Develop Reference

Java - Delete file after reading from it

I am trying to figure out why my inputFile.delete() will not delete the file. After looking at numerous topics it looks like something is still using the file and hence it won't delete. But I can't figure it out. What am I missing??
File inputFile = new File("data/Accounts.txt");
File tempFile = new File("data/tmp.txt");
try {
tempFile.createNewFile();
BufferedReader reader = new BufferedReader(new FileReader(inputFile));
BufferedWriter writer = new BufferedWriter(new FileWriter(tempFile));
String line;
int i = 0;
for (User u : data) {
String toRemove = getIDByUsername(username);
while ((line = reader.readLine()) != null) {
if (line.contains(toRemove + " ")) {
line = (i + " " + username + " " + getStatusByUsername(username) + " " + password);
}
writer.write(line + "\n");
i++;
}
}
reader.close();
writer.close();
} catch (FileNotFoundException e) {
ex.FileNotFound();
} catch (IOException ee) {
ex.IOException();
} finally {
inputFile.delete();
tempFile.renameTo(inputFile);
}

You can have that much shorter and easier by using java.nio:
public static void main(String[] args) {
// provide the path to your file, (might have to be an absolute path!)
Path filePath = Paths.get("data/Accounts.txt");
// lines go here, initialize it as empty list
List<String> lines = new ArrayList<>();
try {
// read all lines (alternatively, you can stream them by Files.lines(...)
lines = Files.readAllLines(filePath);
// do your logic here, this is just a very simple output of the content
System.out.println(String.join(" ", lines));
// delete the file
Files.delete(filePath);
} catch (FileNotFoundException fnfe) {
// handle the situation of a non existing file (wrong path or similar)
System.err.println("The file at " + filePath.toAbsolutePath().toString()
+ " could not be found." + System.lineSeparator()
+ fnfe.toString());
} catch (FileSystemException fse) {
// handle the situation of an inaccessible file
System.err.println("The file at " + filePath.toAbsolutePath().toString()
+ " could not be accessed:" + System.lineSeparator()
+ fse.toString());
} catch (IOException ioe) {
// catch unexpected IOExceptions that might be thrown
System.err.println("An unexpected IOException was thrown:" + System.lineSeparator()
+ ioe.toString());
}
}
This prints the content of the file and deletes it afterwards.
You will want to do something different instead of just printing the content, but that will be possible, too ;-) Try it...

I am trying to figure out why my inputFile.delete() will not delete the file.
That's because the old file API is crappy specifically in this way: It has no ability to tell you why something is not succeeding. All it can do, is return 'false', which it will.
See the other answer, by #deHaar which shows how to do this with the newer API. Aside from being cleaner code and the newer API giving you more options, the newer API also fixes this problem where various methods, such as File.delete(), cannot tell you the reason for why it cannot do what you ask.
There are many, many issues with your code, which is why I strongly suggest you go with deHaar's attempt. To wit:
You aren't properly closing your resources; if an exception happens, your file handlers will remain open.
Both reading and writing here is done with 'platform default encoding', whatever that might be. Basically, never use those FileReader and FileWriter constructors. Fortunately, the new API defaults to UTF_8 if you fail to specify an encoding, which is more sensible.
your exception handling is not great (you're throwing away any useful messages, whatever ex.FileNotFound() might be doing here) - and you still try to delete-and-replace even if exceptions occur, which then fail, as your file handles are still open.
The method should be called getIdByUsername
Your toRemove string is the same every time, or at least, the username variable does not appear to be updated as you loop through. If indeed it never updates, move that line out of your loop.

FileWriter not appending to existing file

I am writing a method that takes in a List of Twitter Status objects as a parameter, opens a log file containing String represenatations of Tweets, checks if any of the String representations of the Status objects are already written to the file - if so, it removes them from the list, if not it appends the Status to the file.
Everything is working up until I attempt to write to the file. Nothing is being written at all. I am led to believe that it is due to the method having the file open in two different places: new File("tweets.txt") and new FileWriter("tweets.txt, true).
Here is my method:
private List<Status> removeDuplicates(List<Status> mentions) {
File mentionsFile = new File("tweets.txt");
try {
mentionsFile.createNewFile();
} catch (IOException e1) {
// Print error + stacktrace
}
List<String> fileLines = new ArrayList<>();
try {
Scanner scanner = new Scanner(mentionsFile);
while (scanner.hasNextLine()) {
fileLines.add(scanner.nextLine());
}
scanner.close();
} catch (FileNotFoundException e) {
// Print error + stacktrace
}
List<Status> duplicates = new ArrayList<>();
for (Status mention : mentions) {
String mentionString = "#" + mention.getUser().getScreenName() + " \"" + mention.getText() + "\" (" + mention.getCreatedAt() + "\")";
if (fileLines.contains(mentionString)) {
duplicates.add(mention);
} else {
try {
Writer writer = new BufferedWriter(new FileWriter("tweets.txt", true));
writer.write(mentionString);
} catch (IOException e) {
// Print error + stacktrace
}
}
}
mentions.removeAll(duplicates);
return mentions;
}

I wrote here few thoughts looking your code.
Remember to always close the object Reader and Writer.
Have a look at try-with-resources statement :
try (Writer writer = new BufferedWriter(new FileWriter("tweets.txt", true))) {
writer.write(mentionString);
} catch (IOException e) {
// Print error + stacktrace
}
To read an entire file in a List<String>:
List<String> lines = Files.readAllLines(Paths.get("tweets.txt"), StandardCharsets.UTF_8);
And again, I think it's a bad practice write in the same file you're reading of.
I would suggest to write in a different file if you don't have a particular constraint.
But if you really want have this behavior there are few alternative.
Create a temporary file as output and, when you process is successfully completed, than move it to the old one using Files.move(from, to).

Replace specific expressions in file Java

I want to copy a annotated file, and replace those annotations in the new copy. However I am struggling on how to do the replacing. I am currently reading the whole file into a string and replacing the annotations before saving the string to a new file:
String file = null;
void openAnnotatedSource(String path){
byte[] encoded = null;
try {
encoded = Files.readAllBytes(Paths.get(anotatedpath + "/" + path));
} catch(Exception e) {
System.out.println("Error opening annotated source.");
}
file = new String(encoded, StandardCharsets.UTF_8);
}
void replaceAnotation(String anotation, String config){
file = file.replace(anotation, config);
}
void replaceAnotation(String anotation, int config){
file = file.replace(anotation, String.valueOf(config));
}
void createFinalSource(String path){
try{
Files.write(Paths.get(targetpath + "/" + path), file.getBytes());
} catch(Exception e) {
System.out.println("Couldnt create " + targetpath + "/" + path);
}
}
I don't know if I'm doing this correctly because having the file the whole time as a string does not seem correct to me.

Any decent text editor has a search&replace facility that supports regular expressions.
If however, you have reason to reinvent the wheel in Java, the approach you followed is a decent way, you are writing the modified contents into a different new file, so reading the contents from source file into a string and modifying the contents of string and creating a new file with updated string does not cause any problems.

Text file: Adding a line of text only once?

Within my application I am adding the functionality that allows me to save details to a txt file.
It is working fine, however I am trying to add a header to the txt file just once at the top of the file.
The problem I am getting is that it is being generated on every second line, not just once.
How can I change the method below to sort this problem?
Note: header is a string declared earlier in the activity.
Write to File method:
public void writeToFileEEGPower(String data){
boolean isHeader=true;
Time t= new Time();
t.setToNow();
int timeFileMinute= t.minute;
int timeFileDate= t.yearDay;
int timeFileYear= t.year;
//creating file name
String fileName= "Maths-" +timeFileMinute + timeFileDate + timeFileYear + android.os.Build.SERIAL;
//creating the file where the contents will be written to
File file= new File(dir, fileName + ".txt");
FileOutputStream os;
try{
boolean append= true;
os= new FileOutputStream(file, append);
String writeMe =data + "\n";
if(isHeader){
os.write(header.getBytes());
isHeader=false;
}
os.write(writeMe.getBytes());
os.close();
} catch(FileNotFoundException e){
e.printStackTrace();
}catch(IOException e){
e.printStackTrace();
}
}
particular code section of interest:
if(isHeader){
os.write(header.getBytes());
isHeader=false;
}

public void writeToFileEEGPower(String data, boolean isHeader){
....
}
Pass in "true" for header and pass in "false" for anything after the first one?

I was able to solve the problem by doing as was suggested in the comments and other answer.
Basically I declared the boolean: isHeader=true;within the onCreate() method of the Activity and removed it's declaration from the writeToFileEEGPower() method.

Saving file to arraylist and writing back to file; Android

I've been trying to open a text file and and save each line as the contents of an arraylist. Once this has been completed I would like to save it back to a file. I have been running into errors for so long and have tried numerous techniques. I found that for some reason, the files themselves are not being created. It may just be a simple error I'm overlooking but if you could provide any help I will be thankful.
Here's the code:
public void addToFile(){
File root = new File(Environment.getExternalStorageDirectory().getAbsolutePath() + "/appName/savedlocations");
root.mkdirs();
File fileName = new File(root, "locationslatitude.txt");
File fileName2 = new File(root, "locationslongitude.txt");
String file = fileName.toString();
String file2 = fileName2.toString();
String theContent = Double.toString(currLatitude);
String theContent2 = Double.toString(currLongitude);
s = new Scanner(file);
while (s.hasNext()){
fileList.add(s.next());
}
s.close();
fileList.add(theContent);
s2 = new Scanner(file2);
while (s2.hasNext()){
fileList2.add(s2.next());
}
s2.close();
fileList2.add(theContent2);
try {//works for latitude file
FileWriter writer = new FileWriter(file);
for(String str: fileList) {
writer.write(str);
writer.write("\r\n");
}
writer.close();
} catch (java.io.IOException error) {
//do something if an IOException occurs.
Toast.makeText(this, "Cannot Save Back To A File", Toast.LENGTH_LONG).show();
}
//save the arraylist back to its appropriate file
try {//works for longitude file
FileWriter writer = new FileWriter(file2);
for(String str2: fileList2) {
writer.write(str2);
writer.write("\r\n");
}
writer.close();
} catch (java.io.IOException error) {
//do something if an IOException occurs.
Toast.makeText(this, "Cannot Save Back To A File", Toast.LENGTH_LONG).show();
}
}
I believe I found the answer to the problem and I wanted to post it back on here so if anyone else faces the same problem this might help them.
The problem was that it wasn't creating the file. The directory was created using "root.mkdirs();". However, the files were not created and I was trying to read from non-existing files. This is what I believe caused the error. So, in order to fix this problem I altered the code to this:
try{
s = new Scanner(fileName);
while (s.hasNext()){
fileList.add(s.next());
}
s.close();
fileList.add(theContent);
}catch (FileNotFoundException ex){
ex.printStackTrace();
try{
fileName.createNewFile();
}catch (IOException e){
e.printStackTrace();
Toast.makeText(this, "Hit IOException for file one", Toast.LENGTH_SHORT).show();
}
}
try{
s2 = new Scanner(fileName2);
while (s2.hasNext()){
fileList2.add(s2.next());
}
s2.close();
fileList2.add(theContent2);
}catch (FileNotFoundException ex){
ex.printStackTrace();
try{
fileName2.createNewFile();
}catch (IOException e){
e.printStackTrace();
Toast.makeText(this, "Hit IOException for file two", Toast.LENGTH_SHORT).show();
}
}
This was the only piece of code I had to alter. The code which saved back to the file worked. I hope this will be of use to someone and thanks everyone for your help.

This code works in my project. You can use it to save ArrayList contents to text file. Make sure that the directory is created beforehand. Just iterate through your list and use println method to write it to txt file.
FileWriter outFile = new FileWriter(Environment.getExternalStorageDirectory().getAbsolutePath() + "/appName/savedlocations/nameoftextfile.txt");
PrintWriter out = new PrintWriter(outFile);
out.println("PRINT LINES WITH ME");
out.print("NOT NECCESSARILY A NEW LINE");
out.close(); // at the very end
Do not forget to catch IOException.

Have you added the following permission in the AndroidManifest.xml?
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

Check if the file directory etc exists on the device in the first place that you are using
/appName/savedlocations Good chance these do not exist. Wrong name for appName or savedLocations. Check this using some file explorer program. Tell us if it exists. Print out the full path name of
Environment.getExternalStorageDirectory().getAbsolutePath() + "/appName/savedlocations
and see if it really exists. Just download an app for file viewing or I think you can connect to the device via eclipse as well. If you need more info on how to do it let us know. But you should first check the actual error message and report this back.

don't invent your own serialization format. java already has that.
ArrayList<String> files = ...; // whatever
// write the object to a file
ObjectOutput out = new ObjectOutputStream(new FileOutputStream("filename.ser"));
out.writeObject(files);
out.close();
// read the object back
InputStream is = new FileInputStream("filename.ser");
ObjectInputStream ois = new ObjectInputStream(is);
ArrayList<String> newFiles = = (ArrayList)ois.readObject();
ois.close();