Develop Reference

How to write a binary file from a String and retrieve it again to a String?

I have a string and want to persist it into a file and be able to retrieve it again into a String.
Something is wrong with my code because It's supposing that I must write something binary non readable but when i Open the file I can read this:
Original string:
[{"name":"asdasd","etName":"111","members":[]}]
Stored string in binary file:
[ { " n a m e " : " a s d a s d " , " e t N a m e " : " 1 1 1 " , " m e m b e r s " : [ ] } ]
I detect two problems:
Is not stored in binary! I can read it. It's supposed to be a confused binary text unreadable but I can read it.
When i retrieve it it's being retrieved with that strange space between the characters. So it doesn't works.
This is my code for storing the string:
public static void storeStringInBinary(String string, String path) {
DataOutputStream os = null;
try {
os = new DataOutputStream(new FileOutputStream(path));
os.writeChars(string);
os.flush();
} catch (Exception e) {
e.printStackTrace();
} finally {
if (os != null) {
try {
os.close();
} catch (Exception e) {
e.printStackTrace();
}
}
}
}
And this is my code for reading it from binary to a String:
public static String retrieveStringFromBinary(String file) {
String string = null;
BufferedReader reader = null;
try {
reader = new BufferedReader(new FileReader (file));
String line = null;
StringBuilder stringBuilder = new StringBuilder();
while((line = reader.readLine()) != null) {
stringBuilder.append(line);
}
return stringBuilder.toString();
} catch (Exception e){
e.printStackTrace();
} finally {
if (reader != null) {
try {
reader.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
return string;
}

Firstly, there isn't really a distinction between a text file and a binary file. A text file is just a file who's content falls in the range of byte values that correspond to characters.
If you want to encrypt the content of the file so it is unreadable just by catting the file then you will need to choose an appropriate encryption method.
Secondly Mixing Readers/Writers and Streams in Java is never a good idea, pick one style and stick to it.
The problem with your function that saves the string to a file is that you are using the writeChars() method, which from the doc does the following:
Writes a char to the underlying output stream as a 2-byte value, high byte first. If no exception is thrown, the counter written is incremented by 2.
Since your string is made up of single byte characters this is leading to the padding of your string with null bytes, which are being converted to spaces when read back in. If you change this to writeBytes() then you should get output without the extra null byte.
The null byte will also stop your read function working as the readLine() function will return null on it's first call due to the leading 0x00 in the file.

Try this out:
public static void storeStringInBinary(String string, String path) {
try(ObjectOutputStream os = new ObjectOutputStream(new FileOutputStream(path))) {
os.writeObject(string);
} catch (IOException e) {
e.printStackTrace();
}
}
public static String retrieveStringFromBinary(String file) {
String string = null;
try (ObjectInputStream reader = new ObjectInputStream(new FileInputStream(file))){
string = (String) reader.readObject();
} catch (ClassNotFoundException | IOException e) {
e.printStackTrace();
}
return string;
}

Java too many open files exception

I have a problem on my code; basically I have an array containing some key:
String[] ComputerScience = { "A", "B", "C", "D" };
And so on, containing 40 entries.
My code reads 900 pdf from 40 folder corresponding to each element of ComputerScience, manipulates the extracted text and stores the output in a file named A.txt , B.txt, ecc ...
Each folder "A", "B", ecc contains 900 pdf.
After a lot of documents, an exception "Too many open files" is thrown.
I'm supposing that I am correctly closing files handler.
static boolean writeOccurencesFile(String WORDLIST,String categoria, TreeMap<String,Integer> map) {
File dizionario = new File(WORDLIST);
FileReader fileReader = null;
FileWriter fileWriter = null;
try {
File cat_out = new File("files/" + categoria + ".txt");
fileWriter = new FileWriter(cat_out, true);
} catch (IOException e) {
e.printStackTrace();
}
try {
fileReader = new FileReader(dizionario);
} catch (FileNotFoundException e) { }
try {
BufferedReader bufferedReader = new BufferedReader(fileReader);
if (dizionario.exists()) {
StringBuffer stringBuffer = new StringBuffer();
String parola;
StringBuffer line = new StringBuffer();
int contatore_index_parola = 1;
while ((parola = bufferedReader.readLine()) != null) {
if (map.containsKey(parola) && !parola.isEmpty()) {
line.append(contatore_index_parola + ":" + map.get(parola).intValue() + " ");
map.remove(parola);
}
contatore_index_parola++;
}
if (! line.toString().isEmpty()) {
fileWriter.append(getCategoryID(categoria) + " " + line + "\n"); // print riga completa documento N x1:y x2:a ...
}
} else { System.err.println("Dictionary file not found."); }
bufferedReader.close();
fileReader.close();
fileWriter.close();
} catch (IOException e) { return false;}
catch (NullPointerException ex ) { return false;}
finally {
try {
fileReader.close();
fileWriter.close();
} catch (IOException e) {
e.printStackTrace();
}
}
return true;
}
But the error still comes. ( it is thrown at:)
try {
File cat_out = new File("files/" + categoria + ".txt");
fileWriter = new FileWriter(cat_out, true);
} catch (IOException e) {
e.printStackTrace();
}
Thank you.
EDIT: SOLVED
I found the solution, there was, in the main function in which writeOccurencesFile is called, another function that create a RandomAccessFile and doesn't close it.
The debugger sais that Exception has thrown in writeOccurencesFile but using Java Leak Detector i found out that the pdf were already opened and not close after parsing to pure text.
Thank you!

Try using this utility specifically designed for the purpose.
This Java agent is a utility that keeps track of where/when/who opened files in your JVM. You can have the agent trace these operations to find out about the access pattern or handle leaks, and dump the list of currently open files and where/when/who opened them.
When the exception occurs, this agent will dump the list, allowing you to find out where a large number of file descriptors are in use.

i have tried using try-with resources; but the problem remains.
Also running in system macos built-in console print out a FileNotFound exception at the line of FileWriter fileWriter = ...
static boolean writeOccurencesFile(String WORDLIST,String categoria, TreeMap<String,Integer> map) {
File dizionario = new File(WORDLIST);
try (FileWriter fileWriter = new FileWriter( "files/" + categoria + ".txt" , true)) {
try (FileReader fileReader = new FileReader(dizionario)) {
try (BufferedReader bufferedReader = new BufferedReader(fileReader)) {
if (dizionario.exists()) {
StringBuffer stringBuffer = new StringBuffer();
String parola;
StringBuffer line = new StringBuffer();
int contatore_index_parola = 1;
while ((parola = bufferedReader.readLine()) != null) {
if (map.containsKey(parola) && !parola.isEmpty()) {
line.append(contatore_index_parola + ":" + map.get(parola).intValue() + " ");
map.remove(parola);
}
contatore_index_parola++;
}
if (!line.toString().isEmpty()) {
fileWriter.append(getCategoryID(categoria) + " " + line + "\n"); // print riga completa documento N x1:y x2:a ...
}
} else {
System.err.println("Dictionary file not found.");
}
}
}
} catch (IOException e) {
e.printStackTrace();
}
return true;
}
This is the code that i am using now, although the bad managing of Exception, why the files seem to be not closed?
Now i am making a test with File Leak Detector

Maybe your code raises another exception that you are not handling. Try add catch (Exception e) before finally block
You also can move BufferedReader declaration out the try and close it in finally

End of File Exception on ObjectInputStream.readObject

My application streams twitter data and writes them to files.
while(true){
Status status = queue.poll();
if (status == null) {
Thread.sleep(100);
}
if(status!=null){
list.add(status);
}
if(list.size()==10){
FileOutputStream fos = null;
ObjectOutputStream out = null;
try {
String uuid = UUID.randomUUID().toString();
String filename = "C:/path/"+topic+"-"+uuid+".ser";
fos = new FileOutputStream(filename);
out = new ObjectOutputStream(fos);
out.writeObject(list);
tweetsDownloaded += list.size();
if(tweetsDownloaded % 100==0)
System.out.println(tweetsDownloaded+" tweets downloaded");
// System.out.println("File: "+filename+" written.");
out.close();
} catch (IOException e) {
e.printStackTrace();
}
list.clear();
}
I have this code which gets data from files.
while(true){
File[] files = folder.listFiles();
if(files != null){
Arrays.sort(//sorting...);
//Here we manage each single file, from data-load until the deletion
for(int i = 0; i<files.length; i++){
loadTweets(files[i].getAbsolutePath());
//TODO manageStatuses
files[i].delete();
statusList.clear();
}
}
}
The method loadTweets() does the following operations:
private static void loadTweets(String filename) {
FileInputStream fis = null;
ObjectInputStream in = null;
try{
fis = new FileInputStream(filename);
in = new ObjectInputStream(fis);
statusList = (List<Status>) in.readObject();
in.close();
}
catch(IOException | ClassNotFoundException ex){
ex.printStackTrace();
}
}
Unfortunately, I don't know why sometimes it throws a
EOFException
when running this line
statusList = (List<Status>) in.readObject();
Anybody knows how I can solve this? Thank you.

I've seen that you're passing the file correctly with the getAbsolutePath() based on a previous question of yours
From what I've read that can be a couple of things, one of them the file being null.
Explaining this idea, you might have written the file but something caused the file to have nothing inside, this might cause an EOFException. The file in fact exists it's just empty
EDIT
Try to enclose the code in while(in.available() > 0)
It would look like this
private static void loadTweets(String filename) {
FileInputStream fis = null;
ObjectInputStream in = null;
try{
fis = new FileInputStream(filename);
in = new ObjectInputStream(fis);
while(in.available() > 0) {
statusList = (List<Status>) in.readObject();
}
in.close();
}
catch(IOException | ClassNotFoundException ex){
ex.printStackTrace();
}
}

Found out what was necessary to solve this. Thanks to #VGR's comment, I thought to pause the executing thread for 0.2 seconds if the file has been created less than a second ago.
if(System.currentTimeMillis()-files[i].lastModified()<1000){
Thread.sleep(200);
This prevents the exception and the application works now fine.

The gzip compressor is not going with the while loop

I am trying to query from database with Java JDBC and compress data in one column to gzip file in specific directory. I have tested my JDBC query and it working fine, but the Gzip code not going with the while loop, it's run with the loop firt row and stuck there. Why it's stuck? help me please!
These folders already existed: D:\Directory\My\year\id1\id2
//Some query JDBC code here, it's work well. I query all rows Data, year, id1,id2,id3
while (myRs1.next()){
String str = Data;
File myGzipFile = new File("D:\\Directory\\My\\"+year+"\\"+id1+"\\"+id2+"\\"+id3+".gzip");
GZIPOutputStream gos = null;
InputStream is = new ByteArrayInputStream(str.getBytes());
gos = new GZIPOutputStream(new FileOutputStream(myGzipFile));
byte[] buffer = new byte[1024];
int len;
while ((len = is.read(buffer)) != -1) {
gos.write(buffer, 0, len);
System.out.print("done for:"+id3);
}
try { gos.close(); } catch (IOException e) { }
}

Try formatting the source like this to catch exceptions.
public class InputStreamDemo {
public static void main(String[] args) throws Exception {
InputStream is = null;
int i;
char c;
try{
is = new FileInputStream("C://test.txt");
System.out.println("Characters printed:");
// reads till the end of the stream
while((i=is.read())!=-1)
{
// converts integer to character
c=(char)i;
// prints character
System.out.print(c);
}
}catch(Exception e){
// if any I/O error occurs
e.printStackTrace();
}finally{
// releases system resources associated with this stream
if(is!=null)
is.close();
}
}
}

Initializing In Try/Catch

I have run into quite a snag while writing my app. Here is my issue:
I am trying to initialize the file input stream like so:
FileInputStream fis
fis = openFileInput(selectedFile);
Then put this 1 line later:
byte[] input = new byte[fis.available()];
Problem is both bits of code need try/catch statements and the second block cannot recognize fis because it was initialized within a try/catch. Here is my code:
private void openFile(String selectedFile) {
String value = "";
FileInputStream fis;
try {
fis = openFileInput(selectedFile);
} catch (FileNotFoundException e) {
e.printStackTrace();
}
try {
byte[] input = new byte[fis.available()];
} catch (IOException e) {
e.printStackTrace();
}
What should I do? (Thanks in advance)

The best approach in this situation is not to catch IOException at all.
private void openFile(String selectedFile) throws IOException {
FileInputStream fis = openFileInput(selectedFile);
byte[] input = new byte[fis.available()];
It does not make sense to continue after you got FileNotFoundException

Set FileInputStream fis = null; when you first declare the variable.
You could also run your code like this because IOException will also catch the file not found exception.
String value = "";
FileInputStream fis;
try {
fis = openFileInput(selectedFile);
byte[] input = new byte[fis.available()];
} catch (IOException e) {
e.printStackTrace();
}

Set the FileInputStream to a temporary value. null would be the best option, as in:
FileInputStream fis = null;
The reason for this is because if your try statement throws an error, then the fis will never me initialized. Then you'll have problems. If you don't exit the thing entirely, you should also add the statement after the try/catch blocks that tests if the value is null, just so that the program does not throw a null pointer exception.
So maybe something like:
if(fis == null) {
return; // Which will just end the method.
}
Also might want to put the try/catches together (you should still declare the other stuff outside of the try, at least anything you plan on using directly later on in the code) but it just might be more efficient coding wise), as in:
FileInputStream fis = null;
byte[] input = null;
try {
fis = openFileInput(selectedFile);
input = new byte[fis.available()];
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}