CODEWITHSUNDEEP
javamultithreading
misnomer42
misnomer42

Reputation: 589

Creating files in a separate thread

I have a method that starts creating JSON files in each of the folders in my tree. 

public static void fill(List<String> subFoldersPaths) {
    for (int i = 0; i < subFoldersPaths.size(); i++) {
        String fullFileName = subFoldersPaths.get(i) + FILE_NAME;
        String formatFullFileName = String.format(fullFileName, i)+"%d";
        Runnable runnable = new JsonCreator(formatFullFileName);
        new Thread(runnable).start();
    }
}

List<String> subFoldersPaths is a list that contains paths to each folder in order.

Here is my folder structure:

folder structure

I want each folder to be filled with files in a separate thread every 0.08 seconds. But my class will not fill every folder.

Here is a class that implements Runnable, which should perform the filling:

import com.epam.lab.model.Author;
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import net.andreinc.mockneat.MockNeat;
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;

import java.io.FileWriter;
import java.io.IOException;

public class JsonCreator implements Runnable {
    private static Logger logger = LogManager.getLogger();
    private static String fileName;
    private static final int FILES_COUNT = 100;

    public JsonCreator(String s){
        this.fileName = s;
    }

    @Override
    public void run() {
        for (int i = 0; i < FILES_COUNT; i++) {
            try {
                String formatFullFileName = String.format(fileName, i)+".json";
                FileWriter fileWriter = new FileWriter(formatFullFileName);
                fileWriter.write(createJsonString());
                fileWriter.close();
                Thread.sleep(80);
            } catch (IOException | InterruptedException e) {
                logger.error("File was not created", e);
            }
        }
    }

    private static String createJsonString() {
        MockNeat mockNeat = MockNeat.threadLocal();
        Gson gson = new GsonBuilder()
                .setPrettyPrinting()
                .create();
        String json = mockNeat
                .reflect(Author.class)
                .field("authorName", mockNeat.names().first())
                .field("authorSurname", mockNeat.names().last())
                .map(gson::toJson)
                .val();
        return json;
    }
}

But this class fills not every folder with files. (maybe there is a problem with the file names) I can not figure it out.

And I want each folder below "foo" to be filled in a separate thread of JSON files in the amount of FILES_COUNT = 10

some examples of algorithm execution:

example1 example2

The folder structure is created with the participation of the random, so it is almost always different. but this does not affect the fact that files are not created in all folders

Upvotes: 0

Views: 105

Answers (1)

rzwitserloot
rzwitserloot

Reputation: 103893

  1. Your code is buggy; you cannot ever use that FileWriter constructor. Use new FileWriter(formatFullFileName, StandardCharsets.UTF_8), which is only in jdk11. If you're not on JDK11, you can't use FileWriter at all (it uses platform default encoding, and that is not acceptable; JSON must be in UTF-8 as per the JSON spec, and you have no guarantee that UTF-8 is your platform default).

  2. you aren't guarding your FileWriter with an ARM block - you should add that.

  3. In the initial block, formatFullFileName is a variable that is a format string. In the run() method, it's the opposite (it's the result of running a String.format op on one). Makes your code very hard to read.

  4. Most likely your filenames are incorrect. You should be using List<Path> which would have removed any doubt. If your List<String> subFoldersPaths contains, for example, /home/misnomer/project/foo/1stLayerSubFolder0 in it, and the constant FILE_NAME (which you did not put in your pastes) is, say, example, then the path for the very first file to be created becomes: /home/misnomer/project/foo/1stLayerSubFolder0example0.json which is not what you wanted - you're missing a slash.

  5. NB: If using the newer path API, writing a string to a file becomes vastly simpler: Files.write(path, string) is all you need (and note that the Files API defaults to UTF-8, unlike most other parts of the java libraries that involve turning strings to bytes or vice versa).

  6. The paste needs more info, or you should debug this on your own: Print when you write a file, preferably including the thread ID (you can get it with Thread.currentThread().getName()). That's how programming works: You don't just stare at it, go --heck, I dunno, better ask stack overflow!-- and then give up. You debug it. Use a debugger, or if you can't/don't want to, use the poor man's debugger: Add a whole bunch of System.out.println statements. Go through your code and imagine (write it down if you have to) which each step is doing. Then, add a println statement that confirms this. The very place where what the program says it is doing does not match with what you thought it would do? That's where a bug is. Fix it, and keep going until all bugs are eliminated.

Upvotes: 3

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