Banning users by reading variable via Java

Banning users by reading variable via Java - java

I am creating a basic password based login system. It uses MD5 to secure the password. The correct password is "csk" (without quotes). If anyone enters that correctly, he gets access to a key.html file in the local computer. But if someone enters the wrong password for three consecutive times, he gets "banned" from logging in again. But the design that I have constructed bans the user only for that particular session. If he opens the terminal again, it starts from the very beginning. If the variable count is greater than 3 (three) from the last time, then the program, on execution via void main() would display "You are banned". I want to keep it basic and not use JDBC and SQL and such. Also, this is a local application and not a web-based one. I'm quite confused what approach I should take on this. Here's my code that I've cooked up:
import java.math.*;
import java.security.*;
import java.io.*;
import java.util.*;
import java.net.HttpURLConnection;
public class pwd {
public static void main(String[] args)throws NoSuchAlgorithmException, IOException, InterruptedException {
int count = 1;
boolean run = true;
while (run && count<4){
System.out.println("Enter the password");
Scanner kb = new Scanner(System.in);
String pass = kb.nextLine();
String pd = "ea0882721f7f44384ce772375696f9a6"; //Password is "csk" without quotes geeks, this is it's MD5
// so enter "csk" in the terminal
// to run the program on execution
String md5sum = md5(pass);
String os = System.getProperty("os.name");
boolean o = false;
int win = os.indexOf("Windows");
if (md5sum.equals(pd)){
System.out.println("You've logged in successfully, get the Key now");
String url = "file:///C:/Users/<username>/Desktop/key.html"; // example www
Runtime.getRuntime().exec("rundll32 url.dll,FileProtocolHandler " + url);
run = false;
}
else {
System.out.println("You've entered the wrong password, try again.");
System.out.println();
run = true;
if (count>=3) {
System.out.println("You are banned from logging in, due to repeated unsuccessful login attempts.");
}
++count;
}
}
}
public static String md5(String input)throws NoSuchAlgorithmException, IOException {
String md5 = null;
MessageDigest digest = MessageDigest.getInstance("MD5");
digest.update(input.getBytes(), 0, input.length());
md5 = new BigInteger(1, digest.digest()).toString(16);
return md5;
}
}
EDIT: There's no need for me to change MD5 hashing to anything else, it's just a basic one.

you can simply write to a file with java.io.FileWriter
FileWriter writer = null;
String text = "username";
try{
writer = new FileWriter("banned.txt", true);
writer.write("\r\n");
writer.write(text,0,text.length());
}catch(IOException ex){
ex.printStackTrace();
}finally{
if(writer != null){
writer.close();
}
}
The above code allows you to add a line in a file.
To read the file, you can do like this (java.io.BufferedReader):
BufferedReader reader = new BufferedReader(new FileReader("banned.txt"));
String line = null;
while ((line = reader.readLine()) != null) {
// check the username here
}

Hum what you want to do can be done but you have to create a kind of "login page" because as it is now (with the code you gave) there is no user information involved.
To save the important information of the ban, you can for example save a boolean in a file (or the user when you have it) and read this same file at the beginning of your code in order to know if user is ban or not. In this case you have to change your code to add the information of ban or not before trying the new input codes ;)
If you don't have a login page, so no user once you ban someone no one will be able to log any more :)
PS: Java class start with a Upper case not pwd but Pwd normally
PS2: Your count will always be increased because it's not in a else ;) so every try of new code will increase it even if the user is ban ;)

Related

Trying to finish off a java code program

I am working on a java code for school and I have spent days on it and I just don't think that I'm heading in the right direction. Here is the info on the project:
For security-minded professionals, it is important that only the appropriate people gain access to data in a computer system. This is called authentication. Once users gain entry, it is also important that they only see data related to their role in a computer system. This is called authorization. For the zoo, you will develop an authentication system that manages both authentication and authorization. You have been given a credentials file that contains credential information for authorized users. You have also been given three files, one for each role: zookeeper, veterinarian, and admin. Each role file describes the data the particular role should be authorized to access. Create an authentication system that does all of the following:
 Asks the user for a username
 Asks the user for a password
 Converts the password using a message digest five (MD5) hash
It is not required that you write the MD5 from scratch. Use the code located in this document and follow the comments in it to perform this operation.

Checks the credentials against the valid credentials provided in the credentials file
Use the hashed passwords in the second column; the third column contains the actual passwords for testing and the fourth row contains the
role of each user.

Limits failed attempts to three before notifying the user and exiting the program

Gives authenticated users access to the correct role file after successful authentication
The system information stored in the role file should be displayed. For example, if a zookeeper’s credentials is successfully authenticated, then the contents from the zookeeper file will be displayed. If an admin’s credentials is successfully authenticated, then the contents from the admin file will be displayed.
 Allows a user to log out
 Stays on the credential screen until either a successful attempt has been made, three unsuccessful attempts have been made, or a user chooses to exit
Here are the five text files I was given:
admin.txt
Hello, System Admin!
As administrator, you have access to the zoo's main computer system.
This allows you to monitor users in the system and their roles.
credentials.txt
griffin.keyes 108de81c31bf9c622f76876b74e9285f "alphabet soup" zookeeper
rosario.dawson 3e34baa4ee2ff767af8c120a496742b5 "animal doctor" admin
bernie.gorilla a584efafa8f9ea7fe5cf18442f32b07b "secret password" veterinarian
donald.monkey 17b1b7d8a706696ed220bc414f729ad3 "M0nk3y business" zookeeper
jerome.grizzlybear 3adea92111e6307f8f2aae4721e77900 "grizzly1234" veterinarian
bruce.grizzlybear 0d107d09f5bbe40cade3de5c71e9e9b7 "letmein" admin
validateCredentials.txt
/*
* To change this license header, choose License Headers in Project Properties.
* To change this template file, choose Tools | Templates
* and open the template in the editor.
*/
package authentication;
import java.security.MessageDigest;
import java.io.FileInputStream;
import java.io.IOException;
import java.util.Scanner;
/**
*
* #author JoeP
*/
public class ValidateCredentials {
private boolean isValid;
private String filePath;
private String credentialsFileName;
public ValidateCredentials() {
isValid = false;
//filePath = "C:\\Users\\joep\\Documents\\NetBeansProjects\\ Authentication\\";
filePath = "";
credentialsFileName = "credentials";
}
public boolean isCredentialsValid(String userName, String passWord) throws Exception {
String original = passWord;
MessageDigest md = MessageDigest.getInstance("MD5");
md.update(original.getBytes());
byte[] digest = md.digest();
StringBuffer sb = new StringBuffer();
for (byte b : digest) {
sb.append(String.format("%02x", b & 0xff));
}
System.out.println("");
System.out.println("original:" + original);
System.out.println("digested:" + sb.toString()); //sb.toString() is what you'll need to compare password strings
isValid = readDataFiles(userName, sb.toString());
return isValid;
}
public boolean readDataFiles(String userName, String passWord) throws IOException {
FileInputStream fileByteStream1 = null; // File input stream
FileInputStream fileByteStream2 = null; // File input stream
Scanner inFS1 = null; // Scanner object
Scanner inFS2 = null; // Scanner object
String textLine = null;
boolean foundCredentials = false;
// Try to open file
System.out.println("");
System.out.println("Opening file " + credentialsFileName + ".txt");
fileByteStream1 = new FileInputStream(filePath + "credentials.txt");
inFS1 = new Scanner(fileByteStream1);
System.out.println("");
System.out.println("Reading lines of text.");
while (inFS1.hasNextLine()) {
textLine = inFS1.nextLine();
System.out.println(textLine);
if (textLine.contains(userName) && textLine.contains(passWord)) {
foundCredentials = true;
break;
}
}
// Done with file, so try to close it
System.out.println("");
System.out.println("Closing file " + credentialsFileName + ".txt");
if (textLine != null) {
fileByteStream1.close(); // close() may throw IOException if fails
}
if (foundCredentials == true) {
// Try to open file
System.out.println("");
System.out.println("Opening file " + userName + ".txt");
fileByteStream2 = new FileInputStream(filePath + userName + ".txt");
inFS2 = new Scanner(fileByteStream2);
System.out.println("");
while (inFS2.hasNextLine()) {
textLine = inFS2.nextLine();
System.out.println(textLine);
}
// Done with file, so try to close it
System.out.println("");
System.out.println("Closing file " + userName + ".txt");
if (textLine != null) {
fileByteStream2.close(); // close() may throw IOException if fails
}
}
return foundCredentials;
}
}
veterinarian.txt
Hello, Veterinarian!
As veterinarian, you have access to all of the animals' health records. This allows you to view each animal's medical history, current treatments/illnesses (if any), and maintain a vaccination log.
zookeeper.txt
Hello, Zookeeper!
As zookeeper, you have access to all of the animals information and their daily monitoring logs. This allows you to track their feeding habits, habitat conditions, and general welfare.
Finally, this is the code that I have so far, but when I try to run it in Netbeans it just won't work.
import java.io.File;
import java.nio.charset.Charset;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.security.MessageDigest;
import java.util.List;
import java.util.Scanner;
public class Authentication {
public static void main(String args[]) {
try {
Scanner scan = null;
scan = new Scanner(new File("credentials.txt"));
String credentials[][] = new String[100][4];
int count = 0;
while (scan.hasNextLine()) {
//read name and hased pass
credentials[count][0] = scan.next();
credentials[count][1] = scan.next();
//get original pass from file
String l[] = scan.nextLine().split("\"[ ]+");
l[0] = l[0].trim();
l[0] = l[0].replace("\"", "");
credentials[count][2] = l[0];
credentials[count][3] = l[1].trim();
count++;
}
//ask for user input
Scanner scanio = new Scanner(System.in);
boolean RUN = true;
int tries = 0;
while (RUN) {
System.out.println("**WELCOME**");
System.out.println("1) Login");
System.out.println("2) Exit");
int ch = Integer.parseInt(scanio.nextLine().trim());
if (ch == 1) {
//increment number of attempts
tries++;
//ask for user and pass
System.out.print("Input username:");
String username = scanio.nextLine();
System.out.print("Input password:");
String password = scanio.nextLine();
//generate hash
MessageDigest md;
md = MessageDigest.getInstance("MD5");
md.update(password.getBytes());
byte[] digest = md.digest();
StringBuilder sb = new StringBuilder();
for (byte b : digest) {
sb.append(String.format("%02x", b & 0xff));
}
String hPassword = sb.toString();
boolean badUser = true;
for (int i = 0; i < count; i++) {
if (username.contentEquals(credentials[i][0])) {
if (hPassword.contentEquals(credentials[i][1])) {
//everything looks good. login
List<String> data = null;
//check type of user and print
switch (credentials[i][3]) {
case "zookeeper":
data = Files.readAllLines(Paths.get("zookeeper.txt"), Charset.defaultCharset());
break;
case "admin":
data = Files.readAllLines(Paths.get("admin.txt"), Charset.defaultCharset());
break;
case "veterinarian":
data = Files.readAllLines(Paths.get("veterinarian.txt"), Charset.defaultCharset());
break;
default:
break;
}
for (String s : data) {
System.out.println(s);
}
//reset tries
tries = 0;
//now what to do?
System.out.println("\n1) Logout.");
System.out.println("2) Exit.");
ch = Integer.parseInt(scanio.nextLine().trim());
if (ch == 2) {
RUN = false;
}
badUser = false;
break;
}
}
}
if (badUser) {
System.out.println("Invalid Username or password.");
}
} else {
RUN = false;
break;
}
//thief alert!!
if (tries == 3) {
RUN = false;
System.out.println("Too many invlaid attempts.");
}
}
} catch (Exception ex) {
ex.printStackTrace();
}
}
}
PLEASE HELP ME!!!
THANK YOU!!!

Youa re getting a FileNotFoundException. That is, Netbeans is not finding your credentials.txt file (which possibly is located in a different directory). Make sure your credentials.txt file is located in your Netbeans project directory, as follows:
1) Find your project directory by going to the "Netbeans "Projects" tab, right-clicking in your project folder and selecting "Properties". The "Project folder" will be shown on at the top of the new window displayed (i.e. "C:\Users\admin\Documents\NetBeansProjects\YourProjectName").
2) Place your credentials.txt file in that project directory.
3) Re-run your code.

Java .txt username and password not working [closed]

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Edit the question to include desired behavior, a specific problem or error, and the shortest code necessary to reproduce the problem. This will help others answer the question.
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I was just experimenting with java (NetBeans) and I though up a quick text based adventure game. I'm trying to get it to check for your username and password in two text files "users.txt" and "passwords.txt" and i was following a guide on Cave of Programming
Here are the imports
import java.io.*;
import javax.swing.JFrame;
This is where the errors are,
private void loginActionPerformed(java.awt.event.ActionEvent evt) {
String usernametxt = "users.txt";
String passwordtxt = "passwords.txt";
String user = null;
String pass = null;
try {
// file reader for username \\
FileReader fileReader = new FileReader(usernametxt);
// file reader for password \\
FileReader fr = new FileReader(passwordtxt);
// buffered reader for username \\
BufferedReader bufferedReader = new BufferedReader(fileReader);
// buffered reader for password \\
BufferedReader br = new BufferedReader(fr);
// check for if user doesn't equal null \\
while((user = bufferedReader.readLine()) != null){
// if username equals first line of username.txt \\
if (username.getText().equalsIgnoreCase(user)){
// check for if pass doesn't equal null \\
while((pass = br.readLine()) != null){
// if password equals first line of passwords.txt \\
if (password.getPassword().equals(pass)){
// if password = pass than it will exit \\
System.exit(1);
}
// else continue \\
else{
continue;
}
}
}
}
bufferedReader.close();
br.close();
}
catch(FileNotFoundException ex){
System.out.println("Unable to open file ");
}
catch(IOException ex){
System.out.println("Error reading file");
}
}
Here are the text files
users.txt
matthew
passwords.txt
matt
Full code available here
http://textuploader.com/57urs
Newest Code Here
http://textuploader.com/577qk
feel free to ask me questions here.
Thank you for the help in advance!
Newest Code
private void loginActionPerformed(java.awt.event.ActionEvent evt) {
String usernames = username.getText();
String passwords = password.toString();
boolean signedin = false;
String usernametxt = "users.txt";
String passwordtxt = "passwords.txt";
String user = null;
String pass = null;
try {
FileReader fr1 = new FileReader(usernametxt);
FileReader fr2 = new FileReader(passwordtxt);
BufferedReader br1 = new BufferedReader(fr1);
BufferedReader br2 = new BufferedReader(fr2);
System.out.println("Username: "+br1.readLine());
System.out.println("Password: "+br2.readLine());
// While loops not running (not a if statement error \
while ((user = br1.readLine()) != null){
// checks if username is not equal to usernames.txt \\
if (user.equalsIgnoreCase(usernames)){
System.out.println("while loop running, username (right)");
break;
}
else{
System.out.println("while loop running, username (wrong)");
}
}
br1.close();
while ((pass = br2.readLine())!= null){
if (pass.equalsIgnoreCase(passwords)){
signedin = true;
System.out.println("While loop running, password (right)");
break;
}
else{
System.out.println("While loop running, password (wrong)
}
}
br2.close();
// Commented out the if statements because i dont want to to close while testing \
// if (signedin){
// System.out.println("SIGNEDIN = TRUE");
// new error1().setVisible(true);
// this.dispose();
// }
// if (!signedin){
// System.out.println("SIGNEDIN = FALSE");
// System.exit(1);
// }
}
catch(FileNotFoundException ex){
System.out.println("Unable to open file ");
}
catch(IOException ex){
System.out.println("Error reading file");
}
}
New Problem
The while loops do not run, this is confirmed when it doesn't print "While loop running, User/Pass", This is not a if/then statement error as I have added the else statement to print if the username is right or wrong. Please help, Thanks Matthew.

If i understood it correctly:
Two files:
users.txt holds the usernames.
passwords.txt holds the passwords.
We want:
Keep reading the user file until the file ends or we've found our user.
Read the corresponding line on the password file and check if the password matches.
Checking the code, while((user = bufferedReader.readLine()) != null) does the first part nicely. We DO want to keep reading the entire file trying to find our user, right?
but the nested while seems a bit fishy. We only need to check a SINGLE password for a given user, right? RIGHT?
Digging a bit deeper into your code, we see:
if (password.getPassword().equals(pass)) {
// if password = pass than it will exit
System.exit(1);
} // plus Lots of code...
Hey! I don't think System.exit does what you're looking for!
System.exit will exit the program, going back to DOS or whatever the cool kids are using these days. The integer it returns is called an error code, and can be used to feed info back to the terminal/shell that started our program.
The keyword you're most likely looking for is break: that will exit a given loop pronto, no questions asked.
Let's do some break/continue mashups! Suppose we "Win at life" if the password is indeed correct:
boolean winAtLife = false;
while((user = bufferedReader.readLine()) != null){
String candidatePassword = br.readLine();
if (candidatePassword == null) {
// So the password file is shorter than the userfile?
// We probably want to log or alert the poor DevOp guys.
// throwing an exception seems like the right thing to do here!
break;
}
if (!user.equalsIgnoreCase(username.getText())) {
// These are not the droid we're looking for, Better luck next line!
continue;
// Also notice that, since we KNOW that user can't be null,
// we're using the force to save ourselves from dreaded NullPointerExceptions!
}
if (!candidatePassword.equals(password.getPassword())) {
// Hmmm, wrong password, I guess?
// Not sure what do do next, but we DO NOT need to keep looping
// since we've found our droid/user/whatever.
// So let's break and save some EC2 Cycles.
break;
}
// If we ever reach here, we got ourselves a winner!
pass = candidatePassword
winAtLife = true;
}
EDIT: Ok... So I've heard that:
The cool kids use Scanner nowadays.
Auto-closing resources is good for our health.
Something about separation of concerns and mixing domain-code with the UI. In code samples. Whatever.
So here we go, take two, now as a method:
public boolean checkCredentials(String username, String password) throws IOException {
// these two are begging to be constants or inlined.
final String usernametxt = "users.txt";
final String passwordtxt = "passwords.txt";
if (username == null || password == null) {
// You probably don't want this in production code.
// Exceptions are your best friends when something unexpected occurs.
return false;
}
try (final Reader fileReader = new FileReader(usernametxt);
final Reader passwordReader = new FileReader(passwordtxt)) {
Scanner userScanner = new Scanner(fileReader);
Scanner passwordScanner = new Scanner(passwordReader);
while(userScanner.hasNext()) {
final String user = userScanner.next();
if (!passwordScanner.hasNext()) {
// So the password file is shorter than the userfile?
// We probably want to log or alert the poor DevOp guys.
// throwing an exception seems like the right thing to do here!
return false;
}
final String candidatePassword = passwordScanner.next();
if (!user.equalsIgnoreCase(username)) {
// This is not the droid we're looking for
// Also notice that, since we KNOW that user can't be null,
// we're using the force to save ourselves
// from dreaded NullPointerExceptions!
continue;
}
if (!candidatePassword.equals(password)) {
// Hmmm, wrong password, I guess?
// Not sure what do do next, but we DO NOT need to keep looping
// So let's return early and save some EC2 Cycles.
return false;
}
// If we ever reach here, we got ourselves a winner!
return true;
}
} // yay for autocloseable
return false;
}

Java does not append to the .DAT file

I am writing a basic program that has 3 menu options: Create User, Sign In, and Exit. The user can then choose one of these menu options.
If they choose Create User, they will be prompted to enter a User ID and password (which must follow patterns), and will then check against a .DAT file to ensure the User ID has not already been taken. After successful completion, the program will write the new User ID and password to the end of the .DAT file.
If they choose Sign In, they will be prompted to enter their User ID, followed by their Password, and the program will then read the .DAT file to validate they are on record.
Choosing exit will display a message, "You have signed out."
I am fairly new at java programming just as a forewarning.
Issues I am encountering with my code:
Choosing new user does not append to the .DAT file
Choosing Sign In - program does not seem to correctly check .DAT file because even-
though I am entering an existing account information it still gives my error "Invalid User ID."
import java.io.*;
import java.util.*;
/**
* This program will utilize a menu structure and validate input if the user doesn't choose
* a correct option. Writes a new ID and password to .dat file when user chooses to
* create new user from menu.
*
* #author CMS
* #Date 7/28/2014
*/
public class Passwordv2 {
static boolean answer = true;
static final String MENUANSW = "[1-3]{1}", USERID = "[A-Z,a-z]{6}-[0-9]{2}"; //, PASSWORD = "";
static String iMenuOption="", iID, recPassword, recUserID, password;
static Scanner scanner,scannerDat;
static PrintWriter pw;
public static void main(String[] args) {
init();
while (answer == true) {
menu();
if (iMenuOption.equals("1")) createUser();
else
if (iMenuOption.equals("2")) signIn();
else {answer = false;}
}
closing();
} // end of main
public static void init(){
//User input scanner
scanner = new Scanner(System.in);
//PrintWriter
try {
pw = new PrintWriter(new FileOutputStream (new File ("account.dat"),true) );
}
catch(FileNotFoundException ex) {
}
} // end of INIT
public static String menu(){
do {System.out.println("Please select from the following:");
System.out.println("1. Create a New User");
System.out.println("2. Sign in");
System.out.println("3. Exit");
iMenuOption = scanner.next();
answer = isValMenuOption(iMenuOption);
if (answer == false) { System.out.print("Incorrect Choice. ");}
} while (!answer);
return iMenuOption;
}
public static boolean isValMenuOption(String iMenuOption) {
return(iMenuOption.matches(MENUANSW));
}
public static void createUser() {
boolean validID = true, newID = true;
do {if (!validID) {System.out.println("User ID did not meet requirements.");}
if (!newID) {System.out.println("This User ID has been taken.");}
System.out.println("Please select a User Id (6 letters, followed by a dash (-), followed by 2 numbers).");
iID = scanner.next();
validID = isValidID(iID);
newID = isNewID(iID);}
while (validID==false || newID == false);
boolean valLength = true, valNum = true, valUpper = true, valLower = true;
do{ System.out.println("Please select a Password:");
System.out.println("(6-12 characters, one number, one upper case, one lower case, no white space or symbols).");
password = scanner.next();
valLength = isValLength(password);
valNum = valNum(password);
valUpper = valUpper(password);
valLower = valLower(password);}
while (!valLength || !valNum || !valUpper || !valLower);
pw.println(iID);
pw.println(password);
//menu();
}
public static boolean isValidID(String iID){
return(iID.matches(USERID));
}
public static boolean isNewID(String iID){
answer = true;
// Dat file scanner
try {
scannerDat = new Scanner(new File("account.dat"));
scannerDat.useDelimiter("\r\n");
}
catch (Exception e) {
e.printStackTrace();
System.out.println("File error");
System.exit(1);
}
while (scannerDat.hasNext()) {
recUserID = scannerDat.next();
recPassword = scannerDat.next();
if (recUserID.equals(iID)) {
answer = false;
break;
}
}
return answer;
}
public static boolean isValLength(String password) {
if (password.length() <6 || password.length() > 12) System.out.println("Password did not meet length requirements. ");
return(password.length() >= 6 && password.length() <= 12);
}
public static boolean valNum(String password) {
if (password.matches(".*[0-9].*") == false) System.out.println("Password must contain at least one number. ");
return(password.matches(".*[0-9].*"));
}
public static boolean valUpper(String password){
if (password.matches(".*[A-Z].*") == false) System.out.println("Password must contain one upper case letter.");
return (password.matches(".*[A-Z].*"));
}
public static boolean valLower(String password){
if (password.matches(".*[a-z].*") == false) System.out.println("Password must contain one lower case letter.");
return (password.matches(".*[a-z].*"));
}
public static void signIn() {
boolean newID;
System.out.println("Enter User ID.");
iID = scanner.next();
System.out.println("Enter Password.");
password = scanner.next();
newID = isNewID(iID);
if (newID == false) {
if (password.equals(recPassword)) {System.out.println("Authenticated. You have signed in.");}
else {System.out.println("Invalid Password.");}
}
else {System.out.println("Invalid User ID.");}
}
public static void closing(){
System.out.println("You signed out.");
pw.close();
}
} // end of program
My .DAT file simply has
aabbcc-11
Onetwo3
aaabbb-22
Onetwo34

Change this line:
scannerDat.useDelimiter("\r\n");
to
scannerDat.useDelimiter("\n");
Works for me!

The first bad thing you are doing is that you have a PrintWriter (pw) and a Scanner (scannerDat) both accessing the same file and neither of them closing the access to the file, except right at the end, the pw is closed.
isNewId is the main culprit. Inside here you are better off using a FileReader instead of a Scanner. Declare the FileReader locally within the method and ensure that the file access is closed before exiting, this procedure.
Also within isNewId - don't call System.exit(); In a program this size it's OK, but anything bigger than this it is a cardinal sin and you should never just exit a program as ungracefully as this.

You need to flush your PrintWriter in order for it to do append to the file immediately. Otherwise it would just store it in the buffer to write it into the file eventually
Also, please check what user #simo.3792095 said about your code. You should not have several file streams opened at the same time. Either open/close your streams every time you do something with them, or read the whole data file on program start, then work with in-memory data, then save on exit. It is much easier to work with in-memory data, but if your program crashes all of the in-memory changes will be lost.

Thanks for all who replied. In the end, the problem ended up being that I had a "rough draft" java class, which I then copied and pasted the code of into a new java class under the same java project, which seemed to be giving me issues. Once I created a new java project and used the valid java class it worked fine. I also added the pw.flush(); method to my code so I was able to append to the file immediately instead of upon closing. Also removed the system.exit.

Add History to Custom Shell

I am creating a custom shell in Java. I have added history to it so that when up arrow is pressed it goes to the previous command, but the up arrow seems to not be working
Here is my code:
public class MyShell {
public static class JavaStringHistory
{
private List<String> history = new ArrayList<String>();
}
public static void main(String[] args) throws java.io.IOException {
JavaStringHistory javaStringHistory = new JavaStringHistory();
javaStringHistory.history.add("");
Integer indexOfHistory = 0;
String commandLine;
BufferedReader console = new BufferedReader
(new InputStreamReader(System.in));
//Break with Ctrl+C
while (true) {
//read the command
System.out.print("Shell>");
commandLine = console.readLine();
javaStringHistory.history.add(commandLine);
//if just a return, loop
if (commandLine.equals(""))
continue;
//history
if (commandLine.equals(KeyEvent.VK_UP))
{
System.out.println("up arrow");
}
//help command
if (commandLine.equals("help"))
{
System.out.println();
System.out.println();
System.out.println("Welcome to the shell");
System.out.println("Written by: Alex Frieden");
System.out.println("--------------------");
System.out.println();
System.out.println("Commands to use:");
System.out.println("1) cat");
System.out.println("2) exit");
System.out.println("3) clear");
System.out.println();
System.out.println();
System.out.println("---------------------");
System.out.println();
}
if (commandLine.equals("clear"))
{
for(int cls = 0; cls < 10; cls++ )
{
System.out.println();
}
}
if(commandLine.startsWith("cat"))
{
System.out.println("test");
//ProcessBuilder pb = new ProcessBuilder();
//pb = new ProcessBuilder(commandLine);
}
else
{
System.out.println("Incorrect Command");
}
if (commandLine.equals("exit"))
{
System.out.println("...Terminating the Virtual Machine");
System.out.println("...Done");
System.out.println("Please Close manually with Options > Close");
System.exit(0);
}
indexOfHistory++;
}
}
}
All I am getting is
Shell>^[[A
Incorrect Command
Shell>
Any thoughts?

There are several problems with your approach:
User blackSmith has mentioned before me that system console handling is platform-dependent when it comes to cursor key handling and similar topics.
BufferedReader.readLine is not a smart choice to use for history cycling in a shell because you want the shell to immediately react to cursor keys and not force the user to press Return or Enter. Reading whole lines is only required for user commands. Thus, you need to scan the keyboard input for each single character or key code and decide by yourself if it is e.g. a cursor key (up/down for history cycling, left/right for cursor movement within the command line) or delete/backspace for command line editing and so forth.
The text strings which are created by reading control characters via readLine can depend on the OS, maybe even on the shell and the character set (UTF-8, ISO-8859-1, US ASCII etc.) on the console.
Built-in shell editing functions like command history might get in the way with readLine, e.g. on Linux I see the "^[[A" stuff for cursor up, on Windows the cursor keys are passed through to the built-in command history feature of cmd.exe. I.e. you need to put the console in raw mode (line editing bypassed and no Enter key required) as opposed to cooked mode (line editing with Enter key required).
Anyway, so as to answer your initial question about how to find out which key codes are produced by BufferedReader.readLine, it is actually quite simple. Just dump the bytes to the console like so:
commandLine = console.readLine();
System.out.println("Entered command text: " + commandLine);
System.out.print ("Entered command bytes: ");
for (byte b : commandLine.getBytes())
System.out.print(b + ", ");
System.out.println();
Under Linux cursor up might be something like "27, 91, 65" or just "91, 65", depending on the terminal. cursor down ends with "66" instead on my system. So you could do something like:
public class MyShell {
private static final String UP_ARROW_1 = new String(new byte[] {91, 65});
private static final String UP_ARROW_2 = new String(new byte[] {27, 91, 65});
private static final String DN_ARROW_1 = new String(new byte[] {91, 66});
private static final String DN_ARROW_2 = new String(new byte[] {27, 91, 66});
// (...)
public static void main(String[] args) throws IOException {
// (...)
// history
else if (commandLine.startsWith(UP_ARROW_1) || commandLine.startsWith(UP_ARROW_2)) {
System.out.println("up arrow");
}
else if (commandLine.startsWith(DN_ARROW_1) || commandLine.startsWith(DN_ARROW_2)) {
System.out.println("down arrow");
}
// (...)
}
}
But all this is just for explanation or demonstration and so as to answer your question - I do like to get the bounty. ;-)
Maybe a way to go is not to re-invent the wheel and use the work of others, e.g. a framework like JLine. It is not perfect either from what I have heard, but goes way further than anything you can develop by yourself in a short time. Someone has written a short introductory blog post about JLine. The library seems to do just what you need. Enjoy!
Update: I gave JLine 2.11 a little try with this code sample (basically the one from the blog post plus tab filename completion:
import java.io.IOException;
import jline.TerminalFactory;
import jline.console.ConsoleReader;
import jline.console.completer.FileNameCompleter;
public class MyJLineShell {
public static void main(String[] args) {
try {
ConsoleReader console = new ConsoleReader();
console.addCompleter(new FileNameCompleter());
console.setPrompt("prompt> ");
String line = null;
while ((line = console.readLine()) != null) {
console.println(line);
}
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
TerminalFactory.get().restore();
} catch (Exception e) {
e.printStackTrace();
}
}
}
}
It works nicely on Windows and Linux, but for me tab completion only works on Linux, not on Windows. Anyway, command history works well on both platforms.

VK_UP is an integer constant, while in.readLine() is a string.
They won't equal each other. Why don't you try to test for the code that appears in console usually when you click up arrow? So like:
if (in.readLine().equals("^[[A"))
and then you could clear the line, and write the command in the arraylist with the highest index.
Also, I tested this and found a bug. Change your if statements besides the first to else if; after any command it will eventually get to the else and display "Incorrect Command"

Hide input on command line

I know that command line interfaces like Git and others are able to hide input from a user (useful for passwords). Is there a way to programmtically do this in Java? I'm taking password input from a user and I would like their input to be "hidden" on that particular line (but not on all of them). Here's my code for it (though I doubt it would be helpful...)
try (Scanner input = new Scanner(System.in)) {
//I'm guessing it'd probably be some property you set on the scanner or System.in right here...
System.out.print("Please input the password for " + name + ": ");
password = input.nextLine();
}

Try java.io.Console.readPassword. You'll have to be running at least Java 6 though.
/**
* Reads a password or passphrase from the console with echoing disabled
*
* #throws IOError
* If an I/O error occurs.
*
* #return A character array containing the password or passphrase read
* from the console, not including any line-termination characters,
* or <tt>null</tt> if an end of stream has been reached.
*/
public char[] readPassword() {
return readPassword("");
}
Beware though, this doesn't work with the Eclipse console. You'll have to run the program from a true console/shell/terminal/prompt to be able to test it.

Yes can be done. This is called Command-Line Input Masking. You can implement this easily.
You can uses a separate thread to erase the echoed characters as they are being entered, and replaces them with asterisks. This is done using the EraserThread class shown below
import java.io.*;
class EraserThread implements Runnable {
private boolean stop;
/**
*#param The prompt displayed to the user
*/
public EraserThread(String prompt) {
System.out.print(prompt);
}
/**
* Begin masking...display asterisks (*)
*/
public void run () {
stop = true;
while (stop) {
System.out.print("\010*");
try {
Thread.currentThread().sleep(1);
} catch(InterruptedException ie) {
ie.printStackTrace();
}
}
}
/**
* Instruct the thread to stop masking
*/
public void stopMasking() {
this.stop = false;
}
}
With using this thread
public class PasswordField {
/**
*#param prompt The prompt to display to the user
*#return The password as entered by the user
*/
public static String readPassword (String prompt) {
EraserThread et = new EraserThread(prompt);
Thread mask = new Thread(et);
mask.start();
BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
String password = "";
try {
password = in.readLine();
} catch (IOException ioe) {
ioe.printStackTrace();
}
// stop masking
et.stopMasking();
// return the password entered by the user
return password;
}
}
This Link discuss in details.

JLine 2 may be of interest. As well as character masking, it'll provide command-line completion, editing and history facilities. Consequently it's very useful for a CLI-based Java tool.
To mask your input:
String password = new jline.ConsoleReader().readLine(new Character('*'));

There is :
Console cons;
char[] passwd;
if ((cons = System.console()) != null &&
(passwd = cons.readPassword("[%s]", "Password:")) != null) {
...
java.util.Arrays.fill(passwd, ' ');
}
source
but I don't think this works with an IDE like Eclipse because the program is run as a background process rather than a top level process with a console window.
Another approach is to use the JPasswordField in swing with the accompanying actionPerformed method:
public void actionPerformed(ActionEvent e) {
...
char [] p = pwdField.getPassword();
}
source

Here is an example using console.readPassword(...); in an IDE. I use Netbeans. Note: In your IDE, Scanner will be used and it will show the password!. In the console, console.readPassword(..) will be used and it will not show the password!.
public static void main(String[] args) {
//The jar needs to be run from the terminal for console to work.
Scanner input = new Scanner(System.in);
Console console = System.console();
String username = "";
String password = "";
if (console == null)
{
System.out.print("Enter username: ");
username = input.nextLine();
System.out.print("Enter password: ");
password = input.nextLine();
}
else
{
username = console.readLine("Enter username: ");
password = new String(console.readPassword("Enter password: "));
}
//I use the scanner for all other input in the code!
//I do not know if there are any pitfalls associated with using the Scanner and console in this manner!
}
Note: I do not know if there are any pitfalls associated with using the Scanner and console in this manner!

The class Console has a method readPassword() that might solve your problem.

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