Read text file in spring batch upside down

Question

I'm trying to read a file in spring batch upside down and for that I've created a custom reader as shown bellow:

import org.springframework.batch.item.ItemReader;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class UpsideDownItemReader implements ItemReader<String> {

    private BufferedReader bufferedReader;
    private List<String> lines;

    public UpsideDownItemReader(String filePath) throws IOException {
        bufferedReader = new BufferedReader(new InputStreamReader(getClass().getResourceAsStream(filePath)));
        initializeLines();
    }

    private void initializeLines() throws IOException {
        lines = new ArrayList<>();
        String line;
        while ((line = bufferedReader.readLine()) != null) {
            lines.add(line);
        }
        Collections.reverse(lines);
    }

    @Override
    public String read() throws Exception {
        if (!lines.isEmpty()) {
            return lines.remove(0);
        } else {
            bufferedReader.close();
            return null;
        }
    }
}

is there any other easier way to do this ?

Answer 1

So, if anyone is wondering here is how to read a file upside down in spring batch:

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.util.Stack;

import org.springframework.batch.item.ItemReader;

public class UpsideDownItemReader implements ItemReader<String> {

    private BufferedReader bufferedReader;
    private Stack<String> lines;

    public UpsideDownItemReader(String filePath) throws IOException {
        bufferedReader = new BufferedReader(new FileReader(filePath));
        initializeLines();
    }

    private void initializeLines() throws IOException {
        lines = new Stack<>();
        String line;
        while ((line = bufferedReader.readLine()) != null) {
            lines.push(line);
        }
    }

    @Override
    public String read() throws Exception {
        if (!lines.isEmpty()) {
            return lines.pop();
        } else {
            bufferedReader.close();
            return null;
        }
    }
}

And then you need to define your custom reader:

@Bean
@StepScope
public UpsideDownItemReader upsideDownItemReader(@Value("#{jobParameters['filePath']}") String filePath) throws IOException {
        return new UpsideDownItemReader(filePath);
    }