Read the files in a folder and then store each user id in a linkedhashset

Question

I have around 100 files in a folder. And I am trying to read all those files one by one. Each file will have data like this and each line resembles an user id.

So I need to read that file line by line and then store each user id in a LinkedHashSet. I am able to read all the files from a particular folder with the below code. But with the below java code that I wrote, I am not sure how to read those files line by line and then store each user id in a LinkedHashSet?

public static void main(String args[]) {

    File folder = new File("C:\\userids-20130501");
    File[] listOfFiles = folder.listFiles();

    for (int i = 0; i < listOfFiles.length; i++) {
        File file = listOfFiles[i];
        if (file.isFile() && file.getName().endsWith(".txt")) {
            try {
                String content = FileUtils.readFileToString(file);
                System.out.println(content);
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

Any help will be appreciated on this? And any better way to do the same process?

JHS · Accepted Answer · 2013-06-19T20:16:32.870

3

Since you are using FileUtils. The class has the method readLines() which returns a list of String.

You can then add this List of String to LinkedHashSet by using the addAll() method.

Try this -

public static void main(String args[]) {
File folder = new File("C:\\userids-20130501");
File[] listOfFiles = folder.listFiles();

Set<String> userIdSet = new LinkedHashSet<String>();
for (int i = 0; i < listOfFiles.length; i++) {
    File file = listOfFiles[i];
    if (file.isFile() && file.getName().endsWith(".txt")) {
        try {
            List<String> content = FileUtils.readLines(file, Charset.forName("UTF-8"));
            userIdSet.addAll(content);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
 }

edited Jun 19 '13 at 20:16

answered Jun 19 '13 at 19:03

JHS

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Thanks Junaid for the suggestion. In your example, it will create a new LinkedHashSet everytime. And I want to keep on appending the user id's to same linkedhashset. – arsenal Jun 19 '13 at 20:08
Changed the code to use the same LinkedHashSet. Hope this is was you want. – JHS Jun 19 '13 at 20:11

score 1 · Answer 2 · answered Jun 19 '13 at 18:56

You can use the readLine() method of BufferedReader to read a file line by line as below:

public static void main(String args[]) {

File folder = new File("C:\\userids-20130501");
File[] listOfFiles = folder.listFiles();

Set<String> userIdSet = new LinkedHashSet<String>();
for (int i = 0; i < listOfFiles.length; i++) {
    File file = listOfFiles[i];
    if (file.isFile() && file.getName().endsWith(".txt")) {
        try {
          BufferedReader br = new BufferedReader(new FileReader(file));
          String line;
          while((line = br.readLine()) != null) {
              userIdSet.add(line);
           }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
 }
}

Smit · Answer 3 · 2013-06-19T19:21:13.133

If I understood you correctly then you can do something like below.

// Change generic if you want Integer
Set<String> userIdSet = new LinkedHashSet<String>(); 

// Your code


String content = FileUtils.readFileToString(file);
// Creating array by splitting for every new line content
String[] stn = content.split("\\n");
     for(String xx : stn){
        // parse it as Integer if you changed the generic
        // Adding the file content to Set
        userIdSet.add(xx); 
}

score 1 · Answer 4 · edited May 23 '17 at 12:32

Here are a the things I would do different.

Using an iterator for the files
The new try statement allows opening up a “resource” in a try block and automatically closing the resource when the block is done. Ref
Excluding invalid files with a continue statement. This removes one level of nesting. See this post.

All of these changes are highly opinionated of course.

    public static void main(String[] args) {

       Set<Integer> users = new LinkedHashSet<Integer>();

       File dir = new File("C:\\userids-20130501");
       for (File child : dir.listFiles()) {
         if (!child.isFile() || !child.getName().endsWith(".txt")) {
           continue;
         }

         try (BufferedReader in = new BufferedReader(
             new FileReader(child.getPath()))) {

           String id = null;
           while ((id = in.readLine()) != null) {
             users.add(Integer.parseInt(id));
           }
         } catch (IOException ex) {
           ex.printStackTrace();
         }
       }
   }

Read the files in a folder and then store each user id in a linkedhashset

4 Answers4