/21/2015 Wed 10:21:54 PM Item number: 10 Item price: $4.59 Quantity ordered: 12,321 Total: $56,553.39
I am at a loss when it comes to appending Strings to a text file in Java. I was tasked (yes, homework) to complete a program that does the following simple things:
Print out the contents of a text file to the user (got that!)
Ask the user if the want to add any customers to this text file (got it!)
Add those customer's name's, addresses, postal codes and cities. (got that too)
Verify the postal code is in the proper format (yep!)
Add the new information to the text file, and display it to the user (Nope...)
The program is, essentially, supposed to keep track of the user's customers, and store this information to a text file. However, when I run the following code, I get a number of errors:
So I am calling this method several times and trying to write multiple records to a file. Problem is that every time I call the method it overwrites the file from before and doesn't add it.
public void fileWriterMethod() throws IOException{ RandomAccessFile raf = new RandomAccessFile(filename, "rw"); raf.writeInt(id); raf.writeInt(existingMileage); raf.writeInt(gasCost); raf.writeInt(ndays); raf.writeInt(rate);
I'm currently working on a java project simply to learn java. So far, it creates a window and makes a properties file, or appends data to it if it already exists. The problem is that I'm not quite sure how to check if the file already exists to append data to it. I'm currently using a boolean (configCreated) that appends data when true, and creates a file when false. The problem is that this boolean is always false since it's at the beginning.
I am creating a web application that runs on server X(unix) and it has another unix system mounted on it. I want to generate the file tree structure of this mounted unix file system and show it on to a web application so that users can select a file and move it onto this current unix machine.
I know this sounds stupid and you may want to say why cant we directly copy the file, I am doing a proof of concept and using this as a basis.
I'm having trouble getting new objects to add to an ArrayList. Instead, every time a new object is created and added, it overwrites the first object. So if I read in four lines from a text file and make them into four objects, each overwrites the previous and only the last object is printed. I can print out the contents correctly if I move the println statement within the if-loop; however, I need all the objects to saved to the list for searching (later implementation). i believe it has something to do with the instances of the object, but I'm a little confused about how to fix it. Here's the portion of the code I'm looking at:
Java Code:
if (fileChooser.showOpenDialog(null) == JFileChooser.APPROVE_OPTION) { File file = fileChooser.getSelectedFile(); Scanner scanner = new Scanner(new FileReader(file)); String currentLine; System.out.printf("%-20s %-20s %-20s
What I mean is, I have this set and it is supposed to take out all the duplicates. If I enter aaabbbcccd the output should be abcd, but instead my code just outputs the last word, or in this case letter entered.
import java.util.*; public class setdemo { public static void main(String[] args)
I have a code that clear old text then add new text to text file afterthat download the file but the problem my code dose not add new text
FileInputStream fileToDownload ; private static final int BYTES_DOWNLOAD = 1024; response.setContentType("text/plain"); String name = request.getParameter("n"); String text = new String(request.getParameter("text").getBytes("iso-8859-1"), "UTF-8");
[Code] ....
How to clear old text then add new text to text file
I would like to create a component to detect the file being modify before process.is it the right way to detect the file modification based on file size value?
Below are the flow:
1. Get the file size of a file 2. Used file size value encrypt it with MD5 algorithm, and say it generated us encrypted value "0123sdf" 3. to avoid user modify the file content, before file process, we take the file and do the encryption with md5 again, if it return value "0123sdf", then we are sure it doesn't have modification.
my question: a. is it the right approach to detect file modification? b. what the library advise to use or using java.security.DigestInputStream will do?
I am looking for a pure java api that can read metadata from an mp4 file, I have looked online but all apis I found are wrappers to native code. How to read mp4 with java .....
I have been going over my code line by line, over and over again for nearly and hour now...When I execute method `file.createNewFile()`, the method returns true and throws no exceptions. It even says that the file exists. However, the file is not created and cannot be accessed until the program has exited.
File portLib = new File(""); private class RememberPortAction extends AbstractMenuItemAction { methods... protected void actionPerformed() { LibraryCreator creator = new LibraryCreator(self, logger); File newPortLib;
I have to divide a text file into blocks of 128 bits. I think i must use the ByteArrayInputStream and ByteArrayOutputStream classes. is there any website showing how to user these two ByteArrayInputStream and ByteArrayOutputStream classes in detail. or it would be much better if you could show me a portion of the code.
When I am trying to read data from BufferedReader and writing into excel using FileOutputStream object with POI APIs then i am getting the data in excel file in bad formats. you can check the log file and excel file attached for more information.
Here my problem is I cannot use BufferedWriter in place of FileOutputStream because POI class XSSFWorkbook only have one write method and we can only pass FileOutputStream class object there.
I am completing a USACO online problem and am trying to create a print writer to write to my file(ride.out). I did this:
PrintWriter out = new PrintWriter(new BufferedReader(new FileWriter("ride.out")));
However, a load of undefined constructor errors come up for PrintWriter(BufferedWriter) and BufferedWriter(FileWriter). I have imported java.io.* so I don't know what the issue is. This has worked before.
I'm having a bit of trouble with using the Scanner and the Printwriter. I start with a file like this (1 = amount of Houses in the file)
1 FOR SALE: Emmalaan 23 3051JC Rotterdam 7 rooms buyprice 300000 energylevel C
The user gets (let's say for simplicity) 3 options:
1. Add a House to the file, 2. Get all Houses which fullfil requirements (price, FOR SALE / SOLD etc.) and 3. Close the application.
This is how I start:
Scanner sc = new Scanner (System.in); while (!endLoop) { System.out.println("Make a choice); System.out.println("1) Add House"); System.out.println("2) Show Houses"); System.out.println("3) Exit"); int choice = sc.nextInt();
Then I have a switch for all of the three cases. I keep the scanner open, so Java can get the user input (house = for sale or sold, price = ... etc). If the user chose option 1, and all information needed is inputted and scanned, the House will be written to the file (which looks like what I typed above).
For this, I use try (PrintWriter out = new PrintWriter(new BufferedWriter(new FileWriter("Makelaar.txt", false)))). This works perfectly (at least so it seems.)
If the user chose option 1, and all requirements are inputted and scanned, the Houses will be read (scanner) from the file and outputted. For this I use the same Scanner sc. This also works perfectly (so it seems atleast).
My problem is as follows: If a House has been added, I can only read the House(s) which were already in the file. Let's say I have added 2 houses, and there were from the start 3 houses. If option 2 is chosen, the first 3 houses will be scanned perfectly. An exception will be caught for the remaining 2 (just added) Houses. How can I solve this? I tried to close the Scanner, and reopening it, but apparently Java doesn't agree with this
