How to add a new line of text to an existing file in Java?
JavaFile IoText ProcessingJava Problem Overview
I would like to append a new line to an existing file without erasing the current information of that file. In short, here is the methodology that I am using the current time:
import java.io.BufferedWriter;
import java.io.FileWriter;
import java.io.Writer;
Writer output;
output = new BufferedWriter(new FileWriter(my_file_name)); //clears file every time
output.append("New Line!");
output.close();
The problem with the above lines is simply they are erasing all the contents of my existing file then adding the new line text.
I want to append some text at the end of the contents of a file without erasing or replacing anything.
Java Solutions
Solution 1 - Java
you have to open the file in append mode, which can be achieved by using the FileWriter(String fileName, boolean append)
constructor.
output = new BufferedWriter(new FileWriter(my_file_name, true));
should do the trick
Solution 2 - Java
The solution with FileWriter
is working, however you have no possibility to specify output encoding then, in which case the default encoding for machine will be used, and this is usually not UTF-8!
So at best use FileOutputStream
:
Writer writer = new BufferedWriter(new OutputStreamWriter(
new FileOutputStream(file, true), "UTF-8"));
Solution 3 - Java
Starting from Java 7:
Define a path and the String containing the line separator at the beginning:
Path p = Paths.get("C:\\Users\\first.last\\test.txt");
String s = System.lineSeparator() + "New Line!";
and then you can use one of the following approaches:
-
Using
Files.write
(small files):try { Files.write(p, s.getBytes(), StandardOpenOption.APPEND); } catch (IOException e) { System.err.println(e); }
-
Using
Files.newBufferedWriter
(text files):try (BufferedWriter writer = Files.newBufferedWriter(p, StandardOpenOption.APPEND)) { writer.write(s); } catch (IOException ioe) { System.err.format("IOException: %s%n", ioe); }
-
Using
Files.newOutputStream
(interoperable withjava.io
APIs):try (OutputStream out = new BufferedOutputStream(Files.newOutputStream(p, StandardOpenOption.APPEND))) { out.write(s.getBytes()); } catch (IOException e) { System.err.println(e); }
-
Using
Files.newByteChannel
(random access files):try (SeekableByteChannel sbc = Files.newByteChannel(p, StandardOpenOption.APPEND)) { sbc.write(ByteBuffer.wrap(s.getBytes())); } catch (IOException e) { System.err.println(e); }
-
Using
FileChannel.open
(random access files):try (FileChannel sbc = FileChannel.open(p, StandardOpenOption.APPEND)) { sbc.write(ByteBuffer.wrap(s.getBytes())); } catch (IOException e) { System.err.println(e); }
Details about these methods can be found in the Oracle's tutorial.
Solution 4 - Java
Try: "\r\n"
Java 7 example:
// append = true
try(PrintWriter output = new PrintWriter(new FileWriter("log.txt",true)))
{
output.printf("%s\r\n", "NEWLINE");
}
catch (Exception e) {}
Solution 5 - Java
In case you are looking for a cut and paste method that creates and writes to a file, here's one I wrote that just takes a String input. Remove 'true' from PrintWriter if you want to overwrite the file each time.
private static final String newLine = System.getProperty("line.separator");
private synchronized void writeToFile(String msg) {
String fileName = "c:\\TEMP\\runOutput.txt";
PrintWriter printWriter = null;
File file = new File(fileName);
try {
if (!file.exists()) file.createNewFile();
printWriter = new PrintWriter(new FileOutputStream(fileName, true));
printWriter.write(newLine + msg);
} catch (IOException ioex) {
ioex.printStackTrace();
} finally {
if (printWriter != null) {
printWriter.flush();
printWriter.close();
}
}
}
Solution 6 - Java
On line 2 change new FileWriter(my_file_name)
to new FileWriter(my_file_name, true)
so you're appending to the file rather than overwriting.
File f = new File("/path/of/the/file");
try {
BufferedWriter bw = new BufferedWriter(new FileWriter(f, true));
bw.append(line);
bw.close();
} catch (IOException e) {
System.out.println(e.getMessage());
}
Solution 7 - Java
You can use the FileWriter(String fileName, boolean append)
constructor if you want to append data to file.
Change your code to this:
output = new BufferedWriter(new FileWriter(my_file_name, true));
From FileWriter javadoc:
> Constructs a FileWriter object given a > file name. If the second argument is > true, then bytes will be written to > the end of the file rather than the > beginning.