CODEWITHSUNDEEP
javainput
user3013909
user3013909

Reputation: 89

Check if input already exists in textfile with Java

I want to create a small project where a name can be inserted and that is saved with the data of the input in a textfile. Additionally it should check, if this name is already in the document and if so, there should be an alert and the name should not be added.

The code below is how I add the names to the textfile.

else if (i == 1) {  
     Scanner input = new Scanner(System.in);

    System.out.println("Surname: ");
    surname = input.nextLine();

    System.out.println("First name: ");
    firstname = input.nextLine();

    Date date = new Date();
    SimpleDateFormat sdf = new SimpleDateFormat("dd/MM/yyyy");
    System.out.println(sdf.format(date));


    File file = new File("C://Users/Prakt1/Desktop/projektverwaltung.txt");
    String content = ("Surname " + (surname) + LINE_SEPARATOR + "First name: " + (firstname) + LINE_SEPARATOR + "Added: " +
    (sdf.format(date)) + LINE_SEPARATOR);

    try(PrintWriter out = new PrintWriter(new BufferedWriter(new FileWriter("C://Users/Prakt1/Desktop/projektverwaltung.txt", true)))) {
       out.println(content);          
    }catch (IOException e) {
     e.printStackTrace();
    }

How can I do this in Java without jQuery/JavaScript?

Thank you for you help, Chris

Upvotes: 0

Views: 4834

Answers (3)

jr.
jr.

Reputation: 1739

I'd suggest streaming line by line to reduce the memory footprint. This method does no validation and assumes that your file is formatted the way you suggested in your code.

try( FileReader fileReader = new FileReader(
        "C://Users/Prakt1/Desktop/projektverwaltung.txt" );
     BufferedReader reader  = new BufferedReader( fileReader ) )
{
    String line = null;
    String currentSurname = null;
    String currentFirstName = null;
    while( ( line = reader.readLine() ) != null )
    {
        if( line.startsWith( "Surname " ) )
        {
            currentSurname = line.substring( "Surname ".length() );
        }
        else if( line.startsWith( "First name: " ) )
        {
            currentFirstName = line.substring( "First name: ".length() );
        }
        else
        {
            if( currentSurname != null &&
                currentFirstName != null &&
                currentSurname.equals( surname ) &&
                currentFirstName.equals( firstName ) )
            {
                System.out.println( "Name already in file." );
                break;
            }
            currentSurname = null;
            currentFirstName = null;
        }
    }
}

Upvotes: 0

Sarz
Sarz

Reputation: 1976

Hey you can do this like sample:

you have to follow these steps:

  1. Read file till end
  2. match ceriteria
  3. if not found till end of file

  4. append it / else already exist

    public void appendFile(String surName, String firstName){
File file = new File("C:/robots.txt");
    FileInputStream fis = null;
    try {
        fis = new FileInputStream(file);
        String line = reader.readLine();
        boolean isFound = false;
        while(line != null){
            System.out.println(line);
               // or the match you want to e.g. surname
            if(line.equals(surName)){
                isFound = true;
                break;
            }
            line = reader.readLine();
        }
        //This is End of File
        if(!isFound)}{
            //Not in file append it at the end of file
        }else{
            //Already exist in file
        }
    } catch (IOException e) {
        e.printStackTrace();
    } finally {
        try {
            if (fis != null)
                fis.close();
        } catch (IOException ex) {
            ex.printStackTrace();
        }
    }
}

    }

Upvotes: 0

gexicide
gexicide

Reputation: 40118

Here is a simple solution: First build the name string, then read the file and check if it is in there. If it is alert, otherwise, perform your insert

// Build the string
String content = ("Surname " + (surname) + LINE_SEPARATOR + "First name: " + (firstname);

// Read all contents into a String
byte[] bytes = Files.readAllBytes(Paths.get("C://Users/Prakt1/Desktop/projektverwaltung.txt"));
String s = new String(bytes);

// Check if the name is contained
if(s.indexOf(content) != -1){
     System.out.println("Name already present!");
} else {
     ... // Do your usual insertion
}

Note that you must specify an encoding in the new String constructor, unless your file uses your platform's default encoding. For example, it might look like this for UTF8:

String s = new String(bytes,StandardCharsets.UTF_8);

Also note that this approach reads the file into memory thoroughly. Thus, if you have a really huge file (>50 MB) that would yield an OutOfMemory error upon reading, you should rather use a BufferedReader and read the file line by line.

Upvotes: 3

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