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
Related
I'm working on appending objects to a binary file. My file is:
File f=new File("person.dat");
I'm getting an error (java.io.StreamCorruptedException: invalid stream header: 79737200) when I attempt to open the binary file. As far as I can tell the program writes the data just fine, but as soon as I try reading from it, I get the above error. Any help is appreciated!
My Code to write:
AppendObjectOutputStream out = null;
try {
out = new AppendObjectOutputStream(new FileOutputStream(f, true));
out.writeObject(new Student(name, age));
out.flush();
}
catch (Exception ex) {
ex.printStackTrace();
}
finally {
out.close();
}
My class for making appendable:
public class AppendObjectOutputStream extends ObjectOutputStream {
public AppendObjectOutputStream(OutputStream out) throws IOException {
super(out);
}
#Override
protected void writeStreamHeader() throws IOException {
reset();
}
}
My partial code for reading and adding objects to an ArrayList:
Course course = new Course();
Student st = null;
ObjectInputStream in = null;
try {
in = new ObjectInputStream(new FileInputStream("person.dat"));
try
{
while (true)
{
st = (Student) in.readObject();
course.addAccount(st); //adds student object to an ArrayList in
//class Course
}
}
catch (EOFException ex) {
}
}
catch (Exception ex) {
ex.printStackTrace();
} finally {
in.close();
}
UPDATE:
Current code to read but its not printing anything to screen:
try(ObjectInputStream ois = new ObjectInputStream(
new BufferedInputStream(Files.newInputStream(f))))
{
while (ois.available() > 0)
{
st = (Student) ois.readObject();
studentlist.addAccount(st);
System.out.println(st.getStudentNumber());
}
}
catch (Exception ex)
{
ex.printStackTrace();
}
This is how I write to file:
Path f = Paths.get("person.dat");
try (ObjectOutputStream oos = new ObjectOutputStream(
new BufferedOutputStream(Files.newOutputStream(f, StandardOpenOption.APPEND))))
{
oos.writeObject(new Student(name,age));
}
catch(Exception ex)
{
ex.printStackTrace();
}
Rather than trying to fix your utility classes, I suggest to use the standard classes of the NIO.2 File API.
Try something like (untested):
Path personDataFilePath = Paths.get("person.dat");
// or Java 11:
// Path personDataFilePath = Path.of("person.dat");
try (ObjectOutputStream oos = new ObjectOutputStream(new BufferedOutputStream(Files.newOutputStream(personDataFilePath, StandardOpenOption.APPEND)))){
oos.writeObject(new Student(name,age));
} catch (IOException ex) {
// do some error handling here
}
and to read the file, something like (untested):
List<Student> students = new ArrayList<>();
try (ObjectInputStream ois = new ObjectInputStream(new BufferedInputStream(Files.newInputStream(personDataFilePath)))){
while (ois.available() > 0){
students.add((Student) ois.readObject());
}
} catch (IOException ex) {
// do some error handling here
}
I have modified the code to work around making a file "appendable". I write a single arraylist object to the file (the arraylist holds a list of student objects). When I want to add a student, I read the object (arraylist) from the file, add my new student to the arraylist and write the arraylist back to the file. It is now working and my file does not have an append format.
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;
}
}
}
I am have a program were there are two forms one for the consultant and for the customer. On the first form the user will enter the consultant details and his ID will be saved in a csv file and this works fine.
Consultant cons_save = new Consultant();
cons_save.setPersonfirstname(this.jTextField1.getText());
cons_save.setPersonlastname(this.jTextField2.getText());
cons_save.setPersonID(this.jTextField4.getText());
this.jTextField1.setText("");
this.jTextField2.setText("");
this.jTextField3.setText("");
cons_save.ConsultantID = cons_save.PersonID;
cons_save.setConsultantID(this.jTextField4.getText());
this.jTextField4.setText("");
try
{
BufferedWriter writer = new BufferedWriter(new FileWriter("E:\\ryan_assignment_sit2\\ConsID\\consID.csv", true));
writer.append(cons_save.ConsultantID);
writer.append(",");
writer.flush();
writer.close();
}
catch(IOException e)
{
e.printStackTrace();
}
cons_save.savecons();
After the id is saved the Id is called out from the csv to an array and this works fine as well.
public CreateCustomer() {
initComponents();
ArrayList<String> ConsIDList = new ArrayList<String>();
String csvFileToRead = "E:\\ryan_assignment_sit2\\ConsID\\consID.csv"; // Reads the CSV File.
BufferedReader br = null; // Creates a buffer reader.
String line = "";
String splitBy = ","; // Reader Delimiter
try {
br = new BufferedReader(new FileReader(csvFileToRead)); // Buffer Reader with file name to read.
Scanner reader = new Scanner(System.in);
while ((line = br.readLine()) != null) { //While there is a line to read.
reader = new Scanner(line);
reader.useDelimiter(splitBy);
while (reader.hasNext()) { // While there is a next value (token).
ConsIDList.add(reader.next());
}
}
} catch (FileNotFoundException exception) { // Exception Handler if the File is not Found.
exception.printStackTrace();
} catch (IOException exception) { // Input/Output exception
exception.printStackTrace();
} finally {
if (br != null) {
try {
br.close(); // Close the Scanner.
} catch (IOException exception) {
exception.printStackTrace();
}
}
Vector<String> vectorData = new Vector<String>(ConsIDList);
DefaultComboBoxModel<String> comboBoxModel = new DefaultComboBoxModel<>(vectorData);
this.jComboBox1.setModel(comboBoxModel);
}
}
The array is working fine but the combo box is not getting populated with the arraylist.
I have the following code to write in three files. I have printed the Strings before writing to ensure they have some data in them, the printed Strings show the data given to them by calling this function but on creation of file the files are empty.
Please suggest something.
public static void save(String editedFileText,String srcFileText,String translFileText)throws IOException {
JFileChooser chooser = new JFileChooser();
System.out.println(editedFileText);
System.out.println(srcFileText);
System.out.println(translFileText);
int retrival = chooser.showSaveDialog(null);
if (retrival == JFileChooser.APPROVE_OPTION) {
try {
FileWriter edit = new FileWriter(chooser.getSelectedFile()+".txt");
edit.write(editedFileText.toString());
FileWriter srcFile = new FileWriter(chooser.getSelectedFile()+"_srcText"+".txt");
srcFile.write(srcFileText.toString());
FileWriter trans = new FileWriter(chooser.getSelectedFile()+"_translFile"+".txt");
trans.write(translFileText.toString());
} catch (Exception ex) {
ex.printStackTrace();
}
}
Get in the habit of creating all Writers, Readers, InputStreams and OutputStreams in try-with-resources statements. It ensures they will be properly closed:
try (FileWriter edit = new FileWriter(chooser.getSelectedFile()+".txt")) {
edit.write(editedFileText);
}
try (FileWriter srcFile = new FileWriter(chooser.getSelectedFile()+"_srcText"+".txt")) {
srcFile.write(srcFileText);
}
try (FileWriter trans = new FileWriter(chooser.getSelectedFile()+"_translFile"+".txt")) {
trans.write(translFileText);
}
If you're just writing a single String, you have the option of using Files.write, which allows you to forego the use of a Writer altogether:
Files.write(Paths.get(chooser.getSelectedFile()+".txt"),
editedFileText.getBytes());
Files.write(Paths.get(chooser.getSelectedFile()+"_srcText"+".txt"),
srcFileText.getBytes());
Files.write(Paths.get(chooser.getSelectedFile()+"_translFile"+".txt"),
translFileText.getBytes());
Add a finally to close the opened files, but first you need to declare them outside the try catch finally:
FileWriter edit,srcFile, trans;
edit = srcFile = trans = null;
try {
edit = new FileWriter(chooser.getSelectedFile()+".txt");
edit.write(editedFileText.toString());
srcFile = new FileWriter(chooser.getSelectedFile()+"_srcText"+".txt");
srcFile.write(srcFileText.toString());
trans = new FileWriter(chooser.getSelectedFile()+"_translFile"+".txt");
trans.write(translFileText.toString());
} catch (Exception ex) {
ex.printStackTrace();
}finally{
if(edit != null)
edit.close();
if(srcFile != null)
srcFile.close();
if(trans != null)
trans.close();
}
FileWriter writer=null;
try {
writer = new FileWriter(filename);
writer.write(sb.toString());
} catch (Exception e) {
} finally {
if (writer != null)
try {
writer.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
I have a problem with reading objects from file Java.
file is anarraylist<projet>
This is the code of saving objects :
try {
FileOutputStream fileOut = new FileOutputStream("les projets.txt", true);
ObjectOutputStream out = new ObjectOutputStream(fileOut);
for (projet a : file) {
out.writeObject(a);
}
out.close();
} catch (Exception e) {
e.printStackTrace();
}
And this is the code of reading objects from file ::
try {
FileInputStream fileIn = new FileInputStream("les projets.txt");
ObjectInputStream in = new ObjectInputStream(fileIn);
while (in.available() > 0){
projet c = (projet) in.readObject();
b.add(c);
}
choisir = new JList(b.toArray());
in.close();
} catch (Exception e) {
e.printStackTrace();
}
Writing is working properly. The problem is the reading... it does not read any object (projet) What could be the problem?
As mentioned by EJP in comment and this SO post . if you are planning to write multiple objects in a single file you should write custom ObjectOutputStream , because the while writing second or nth object header information the file will get corrupt.
As suggested by EJP write as ArrayList , since ArrayList is already Serializable you should not have issue. as
out.writeObject(file) and read it back as ArrayList b = (ArrayList) in.readObject();
for some reason if you cant write it as ArrayList. create custome ObjectOutStream as
class MyObjectOutputStream extends ObjectOutputStream {
public MyObjectOutputStream(OutputStream os) throws IOException {
super(os);
}
#Override
protected void writeStreamHeader() {}
}
and change your writeObject as
try {
FileOutputStream fileOut= new FileOutputStream("les_projets.txt",true);
MyObjectOutputStream out = new MyObjectOutputStream(fileOut );
for (projet a : file) {
out.writeObject(a);
}
out.close();
}
catch(Exception e)
{e.printStackTrace();
}
and change your readObject as
ObjectInputStream in = null;
try {
FileInputStream fileIn = new FileInputStream("C:\\temp\\les_projets1.txt");
in = new ObjectInputStream(fileIn );
while(true) {
try{
projet c = (projet) in.readObject();
b.add(c);
}catch(EOFException ex){
// end of file case
break;
}
}
}catch (Exception ex){
ex.printStackTrace();
}finally{
try {
in.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}