Read a txt file from a particular layout

Question

I need to read a file txt that has various values.

Example:

41976127992Jhonatan   3129176513

Only I want to take only parts of these values based on a layout, for example:

CPF = Posição 1 a 11
Nome = Posição 12 a 22 ( neste caso tem espaços no arquivo ) 
Agencia = Posição 23 a 26
Conta = Posição 27a 32 

And I would like to record these values in a variable, then I will take this variable and compare it with another variable.

Answer 1

You don’t need to read each separate snippet based on positions. An easier approach is to simply read the whole line and then use substring to get each section of the line separately:

String nomeArquivo = "arquivo.txt";
try (BufferedReader br =
         new BufferedReader(new InputStreamReader(new FileInputStream(nomeArquivo), "UTF-8"))) {
    String linha; // para cada linha
    while ((linha = br.readLine()) != null) {
        String cpf = linha.substring(0, 11);
        String nome = linha.substring(11, 22);
        String agencia = linha.substring(22, 26);
        String conta = linha.substring(26);
        System.out.printf("CPF=%s, nome=%s, agencia=%s, conta=%s\n", cpf, nome, agencia, conta);
    }
} catch (IOException e) {
    // trate o erro como achar melhor
}

Note that I used the syntax of Try-with-Resources, which ensures that the file will be closed at the end of the execution. It still took a catch, for the FileInputStream can launch an exception if the file does not exist, the readLine() may launch another if any error occurs while reading, etc.

With that I use readLine() to read the entire file line, and then use substring to get the snippets that interest me. In the first 3 cases, the initial and final index is used, and the String always starts at zero, and the final index is not included.

For example, substring(0, 11) take the index zero to 10 (i.e., the first 11 characters, which in this case correspond to the digits of the CPF). Already in the last case, I put only the initial index (26), and in this case substring takes everything from this index to the end of the String.

I also set up the encoding of the file as UTF-8, but you can switch to the encoding that your file is using. The output is:

CPF=41976127992, nome=Jhonatan   , agencia=3129, conta=176513

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From Java 8 it is also possible to use streams:

import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.stream.Stream;

try (Stream<String> stream = Files.lines(Paths.get(nomeArquivo), StandardCharsets.UTF_8)) {
    stream.forEach(linha -> {
        String cpf = linha.substring(0, 11);
        String nome = linha.substring(11, 22);
        String agencia = linha.substring(22, 26);
        String conta = linha.substring(26);
        System.out.printf("CPF=%s, nome=%s, agencia=%s, conta=%s\n", cpf, nome, agencia, conta);
    });
} catch (IOException e) {
    // trate o erro como achar melhor
}

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Based in his comment, if each line has different information, just keep a line counter, and according to the line number, read the respective information. Example:

try (BufferedReader br = ...) {
    String linha; // para cada linha
    int numeroLinha = 0; // em qual linha estou
    while ((linha = br.readLine()) != null) {
        numeroLinha++; // atualiza número da linha
        switch (numeroLinha % 2) {
            case 1: // primeira linha
                String cpf = linha.substring(0, 11);
                String nome = linha.substring(11, 22);
                String agencia = linha.substring(22, 26);
                String conta = linha.substring(26);
                System.out.printf("CPF=%s, nome=%s, agencia=%s, conta=%s\n", cpf, nome, agencia, conta);
                break;
            case 0: // segunda linha
                // ler endereço
                break;
        }
    }

In this case, I am assuming that the file has one line with CPF/Name/etc and another with address, then another with CPF/Name/etc and another with address and so on. That’s why I used numeroLinha % 2 (the remainder of the division of the line number by 2). When the rest of the division is 1, I am on an odd line, and so is a line that contains the CPF/Name/etc. When the rest is zero, I am on an even line, and so is the address.

Adapt the code to the format of your file. If you have more different line types, just update the values. For example, if it is the first line with name/CPF, the second with address, the third with phone, the fourth with credit card, just do something like:

while ((linha = br.readLine()) != null) {
    numeroLinha++; // atualiza número da linha
    switch (numeroLinha % 4) {
        case 1: // primeira linha
            // ler nome/CPF
            break;
        case 2: // segunda linha
            // ler endereço
            break;
        case 3: // terceira linha
            // ler telefone
            break;
        case 0: // quarta linha
            // ler cartão de crédito
            break;
    }

And so on and so forth. Again, I’m assuming that your file format follows this pattern of always having N lines, each with a type of information, repeating itself without breaking.

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^{If the format is different, please edit question and update information with file format.}