Question

I’m having a problem figuring out how to split a string to multiple files. At the moment I should get two files both with JSON data. The code below writes to the first file but leaves the second empty. Any ideas why?

public void splitFile(List<String> results) throws IOException {

  int name = 0;
  for (int i=0; i<results.size(); i ++) {

    write = new FileWriter("/home/tom/files/"+ name +".json");
    out = new BufferedWriter(write);
    out.write(results.get(i));

    if (results.get(i).startsWith("}")) {
      name++;
    }      
  } 
}

Edit: it splits at line starting with { because that denotes the end of a JSON document.

Answer 1

Enhance the cut-control

Get togher this:

write = new FileWriter("/home/tom/files/"+ name +".json");
out = new BufferedWriter(write);

and this:

name++;

Check for starting, not for end

Check for line starting with {, and execute those three lines to open the file.

Remember to close and flush

If it’s not the first line (i > 0) then close the last writer (write.close();).

Close the last opened writer

if (!results.isEmpty())
    out.close();

Result

It should look something like this:

public void splitFile(List<String> results) throws IOException {

  int name = 0;

  BufferedWriter out = null;
  for (int i=0; i<results.size(); i ++) {
    String line = results.get(i);
    if (line.startsWith("{")) {
       if (out != null) // it's not the first
          out.close(); // tell buffered it's going to close, it makes it flush
       FileWriter writer = new FileWriter("/home/tom/files/"+ name +".json");
       out = new BufferedWriter(writer);
       name++;
    }
    if (out == null)
       throw new IllegalArgumentException("first line doesn't start with {");
    out.write(line);
  } 

  if (out != null) // there was at least one file
     out.close();
}