CODEWITHSUNDEEP
java
user2945412
user2945412

Reputation: 297

How to append existing line in text file

How do i append an existing line in a text file? What if the line to be edited is in the middle of the file? Please kindly offer a suggestion, given the following code.

Have went through & tried the following:

My code:

    filePath = new File("").getAbsolutePath();
    BufferedReader reader = new BufferedReader(new FileReader(filePath + "/src/DBTextFiles/Customer.txt"));
    try
    {                           
        String line = null;         
        while ((line = reader.readLine()) != null)
        {
            if (!(line.startsWith("*")))
            {
                //System.out.println(line);

                //check if target customer exists, via 2 fields - customer name, contact number
                if ((line.equals(customername)) && (reader.readLine().equals(String.valueOf(customermobilenumber))))
                {
                    System.out.println ("\nWelcome (Existing User) " + line + "!");

                    //w target customer, alter total number of bookings @ 5th line of 'Customer.txt', by reading lines sequentially
                    reader.readLine();
                    reader.readLine();
                    int total_no_of_bookings = Integer.valueOf(reader.readLine());

                    System.out.println (total_no_of_bookings);
                    reader.close();
                    valid = true;


                    //append total number of bookings (5th line) of target customer @ 'Customer.txt'
                    try {
                        BufferedWriter writer = new BufferedWriter(new FileWriter(new File(filePath + "/src/DBTextFiles/Customer.txt")));
                        writer.write(total_no_of_bookings + 1);
                        //writer.write("\n");
                        writer.close();
                    }
                    catch (IOException ex) 
                    {
                        ex.printStackTrace();
                    } 
                    //finally 
                   // {
                        //writer.close();
                    //}
                }                   
            }
        }

Upvotes: 2

Views: 3165

Answers (4)

Matthew Tory
Matthew Tory

Reputation: 1306

The reader.readLine() method increments a line each time it is called. I am not sure if this is intended in your program, but you may want to store the reader.readline() as a String so it is only called once.

To append a line in the middle of the text file I believe you will have to re-write the text file up to the point at which you wish to append the line, then proceed to write the rest of the file. This could possibly be achieved by storing the whole file in a String array, then writing up to a certain point.

Example of writing:

BufferedWriter writer = new BufferedWriter(new FileWriter(new File(path)));
writer.write(someStuff);
writer.write("\n");
writer.close();

Upvotes: 1

Josh
Josh

Reputation: 1553

You should probably be following the advice in the answer to the second link you posted. You can access the middle of a file using a random access file, but if you start appending at an arbitrary position in the middle of a file without recording what's there when you start writing, you'll be overwriting its current contents, as noted in this answer. Your best bet, unless the files in question are intractably large, is to assemble a new file using the existing file and your new data, as others have previously suggested.

Upvotes: 1

Andrea
Andrea

Reputation: 2764

AFAIK you cannot do that. I mean, appending a line is possible but not inserting in the middle. That has nothing to do with java or another language...a file is a sequence of written bytes...if you insert something in an arbitrary point that sequence is no longer valid and needs to be re-written.

So basically you have to create a function to do that read-insert-slice-rewrite

Upvotes: 0

A4L
A4L

Reputation: 17595

To be able to append content to an existing file you need to open it in append mode. For example using FileWriter(String fileName, boolean append) and passing true as second parameter.

If the line is in the middle then you need to read the entire file into memory and then write it back when all editing was done.

This might be workable for small files but if your files are too big, then I would suggest to write the actual content and the edited content into a temp file, when done delete the old one an rename the temp file to be the same name as the old one.

Upvotes: 2

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