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Read from file and manipulate then write in another file using java?

I have data file “ReadFile1.txt”. I want to read each data from ReadFile1.txt and manipulate those data then write the results in another file “WriteFile2.txt”. Here is my function. The problem is it only reads 2nd,4th, and so on and does write only 2nd result. What’s wrong in this code? I appreciate your help.
public void doManipulate() throws NumberFormatException, IOException {
int multiple = 10;
try {
FileInputStream file = new FileInputStream("ReadFile1.txt");
InputStreamReader input = new InputStreamReader(file);
BufferedReader reader = new BufferedReader(input);
String data1;
while ((data1 = reader.readLine()) != null) {
int data2 = 0;
data1 = reader.readLine();
data2 = Integer.parseInt(data1);
int compressedFrames = data2*multiple;
File file2 = new File("WriteFile2.txt");
FileWriter writer = new FileWriter(file2);
writer.write(String.valueOf(compressedFrames) + "\n");
writer.flush();
writer.close();
}
reader.close();
} catch (IOException e) {
e.printStackTrace();
}
}

You're calling reader.readLine() twice for every iteration of the while loop - the first time is in the loop declaration, which reads every odd line, and the second is just a couple of lines down (data1 = reader.readLine();). The second call is blowing away anything read by the first before you have a chance to parse it. Removing the second call should fix the "every other line" issue.
Another issue is that you're closing the writer at every iteration of the while loop - don't close the writer until the while loop is done or your output file will only have the first parsed data element in it after your program closes.

writing to text file using BufferedReader

my problem is to read non primes from txt file and write prime factors in same file.
i actually dont know how BufferedReader works.from my understanding i am trying to read the file data to buffer(8kb) and write prime factors to file.(by creating a new one)
class PS_Task2
{
public static void main(String[] args)
{
String line=null;
int x;
try
{
FileReader file2 = new FileReader("nonprimes.txt");
BufferedReader buff2=new BufferedReader(file2);
File file1 = new File("nonprimes.txt");
file1.createNewFile();
PrintWriter d=new PrintWriter(file1);
while((line = buff2.readLine()) != null)
{
x=Integer.parseInt(line);
d.printf ("%d--> ", x);
while(x%2==0)
{
d.flush();
d.print("2"+"*");
x=x/2;
}
for (int i = 3; i <= Math.sqrt(x); i = i+2)
{
while (x%i == 0)
{
d.flush();
d.printf("%d*", i);
x = x/i;
}
}
if (x > 2)
{
d.flush();
d.printf ("%d ", x);
}
d.flush();//FLUSING THE STREAM TO FILE
d.println("\n");
}
d.close(); // CLOSING FILE
}
feel free to give detailed explanation. :D thanks ~anirudh

reading and writing to a file in java doesnt EDIT the file, but clear the old one and creates a new one, you can use many approachesfor example, to get your data, modify it, and either save it on memory in a StringBuilder or a collection or what ever and re-write it again
well i created fileOne.txt containing the following data :
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
and i want to multiply all those numbers by 10, then re-write them again :
public static void main(String [] args) throws Exception{ // just for the example
// locate the file
File fileOne = new File("fileOne.txt");
FileReader inputStream = new FileReader(fileOne);
BufferedReader reader = new BufferedReader(inputStream);
// create a LinkedList to hold the data read
List<Integer> numbers = new LinkedList<Integer>();
// prepare variables to refer to the temporary objects
String line = null;
int number = 0;
// start reading
do{
// read each line
line = reader.readLine();
// check if the read data is not null, so not to use null values
if(line != null){
number = Integer.parseInt(line);
numbers.add(number*10);
}
}while(line != null);
// free resources
reader.close();
// check the new numbers before writing to file
System.out.println("NEW NUMBERS IN MEMORY : "+numbers);
// assign a printer
PrintWriter writer = new PrintWriter(fileOne);
// write down data
for(int newNumber : numbers){
writer.println(newNumber);
}
// free resources
writer.flush();
writer.close();
}
this approach is not very good when dealing with massive data

As per your problem statement, you need to take input from a file, do some processing and write back the processed data in the same file. For this, please note the below points:
You may not create a file with same name in a directory, so you must create the new file at some other location; or write the content into different file and later rename it after deleting original one.
While your file is open for reading, modifying the same file is not a good idea. you could use below approach:
Read the content of the file and store in a data structure liek Arrays, ArrayList.
Close the file.
Process the data stored in the data structure.
Open the file in write mode (over-write mode rather than append mode)
Write back the processed data into the file.

How do I quadruple the integer values in a text file? [closed]

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Closed 9 years ago.
I guess this comes down to reading and writing to the same file. I would like to be able to return the same text file as is input, but with all integer values quadrupled. Should I even be attempting this with Java, or is it better to write to a new file and overwrite the original .txt file?
In essence, I'm trying to transform This:
12
fish
55 10 yellow 3
into this:
48
fish
220 40 yellow 12
Here's what I've got so far. Currently, it doesn't modify the .txt file.
import java.io.*;
import java.util.Scanner;
public class CharacterStretcher
{
public static void main(String[] args)
{
Scanner keyboard = new Scanner( System.in );
System.out.println("Copy and paste the path of the file to fix");
// get which file you want to read and write
File file = new File(keyboard.next());
File file2 = new File("temp.txt");
BufferedReader reader;
BufferedWriter writer;
try {
// new a writer and point the writer to the file
FileInputStream fstream = new FileInputStream(file);
// Use DataInputStream to read binary NOT text.
reader = new BufferedReader(new InputStreamReader(fstream));
writer = new BufferedWriter(new FileWriter(file2, true));
String line = "";
String temp = "";
int var = 0;
int start = 0;
System.out.println("000");
while ((line = reader.readLine()) != null)
{
System.out.println("a");
if(line.contains("="))
{
System.out.println("b");
var = 0;
temp = line.substring(line.indexOf('='));
for(int x = 0; x < temp.length(); x++)
{
System.out.println(temp.charAt(x));
if(temp.charAt(x)>47 && temp.charAt(x)<58) //if 0<=char<=9
{
if(start==0)
start = x;
var*=10;
var+=temp.indexOf(x)-48; //converts back into single digit
}
else
{
if(start!=0)
{
temp = temp.substring(0, start) + var*4 + temp.substring(x);
//writer.write(line.substring(0, line.indexOf('=')) + temp);
//TODO: Currently writes a bunch of garbage to the end of the file, how to write in the middle?
//move x if var*4 has an extra digit
if((var<10 && var>2)
|| (var<100 && var>24)
|| (var<1000 && var>249)
|| (var<10000 && var>2499))
x++;
}
//start = 0;
}
System.out.println(temp + " " + start);
}
if(start==0)
writer.write(line);
else
writer.write(temp);
}
}
System.out.println("end");
// writer the content to the file
//writer.write("I write something to a file.");
// always remember to close the writer
writer.close();
//writer = null;
file2.renameTo(file); //TODO: Not sure if this works...
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
}

Given that this is a pretty quick and simple hack of a formatted text file, I don't think you need to be too clever about it.
Your logic for deciding whether you are looking at a number is pretty complex and I'd say it's overkill.
I've written up a basic outline of what I'd do in this instance.
It's not very clever or impressive, but should get the job done I think.
I've left out the overwriting and reading the input form the console so you get to do some of the implementation yourself ;-)
import java.io.*;
public class CharacterStretcher {
public static void main(String[] args) {
//Assumes the input is at c:\data.txt
File inputFile = new File("c:\\data.txt");
//Assumes the output is at c:\temp.txt
File outputFile = new File("c:\\temp.txt");
try {
//Construct a file reader and writer
final FileInputStream fstream = new FileInputStream(inputFile);
final BufferedReader reader = new BufferedReader(new InputStreamReader(fstream));
final BufferedWriter writer = new BufferedWriter(new FileWriter(outputFile, false));
//Read the file line by line...
String line;
while ((line = reader.readLine()) != null) {
//Create a StringBuilder to build our modified lines that will
//go into the output file
StringBuilder newLine = new StringBuilder();
//Split each line from the input file by spaces
String[] parts = line.split(" ");
//For each part of the input line, check if it's a number
for (String part : parts) {
try {
//If we can parse the part as an integer, we assume
//it's a number because it almost certainly is!
int number = Integer.parseInt(part);
//We add this to out new line, but multiply it by 4
newLine.append(String.valueOf(number * 4));
} catch (NumberFormatException nfEx) {
//If we couldn't parse it as an integer, we just add it
//to the new line - it's going to be a String.
newLine.append(part);
}
//Add a space between each part on the new line
newLine.append(" ");
}
//Write the new line to the output file remembering to chop the
//trailing space off the end, and remembering to add the line
//breaks
writer.append(newLine.toString().substring(0, newLine.toString().length() - 1) + "\r\n");
writer.flush();
}
//Close the file handles.
reader.close();
writer.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
}

You may want to consider one of these:
Build the new file in memory, rather than trying to write to the same file you are reading from. You could use StringBuilder for this.
Write to a new file, then overwrite the old file with the new one. This SO Question may help you there.
With both of these, you will be able to see your whole output, separate from the input file.
Additionally, with option (2), you don't have the risk of the operation failing in the middle and giving you a messed up file.
Now, you certainly can modify the file in-place. But it seems like unnecessary complexity for your case, unless you have really huge input files.
At the very least, if you try it this way first, you can narrow down on why the more complicated version is failing.

You cannot read and simultaneously write to the same file, because this would modify the text you currently read. This means, you must first write a modified new file and later rename it to the original one. You probably need to remove the original file before renameing.
For renaming, you can use File.renameTo or see one of the many SO's questions
You seem to parse integers in your code by collecting single digits and adding them up. You should consider using either a Scanner.nextInt or employ Integer.parseInt.
You can read your file line by line, split the words at white space and then parse them and check if it is either an integer or some other word.

Iterator writing to File.txt Java

Here is my issue: I need to write the Interator to the file "random.txt" I am able to see all the data. The data is Store where suppose to, I can see it with the System.out.print but my file is in blank. I am able to create the file but not to writer to it.
I am reading a file from my comp. store in the Treemap and trying to write to the text file. ( I am able to doit with Array with not problem) But this Map with Iterator is bouncing my head.
If some one can help me a litter I will appreciated.
I need to use the TreeMap and the Iterator.
public static void main(String[] args) throws FileNotFoundException, IOException {
Map<String, String> Store = new TreeMap<>();
Scanner text=new Scanner(System.in);
System.out.println("enter file: ");
//C:\Users\Alex\Desktop\Fruits\fruits.txt
String rap=text.next();
File into = new File(rap);
try (Scanner in = new Scanner(into)) {
while (in.hasNext()){
String name=in.next();
String fruta = in.next();
Integer num= Integer.parseInt(in.next());
System.out.println(fruta+"\t"+name+"\t"+num);
if (Store.containsKey(fruta)){
Store.put(name,Store.get(name)+fruta );
}
else{
Store.put(name,fruta);
}
}
in.close();
}
System.out.println();
// insert data to store MAP
Set top=Store.entrySet();
Iterator it = top.iterator();
// debugging
System.out.println(top);
// Creating file???????
FileWriter fstream = new FileWriter("random.txt");
//identify File to be write??????
BufferedWriter out = new BufferedWriter(fstream);
//iterator Loop
while(it.hasNext()) {
Map.Entry m = (Map.Entry)it.next();
String key = (String)m.getKey();
String value = (String)m.getValue();
//writing to file?????
out.write("\t "+key+"\t "+value);
// debugging
System.out.println(key +"\t"+ value);
}
System.out.println("File created successfully.");
}

After your while loop (the one writing to file) is finished, do:
out.flush();
out.close();
Short explanation: BufferedWriter buffers in memory what you write. It doesn't immediately write to file when you call the write method. Once the while loop is finished and the data to write to file is prepared in buffer memory, you should call flush to do the actual writing to hard disk. And finally you should always close the BufferedWriter that will no longer be used, to avoid memory leaks.

Java Server reply is not printed as expected

I am building a simple client-server program , I have in main :
FTPClient ftp = new FTPClient("www.kernel.org");
ftp.getReply();
ftp.sendCommand("USER " + "anonymous");
ftp.getReply();
ftp.sendCommand("PASS " + "anonymous");
ftp.getReply();
String com="";
while (!com.equalsIgnoreCase("quit")){
System.out.println("Enter your Commands . or Enter quit");
BufferedReader Keyboard = new BufferedReader(new InputStreamReader(System.in));
com = Keyboard.readLine();
ftp.sendCommand((com));
ftp.getReply();
System.out.println("===============");
}
ftp.close();
the problem is in the getReply() function, this function is :
public void getReply() throws IOException {
String line="";
while (br.ready())
{
line = br.readline();
System.out.println(line);
System.out.flush();
}
}
br is a BufferedReader.Now all the problem is that when the program starts it doesn't show the welcome message from the Server until I press Enter or any command, when I Debug the program Step by Step every thing is working perfectly.So is the problem in the readline and I should use something else or what?

The problem is likely that the end of the server response does not contain a newline character. The BufferedReader's readLine method will block until a line of data is received, where "a line" consists of some characters followed by a newline character (or the end of the stream). Consequently, the readLine call will not return if no newline is received.
In this situation then, the BufferedReader isn't doing you any good. You'd be better off using the underlying Reader yourself, reading into an array and emitting the output as soon as it comes in, such as the following:
final char[] buffer = new char[256]; // or whatever size you want
int nRead;
while ((nRead = reader.read(buffer)) != -1)
{
System.out.println(new String(buffer, 0, nRead));
System.out.flush();
}
The condition in the while loop there might look confusing if you're not used to it before, but it combines the read operation (which reads into the buffer) with the check that the end of the stream has not been reached. Likewise, the construction of the String within the while loop takes into account the fact that the buffer may not have been filled entirely, so only as many characters as were supplied are used.
Note that this particular snippet keeps looping until the stream is empty; you may wish to add another exit condition in your particular case.