CODEWITHSUNDEEP
javaio
megaplesful AS
megaplesful AS

Reputation: 43

How to read a file from a specific line to another specific line?

So I'm trying to make a file reader to read from x line to y line but when i execute the program it reads all the lines of the file and not the lines that should have started and ended, For example if i'm looking an ID in the file it should print de ID, The name of the holder(the next line of the ID Line), and his/her address(Next line of the name Line), but instead of print just that it prints all the ID'S, Names and Addresses of everyone in the file.

System.out.println("Escriba el ID Del Cliente");
         CL.setID(reader.next());
         String line2;
         int count = 0;
         try {
             BufferedReader input = new BufferedReader(new FileReader(file));
             Scanner input2 = new Scanner(file);
             PrintWriter output = new PrintWriter(new FileOutputStream(file, true));
             LineNumberReader readers = new LineNumberReader(new InputStreamReader(new FileInputStream(file), "UTF-8"));

             while((line2 = input.readLine()) != null)
             {

                 if(line2.contains(CL.getID()))
                 {
                     while(((line2 = readers.readLine()) != null) && readers.getLineNumber() <= count + 3)
                     {
                         count++;
                         System.out.println(line2);


                     }

                     input.close();
                     input2.close();
                     output.close();
                     readers.close();
                     break;
                }





             }

         }catch(IOException ex)
         {
             System.out.println("ERRORR!!!!!!");
         }

Upvotes: 1

Views: 507

Answers (2)

bachph
bachph

Reputation: 153

Assuming you have a file with 100 lines and you want to check and print out line 5 to 10 you could try this:

System.out.println("Escriba el ID Del Cliente");
CL.setID(reader.next());
String line;
int count = 0;
int xLine = 5;
int yLine = 10;
try (BufferedReader input = new BufferedReader(new FileReader(file)))
{
    while((line = input.readLine()) != null)
    {
        if(count < xLine)
        {
            // skip all lines lower then start
            continue;
        }
        else if(count >= xLine && count <= yLine && line.contains(CL.getID()))
        {
            // print line if line is between lines to read
            // and if line contains ID
            System.out.println(line);
        }
        else
        {
            // break if count is bigger then yLine
            break;
        }
        count++;
    }
}
catch(IOException ex)
{
    System.out.println("ERRORR!!!!!!");
}

You read all lines till the BufferedReader reaches null. You check if the line contains your ID. Then you check if the count is between the linenumbers you want to check / print. Then you increment the count for the lines processed.

I simplified the try-catch-Block with a try-with-ressources Statement. As for now I don't see what your plans with output and scanner were, so I removed them.

Upvotes: 0

user1234SI.
user1234SI.

Reputation: 1860

I've modified your code because the problem was at the count++ which will eventually led to reading all the lines from your files, and at the line2 = readers.readLine() which will read from the first line of the file again ( the program works half correct because it reads only 3 lines and only if line2 contains your ID ). Now, to make your program work correctly, you need to either use the BufferedReader or the LineNumberReader. 

public static void main(String[] args) {
    System.out.println("Escriba el ID Del Cliente");
    String line2;
    File file = new File(yourpathhere);
    int lineCount = 0;
    try {
        PrintWriter output = new PrintWriter(new FileOutputStream(file, true));
        LineNumberReader readers = new LineNumberReader(new InputStreamReader(new FileInputStream(file), "UTF-8"));
        while ((line2 = readers.readLine()) != null) {
            lineCount++;
            if (line2.contains(CL.getId())) {
                while (line2 != null && readers.getLineNumber() <= lineCount + 3) {
                    System.out.println(line2);
                    line2 = readers.readLine();
                }
                output.close();
                readers.close();
                break;
            }
        }

    } catch (IOException ex) {
        System.out.println("ERRORR!!!!!!");
    }
    }

PS : pay attention for the getLineNumber() method because it increments the lines read until the moment you're calling it. It means that if we didn't had the lineCount and the ID we're trying to find was at the 6th line, the getLineNumber() value at the moment when line2.contains(CL.getId()) == true was 6, so the readers.getLineNumber() <= 3 will be FALSE and the program won't work correctly anymore. ( We need to keep track for the lines read until the moment we check for the id )

Upvotes: 1

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