I have a file of 250 line. I wanted to insert some text after line 128.
I only found that I can append a text at the end of file
like
try {
PrintWriter out = new PrintWriter(new BufferedWriter(new FileWriter("outfilename", true)));
out.println("the text");
out.close();
} catch (IOException e) {
//oh noes!
}
That is found on this post How to append text to an existing file in Java
But with no mention to the line number or sth.
There's no way to insert text in the middle of a file because of how file systems work. They implement operations to modify the data blocks of a file and to add and remove blocks from the end of a file. What they don't implement is adding or removing data blocks anywhere else because of inherent complexities of these operations.
What you have to do is copy the first 125 lines to a new file, add what you want to add, and then copy the rest of the file. If you want to you can then rename the new file as the old file so you don't accumulate temporary files.
You can read the original file and write the content in a temp file with new line inserted. Then, delete the original file and rename the temp file to the original file name.
The following code can help you to insert a given string at a given position in an existing file:
public static void writeStrToFileAtGivenLineNum(String str, File file, int lineNum) throws IOException {
List<String> lines = java.nio.file.Files.readAllLines(file.toPath());
lines.add(lineNum, str);
java.nio.file.Files.write(file.toPath(), lines);
}
Related
I have an xml file and there are contents inside the tags. I am trying to read this file in java. I am parsing through the contents of the file word by word. I want to divide the file into chunks. For example if I found a string code=”34076-0” I want to start writing the next token from the found string to another file till another code=”1234-5” is found . However, I am not able to stop the file parsing or collect the contents after the string has matched to write it to another file. I have tried the following code.
try {
Scanner sc2 = null;
sc2 = new Scanner(new File("A:/OneDrive - PharmaCompany, Inc/Diksha Work/lipitorx.xml"));
while(sc2.hasNextLine())
{
String s = sc2.next();
if(sc2.next()==("code=\"34076-0\"" ))
{
// Here I want to write the contents of the file after matching the code=34076-0 till the next code into another file
}
System.out.println(s);
}
} catch (Exception e) {
// TODO: handle exception
System.out.println("Unable to open the file");
}
}
I am trying to write some coordinates to a file and later read it in as a string. So I need to have them written to file attached...without space or a new line, but my code writes only the first coordinate, that is pos_Let, but does not write pos_Num at all, not even with a space or on a new line.
So how can I get the code to write to file pos_LetposNum like that? Obviously I mean their references ;) ..thanks in advance
protected void writeCoordtoFile () throws IOException
{
File file = new File("FermiPresentCoord.txt");
boolean yes = file.createNewFile() ;
//boolean yes = exists();
if (yes == true)
{
// create a FileWriter Object
FileWriter writer = new FileWriter(file, true);
// Writes the content to the file
writer.write("");
writer.flush();
writer.write(pos_Let);
writer.flush();
writer.write(pos_Num);
writer.close();
}
else
{
// creates the file
file.createNewFile();
// creates a FileWriter Object
FileWriter out = new FileWriter(file);
// Writes the content to the file
out.write(pos_Let);
out.flush();
out.write(pos_Num);
out.flush();
out.close();
}
}
Quoting the method createNewFile():
Atomically creates a new, empty file named by this abstract pathname if and only if a file with this name does not yet exist. The check for the existence of the file and the creation of the file if it does not exist are a single operation that is atomic with respect to all other filesystem activities that might affect the file.
Note: this method should not be used for file-locking, as the resulting protocol cannot be made to work reliably. The FileLock facility should be used instead.
Returns:
true if the named file does not exist and was successfully created; false if the named file already exists
in your case, you first create the file, and createNewFile() returns true, so you go to the if block, appending the line to the current file. Then, createNewFile() returns false, since, the file exists! So, you go to the else block, and create the file again from scratch...
So, basically, just inverse the if with else, and don't call createNewFile() twice... With the least possible changes (so that you do not get confused) here is my simple suggestion:
protected void writeCoordtoFile () throws IOException
{
File file = new File("FermiPresentCoord.txt");
boolean fileDoesNotExist = file.createNewFile() ;
//boolean fileDoesNotExist = file does **not** exist!
if (fileDoesNotExist)
{
// create a FileWriter Object
FileWriter writer = new FileWriter(file);
// Writes the content to the file
writer.write(pos_Let);
writer.write(pos_Num);
writer.close();
}
else
{
// creates a FileWriter Object
FileWriter out = new FileWriter(file,true);
// Writes the content to the file
out.write(""); //not sure why you need that...
out.write(pos_Let);
out.write(pos_Num);
out.close();
}
}
I can not find out why you are checking the existence of the output file. Because, when you are using FileWriter if the file specified in the path does not exist, it would create it and open a character output stream to it. Also if it exists in that path, only opens the output stream and it is ready to write into.
Try the following code and see whats happening when you run it more than one times:
float posLat = 156.23589965f;
float posLon = 12.987564f;
File file = new File("c:/FermiPresentCoord.txt");
FileWriter writer = new FileWriter(file, true);
writer.append(posLat+",");
writer.append(posLon+",");
writer.flush();
writer.close();
There is no need to invoke the file.createNewFile() and/or checking the for the existence of the file when you want to write into it.
The second argument for the FileWriter constructor is append flag. So every time you create an output stream to a file with FileWriter(file, true) constructor it automatically appends to the data of the file.
Good Luck.
I'm trying to store multiple data files that I have created into one file. Each file has an ID# (0-35) and each holds some data. But what I want is to be able to store all the files in one file called 'data.xx', then be able to access the each of the files data inside the data.xx file.
public static void pack(int id) {
try {
RandomAccessFile raf = new RandomAccessFile("./data/data.xx", "rw");
ByteArrayInputStream bis = null;
try {
byte[] data = toByteArray(id);
bis = new ByteArrayInputStream(data);
raf.seek(raf.length());
System.out.println(raf.length());
while (bis.read(data, 0, data.length) >= 0) {
raf.write(data, 0, data.length);
}
} finally {
bis.close();
raf.close();
}
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
toByteArray(id) calls the separate data files then puts it into byte array. All the files seem to write fine to the data.xx file. The problem I'm having is I'm not really sure how to read the data.xx file so I can get the data from the files that are stored in it. I hope this makes sense. Also I don't need any compression and I don't want to use a library for this.
Thank you
The simplest way is use markup:
<id_0> content of file 0 </id_0>
...
<id_35> content of file 35 </id_35>
You write file like that and read content inside tags with substring
I would prepend the output file with the offsets of the start of each contained file. A special "token" is a nice idea, but files can contain any byte or bytes; making the idea not realistic. That way your "index" will terminate with something you can't confuse with file data because the information occurres before you expect arbitrary data ... say, 0? Please comment if I misunderstood this question.
I use this simple code to write a few strings to the file called "example.csv", but each time I run the program, it overwrites the existing data in the file. Is there any way to append the text to it?
void setup(){
PrintWriter output = createWriter ("example.csv");
output.println("a;b;c;this;that ");
output.flush();
output.close();
}
import java.io.BufferedWriter;
import java.io.FileWriter;
String outFilename = "out.txt";
void setup(){
// Write some text to the file
for(int i=0; i<10; i++){
appendTextToFile(outFilename, "Text " + i);
}
}
/**
* Appends text to the end of a text file located in the data directory,
* creates the file if it does not exist.
* Can be used for big files with lots of rows,
* existing lines will not be rewritten
*/
void appendTextToFile(String filename, String text){
File f = new File(dataPath(filename));
if(!f.exists()){
createFile(f);
}
try {
PrintWriter out = new PrintWriter(new BufferedWriter(new FileWriter(f, true)));
out.println(text);
out.close();
}catch (IOException e){
e.printStackTrace();
}
}
/**
* Creates a new file including all subfolders
*/
void createFile(File f){
File parentDir = f.getParentFile();
try{
parentDir.mkdirs();
f.createNewFile();
}catch(Exception e){
e.printStackTrace();
}
}
You have to use a FileWriter (pure Java (6 or 7)) rather than PrintWriter from the Processing API.
FileWriter has a second argument in it's constructor that allows you to set a Boolean to decide whether you will append the output or overwrite it (true is to append, false is to overwrite).
The documentation is here: http://docs.oracle.com/javase/7/docs/api/java/io/FileWriter.html
Note you can also use a BufferedWriter, and pass it a FileWriter in the constructor if that helps at all (but I dont think it's necessary in your case).
Example:
try {
FileWriter output = new FileWriter("example.csv",true); //the true will append the new data
output.println("a;b;c;this;that ");
output.flush();
output.close();
}
catch(IOException e) {
println("It Broke :/");
e.printStackTrace();
}
As above, this will work in the PDE - and in Android - but if you need to use it in PJS, PyProcessing, etc, then you will have to hack it
dynamically read the length of the existing file and store it in an ArrayList
add a new line to the ArrayList
use the ArrayList index to control where in the file you are currently writing
If you want to suggest an enhancement to the PrintWriter API (which is probably based off of FileWriter), you can do so at Processing's Issue page on GitHub:
https://github.com/processing/processing/issues?state=open
Read in the file's data, append your new data to that, and write the appended data back to the file. Sadly, Processing has no true "append" mode for file writing.
I'm currently stuck on a spot in my code. I need to write data to a text file, I have sorts going and they are taking the time that each sort takes to complete and then puts them into a txt file that I can then use to create graphs. Problem is that I just get one line after I run the program. I can't get it to keep each result.
public static void resultsToFile(String sort, double seconds, File file)
{
try (PrintWriter out = new PrintWriter(new FileWriter(file)))
{
out.write(sort + "\t");
out.write(seconds + " seconds\n");
out.flush();
out.close();
}catch (IOException e)
{
e.printStackTrace();
}
}
This is what I have so far for my writing to files method. Any help would be greatly appreciated!
You're creating a new PrintWriter object each time you write a line of results to the file and thus over-writing any previously existing File that held the previous line of data. Why not create your PrintWriter once in the class, and then close it when you're done writing all of the data to file?
As HovercraftFullOfEals mentioned, you open the file for each line, and this is a big performance overhead.
Yet the problem you see is because you don't open the file to append to it, but to write to it from the beginning. To append to the file, open it using the constructor FileWriter(File,boolean):
try (PrintWriter out = new PrintWriter(new FileWriter(file, true)))