java check if text file exists without overwrite

Question

I want to check if a text file exists, and set a PrintWriter to write in it. for now any new PrintWriter instance overwrite the last one. My main:

TextFileForStatus textFile = new TextFileForStatus(); int startingIndex = 1; try{ String output = textFile.readIndex(); System.out.println("In file: " + output); if(output == null) { textFile.writeToFile(Integer.toString(startingIndex)); } else { System.out.println("output: " + output); startingIndex = Integer.parseInt(output); } } catch(ReaderException RE){ RE.getMessage().toString(); }catch(Exception EX){ EX.getMessage().toString(); }

and the class I created to create the file:

public class TextFileForStatus { private final String fileName = "status"; private final String Format = "UTF-8"; private BufferedReader reader = null; private PrintWriter writer = null; public TextFileForStatus() throws FileNotFoundException, UnsupportedEncodingException { writer = new PrintWriter(fileName, Format); reader = new BufferedReader(new FileReader(fileName)); } public void writeToFile(String currentStatus){ writer.println(currentStatus); System.out.println("writer wrote: "+ currentStatus + " to file"); writer.flush(); } public String readIndex() throws IOException{ String indexInFile = ""; while((indexInFile = reader.readLine())!=null){ indexInFile += reader.readLine(); } return indexInFile; } }

Can I use the text file that already exists?

Possible duplicate of How to append text to an existing file in Java — Mad Physicist
– Mad Physicist, Commented Nov 19, 2015 at 12:46
I wrote only the relevant parts. the code compiles and writes to file. — Itsik Mauyhas
– Itsik Mauyhas, Commented Nov 19, 2015 at 12:46
Use Files.newBufferedWriter(... StandardOpenOption.WRITE, APPEND) — Joop Eggen
– Joop Eggen, Commented Nov 19, 2015 at 12:47

ParkerHalo · Accepted Answer · 2015-11-19 12:53:32Z

You can use new File(fileName).exists() to check if a file exists or not. So you may want to try:

public class TextFileForStatus { private final String fileName = "status"; private final String Format = "UTF-8"; private BufferedReader reader = null; private PrintWriter writer = null; private boolean fileExists; // flag public TextFileForStatus() throws FileNotFoundException, UnsupportedEncodingException { fileExists = new File(fileName).exists(); writer = new PrintWriter(fileName, Format); reader = new BufferedReader(new FileReader(fileName)); } public void writeToFile(String currentStatus) { if (fileExists) { writer.println(currentStatus); System.out.println("writer wrote: " + currentStatus + " to file"); writer.flush(); } } public String readIndex() throws IOException { if (!fileExists) return ""; String indexInFile = ""; while ((indexInFile = reader.readLine()) != null) { indexInFile += reader.readLine(); } return indexInFile; } }

Glorfindel · Accepted Answer · 2021-07-29 05:48:53Z

Use JDK7 Files:

public void writeToFile(String path, String fileName, String status) throws Exception { String text = "writer wrote: "+ status + " to file"; Path p = Paths.get(path, fileName); if (Files.isWritable(p)) { //checks for existence too Files.write(p, text.getBytes(), StandardOpenOption.APPEND); // see https://docs.oracle.com/javase/tutorial/essential/io/file.html#openOptions } }

Check OpenOption for writing options.

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