Develop Reference

ObjectInputStream gives IOException when readObject() is called

I'm trying to copy a file with .dat extension from a certain directory decided by the user into the project directory. When I try to read the saved object selected by the user, the program always gives IOException.
File f = new File(chooser.getSelectedFile().getPath());
if(f.exists() && !f.isDirectory()) {
FileInputStream flusso= null;
ObjectInputStream leggiObj=null;
try {
flusso = new FileInputStream(chooser.getSelectedFile().getPath());
System.out.println(chooser.getSelectedFile().getPath());
leggiObj = new ObjectInputStream(flusso);
if (leggiObj.readObject().getClass().equals(DatiProgresso.class)) {
DatiProgresso dp = (DatiProgresso) leggiObj.readObject();//<----THIS LINE GIVES THE EXEPTION
leggiObj.close();
flusso.close();
System.out.println("Ciao");
FileOutputStream fop = new FileOutputStream("salvataggi/" + dp.getNome() + ".dat");
ObjectOutputStream scriviObj = new ObjectOutputStream(fop);
scriviObj.writeObject(dp);
scriviObj.flush();
fop.close();
} else {
JOptionPane.showMessageDialog(this, "Unacceptable file", "Error", JOptionPane.ERROR_MESSAGE);
}
} catch (HeadlessException ex) {
System.out.println("HeadlessException");
ex.printStackTrace();
} catch (FileNotFoundException ex) {
System.out.println("FileNotFoundException");
ex.printStackTrace();
} catch (IOException ex) {
System.out.println("IOException");
ex.printStackTrace();
} catch (ClassNotFoundException ex) {
System.out.println("ClassNotFoundException");
ex.printStackTrace();
}
}
}
else
{
JOptionPane.showMessageDialog(this, "Unacceptable file", "Error" ,JOptionPane.ERROR_MESSAGE);
}
DatiProgresso dp = (DatiProgresso) leggiObj.readObject();
This line gives the exception.

leggiObj.readObject().getClass().equals(DatiProgresso.class) - here you read your object from the data stream. On next line you attempt to read 2nd object from the stream. If there is no another object then stream fails.

IOUtils.write creates new file but doesn't write data

using IOUtils.write to write a string to a file
try {
IOUtils.write("test", new FileWriter(configFile));
} catch (Exception e) {
e.printStackTrace();
}
where configfile is the location of the configuration file ("./resources/config.json")
This seems to delete the file and replace it with a file that has no contents.
no exceptions are thrown either.

Make sure to close the stream after use, else the data might not be written to the file.
FileWriter fw=null;
try {
fw= new FileWriter(configFile);
IOUtils.write("test",fw);
}catch (Exception e) {
e.printStackTrace();
}finally
{
IOUtils.closeQuietly(fw);
}

You need to close the writer, or use try with resources. Otherwise everything might not be flushed to disk:
try (FileWriter fw = new FileWriter(configFile)) {
IOUtils.write("test", fw);
} catch (IOException e) {
e.printStackTrace();
}

Try this code:
FileWriter fw = null;
try {
fw = new FileWriter(configFile);
IOUtils.write("test", fw);
} catch (IOException e) {
e.printStackTrace();
} finally {
if(fw != null)
fw.close();
}

java typing into file, file not showing, using bytes

i need some help here.
I changed a int to an hex after that changing it to byte and tried writing it into a file.
But the file does not appear in the directory as the jar file i build.
File ModFile =new File(NameText.getText() + ".mod");
FileOutputStream writer = null;
String toProcess = CodesBox.getText();
int i = Integer.parseInt(CodesBox.getText());
byte codes = (byte) i;
try {
writer = new FileOutputStream(ModFile);
writer.write(codes);
} catch (IOException ex) {
Logger.getLogger(ModMakerGui.class.getName()).log(Level.SEVERE, null, ex);
}finally{
try {
writer.close();
} catch (IOException e) {
e.printStackTrace();
}
}
NameText.getText() is definitely there
and the CodesBox.getText() is also definitely correct.
As you can see this is what i get when i open the generated file in an hex editor.
But i would want this instead.
May i know how to fix this?
I know the output file is "vPTP " with spaces, i need the spaces, thank you

Please use either FileWriter or PrintWriter.
For example:
modFile = new File(NameText.getText() + ".mod");
FileWriter writer = null;
if(!modFile.exists()){
try {
modFile.createNewFile();
writer = new FileWriter(ModFile);
System.out.println("Mod file has been created to the current directory");
writer.write(CodesBox.getText());
} catch (IOException ex) {
Logger.getLogger(ModMakerGui.class.getName()).log(Level.SEVERE, null, ex);
}
}

Try this if you use FileOutputStream as well as to write bytes.
File ModFile =new File(NameText.getText() + ".mod");
FileOutputStream writer = null;
try {
writer = new FileOutputStream(ModFile);
writer.write(CodesBox.getText().getBytes(),0,CodesBox.getText().getBytes().length);
} catch (IOException ex) {
Logger.getLogger(ModMakerGui.class.getName()).log(Level.SEVERE, null, ex);
}finally{
try {
writer.close();
} catch (IOException e) {
e.printStackTrace();
}
}

How to use JOptionPane string for BufferedReader?

I am using a JOptionPane to ask the user for a file, which I then give to BufferedReader. However, my code keeps throwing a FileNotFoundException. Could someone please help me to understand why.
Here is my code...
edit = JOptionPane.showInputDialog("Enter a file to edit");
try {
BufferedReader fIn = new BufferedReader(new FileReader(edit));
String in;
try {
while((in = fIn.readLine()) != null) {
System.out.println(in);
}
fIn.close();
}
catch (IOException ex) {
Logger.getLogger(WordProcessor.class.getName()).log(Level.SEVERE, null, ex);
}
try {
fIn.close();
}
catch (IOException ex) {
Logger.getLogger(WordProcessor.class.getName()).log(Level.SEVERE, null, ex);
}
}
catch (FileNotFoundException ex) {
JOptionPane.showMessageDialog(null, "File does not exist");
}

JOptionPane.showMessageDialog(null, "File does not exist");
Here you should do ex.printStackTrace() it will reveal exact problem.
Note that current directory of program will be one from where it is launched so any relative path should be in relation to that not the source directory..

How to delete only the content of a file in Java?

How can I delete the content of a file in Java?

How about this:
new RandomAccessFile(fileName).setLength(0);

new FileOutputStream(file, false).close();

You could do this by opening the file for writing and then truncating its content, the following example uses NIO:
import static java.nio.file.StandardOpenOption.*;
Path file = ...;
OutputStream out = null;
try {
out = new BufferedOutputStream(file.newOutputStream(TRUNCATE_EXISTING));
} catch (IOException x) {
System.err.println(x);
} finally {
if (out != null) {
out.flush();
out.close();
}
}
Another way: truncate just the last 20 bytes of the file:
import java.io.RandomAccessFile;
RandomAccessFile file = null;
try {
file = new RandomAccessFile ("filename.ext","rw");
// truncate 20 last bytes of filename.ext
file.setLength(file.length()-20);
} catch (IOException x) {
System.err.println(x);
} finally {
if (file != null) file.close();
}

May problem is this leaves only the head I think and not the tail?
public static void truncateLogFile(String logFile) {
FileChannel outChan = null;
try {
outChan = new FileOutputStream(logFile, true).getChannel();
}
catch (FileNotFoundException e) {
e.printStackTrace();
System.out.println("Warning Logfile Not Found: " + logFile);
}
try {
outChan.truncate(50);
outChan.close();
}
catch (IOException e) {
e.printStackTrace();
System.out.println("Warning Logfile IO Exception: " + logFile);
}
}

Open the file for writing, and save it. It delete the content of the file.

try {
PrintWriter writer = new PrintWriter(file);
writer.print("");
writer.flush();
writer.close();
}catch (Exception e)
{
}
This code will remove the current contents of 'file' and set the length of file to 0.