How to read fixed length file in java

Question

I’m reading flat files in java with fixed length I’m new to this can anyone help me out how to do fixed length reader ?

Answer 1

When it is a text file, with fixed length lines, a normal reader suffices.

This assumes that there is a newline at the end of each record.

List<MyRecord> result = new ArrayList<>();

Path file = Paths.get("C:/Import/20190308.txt");
Charset charset = Charset.defaultCharset();

Files.lines(path, charset)
    .filter(line -> line.length() != 142)
    .forEach(line -> {
        MyRecord record = new MyRecord();
        record.id = Long.parseLong(line.substring(0, 10).trim());
        record.name = line.substring(10, 50).trim();
        record.age = Integer.parseInt(line.substring(50, 53).trim());
        ...
        result.add(record);
    });

The String.trim() removing the padding spaces before ("Mary ") and after (" 89"). The String.substring(position, nextPosition) picking the fixed field.

The read line is without newline character(s) - \r\n or \n in general. There is a check on the line length (here 142). This is the length in chars, but most likely is the length in bytes too, as fixed length records probably are in a single byte charset.

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For some custom class MyRecord mirroring a CSV line:

public class MyRecord {
    public long id;
    public String name;
    public int age;
    ...
}