Develop Reference

Java-Shifting Characters from Binary Files

I looked at some previous threads about binary files and I am doing the dataStream like it says, but I am not for sure why mine isn't working as I think I am doing the same thing as threads say I am. My goal is to make a method that takes in a file name that is in .bin format with a shift integer. I will make a new file of the .bin type with the characters shifted. Only capital or lower case letters will be shifted though. I don't know the length of the binary file that is being read in and needs to go through all of the characters. The file will only have 1 line though. I have a method that gives me the number of characters on that line and a method that creates a file. The program I know does create the file correctly. Anyways, what is happening is it creates the file, then gives me an EOF exception about the line: char currentChar=data.readChar();
Here is my code:
private static void cipherShifter(String file, int shift) {
String newFile=file+"_cipher";
createFile(newFile);
int numChar;
try {
FileInputStream stream=new FileInputStream(file);
DataInputStream data=new DataInputStream(stream);
FileOutputStream streamOut=new FileOutputStream(newFile);
DataOutputStream dataOut=new DataOutputStream(streamOut);
numChar=readAllInts(data);
for (int i=0;i<numChar;++i) {
char currentChar=data.readChar();
if (((currentChar>='A')&&(currentChar<='Z'))||((currentChar>='a')&&(currentChar<='z'))) {
currentChar=currentChar+=shift;
dataOut.writeChar(currentChar);
}
else {
dataOut.writeChar(currentChar);
}
}
data.close();
dataOut.flush();
dataOut.close();
} catch(IOException error) {
error.printStackTrace();
}
}
private static void createFile(String fileName) {
File file=new File(fileName);
if (file.exists()) {
//Do nothing
}
else {
try {
file.createNewFile();
} catch (IOException e) {
//Do nothing
}
}
}
private static int readAllInts(DataInputStream din) throws IOException {
int count = 0;
while (true) {
try {
din.readInt(); ++count;
} catch (EOFException e) {
return count;
}
}
}
So the error I do not think should be happening because I do have the correct data type and I am telling it to read just a character. Any help would be great. Thanks in advance.

Based on the description above, your error is reported at the data.readChar() method invocation and not inside the readAllInts method. I simulated the code near your error and got the same Exception on a text file at the same location.
I used the readByte method to read one byte at a time since you are mainly interested in ASCII bytes. I also changed readAllInts to be readAllBytes so I work with total byte count.
private static void cipherShifter(String file, int shift) {
String newFile=file+"_cipher";
createFile(newFile);
int numChar;
try {
FileInputStream stream=new FileInputStream(file);
DataInputStream data=new DataInputStream(stream);
FileOutputStream streamOut=new FileOutputStream(newFile);
DataOutputStream dataOut=new DataOutputStream(streamOut);
numBytes=readAllBytes(data);
stream.close();
data.close();
stream=new FileInputStream(file);
data=new DataInputStream(stream);
for (int i=0;i<numBytes;++i) {
byte currentByte=data.readByte();
if (((currentByte>=65)&&(currentByte<=90))||((currentByte>=97)&&(currentByte<=122))) {
currentByte=currentByte+=shift; //need to ensure no overflow beyond a byte
dataOut.writeByte(currentByte);
}
else {
dataOut.writeByte(currentByte);
}
}
data.close();
dataOut.flush();
dataOut.close();
} catch(IOException error) {
error.printStackTrace();
}
}
private static void createFile(String fileName) {
File file=new File(fileName);
if (file.exists()) {
//Do nothing
}
else {
try {
file.createNewFile();
} catch (IOException e) {
//Do nothing
}
}
}
private static int readAllBytes(DataInputStream din) throws IOException {
int count = 0;
while (true) {
try {
din.readByte(); ++count;
} catch (EOFException e) {
return count;
}
}
}

It looks like you're getting the EOFException because you're passing the DataInputStream object to your readAllInts method, reading through the stream, then trying to read from it again inside your for loop. The problem there is that the pointer that keeps track of where you are in the stream is already near the end of the stream (or at the end of it) when readAllInts returns. I suspect it's near the end, rather than at it since the readChar() method is throwing the EOFException immediately, which it does when it only reads one of the two bytes it expects to be able to read before hitting the EOF.
To solve that problem, you could call data.mark() before passing the reader to the readAllInts method, then calling data.reset() after that method returns; that would repoint the pointer to the beginning of the stream. (This assumes data.markSupported() is true.)
You also have the problem we talked about above that your counter is reading in four bytes at a time, and your character reader is reading in two at a time. Your suggested method of doubling the return value of readAllInts would help (you could also use readChar() instead of readInt().)
You still need to think about how you're going to handle the case of binary files that are odd-numbered bytes long. There are a variety of ways you could handle that one. I'm too beat to write up a code sample tonight, but if you're still stuck tomorrow, add a comment and I'll see what I can do to help.

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();
}
}
}

How to convert .txt files to multiline String in Android Java

I've been stuck on this for a couple of days, I just cant find a good method to open a .txt file. I need to convert it into a multiline string and set it as a textview. Can someone help me please?
as for the file location, I'm using:
String saveLoc = Environment.getExternalStorageDirectory()+"/My Documents/";
public String title;
public String Ftype = ".txt";
(saveLoc+title+Ftype) //is the file location.
I can normally read the data into a file input stream, but if I try and do anything with it I get loads of errors that wont let my app even run.

use Apache Commons IO FileUtils.readLines()
readLines
public static List readLines(File file,
Charset encoding)
throws IOException
Reads the contents of a file line by line to a List of Strings. The file is always closed.
Parameters:
file - the file to read, must not be null
encoding - the encoding to use, null means platform default
Returns:
the list of Strings representing each line in the file, never null
Throws:
IOException - in case of an I/O error
Since:
2.3

private static String readFile(String path) throws IOException
{
FileInputStream stream = new FileInputStream(new File(path));
try {
FileChannel fc = stream.getChannel();
MappedByteBuffer bb = fc.map(FileChannel.MapMode.READ_ONLY, 0, fc.size());
/* Instead of using default, pass in a decoder. */
return Charset.defaultCharset().decode(bb).toString();
}
catch (IOException e)
{
e.printStackTrace();
}
finally
{
stream.close();
}
}

private String readTxt(){
InputStream inputStream = new FileInputStream("Text File Path Here");
ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
int i;
try {
i = inputStream.read();
while (i != -1)
{
byteArrayOutputStream.write(i);
i = inputStream.read();
}
inputStream.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return byteArrayOutputStream.toString();
}

Java FTP Download progress

I have looked at many examples and tried to understand what i`m doing wrong but with no success, maybe you can help me. It always stops at the second file, but the first one is just crated on c:\ with 0kb size.
files_server.get(i) is ArrayList with all files that i wish to download.
My code:
public FTPConnection() {
StartD std = new StartD();
std.start();
}
class StartD extends Thread{
#Override
public void run()
{
for (int i = 0; i < files_server.size(); i++) {
err = ftpDownload(files_server.get(i), "C:/"+ files_server.get(i));
if (!err)
{
System.out.println("Error in download, breaking");
break;
}
}
}
public boolean ftpDownload(String srcFilePath, String desFilePath)
{
try {
FileOutputStream desFileStream = new FileOutputStream(desFilePath);
InputStream input = mFTPClient.retrieveFileStream(srcFilePath);
byte[] data = new byte[1024];
int count;
while ((count = input.read(data)) != -1)
{
desFileStream.write(data, 0, count);
}
desFileStream.close();
} catch (Exception e) {
return false;
}
return true;
}}
If I use the finction:
public boolean ftpDownload(String srcFilePath, String desFilePath) {
boolean status = false;
try {
FileOutputStream desFileStream = new FileOutputStream(desFilePath);
status = mFTPClient.retrieveFile(srcFilePath, desFileStream);
desFileStream.close();
return status;
} catch (Exception e) {
}
return status;
}
instead, everything works just fine, but i can`t monitor file download progress.

I've only used it for file unzipping and not FTP, but in that case InputStream buffers can return zero, so I'd say it's worth trying changing your while loop to something like:
while ((count = input.read(data)) >= 0)
public int read(byte[] b) throws IOException
Reads some number of bytes from the input stream and stores them into the buffer array b.
The number of bytes actually read is returned as an integer. This
method blocks until input data is available, end of file is detected,
or an exception is thrown.
If the length of b is zero, then no bytes are read and 0 is returned;
It could also be that you're assigning count twice, which could chop the first byte off the data:
int count = input.read(data);
while ((count = input.read(data)) != -1)
So don't assign anything to count when you declare it.

Let's assume your library is the FTP client from the commons-net package. It's not easy to figure out what's wrong with your code, because we can't run it and because your description (the second file stops) is not sufficient (does it throw an exception? Does it hang forever? Does it complete without any side effect?). Anyway I have a couple of advices:
Use a CountingOutputStream (from Apache commons-io) to monitor progress
Use a ProtocolCommandListener to log what's going on
Also, note that the first 1024 bytes are always lost. Eventually, I don't know how safe it is to put a file in C:\ with the same name it has on the server. At the best, it could lead to permission troubles, at the worst it may originate a security flaw - anyway this doesn't hold if you have some degree of control over the filenames, but hey consider this advice.
This is a sample client
public class FTP {
public static void main(String[] args) throws SocketException, IOException {
FTPClient client = new FTPClient();
client.addProtocolCommandListener(new ProtocolCommandListener(){
#Override
public void protocolCommandSent(ProtocolCommandEvent evt) {
logger.debug(evt.getMessage());
}
#Override
public void protocolReplyReceived(ProtocolCommandEvent evt) {
logger.debug(evt.getMessage());
}
});
client.connect("ftp.mozilla.org");
client.login("anonymous", "");
client.enterLocalPassiveMode();
OutputStream out = new CountingOutputStream(new NullOutputStream()) {
#Override
public void beforeWrite(int count) {
super.beforeWrite(count);
logger.info("Downloaded " + getCount() + " bytes");
}
};
for (String filename: new String[] {"MD5SUMS", "SHA1SUMS"})
client.retrieveFile("pub/firefox/releases/15.0b4/" + filename, out);
out.close();
client.disconnect();
}
private static Logger logger;
static {
logger = Logger.getLogger(FTP.class.getCanonicalName());
}
}
Once configured, the logger will output all the raw socket conversation, and it may help you to better understand the problem, provided it's on the FTP side and not in application IO

java the system can not find the file specified

I used Java to copy file but it appeared a exception (the system can not find the file specified).
The codes are
public static void copyFile(String sourceFile, String destFile){
try {
InputStream in = new FileInputStream(sourceFile);
OutputStream os = new FileOutputStream(destFile);
byte[] buffer = new byte[1024];
int count;
while ((count = in.read(buffer)) > 0) {
os.write(buffer, 0, count);
}
in.close();
os.close();
} catch (IOException e) {
e.printStackTrace();
}
}
The test codes
public static void main(String[] args) {
String name = getFileName("D:/z/temp.txt");
String target = "D:/tem.txt";
copyFile(name, target);
}
the exception is java.io.FileNotFoundException: temp.txt(the system can not find the file specified)
The file 'temp.txt' is existence.
The path is right no problem.
I guess that is the problem of Permissions. who can come up with the answer thanks!

We need to see the method getFileName() to be sure, but based on the error message and the method name, I suspect the problem is just that this method returns only the name of the file, removing the path info, so that the file is, indeed, not found.