Develop Reference

Can't read from binary file - read some lines in UTF-8, some in binary

I have this code:
import java.io.*;
import java.nio.charset.StandardCharsets;
public class Main {
public static void main(String[] args) {
zero("zero.out");
System.out.println(zeroRead("zero.out"));
}
public static String zeroRead(String name) {
try (FileInputStream fos = new FileInputStream(name);
BufferedInputStream bos = new BufferedInputStream(fos);
DataInputStream dos = new DataInputStream(bos)) {
StringBuffer inputLine = new StringBuffer();
String tmp;
String s = "";
while ((tmp = dos.readLine()) != null) {
inputLine.append(tmp);
System.out.println(tmp);
}
dos.close();
return s;
}
catch (IOException e) {
e.printStackTrace();
}
return null;
}
public static void zero(String name) {
File file = new File(name);
String text = "König" + "\t";
try (FileOutputStream fos = new FileOutputStream(file);
BufferedOutputStream bos = new BufferedOutputStream(fos);
DataOutputStream dos = new DataOutputStream(bos)) {
dos.write(text.getBytes(StandardCharsets.UTF_8));
dos.writeInt(50);
} catch (IOException e) {
e.printStackTrace();
}
}
}
zero() method writes data into file: the string is written in UTF-8, while the number is written in binary. zeroRead() read the data from file.
The file looks like this after zero() is executed:
This is what zeroRead() returns:
How do I read the real data König\t50 from the file?

DataInputStream's readLine method has javadoc that is almost yelling that it doesn't want to be used. You should heed this javadoc: That method is bad and you should not use it. It doesn't do charset encoding.
Your file format is impossible as stated: You have no idea when to stop reading the string and start reading the binary numbers. However, the way you've described things, it sounds like the string is terminated by a newline, so, the \n character.
There is no easy 'just make this filter-reader and call .nextLine on it available, as they tend to buffer. You can try this:
InputStreamReader isr = new InputStreamReader(bos, StandardCharsets.UTF_8);
However, basic readers do not have a readLine method, and if you wrap this in a BufferedReader, it may read past the end (the 'buffer' in that name is not just there for kicks). You'd have to handroll a method that fetches one character at a time, appending them to a stringbuilder, ending on a newline:
StringBuilder out = new StringBuilder();
for (int c = isr.read(); c != -1 && c != '\n'; c = isr.read())
out.append((char) c);
String line = out.toString();
will get the job done and won't read 'past' the newline and gobble up your binary number.

Java - Take any char one by one input from the Scanner [duplicate]

I am used to the c-style getchar(), but it seems like there is nothing comparable for java. I am building a lexical analyzer, and I need to read in the input character by character.
I know I can use the scanner to scan in a token or line and parse through the token char-by-char, but that seems unwieldy for strings spanning multiple lines. Is there a way to just get the next character from the input buffer in Java, or should I just plug away with the Scanner class?
The input is a file, not the keyboard.

Use Reader.read(). A return value of -1 means end of stream; else, cast to char.
This code reads character data from a list of file arguments:
public class CharacterHandler {
//Java 7 source level
public static void main(String[] args) throws IOException {
// replace this with a known encoding if possible
Charset encoding = Charset.defaultCharset();
for (String filename : args) {
File file = new File(filename);
handleFile(file, encoding);
}
}
private static void handleFile(File file, Charset encoding)
throws IOException {
try (InputStream in = new FileInputStream(file);
Reader reader = new InputStreamReader(in, encoding);
// buffer for efficiency
Reader buffer = new BufferedReader(reader)) {
handleCharacters(buffer);
}
}
private static void handleCharacters(Reader reader)
throws IOException {
int r;
while ((r = reader.read()) != -1) {
char ch = (char) r;
System.out.println("Do something with " + ch);
}
}
}
The bad thing about the above code is that it uses the system's default character set. Wherever possible, prefer a known encoding (ideally, a Unicode encoding if you have a choice). See the Charset class for more. (If you feel masochistic, you can read this guide to character encoding.)
(One thing you might want to look out for are supplementary Unicode characters - those that require two char values to store. See the Character class for more details; this is an edge case that probably won't apply to homework.)

Combining the recommendations from others for specifying a character encoding and buffering the input, here's what I think is a pretty complete answer.
Assuming you have a File object representing the file you want to read:
BufferedReader reader = new BufferedReader(
new InputStreamReader(
new FileInputStream(file),
Charset.forName("UTF-8")));
int c;
while((c = reader.read()) != -1) {
char character = (char) c;
// Do something with your character
}

Another option is to not read things in character by character -- read the entire file into memory. This is useful if you need to look at the characters more than once. One trivial way to do that is:
/** Read the contents of a file into a string buffer */
public static void readFile(File file, StringBuffer buf)
throws IOException
{
FileReader fr = null;
try {
fr = new FileReader(file);
BufferedReader br = new BufferedReader(fr);
char[] cbuf = new char[(int) file.length()];
br.read(cbuf);
buf.append(cbuf);
br.close();
}
finally {
if (fr != null) {
fr.close();
}
}
}

Wrap your input stream in a buffered reader then use the read method to read one byte at a time until the end of stream.
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
public class Reader {
public static void main(String[] args) throws IOException {
BufferedReader buffer = new BufferedReader(
new InputStreamReader(System.in));
int c = 0;
while((c = buffer.read()) != -1) {
char character = (char) c;
System.out.println(character);
}
}
}

If I were you I'd just use a scanner and use ".nextByte()". You can cast that to a char and you're good.

You have several options if you use BufferedReader. This buffered reader is faster than Reader so you can wrap it.
BufferedReader reader = new BufferedReader(new FileReader(path));
reader.read(char[] buffer);
this reads line into char array. You have similar options. Look at documentation.

Wrap your reader in a BufferedReader, which maintains a buffer allowing for much faster reads overall. You can then use read() to read a single character (which you'll need to cast). You can also use readLine() to fetch an entire line and then break that into individual characters. The BufferedReader also supports marking and returning, so if you need to, you can read a line multiple times.
Generally speaking, you want to use a BufferedReader or BufferedInputStream
on top of whatever stream you are actually using since the buffer they maintain will make multiple reads much faster.

In java 5 new feature added that is Scanner method who gives the chance to read input character by character in java.
for instance;
for use Scanner method import java.util.Scanner;
after in main method:define
Scanner myScanner = new Scanner(System.in);
//for read character
char anything=myScanner.findInLine(".").charAt(0);
you anything store single character, if you want more read more character declare more object like anything1,anything2...
more example for your answer please check in your hand(copy/paste)
import java.util.Scanner;
class ReverseWord {
public static void main(String args[]){
Scanner myScanner=new Scanner(System.in);
char c1,c2,c3,c4;
c1 = myScanner.findInLine(".").charAt(0);
c2 = myScanner.findInLine(".").charAt(0);
c3 = myScanner.findInLine(".").charAt(0);
c4 = myScanner.findInLine(".").charAt(0);
System.out.print(c4);
System.out.print(c3);
System.out.print(c2);
System.out.print(c1);
System.out.println();
}
}

This will print 1 character per line from the file.
try {
FileInputStream inputStream = new FileInputStream(theFile);
while (inputStream.available() > 0) {
inputData = inputStream.read();
System.out.println((char) inputData);
}
inputStream.close();
} catch (IOException ioe) {
System.out.println("Trouble reading from the file: " + ioe.getMessage());
}

Faster input style in java

Scanner has a method hasNext() but if i want to use BufferedReader insteadOf Scanner how to handle hasNext() types of method in BufferedReader?
I want to do this because BufferedReader is faster than Scanner. Is there any faster input reading way besides BufferedReader?
Need Help! Thanks in advance.

If you are working with Strings use a StringBuilder. It is a built in object in Java and allows you to not have to recreate a String every time you append a String.
I have not worked with a scanner much because I like BufferedReader so much. Java's BufferedReader reads a certain amount of bytes at a time. The default buffer size is 8192 characters. You can change this is you want to if you think you will be reading enormous amounts of characters. An integer as the second parameter would specify the number of bytes to read each time.
This is how you would use a BufferedReader and StringBuilder efficiently:
public static void main(String[] args) {
StringBuilder sb = new StringBuilder();
String output;
try(BufferedReader reader = new BufferedReader(new FileReader(System.getProperty("user.home") + "/Desktop/lotsOfText.txt"), 8192)) { //if you want a bigger buffer - give it a larger number
String line;
while ((line = reader.readLine()) != null) {
sb.append(line).append("\n"); //StringBuilder returns a reference to itself
}
} catch (IOException io) {
System.err.println(io.toString());
}
output = sb.toString();
System.out.println(output);
}
If you are expecting double or ints, you can use a try{}catch (Exception e){} and in the try use either java's class Double or Integer to parse a string:
try {
double d = Double.parse(line);
int i = Integer.parse(line);
catch (NumberFormatException nfe) {
System.err.println(nfe.toString() + "\n\nThe number was unreadable");
}
Your question was really vague, so it is hard to give you an explicit answer. I hope this helps.
Also, as a note, BufferedReader also accepts an InputStreamReader as an argument, so you could have
try(BufferedReader reader = new BufferedReader(new InputStreamReader(System.in)) {} catch...
in order to read user input.
The "truly" correct way to read an InputStream can be found here

Java PrintWriter Print character not displaying the last character

I really not getting where the problem is.
I wanted to print the characters to a text file and im uisng printWriter to do the same.
if the file has a ";", i want to replace it with a new line and this is what im doing,
public static void downloadFile_txt(String sourceFilePathName, String contentType, String destFileName, HttpServletResponse response) throws IOException, ServletException
{
File file = new File(sourceFilePathName);
//FileInputStream fileIn = new FileInputStream(file);
FileReader fileIn = new FileReader(file);
long fileLen = file.length();
response.setContentType(contentType);
response.setContentLength((int)fileLen);
response.setHeader("Content-Disposition", String.valueOf((new StringBuffer("attachment;")).append("filename=").append(destFileName)));
PrintWriter pw = response.getWriter();
// Loop to read and write bytes.
int c=-1;
while ((c = fileIn.read()) != -1)
{
if(c!=59)
{
pw.print((char)c);
}
else
{
pw.println();
}
}
pw.flush();
pw=null;
fileIn.close();
}
But my file is priting everything except for the last character.
Eg.input =
:00004000,FFAD,2 Byte Ch;
:0000FFBD,FFBE,2 Byte Ch;
:0000FFBF,FFFF,2 Byte Ch;
output which im getting
:00004000,FFAD,2 Byte Ch
:0000FFBD,FFBE,2 Byte Ch
:0000FFBF,FFFF,2 Byte C
the last "h" is not getting printed.
Thanks in advance

A pw.flush(); might help you.
public class FlushPrintWriter {
public static void main(String[] args) throws IOException {
FileReader fileIn = new FileReader("in.txt");
FileWriter out = new FileWriter("out.txt");
PrintWriter pw = new PrintWriter(out);
int c;
while ((c = fileIn.read()) != -1) {
if(c!=59) {
pw.print((char)c);
} else {
pw.println();
}
}
pw.flush();
}
}
outputs
:00004000,FFAD,2 Byte Ch
:0000FFBD,FFBE,2 Byte Ch
:0000FFBF,FFFF,2 Byte Ch
as expected.
(Don't handle your IOExceptions like this - and close your readers and writers - this is for demonstration only!)
edit: now your code doesn't even compile (two vars called fileIn?)!
Even when run through the servlet code you're now mentioning, I can't reproduce your problem, and the output is as you would expect. So this is me giving up. I'm starting to suspect either the final ; isn't in your source file, or there is yet more processing your app is doing that you're not showing us.

Try flush() or close() your print writer.
And may be it is better to read line by line, replacing characters using String.replace()

Run the while loop upto file size
int fileSize=file.length();
while(fileSize>0)
{
//do your task of reading charcter and printing it or whatever you want
fileSize--;
}

Most concise way to read the contents of a file/input stream in Java?

What ist most concise way to read the contents of a file or input stream in Java? Do I always have to create a buffer, read (at most) line by line and so on or is there a more concise way? I wish I could do just
String content = new File("test.txt").readFully();

Use the Apache Commons IOUtils package. In particular the IOUtils class provides a set of methods to read from streams, readers etc. and handle all the exceptions etc.
e.g.
InputStream is = ...
String contents = IOUtils.toString(is);
// or
List lines = IOUtils.readLines(is)

I think using a Scanner is quite OK with regards to conciseness of Java on-board tools:
Scanner s = new Scanner(new File("file"));
StringBuilder builder = new StringBuilder();
while(s.hasNextLine()) builder.append(s.nextLine());
Also, it's quite flexible, too (e.g. regular expressions support, number parsing).

Helper functions. I basically use a few of them, depending on the situation
cat method that pipes an InputStream to an OutputStream
method that calls cat to a ByteArrayOutputStream and extracts the byte array, enabling quick read of an entire file to a byte array
Implementation of Iterator<String> that is constructed using a Reader; it wraps it in a BufferedReader and readLine's on next()
...
Either roll your own or use something out of commons-io or your preferred utility library.

To give an example of such an helper function:
String[] lines = NioUtils.readInFile(componentxml);
The key is to try to close the BufferedReader even if an IOException is thrown.
/**
* Read lines in a file. <br />
* File must exist
* #param f file to be read
* #return array of lines, empty if file empty
* #throws IOException if prb during access or closing of the file
*/
public static String[] readInFile(final File f) throws IOException
{
final ArrayList lines = new ArrayList();
IOException anioe = null;
BufferedReader br = null;
try
{
br = new BufferedReader(new FileReader(f));
String line;
line = br.readLine();
while(line != null)
{
lines.add(line);
line = br.readLine();
}
br.close();
br = null;
}
catch (final IOException e)
{
anioe = e;
}
finally
{
if(br != null)
{
try {
br.close();
} catch (final IOException e) {
anioe = e;
}
}
if(anioe != null)
{
throw anioe;
}
}
final String[] myStrings = new String[lines.size()];
//myStrings = lines.toArray(myStrings);
System.arraycopy(lines.toArray(), 0, myStrings, 0, lines.size());
return myStrings;
}
(if you just want a String, change the function to append each lines to a StringBuffer (or StringBuilder in java5 or 6)

String content = (new RandomAccessFile(new File("test.txt"))).readUTF();
Unfortunately Java is very picky about the source file being valid UTF8 though, or you will get an EOFException or UTFDataFormatException.

You have to create your own function, I suppose. The problem is that Java's read routines (those I know, at least) usually take a buffer argument with a given length.
A solution I saw is to get the size of the file, create a buffer of this size and read the file at once. Hoping the file isn't a gigabyte log or XML file...
The usual way is to have a fixed size buffer or to use readLine and concatenate the results in a StringBuffer/StringBuilder.

I don't think reading using BufferedReader is a good idea because BufferedReader will return just the content of line without the delimeter. When the line contains nothing but newline character, BR will return a null although it still doesn't reach the end of the stream.

String org.apache.commons.io.FileUtils.readFileToString(File file)

Pick one from here.
How do I create a Java string from the contents of a file?
The favorite was:
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();
}
finally {
stream.close();
}
}
Posted by erickson

Or the Java 8 way:
try {
String str = new String(Files.readAllBytes(Paths.get("myfile.txt")));
...
} catch (IOException ex) {
Logger.getLogger(getClass().getName()).log(Level.SEVERE, null, ex);
}
One may pass an appropriate Charset to the String constructor.