Simple CSV writer and reader

CSVMarshaller.java

package test;

import java.io.*;
import java.util.*;

/**
 * @author John Ericksen
 */
public class CSVMarshaller {

    private static final String QUOTE = "\"";
    private static final String NEWLINE = "\n";
    private static final String COMMA = ",";

    public void write(List<List<String>> values, OutputStream stream) throws IOException {
        try(Writer writer = new OutputStreamWriter(stream)) {
            for (List<String> line : values) {
                boolean first = true;
                for(String value : line) {
                    if(first) {
                        first = false;
                    } else {
                        writer.write(COMMA);
                    }
                    writer.write(QUOTE);
                    writer.write(escape(value));
                    writer.write(QUOTE);
                }
                writer.write(NEWLINE);
            }
        }
    }

    private String escape(String value) {
        return value.replace(QUOTE, QUOTE + QUOTE);
    }

    public List<List<String>> read(InputStream stream) throws IOException, MarshallerException {
        List<List<String>> output = new ArrayList<>();
        try (BufferedReader reader = new BufferedReader(new InputStreamReader(stream))) {
            for(String line = reader.readLine(); line != null; line = reader.readLine()) {
                List<String> lineValues = new ArrayList<>();

                int previousSingleQuote = 1;

                int nextSingleQuote = findNextSingeQuote(line, previousSingleQuote);

                while(nextSingleQuote != -1) {
                    assertCharacter(line, QUOTE, previousSingleQuote-1);
                    assertCharacter(line, QUOTE, nextSingleQuote);
                    String value = line.substring(previousSingleQuote, nextSingleQuote).replaceAll("\"\"", "\"");
                    lineValues.add(value);

                    previousSingleQuote = nextSingleQuote + 3;
                    if(nextSingleQuote + 1 < line.length()) {
                        assertCharacter(line, COMMA, nextSingleQuote + 1);
                    }
                    nextSingleQuote = findNextSingeQuote(line, previousSingleQuote);
                }

                output.add(lineValues);
            }
        }
        return output;
    }

    private void assertCharacter(String line, String expected, int index) throws MarshallerException {
        String value = line.substring(index, index + 1);
        if (!value.equals(expected)) {
            throw new MarshallerException("Line \"" + line +
                    "\" at index " + index +
                    " expected: " + expected +
                    " but was " + value);
        }
    }

    private static class MarshallerException extends Exception {
        public MarshallerException(String message) {
            super(message);
        }
    }

    private int findNextSingeQuote(String line, int previousSingleQuote) {
        int startingPoint = previousSingleQuote;
        int nextSingleQuote = line.indexOf("\"", startingPoint);
        int nextDoubleQuote = line.indexOf("\"\"", startingPoint);

        while(nextSingleQuote == nextDoubleQuote && nextSingleQuote != -1) {
            nextSingleQuote = line.indexOf("\"", startingPoint);
            nextDoubleQuote = line.indexOf("\"\"", startingPoint);
            startingPoint = nextSingleQuote + 2;
        }

        return nextSingleQuote;
    }


    public static void main(String[] args) throws Exception {

        List<List<String>> values = new ArrayList<>();
        values.add(Arrays.asList("\"a\"", "b,c,d", "e"));
        values.add(Arrays.asList("1,2,3", "\"4\",\"5", "6\"78\"", "hey"));
        values.add(Arrays.asList("another test", "\"\"\"\"\"\""));

        CSVMarshaller marshaller = new CSVMarshaller();
        ByteArrayOutputStream outputStream = new ByteArrayOutputStream();

        marshaller.write(values, outputStream);

        try(OutputStream fileOut = new FileOutputStream("output.csv")) {
            fileOut.write(outputStream.toByteArray());
        }

        List<List<String>> outputValues = marshaller.read(new ByteArrayInputStream(outputStream.toByteArray()));

        for(int i = 0; i < values.size(); i++) {
            for(int j = 0; j < values.get(i).size(); j++) {
                if(outputValues.size() > i && outputValues.get(i).size() > j) {
                    String original = values.get(i).get(j);
                    String output = outputValues.get(i).get(j);

                    if(!original.equals(output)) {
                        throw new Exception("Not equal at " + i + ", " + j + ", original: " + original + " output: " + output);
                    }
                } else {
                    throw new Exception("Size not the same.");
                }
            }
        }

    }
}