Mimic escapism Python package in Java. #escapism

Escapism.java

import java.util.Objects;

/**
 * Mimic escaping logic from Python {@code escapism} package.
 */
public class Escapism
{
    public static final String SAFE_CHARS = "abcdefghijklmnopqrstuvwxyz0123456789";
 
    public static final char ESCAPE_CHAR = '-';
    
    public static String escape(String s)
    {
        return escape(s, SAFE_CHARS, ESCAPE_CHAR);
    }
    
    public static String unescape(String s)
    {
        return unescape(s, SAFE_CHARS, ESCAPE_CHAR);
    }
    
    public static String escape(String s, String safeChars, Character escapeChar)
    {
        Objects.requireNonNull(safeChars);
        Objects.requireNonNull(escapeChar);
        checkEscapeCharacter(escapeChar, safeChars);
        
        final int n = s.length();
        final StringBuilder sb = new StringBuilder();
        
        for (int i = 0; i < n; ++i) {
            final char c = s.charAt(i);
            if (safeChars.indexOf(c) < 0) {
                sb.append(String.format("%c%02x", escapeChar, (int) c));
            } else {
                sb.append(c);
            }
        }
        
        return sb.toString();
    }
    
    public static String unescape(String s, String safeChars, Character escapeChar)
    {
        Objects.requireNonNull(safeChars);
        Objects.requireNonNull(escapeChar);
        checkEscapeCharacter(escapeChar, safeChars);
        
        final int n = s.length();
        final StringBuilder sb = new StringBuilder();
        int i = 0;
        while (i < n) {
            final char c = s.charAt(i++);
            if (c == escapeChar) {
                int d = Integer.valueOf(s.substring(i, i + 2), 16);
                i += 2;
                sb.append((char) d);
            } else {
                sb.append(c);
            }
        }
        
        return sb.toString();
    }
    
    private static void checkEscapeCharacter(Character escapeChar, String safeChars)
    {
        if (safeChars.indexOf(escapeChar) >= 0) {
            throw new IllegalArgumentException("escape character cannot also be a safe character!");
        }
    }
    
    public static void main(String[] args)
    {
        final String s = "someone-123@example.com";
        final String s1a = "someone_2d123_40example_2ecom";
        final String s1b = escape(s);
        
        System.err.println(s1a);
        System.err.println(s1b);
        
        String x = unescape(s1b);
        System.err.println(s);
        System.err.println(x);
    }
}