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I want to get one line as header and rest data is append in file

I want to get one line as header and then rest of data append in the file.but i am facing issue that it is saving the header repeatedly when i have called the function.
Expected output should be like
Id : Title : Group ID
1 : ab : 2
2 : fd : 3
3 : fwsj : 3
public void writeOutputToFile(int id, String title, int groupId) throws IOException {
OutputStream os = new FileOutputStream(new File("output_report.txt"), true);
os.write("\n Id Title Group ID \n ".getBytes());
os.write((id + " " +title + " " + groupId + "\n").getBytes());
os.close();
}

well, inside your method you write the headers to the file, so obviously whenever you call it they'll get written..
You can separate it to two methods- one that writes the headers (and called only once) and another that writes the data (and called once per row).
Alternatively, use some sort of loop inside your method to write each of the lines to the file, after writing the headers once.

The Problem
It is repeatedly putting in the header, because when you call the method, you are always going to insert the header. Instead, you may want to code a util that inputs headers for a file you are creating, and then a separate method for inserting the data.
The Solution
Solution 1)
The helper util method would look something like this:
// String... allows for multiple string parameters to be entered for all of your headers.
public void prepFile(File f, String... headers) {
StringBuffer buffer = new StringBuffer();
for (String header : headers) {
buffer.append(header + "\t");
}
OutputStream os = new FileOutputStream(f, true);
os.write(buffer.toString().getBytes());
os.close();
}
After the file is prepped, you can then use your writeOutputToFile method for all the data.
Edit
Solution 2)
If you were going to make a stand alone class for this, I would recommend you set it up like so:
import java.io.*;
public class OutputFile {
private File file;
private String[] headers;
private boolean existed;
public OutputFile(File f, String... headers) {
this.file = f;
this.headers = headers;
init();
}
private void init() {
existed = file.exists();
// If the file didn't exist, then you want to create it.
if (!existed) {
try {
file.createNewFile();
// Afterwards, you can then write your headers to it.
if (headers != null) {
writeData(headers);
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
public void writeData(int id, String title, int groupId) {
writeData("" + id, title, "" + groupId);
}
public void writeData(String... strings) {
StringBuffer buffer = new StringBuffer();
for (String s : strings) {
buffer.append(s + "\t");
}
buffer.append("\n");
writeData(buffer.toString());
}
public void writeData(String data) {
OutputStream os = null;
try {
os = new FileOutputStream(file, true);
os.write(data.getBytes());
os.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
if (os != null) {
try {
os.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
}

Why can't I add text to a file in Java? [duplicate]

This question already has answers here:
How to append text to an existing file in Java?
(31 answers)
Closed 3 years ago.
It seems that its creating a new file always I try to write or read.
Each line starts with the name of the player, if exists the player should add the score at the end, if not creates a new line and write the info.
.......................
public class JogadorData {
private String nome_player;
private Scanner is;
private FileWriter os;
// this file exists
private final String path = "src/Data/JogadorData";
public JogadorData(String nome_player) {
this.nome_player = nome_player;
try {
is = new Scanner(new File(path));
} catch (FileNotFoundException e1) {
e1.printStackTrace();
}
try {
os = new FileWriter(path);
} catch (IOException e) {
e.printStackTrace();
}
}
public void escreverScore(String score) {
if (jogadorNovo(nome_player)) {
try {
os.write(nome_player + " " + score);
} catch (IOException e) {
e.printStackTrace();
}
}
else {
escreverResultadoJogadorExistente(score);
}
try {
is.close();
os.close();
} catch (IOException e) {
e.printStackTrace();
}
}
// returns true if it is a new player
private boolean jogadorNovo(String nome_player) {
while (is.hasNextLine()) {
String linha = is.nextLine();
String[] info = linha.split(" ");
if (info[0].equals(nome_player)) {
return false;
}
}
return true;
}
}
....................................
....................................
Test:
public class TESTE {
public static void main(String[] args) {
JogadorData jogador = new JogadorData("Manelina");
jogador.escreverScore("100");
// System.out.println(jogador.lerMelhorResultado());
}
}

The example below is a simplified read/write to file from what you have, done in similar format to what you are trying to do. What this code does is reads every line from the file you are loading from via Files#readAllLines, then runs through each line, (put your logic where I commented the if statement, and then output.add appends the new version of the line you are modifying, storing it in the array list "output", after which the file is saved to the path defined by Files#write
List<String> output = new ArrayList<>();
List<String> lines = Files.readAllLines(Paths.get("Path/To/File.txt"));
for (String line : lines) {
//... if (playerExists(line))
output.add(line + " " + score);
}
Files.write(Paths.get("Path/To/Save/File.txt"), output);

How to overwrite a file that is altering an arraylist

I'm writing a program in order to keep track of DVDs in my library. I'm having trouble altering the text file that saves an added or removed DVD object from the arraylist. Whenever I call my save method, which is the one that overwrites the existing text file holding all the information, it will not change it whatsoever. My add and remove methods work fine but it's just the save method which overwrites the file that I'm reading from that will not work. The following code is what I was attempting to use to save the arraylist to the file. My filename is DVDCollection.txt and the boolean variable flag is a static variable used to check whether or not the code which adds or removes an object from the arraylist was reached.
public void save() {
try{
if(flag=true){
FileWriter instream = new FileWriter("DVDCollection.txt",false);
instream.close();
}else{
return;
}
}catch(IOException e){
System.out.println("The file could not be written to!");
}
}

If you are using java 8 or above it's as simple as:
List<String> lines = Arrays.asList("first line", "second line");
try {
Files.write(Paths.get("my-file.txt"), lines);
} catch (IOException e) {
//handle exception
}
Make sure you provide the right path!

Not sure, why this method should save an array list, as the actual code that writes to this file is missing. Here is simple test, let's start here:
import java.io.*;
import java.util.*;
public class FileSaveTest {
public static void main(String[] args) {
FileSaveTest test = new FileSaveTest();
test.fill();
test.save();
}
public void fill() {
arrayList.add("My disc 1");
arrayList.add("My disc 2");
arrayList.add("Another disc");
}
public void save() {
try {
if(flag) { // you dont need ==true
FileWriter instream = new FileWriter("DVDCollection.txt",false);
for (String entry : arrayList) {
instream.write(entry + "\n");
}
instream.close();
} else {
return;
}
} catch(IOException e) {
System.out.println("The file could not be written to!");
}
}
private ArrayList<String> arrayList = new ArrayList<>();
private static boolean flag = true;
}
Next, it's not very good, to close the file in such manner. If an exception occurs while writing, the file will not be closed. instream.close() should be put into the "finally" block. This block will be executed in any case, regardless of whether an exception occurred or the return keyword met:
public void save() {
Writer instream = null;
try {
if(flag) { // you dont need ==true
instream = new FileWriter("DVDCollection.txt",false);
for (String entry : arrayList) {
instream.write(entry + "\n");
}
} else {
return;
}
} catch(IOException e) {
System.out.println("The file could not be written to!");
} finally {
try {
if (instream != null)
instream.close();
} catch (IOException e) {
System.err.println("Exception during close");
}
}
}
Or, if you are using java 7, you can use try-with-resources syntax:
public void save() {
if(flag) { // you dont need ==true
try (Writer instream = new FileWriter("DVDCollection.txt",false)) {
for (String entry : arrayList)
instream.write(entry + "\n");
} catch(IOException e) {
System.out.println("The file could not be written to!");
}
} // you dont need "return else { return; }" anymore
}

How do I save states to a file and keep the file safe?

I'm trying to create save states for my game, not so much for where your game was left but something simple like score boards. The format would be something like this:
Wins: 5
Losses: 10
GamesPlayed: 15
I need to be able to access the file, and depending on whether the player won/lost it will append +1 to the value in the file.
What would be the best way to go about this? I've heard of a bunch of different ways to save data, for example XML, but aren't those overkill for the size of my data?
Also, I do want to keep this file safe from the users being able to go into the files and change the data. Would I have to do some sort of encryption? And, if the user removes the file and replaces it with an empty one can't they technically reset their values?

You can use plain serialization/deserialization for this. In order to serialize/deserialize a class, it must implement the Serializable interface. Here's a example to start with:
public class Score implements Serializable {
private int wins;
private int loses;
private int gamesPlayed;
//constructor, getter and setters...
}
public class ScoreDataHandler {
private static final String fileName = "score.dat";
public void saveScore(Score score) {
ObjectOutputStreamout = null;
try {
out = new ObjectOutputStream(new FileOutputStream(fileName));
out.writeObject(score);
} catch (Exception e) {
//handle your exceptions...
} finally {
if (out != null) {
try {
out.close();
} catch (IOException ioe) {
}
}
}
}
public Score loadScore() {
ObjectInputStreamin = null;
Score score = null;
try {
in = new ObjectInputStream(new FileInputStream(fileName));
score = (Score)in.readObject();
} catch (Exception e) {
//handle your exceptions...
} finally {
if (in != null) {
try {
in.close();
} catch (IOException ioe) {
}
}
}
return score;
}
}

A properties file I created in the 1st run gets blanked in the 2nd run

Okay, I'm trying to create a custom client for Minecraft (don't worry, my question has nothing to do with Minecraft in particular), and I added an abstract class to manage a configuration file using Java's built-in Properties system. I have a method that loads a properties file or creates it if it doesn't already exist. This method is called at the beginning of all my other methods (although it only does anything the first time its called).
The properties file gets created just fine when I run Minecraft the first time, but somehow when I run it the second time, the file gets blanked out. I'm not sure where or why or how I'm wiping the file clean, can someone please help me? Here's my code; the offending method is loadConfig():
package net.minecraft.src;
import java.util.*;
import java.util.regex.*;
import java.io.*;
/**
* Class for managing my custom client's properties
*
* #author oxguy3
*/
public abstract class OxProps
{
public static boolean configloaded = false;
private static Properties props = new Properties();
private static String[] usernames;
public static void loadConfig() {
System.out.println("loadConfig() called");
if (!configloaded) {
System.out.println("loading config for the first time");
File cfile = new File("oxconfig.properties");
boolean configisnew;
if (!cfile.exists()) {
System.out.println("cfile failed exists(), creating blank file");
try {
configisnew = cfile.createNewFile();
} catch (IOException e) {
e.printStackTrace();
configisnew=true;
}
} else {
System.out.println("cfile passed exists(), proceding");
configisnew=false;
}
FileInputStream cin = null;
FileOutputStream cout = null;
try {
cin = new FileInputStream(cfile);
cout = new FileOutputStream(cfile);
} catch (FileNotFoundException e) {
e.printStackTrace();
}
if (!configisnew) { //if the config already existed
System.out.println("config already existed");
try {
props.load(cin);
} catch (IOException e) {
e.printStackTrace();
}
} else { //if it doesn't exist, and therefore needs to be created
System.out.println("creating new config");
props.setProperty("names", "oxguy3, Player");
props.setProperty("cloak_url", "http://s3.amazonaws.com/MinecraftCloaks/akronman1.png");
try {
props.store(cout, "OXGUY3'S CUSTOM CLIENT\n\ncloak_url is the URL to get custom cloaks from\nnames are the usernames to give cloaks to\n");
cout.flush();
} catch (IOException e) {
e.printStackTrace();
}
}
String names = props.getProperty("names");
System.out.println("names: "+names);
try {
usernames = Pattern.compile(", ").split(names);
} catch (NullPointerException npe) {
npe.printStackTrace();
}
System.out.println("usernames: "+Arrays.toString(usernames));
configloaded=true;
}
}
public static boolean checkUsername(String username) {
loadConfig();
System.out.println("Checking username...");
for (int i=0; i<usernames.length; i++) {
System.out.println("comparing "+username+" with config value "+usernames[i]);
if (username.startsWith(usernames[i])){
System.out.println("we got a match!");
return true;
}
}
System.out.println("no match found");
return false;
}
public static String getCloakUrl() {
loadConfig();
return props.getProperty("cloak_url", "http://s3.amazonaws.com/MinecraftCloaks/akronman1.png");
}
}
If it's too hard to read here, it's also on Pastebin: http://pastebin.com/9UscXWap
Thanks!

You are unconditionally creating new FileOutputStream(cfile). This will overwrite the existing file with an empty one. You should only invoke the FileOutputStream constructor when writing a new config file.
if (configloaded)
return;
File cfile = new File("oxconfig.properties");
try {
if (cfile.createNewFile()) {
try {
FileOutputStream cout = new FileOutputStream(cfile);
props.setProperty("names", "oxguy3, Player");
props.setProperty("cloak_url", "http://...");
...
cout.flush();
} finally {
cout.close();
}
} else {
FileInputStream cin = new FileInputStream(cfile);
try {
props.load(cin);
} finally {
cin.close();
}
}
configloaded=true;
} catch(IOException ex) {
e.printStackTrace();
}