Develop Reference

How to raise and handle a FileNotFoundException() error

The task is to throw a FileNotFoundException() exception and handle it. You also need to check if the file exists on the computer and read data from it.
I wrote 2 methods, one searches for a file, the second one reads, but I am completely confused how to handle this exception. Can you suggest how to refactor this code to handle FileNotFoundException. And point out the errors of the code itself, since it is very terrible (I am just starting to learn Java)
public static boolean findFile(String path, String filename) throws FileNotFoundException {
File f = new File(path + "\\" + filename);
if (f.exists()) {
System.out.println("File found");
return true;
}
else {
System.out.println("File not found, please check that you entered the correct path and file name");
throw new FileNotFoundException();
}
}
public static ArrayList<String> readFromFile(String path, String filename) throws FileNotFoundException {
if(findFile(path,filename)) {
ArrayList<String> ip = new ArrayList<>();
try (BufferedReader br = new BufferedReader(new FileReader(path + "\\" + filename))) {
String line;
ip.add(br.readLine());
while ((line = br.readLine()) != null) {
ip.add(line);
}
} catch (IOException e) {
System.out.println(e.getMessage());
System.exit(-1);
}
return ip;
}
else {
System.out.println("Failed to read the file, check the correct path and file name");
return null;
}
}

The way you've defined the findFile method, it is always going to either return true or throw an exception. So it doesn't really make any sense to test the value returned by findFile(), or for that method to even return a value. Instead, you can assume that if the method does not throw an exception, then the file was found. For the case where it wasn't, you want to catch the exception and deal with it. Here's what that all looks like:
public static void findFile(String path, String filename) throws FileNotFoundException {
File f = new File(path + "\\" + filename);
if (f.exists()) {
System.out.println("File found");
}
else {
System.out.println("File not found, please check that you entered the correct path and file name");
throw new FileNotFoundException();
}
}
public static ArrayList<String> readFromFile(String path, String filename) throws FileNotFoundException {
try {
findFile(path,filename);
// Code to read the file...
...
}
catch (FileNotFoundException ex) {
System.out.println("Failed to read the file, check the correct path and file name");
return null;
}
}

The task is to throw a FileNotFoundException() exception and handle
it.
The answer to this question depends a lot on context.
If you are running this from the command line, you will want to add a try catch for the exception and then try again if it happens
Exception e;
do {
e = null;
try {
callAMethod();
} catch(ex) {
e=ex;
}
} while (e != null);
If you are doing this from a GUI/Swing, you can re-rethrow as a RuntimeException and use Log4j or Thread.setUncaughtExceptionHandler(..) to log the error and inform the user. The user can then try again
If you are doing this as a webapp, you will want to change the response code to 404 (FileNotFound) and indicate the file that was not found
Lastly, where you throw the FileNow FoundException, you should include a message
throw new FileNotFoundException(/*incude a string with the file path*/);

Java Create File and Directory if needed

I want to create a file (outside of the workspace) so that everyone who opens my program has his own Textfile.
Currently I have to following Code:
private static final File m_dataFile = new File("C:\\temp\\MainPlayersLoginData.txt");
private static FileWriter writer;
private static Scanner reader;
public static void setMainPlayersLoginData(String name, String password) {
try {
if (!m_dataFile.exists()) {
createDirectory();
}
writer = new FileWriter(m_dataFile);
writer.write(name + "\n" + password);
writer.close();
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
if (writer != null)
writer.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
private static void createDirectory() {
System.out.println("creating directory: " + m_dataFile.getName());
boolean result = false;
try {
m_dataFile.mkdirs();
result = true;
} catch (SecurityException se) {
}
if (result) {
System.out.println("DIR created");
}
}
With this code, the program creates a folder temp as planned, but creates a folder named "MainPlayersLoginData.txt" in it instead of a textfile. In addition I get a FileNotFoundException with the message "Access denied" when initialising the FileWriter.
I tried using m_datafile.mkdir() instead of m_datafile.mkdirs() but this time I get a FileNotFoundException with the message "The system cannot find the specified path" and the folder temp isnt created.
Edit: If i create the folder and the Textfile on my own, everything works fine.

How can I resume code where I left off after FILENOTFOUNDEXCEPTION is thrown

I am writing a file into a directory. There might be the chance that the directory becomes unreachable.
What I want to do is..
As the code is writing to the file, if the directory becomes unreachable or a file not found exception is thrown I want it to keep checking if the directory exists and continue where I left off after the directory exists again.
After some time if the directory does not come back up then I would shut the program down.
My problem is that when a file not found exception is thrown the program just shuts down all together. Here is my code:
public class BusStopsProcessor implements Runnable
{
private BlockingQueue<Bus<buses>> busQueue;
private Bus<buses> BusObject;
public BusStopsProcessor(BlockingQueue<Bus<buses>> busQueue)
{
this.busQueue = busQueue;
}
#Override
public void run()
{
try
{
String path = "C:\\Users\\Me\\Documents\\";
File file = new File(path + "busStopsFile.txt");
FileWriter fw = new FileWriter(file, true);
CSVWriter writer = new CSVWriter(fw, '|', CSVWriter.NO_QUOTE_CHARACTER);
while(true)
{
BusObject = busQueue.take();
//each bus object should have a bus date if it does not then it is a
//poison bus object.
if(BusObject.getBusDate() != null)
{
createBusFile(BusObject, writer);
else
{
try
{
//Finished processing bus stops so close writer.
writer.close();
fw.close();
break;
}
catch (IOException e)
{
e.printStackTrace();
}
}
}
}
catch (InterruptedException e)
{
Thread.currentThread().interrupt();
e.printStackTrace();
}
catch (FileNotFoundException e)
{
//If a FILENOTFOUND exception is thrown here I want
//my code to be able to pick up where I left off
e.printStackTrace();
logger.warn(e.getMessage());
}
catch (IOException e)
{
e.printStackTrace();
}
}
Here is the method that I want to keep checking if the directory exists. If the file is being written into and all of a sudden the directory goes down. I dont want to repeat the same information in the file I want it to continue to write from where it left off but I just cant figure out how to do that. thank you.
private void createBusFile(Bus<buses> aBusObject, CSVWriter writer) throws InterruptedException
{
//Get bus information here
for(Bus<buses> busStop : aBusObject.getBusStops())
{
busNumber = busStop.getBusNumber();
busArrivalTime = busStop.getBusArrivalTime();
busStop = busStop.getBusStop();
String[] busFields = {busNumber, busDate, busStop};
//If a file not found exception is thrown here I want it to keep checking if the directory exists. And pick up from where I left off
writer.writeNext(busFields);
}
}
}

How to Pass File without full Path?

I created Simple program for File update throgh java Program
public class AppendToFileExample {
private static final String FILENAME = "TestFile.txt";
public static void main(String[] args) {
BufferedWriter bw = null;
FileWriter fw = null;
try {
String data = " This is new content after edit";
File file = new File(FILENAME);
fw = new FileWriter(file, true);
bw = new BufferedWriter(fw);
bw.write(data);
System.out.println("Done");
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
if (bw != null)
bw.close();
if (fw != null)
fw.close();
} catch (IOException ex) {
ex.printStackTrace();
}
}
}
}
Which is working successfully
But Then i tried to do same thing with the help of ServletContextListener but with servlet everything working fine except I have to put Full file path like this
String FILENAME = "C:\\Users\\admin\\workspacetasks\\UpdateText\\TestFile.txt";
With this full path its working fine but its not updating file when i try to pass only file name like this
String FILENAME = "test.txt";
So my question is how to pass file without full path of file..Is there any other way or anything?or any link for reference?
Thank You.
Below is mine ServletContextListener
public class StartupListener implements ServletContextListener {
private static Logger log = Logger.getLogger(StartupListener.class);
#Override
public void contextInitialized(ServletContextEvent arg0) {
System.out.println("contextInitialized");
UpdateTextFile updateTextFile = new UpdateTextFile();
System.out.println("Before");
updateTextFile.exec();
System.out.println("after");
}
#Override
public void contextDestroyed(ServletContextEvent arg0) {
// TODO Auto-generated method stub
}
}
and then this will call method in java program that program is here
public class UpdateTextFile
{
private static Logger log = Logger.getLogger(UpdateTextFile.class);
public void exec() {
// String FILENAME = "C:\\Users\\admin\\workspacetasks\\UpdateText\\TestFile.txt";
String FILENAME = "TestFile.txt";
System.out.println("Inside exce ");
BufferedWriter bw = null;
FileWriter fw = null;
try {
String data = "Aloha after edit \n";
System.out.println(data);
File file = new File(FILENAME);
System.out.println(FILENAME);
System.out.println("Before FileWriter");
fw = new FileWriter(file, true);
System.out.println("After FileWriter");
System.out.println("Before BufferedWriter");
bw = new BufferedWriter(fw);
System.out.println("After BufferedWriter");
System.out.println("Before Write Data");
bw.write(data);
System.out.println("After Write Data");
System.out.println("Done");
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
if (bw != null)
bw.close();
if (fw != null)
fw.close();
} catch (IOException ex) {
ex.printStackTrace();
}
}
}
}

If your code doesn't throw any exceptions, the file is definitely being created, just not where you think. A file with a relative path will be created relative to the current working directory of your application, whatever that may be. In the case of a servlet container it certainly won't be anywhere inside the webapp's own directory. For example in Tomcat it might be Tomcat's bin directory.
NB:
Contrary to the now-deleted answer by #SilvanBregy, the CWD of an application doesn't necessarily have anything to do with where its own JAR file is located, and contrary to the comment by #soufrk it has exactly nothing to do with the classpath.
The exists() test and createNewFile() calls are both complete wastes of time. new FileOutputStream() already does that, so you're forcing the system to do it all twice, as well as deleting the file you just created.
You don't need to call getAbsoluteFile() either: the File alone is sufficient.
You do however need to close the BufferedWriter.

Yes its SOLVED.If any one in future have same problem then
just click right on program Run As > Run Configuration > Tomcat 8 on left panel > Arguments and then set Other working directory as you want...
Dont know its correct approach to do but thats what i got..if any one get any other way without changing working directory then please share else if i get any i will post it

file.delete() wont delete file, java

Okay, this is going to be a bit long. So I made a junit test class to test my program. I wanted to test if a method that uses a Scanner to read a file into the program threw and exception, if the file didn't exist like this:
#Test
public void testLoadAsTextFileNotFound()
{
File fileToDelete = new File("StoredWebPage.txt");
if(fileToDelete.delete()==false) {
System.out.println("testLoadAsTextFileNotFound - failed");
fail("Could not delete file");
}
try{
assertTrue(tester.loadAsText() == 1);
System.out.println("testLoadAsTextFileNotFound - passed");
} catch(AssertionError e) {
System.out.println("testLoadAsTextFileNotFound - failed");
fail("Did not catch Exception");
}
}
But the test fails at "could not delete file", so I did some searching. The path is correct, I have permissions to the file because the program made it in the first place. So the only other option would be, that a stream to or from the file is still running. So I checked the method, and the other method that uses the file, and as far as I can, both streams are closed inside the methods.
protected String storedSite; //an instance variable
/**
* Store the instance variable as text in a file
*/
public void storeAsText()
{
PrintStream fileOut = null;
try{
File file = new File("StoredWebPage.txt");
if (!file.exists()) {
file.createNewFile();
}
fileOut = new PrintStream("StoredWebPage.txt");
fileOut.print(storedSite);
fileOut.flush();
fileOut.close();
} catch(Exception e) {
if(e instanceof FileNotFoundException) {
System.out.println("File not found");
}
fileOut.close();
} finally {
if(fileOut != null)
fileOut.close();
}
}
/**
* Loads the file into the program
*/
public int loadAsText()
{
storedSite = ""; //cleansing storedSite before new webpage is stored
Scanner fileLoader = null;
try {
fileLoader = new Scanner(new File("StoredWebPage.txt"));
String inputLine;
while((inputLine = fileLoader.nextLine()) != null)
storedSite = storedSite+inputLine;
fileLoader.close();
} catch(Exception e) {
if(e instanceof FileNotFoundException) {
System.out.println("File not found");
return 1;
}
System.out.println("an Exception was caught");
fileLoader.close();
} finally {
if(fileLoader!=null)
fileLoader.close();
}
return 0; //return value is for testing purposes only
}
I'm out of ideas. Why can't I delete my file?
EDIT: i've edited the code, but still this give me the same problem :S

You have two problems here. The first is that if an exception is thrown during your write to the file, the output stream is not closed (same for the read):
try {
OutputStream someOutput = /* a new stream */;
/* write */
someOutput.close();
The second problem is that if there's an exception you aren't notified:
} catch (Exception e) {
if (e instanceof FileNotFoundException) {
/* do something */
}
/* else eat it */
}
So the problem is almost certainly that some other exception is being thrown and you don't know about it.
The 'correct' idiom to close a stream is the following:
OutputStream someOutput = null;
try {
someOutput = /* a new stream */;
/* write */
} catch (Exception e) {
/* and do something with ALL exceptions */
} finally {
if (someOutput != null) someOutput.close();
}
Or in Java 7 you can use try-with-resources.