public static void Replace_Record(String editTerm, String newItem, String newAmount, String newPrice){
String filepath="temp_Food_Item.txt";
String tempfile= "temp_Food_Item_temp.txt";
File oldFile= new File(filepath);
File newFile=new File(tempfile);
String item=""; String quantity=""; String price="";
System.out.println("working ");
try{
//System.out.println("working pt1");
FileWriter fw= new FileWriter(tempfile,true);
BufferedWriter bw= new BufferedWriter(fw);
PrintWriter pw= new PrintWriter(bw);
x = new Scanner(new File(filepath));
x.useDelimiter("[,/n]");
//System.out.println("working pt2");
while(x.hasNext()){
//System.out.println("working pt3");
item=x.next();
quantity=x.next();
price=x.next();
if(item.equalsIgnoreCase(editTerm)){
pw.println(newItem+","+newAmount+","+newPrice);
}
else{
//System.out.println("working pt4 ");
pw.println(item+","+quantity+","+price);
}
}
x.close();
pw.flush();
pw.close();
oldFile.delete();
File dump=new File(filepath);
newFile.renameTo(dump);
}
catch(Exception e){
System.out.println("Error declared");
}
}
I don't understand where I went wrong but it is printing "error declared" so I debugged and found after working pt1 it stops and goes to catch please help?
Additional info includes:
I am making a database for a restaurant and I am inputting info in txt files in the sequence item_name,item_amount,item_price so I am taking my new values from, main and passing them to the method, in theory, it first duplicates a file until it comes to the strings I wanna remove and then replaces them and goes back to copy the strings from the real files. but every time I run this I get catch.
TIA
While I can't answer your question straight away, I can offer a few ideas.
First of, catch a more explicit exception, such as IOException, FileNotFoundException. It is generally good practice to have more explicit code and it's the first step towards improved error handling.
Also do something with it, for startes you can print it in your console and use that information to debug your program. It might tell you exactly what your error is and where it is.
hello everyone thanks for helping me through this problem but I have managed to fix it I took your tips and ran multiple types of exception till I found this was a file io error and I had a problem about naming the files so the compiler could not recognize which file I was calling other than that we Gucci thank you guys
Related
I am trying to create an authentication system of sorts that uses a file called Users.dat to store user data. Currently, I am developing a method to remove users by rewriting the Users.dat file, omitting the user specified. The code below works in a basic environment with an all-encompassing directory containing the .java files and the Users.dat file in the same spot. The old Users.dat file is deleted and Users.dat.tmp is renamed to User.dat. (No problems here, everything works as intended).
public static boolean RemoveUser(String userName) {
// TODO remove username from Users.dat
try {
File originalFile = new File("Users.dat");
System.out.println(originalFile.getAbsolutePath());
BufferedReader read = new BufferedReader(new FileReader("Users.dat"));
String line = null;
while ((line = read.readLine()) != null) {
if (line.indexOf(userName) != -1) {
break;
}
}
String[] userInfo = line.split(", ");
if (!userName.equals(userInfo[2])) {
System.out.println("Username not found. No users removed.");
read.close();
return false;
}
File tempFile = new File(originalFile.getAbsolutePath() + ".tmp");
PrintWriter print = new PrintWriter(new FileWriter(tempFile));
String lineToRemove = line;
BufferedReader read2 = new BufferedReader(new FileReader("Users.dat"));
while ((line = read2.readLine()) != null) {
if (!line.trim().equals(lineToRemove)) {
print.println(line);
print.flush();
}
}
print.close();
read.close();
read2.close();
System.out.println(originalFile.getAbsolutePath());
originalFile.delete(); //This line is not executing correctly
tempFile.renameTo(originalFile); //Nor is this line
} catch (FileNotFoundException ex) {
ex.printStackTrace();
} catch (IOException ex) {
ex.printStackTrace();
}
return true;
}
Users.dat file format:
Joe, Last, jlast, 58c536ed8facc2c2a293a18a48e3e120, true
Sam, sone, samsone, 2c2a293a18a48e3e12058c536ed8facc, false
Jane, Best, jbest, 293a18a48e3e12052058c536ed8facc2c, false
Andrew, Estes, Aestes, 63a490d69aa544fd1272a976014ad570, true
Test, User, tuser, 63a490d69aa544fd1272a976014ad570, true
I have two System.out.println(originalFile.getAbsolutePath()) statements, one at the beginning, one at the end to make sure the path isn't getting screwed up in the process of everything somehow.
Like I said, the code works, however, when I try to implement it in my project, it creates the Users.dat.tmp and it writes the correct data to it, but it does not delete the old Users.dat file, nor does it rename the Users.dat.tmp file to replace Users.dat. I'm certain the directory is correct, as I am literally displaying it as the code executes. I can't figure out any other reason why originalFile.delete() and tempFile.renameTo(originalFile) aren't functioning properly.
EDIT:
Using java.nio.file, I was able to produce an error message. it reads:
java.nio.file.FileSystemException: C:\Path\Users.dat: The process cannot access the file because it is being used by another process.
I don't have the file open when this error message is shown, and I don't get this error using java.nio in my testing environment mentioned at the beginning. I'm not sure what other process the message is referring to.
EDIT 2:
I tried running the code on other machines, one a Mac, the other a Windows laptop, and the code functioned on the Mac just fine, but I was still seeing the same issue on the Windows laptop.
I had the similar issue. My problem was not closing all the streams I read and written to the file. Thanks for your Edit #1, that was helpful
When you wrap
BufferedReader read = new BufferedReader(new FileReader("Users.dat"));
don't you need to close the inner readers too?
If not for the author, but for those who stambled upon this question (like me), hope this suggestion will be useful
I had an earlier function that I was calling in main that was accessing Users.dat, but I never closed the BufferredReader in that function.
I am working on a function that enables the user to check a single student's assessment result. I use try and catch, but when I run the code, the system runs directly to the catch part, and the file's content is blank. I am not sure the reason about this problem. Here is my code:
System.out.println('\n' + "Please enter the Student's uni that you would like to call. Type 'exit' to leave");
String studentInfo = s.nextLine();
if (studentInfo.equalsIgnoreCase("exit")) {
userSelection = "exit";
}
boolean studentFound = false;
for (int i = 0; i < students.size(); i++) {
if (studentInfo.equalsIgnoreCase(students.get(i).getStudentUI())) {
studentFound = true;
try {
File singleStudentList = new File(studentInfo + " .txt");
PrintWriter writer = new PrintWriter(singleStudentList);
System.out.println(studentUniLists.get(i));
writer.println(studentUniLists.get(students.indexOf(studentInfo)));
writer.close();
} catch (Exception e) {
System.out.println("Problem writing the file. Please make sure the path is correct");
}
}
}
Thanks for helping!
My hunch is that your error is in one of these two lines:
System.out.println(studentUniLists.get(i));
writer.println(studentUniLists.get(students.indexOf(studentInfo)));
You haven't included code as to what studentUniLists is, so there is some guesswork here.
My guess is that students.indexOf(studentInfo) could be returning -1, so then when you do studentUniLists.get(-1) on a List, this is going to give you an IndexOutOfBoundsException. You should really only be catching the IOException, so that you can detect this kind of issue
Probably index out of bounds somewhere, e.g:
System.out.println(studentUniLists.get(i));
Are you sure studentUniLists has the index i?
Since you wrote there is no output and it just goes directly to catch.
As commented elsewhere, printing the actual exception helps.
You catch ANY Exception and you print to the console that this is file related problem. It does not have to be.
I suggest you add into your catch clause e.printStackTrace() to print the real problem. Secondly you should consider avoiding catching Exception as it is too broad. It might be worth catching exception that is related to file problems in the first place and leaving the rest uncaught.
Looking at the documentation - PrintWriter will be unlikely to throw errors. Comstructor may throw FileNotFoundException or SecurityException. CheckErrors is the function you need for checking file related errors.
https://docs.oracle.com/javase/7/docs/api/java/io/PrintWriter.html#checkError(). Yet I believe you have non file related problem like NullPointerException or IndexOutOfBoundsException.
Hope this helps.
First, With Jdk 1.7 when you open the file use the try with ressources to let the jvm do the close automaticly.
File singleStudentList;
try (singleStudentList = new File(studentInfo + " .txt")) {
PrintWriter writer = new PrintWriter(singleStudentList);
}
Second, The error is getting by this : new File(studentInfo + " .txt")
you're always creating the empty file "true .txt"
Third, print the error by ex.printStackTrace();
I know that this type of question have been asked many times. But I didn't find any answer for myself. That's why i am asking once more.
I have got an output on my console. I want to copy the same output 1-to-1 to a file. I don't want to redirect. I want some kind of "copy" it and "write" into a file.
I hope the question is clear enough, cause I have seen that the other times, the question wasn't clear.
Anyways, I have tried it with the "System.setOut" methode. But it just redirect everything to the file.
I cannot write all the "System.out.println"s with a write() into a file, that to much.
Thanks for helping.
There is no way you can get console output. You have to do everything before printing
To Write our to a file do this.
try{
FileWriter x = new FileWriter(new File("x.txt"));
x.write("hello");
}catch(IOExecption e){
}
That will write out hello to a file
You could do something like this , the system out will happen after the log to file.
This code will append. Please This is NOT a good example of Exception handling, just an example of what you can do.
protected void writeToFileAndLog(String logEntry)
{
String file = "MyAmazingLog.txt";
try
{
FileOutputStream appendedFile = new FileOutputStream(file, true);
DataOutputStream out = new DataOutputStream(appendedFile);
out.writeBytes(String.format("%s\n", logEntry));
out.flush();
out.close();
System.out.println(logEntry);
}
catch (FileNotFoundException e)
{
e.printStackTrace();
}
catch (IOException e)
{
e.printStackTrace();
}
}
Alright so this is a general question which probably has an obvious answer. How would I go about having a program that outputs to a data file, and everytime it is rerun I would skip to the next line.
So for example..
If I wanted to write the word "hi" to a data file, and when it rerun there would then be two "hi"'s without the previous one being deleted.
Sorry this is a proof of concept type thing so I dont have any actual code to post with this question.
When you open up a FileOutputStream to the file to write to, use the constructor that takes the File (or String file name) and a boolean append option and set that append option to true. From there, you can wrap whatever stream decorator (PrintWriter for example) around that input stream and you should be good to go.
PrintWriter out = new PrintWriter(new FileOutputStream(fileName, true));
You can do something like this:
try
{
String filename= "file.txt";
FileWriter fw = new FileWriter(filename,true);
fw.write("this is a new line\n");
fw.close();
}
catch(IOException ioe)
{
// Error!
System.err.println("IOException: " + ioe.getMessage());
}
I am working through an assignment and have run into a few snags.
My program prints output to the screen, (not how I need it yet) but only prints the first entry to the file. Below is a snippet of the code. The file appears to be reading in the data from the input file, but the loop does not output to the file past the first entry.
Scanner in = new Scanner(System.in); //Scanner object to read input from the file
System.out.println("Enter filename to read "); //file name prompt
String inputFileName = in.nextLine(); //line input reads next line
/*
* TODO 2) Use an unbuffered file input stream to open listings.txt file
* and read in property listings.
*/
Scanner reader = null;
try {
reader = new Scanner(new File(inputFileName));
} catch (FileNotFoundException e) {
System.out.println("Try Again"); //error window if name is null
JOptionPane.showMessageDialog(null, "You must enter a filename", "File input error", JOptionPane.ERROR_MESSAGE);
return;
}
PrintWriter out = new PrintWriter("agentreport.txt"); //This method prints out the file readfile.txt a word at a time
while (reader.hasNextLine()) { //It needs to output to the text file. Currently a file is created, but it is empty?
Scanner s2 = new Scanner(reader.next());
#SuppressWarnings("unused")
boolean b;
while (b = s2.hasNext()) {
String output = s2.next();
String output2 = output.toUpperCase(); //converts output to upper case
System.out.println(output2);
out.print(output2); //only printing the first entry to the agentsreport.txt file. Not stepping thru the file for some reason?
}
Even if you are using automatic flushing, which you aren't in this case, the PrintWriter object would output anything in its internal buffer unless you do one of two things:
1) Use the println(), printf(), or format() to methods
2) Make a call to the flush() method every time you print, this way all of the data in the internal buffer gets written out.
Note: The print() method does not cause the PrintWriter object to flush() its buffer.
try adding a call to flush() after you call print()
Example of split()
PrintWriter out = new PrintWriter("agentreport.txt");
while (reader.hasNextLine()) {
String words = reader.nextLine().split();
#SuppressWarnings("unused")
boolean b;
for(String word : words) {
String output = word ;
String output2 = output.toUpperCase(); //converts output to upper case
System.out.println(output2);
out.print(output2);
}
One thing that immediately jumps out is that you aren't handling your resources properly.
Any time you use an IO resource such as a reader/database connection/etc., you should always close it using a finally block, using this sort of pattern:
Reader reader = /* construct it however */
try {
/* do something with the reader */
}
finally {
reader.close();
}
If you don't do this, there's no guarantee that the reader will actually be closed, and your application will leak file descriptors/connection pool connections/etc., until eventually it won't be able to get hold of any more and your app crashes. (This won't always have fatal consequences, but it's such a straightforward pattern you should use it every time until it becomes automatic).
In this case, you aren't closing your writer at all, which means that it's not guaranteed that it ever actually flushes its output to the file. It would be perfectly in accordance with the Writer interface for it to write everything or nothing - without the flush, you have no guarantees. Note that closing the writer will automatically call flush, so that's the best bet once you're done with it.
So the latter part of your code should look like:
PrintWriter out = new PrintWriter("agentreport.txt");
try {
// Existing code here
}
finally {
// This closes the file and frees the descriptor, but also flushes the buffers
out.close();
}
Also, how are you handling the IOExceptions that can be thrown by the reading and writing? Are you catching them and swallowing them somewhere? If so, it's possible that your code is throwing an exception telling you exactly why it can't write, and you're just ignoring it and then looking puzzled.
Not to put too fine a point on it, error handling is probably the most significant part of good software development. It's not too hard to write software that works when everything's fine; the most challenging part is handling things well when you run out of space on the hard drive, or the network is temporarily down, etc.
In this case the most pragmatic approach would be to just let the exception be thrown out of the top of your main method. In this case your application will "crash", and you'll get a stacktrace + error message on the console, which will make it immediately clear that something went wrong, and give you a very good idea of what it was.
try
out.println(output2);
http://docs.oracle.com/javase/6/docs/api/java/io/PrintWriter.html
also I'd use a var other than "out" as when system.out is imported to use the shortcode 'out.println()', this could cause variable confusion
edit: good point #Hunter McMillen, changed to println as append is for a CharSequence.
try (
Scanner reader = new Scanner(new File(inputFileName));
PrintWriter writer = new PrintWriter(new FileOutputStream("agentreport.txt"), true);
) {
while (reader.hasNextLine()) {
String output = reader.nextLine().toUpperCase();
System.out.println(output);
writer.println(output);
}
} catch (FileNotFoundException e) {
System.out.println("Try Again"); //error window if name is null
JOptionPane.showMessageDialog(null, "You must enter a filename", "File input error", JOptionPane.ERROR_MESSAGE);
}