Develop Reference

Why is this not reading in?

I know I'm not doing something correctly. I know the file needs to be Serializable to read a text file.
I've got implements Serializable on the main class. But my readText and my writeText aren't converting.
Nothing is coming in when I read and when I write out the file is not text.
public static ArrayList<String> readText() {
ArrayList<String> read = new ArrayList<String>();
Frame f = new Frame();
FileDialog foBox = new FileDialog(f, "Reading serialized file",
FileDialog.LOAD);
foBox.setVisible(true);
String foName = foBox.getFile();
String dirPath = foBox.getDirectory();
File inFile = new File(dirPath + foName);
BufferedReader in = null;
ObjectInputStream OIS = null;
try {
in = new BufferedReader(new FileReader(inFile));
} catch (FileNotFoundException e1) {
e1.printStackTrace();
}
String line = null;
try {
line = in.readLine();
} catch (IOException e1) {
e1.printStackTrace();
while (line != null) {
try {
FileInputStream IS = new FileInputStream(inFile);
OIS = new ObjectInputStream(IS);
inFile = (File) OIS.readObject();
} catch (IOException io) {
io.printStackTrace();
System.out.println("An IO Exception occurred");
}
catch (ClassNotFoundException cnf) {
cnf.printStackTrace(); // great for debugging!
System.out.println("An IO Exception occurred");
} finally
{
try {
OIS.close();
} catch (Exception e) {
}
}
}
}
return read;
}
public static void writeText(ArrayList<String> file) {
ArrayList<String> write = new ArrayList<String>();
Frame f = new Frame();
FileDialog foBox = new FileDialog(f, "Saving customer file",
FileDialog.SAVE);
foBox.setVisible(true);
String foName = foBox.getFile();
String dirPath = foBox.getDirectory();
File outFile = new File(dirPath + foName);
PrintWriter out = null;
try {
out = new PrintWriter(new BufferedWriter(new FileWriter(outFile)));
for (int i = 0; i < write.size(); i++) {
String w = write.get(i);
out.println(file.toString());
}
}
catch (IOException io) {
System.out.println("An IO Exception occurred");
io.printStackTrace();
} finally {
try {
out.close();
} catch (Exception e) {
}
}
}

Nothing is coming in
You're never calling read.add(line) and you're attempting to read the file within an infinite loop inside of the catch block, which is only entered if you are not able to read the file.
Just use one try block, meaning try to open and read the file at once, otherwise, there's no reason to continue trying to read the file if it's not able to be opened
List<String> read = new ArrayList<>();
try (BufferedReader br = new BufferedReader(new FileReader(inFile)) {
String line = null;
while ((line = in.readLine()) != null) {
read.add(line); // need this
}
} catch (Exception e) {
e.printStackTrace();
}
return read;
Now, whatever you're doing with this serialized object stuff, that's completely separate, and it isn't the file or your main class that needs set to Serializable, it's whatever object you would have used a writeObject method on. However, you're reading and writing String objects, which are already Serializable.
when I write out the file is not text
Not sure what you mean by not text, but if you followed the above code, you'll get exactly what was in the initial file... Anyway, you do not need a write list variable.
You must use the individual lines of ArrayList<String> file parameter instead, but not file.toString()
for (String line:file) {
out.println(line);
}
out.close(); // always close your files and writers

How can I close BufferedReader in the while loop

When I was trying to close the BufferedReader in the while loop, it will throws an IOException: Stream closed when the loop execute the second time.
My code is like:
import java.io.*;
class Test {
public static void main(String[] args) {
int option = 0;
BufferedReader br = null;
while (option != -1) {
try {
br = new BufferedReader(new InputStreamReader(System.in));
try {
option = Integer.parseInt(br.readLine());
} catch (NumberFormatException e) {
option = -1;
}
br.close();
} catch (IOException e) {
System.err.println(e);
System.exit(-4);
}
System.out.println(option);
}
}
}
What should I do to close BufferedReader? Thanks in advance.

How can I close BufferedReader in the while loop
You are closing it in the while loop, and that's the problem.
Open it before the loop, and don't close it at all, as it's wrapped around System.in, which can't be reopened.

You can do a couple of things
try {
br = new BufferedReader(new InputStreamReader(System.in));
try {
option = Integer.parseInt(br.readLine());
} catch (NumberFormatException e) {
option = -1;
}
br.close();
} catch (IOException e) {
System.err.println(e);
br.close();
System.exit(-4);
}
}
If you're using a recent enough version
try {
br = new BufferedReader(new InputStreamReader(System.in));
try {
option = Integer.parseInt(br.readLine());
} catch (NumberFormatException e) {
option = -1;
}
} catch (IOException e) {
System.err.println(e);
System.exit(-4);
} finally {
br.close();
}
If an exception is incurred, the code will progress immediately to the catch statement, and then the finally statement if it exists.
Also, the whole point of exception handling is to take care of a exception that might happen. You normally wouldn't want to exit a system in an exception--since the code will terminate if you didn't handle the exception anyways.

File is being recreated even though it already exists

How does this code delete the file I had and makes a new one??
public void actualizaJTextArea(String cliente){
mensagens.setText("");
Scanner scanner = null;
File file = createFile(cliente + "chatswith.txt");
try {
scanner = new Scanner(file);
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
(...)
scanner.close();
}
public static File createFile(String s){
File file = new File(s);
if(!file.exists()){
try {
boolean b = file.createNewFile();
System.out.println(b);
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
return file;
}
Does the method createNewFile() do this?
Thanks and I'm sorry if this has been asked before I just can't find it.
EDIT
I am also using createFile() in here to write in it but the use is the same so i guess that can't be it:
public void recebeMensagem(boolean b){
while(true){
Mensagem m = null;
try {
m = (Mensagem)input.readObject();
System.out.println("Mensagem Recebida:"+m);
} catch (ClassNotFoundException e){
} catch (IOException e) {
try {
input.close();
System.out.println("Server desligou...");
break;
} catch (IOException e1) {
}
}
if(m != null){
for(Mensagens mensagens:v){
for(String string: m.getReceivers()){
if (mensagens.getCliente().equals(m.getAuthor()) && mensagens.getContacto().equals(string)){
mensagens.actualizaJTextArea(cliente);
}
}
}
for(String Str :m.getReceivers()){
PrintWriter p = null;
File file = Mensagens.createFile(cliente + "chatswith.txt");
try {
p = new PrintWriter(new FileWriter(file));
p.append(m.getAuthor()+"</<"+Str+"</<"+m.getText()+"\n");
p.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
}

createNewFile() is atomic and it will not delete the file if it is present. Please look at the boolean output, it should be false if your file exists already.
EDIT
add append parameter to FileWriter. It is overwriting every time.
FROM
p = new PrintWriter(new FileWriter(file));
TO
p = new PrintWriter(new FileWriter(file,true));

Why not open the stream after the close?

In the method getFileName() created the object BufferedReader and assigned reference to the object to the variable - reader. Then stream closed in the finally.
Then invoked the method readStringsFromConsole(). There creates the same object. But thrown IOException. Why did it happen ?
ps: sorry for my English :)
stacktrace:
java.io.IOException: Stream closed
at java.io.BufferedInputStream.getBufIfOpen(BufferedInputStream.java:170)
at java.io.BufferedInputStream.read(BufferedInputStream.java:336)
at sun.nio.cs.StreamDecoder.readBytes(StreamDecoder.java:284)
at sun.nio.cs.StreamDecoder.implRead(StreamDecoder.java:326)
at sun.nio.cs.StreamDecoder.read(StreamDecoder.java:178)
at java.io.InputStreamReader.read(InputStreamReader.java:184)
at java.io.BufferedReader.fill(BufferedReader.java:161)
at java.io.BufferedReader.readLine(BufferedReader.java:324)
at java.io.BufferedReader.readLine(BufferedReader.java:389)
at com.test.home04.Solution.readStringsFromConsole(Solution.java:55)
code:
import java.io.*;
import java.util.*;
public class Solution
{
public static void main(String[] args)
{
String fileName = getFileName();
ArrayList<String> listStrings = readStringsFromConsole();
writeToFileFromList(fileName, listStrings);
}
public static void writeToFileFromList (String fileName, ArrayList<String> listInputString)
{
PrintWriter writer = null;
try {
writer = new PrintWriter(fileName, "UTF-8");
for (String stringItem : listInputString)
writer.write(stringItem);
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (Exception e) {
e.printStackTrace();
} finally {
try {
if (writer != null)
writer.close();
} catch (Exception e) {
e.printStackTrace();
}
}
}
public static ArrayList<String> readStringsFromConsole() {
BufferedReader reader = null;
ArrayList<String> listInputString = new ArrayList<String>();
String line = null;
try {
reader = new BufferedReader(new InputStreamReader(System.in));
while (true)
{
line = reader.readLine();
if ("exit".equals(line))
break;
listInputString.add(line);
}
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
if (reader != null)
reader.close();
} catch (Exception e) {
e.printStackTrace();
}
return listInputString;
}
}
public static String getFileName()
{
BufferedReader reader = null;
String fileName = null;
try {
reader = new BufferedReader(new InputStreamReader(System.in));
while (fileName == null) {
fileName = reader.readLine();
}
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
if (reader != null)
reader.close();
} catch (Exception e) {
e.printStackTrace();
}
return fileName;
}
}
}

If you create a reader from System.in and close it, it also closes System.in, which can't be opened again even if you create another reader.
In short - don't close readers which are created from System.in.
Also as Andreas pointed out in the comment, the general guideline should be that System.in should only ever be wrapped once in the lifetime of the command-line program (whether by Scanner, BufferedReader, or something else), and it should never be closed. The wrapping should likely occur at the beginning of main(), and the wrapper object should either be passed around or stored in a field (static or instance).

Why did it happen ?
It happened because you closed System.in in your getFilename method.
Why not open the stream after the close?
Basically, because you can't, or if you are asking about the behavior of the JVM ... >>it<< can't.
When close() is called, the close gets sent to the operating system which closes and releases the underlying file descriptor. Once closed, the OS does not have enough information to reopen the previous file. And if the file descriptor was for an (unnamed) pipe or socket stream, then the connection cannot be remade because:
the application or service at the other end will typically have gone away,
in the case of a TCP/IP socket, the protocol does not allow reconnection.
In short: don't close a stream if you need to read or write more from / to it later, and avoid closing System.{in,out,err} entirely.
Now if your application had a filename or a host / port, it could open a new FileReader or connect a new socket. But in the case of the System.* streams, that information is not available to the application (or the JVM).
But in your particular case, I suspect that your intention is that getFileName returns the filenames supplied one at a time; i.e. each call returns the next filename. If that is the case, you will have to implement it differently:
It shouldn't close the stream or the reader.
It shouldn't open the reader (probably).
It should return the first (or next) line that it reads rather than reading all lines and returning the last one, as it currently does.

You are closing the stream from System.in. Closed stream needs to be opened before reusing it. Don't close them if you create them from System.in.
Try this,
import java.io.*;
import java.util.*;
public class Solution
{
public static void main(String[] args)
{
String fileName = getFileName();
ArrayList<String> listStrings = readStringsFromConsole();
writeToFileFromList(fileName, listStrings);
}
public static void writeToFileFromList (String fileName, ArrayList<String> listInputString)
{
PrintWriter writer = null;
try {
writer = new PrintWriter(fileName, "UTF-8");
for (String stringItem : listInputString)
writer.write(stringItem);
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (Exception e) {
e.printStackTrace();
} finally {
try {
if (writer != null)
writer.close();
} catch (Exception e) {
e.printStackTrace();
}
}
}
public static ArrayList<String> readStringsFromConsole() {
BufferedReader reader = null;
ArrayList<String> listInputString = new ArrayList<String>();
String line = null;
try {
reader = new BufferedReader(new InputStreamReader(System.in));
while (true)
{
line = reader.readLine();
if ("exit".equals(line)) {
break;
}
listInputString.add(line);
}
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
if (reader != null)
//do not close the stream
//reader.close();
} catch (Exception e) {
e.printStackTrace();
}
return listInputString;
}
}
public static String getFileName()
{
BufferedReader reader = null;
String fileName = null;
try {
reader = new BufferedReader(new InputStreamReader(System.in));
while (fileName == null) {
System.out.println("Enter a file name: ");
fileName = reader.readLine();
}
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
if (reader != null)
//do not close the stream
//reader.close();
} catch (Exception e) {
e.printStackTrace();
}
return fileName;
}
}
}

Java, 1 try block, 2 different constructors throws same exception, separate?

In following code, both Scanner and PrintWriter constructor throws FileNotFound-exception.
(PrintWriter throws if e.g. the file is readonly).
I want to make different adjustments depending on whether of the two threw the exception.
How do I accomplish this in a hopefully simple way? Can't find a fitting method in the FileNotFoundException-class.
try {
lineReader = new Scanner( scanFile );
PrintWriter pw = new PrintWriter("ord.txt");
try { ... }
finally {
lineReader.close();
pw.close();
}
}
catch (FileNotFoundException e) {
}

You could do something like this without changing what you have too much (i.e. no more nested trys):
boolean success = false; // <--
try {
lineReader = new Scanner( scanFile );
success = true; // <--
PrintWriter pw = new PrintWriter("ord.txt");
...
} catch (FileNotFoundException e) {
/*
* If 'success' is false, then Scanner threw the
* exception, otherwise it was PrintWriter.
*/
}

Here is a way to do it using another try block
try {
lineReader = new Scanner( scanFile );
try{
PrintWriter pw = new PrintWriter("ord.txt");
try { ... }
finally {
lineReader.close();
pw.close();
}
}
catch (FileNotFoundException e) {
//thrown by printwriter
}
}
catch (FileNotFoundException e) {
//thrown by scanner
}

Try this............
try
{
try {
lineReader = new Scanner( scanFile );
:
}catch (FileNotFoundException e) {
}
try {
PrintWriter pw = new PrintWriter("ord.txt");
:
}catch (FileNotFoundException e) {
}
}
finally {
lineReader.close();
pw.close();
}

Based on #arshajii 's code:
try {
lineReader = new Scanner( scanFile );
PrintWriter pw = new PrintWriter("ord.txt");
...
} catch (FileNotFoundException e) {
if(lineReader==null){
// Reader is at fault
}else{
//PrintWriter is at fault
}
}

Aside from the obvious double try-catch, you can inspect the stacktrace.
Consider the following example:
public class Main {
public static void main(String[] args) {
try {
maybeThrowAnException1();
maybeThrowAnException2();
} catch (FileNotFoundException e) {
System.out.println(e.getStackTrace()[0].getMethodName());
}
}
private static void maybeThrowAnException1() throws FileNotFoundException{
if(new Random().nextInt(2) % 2 == 0){
throw new FileNotFoundException();
}
}
private static void maybeThrowAnException2() throws FileNotFoundException{
if(new Random().nextInt(2) % 2 == 0){
throw new FileNotFoundException();
}
}
}
This will sometimes print MaybeThrowAnException1, sometimes MaybeThrowAnException2.
You can change this to e.getStackTrace()[0].getClassName() to see if it returns Scanner or PrintWriter and perform logic based on that result.