Creating properties file (package java.util.Propertiesを参考に作成、keyでソート、¥nはそのまま出力)

PropertiesSample.java

import java.io.BufferedWriter;
import java.io.IOException;
import java.nio.charset.Charset;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.Map;
import java.util.TreeMap;
import java.util.logging.Level;
import java.util.logging.Logger;

/**
 * creating properties file sample
 * 
 * @author tomo
 */
public class PropertiesSample {

    /**
     * creating properties file sample
     * 
     * @param args the command line arguments
     */
    public static void main(String... args) {
        Map<String, String> map = getKeyValMap();
        Path path;
        if (args.length > 1){
            path = Paths.get(args[0]);
        } else {
            path = Paths.get("/Users", "tomo", "sample.properties");
        }
        createProp(map, path);
    }

    private static Map<String, String> getKeyValMap() {
        Map<String, String> map = new TreeMap<>(); // <-- sort
        map.put("key1", "val1");
        map.put("key2", "val2あ"); // \u3042
        map.put("key3", "val3𩸽"); // \uD867\uDE3D
        map.put("key4", "val4¥n");
        map.put("key5", "val5ア"); // \u30A2
        return map;
    }

    private static void createProp(Map<String, String> map, Path path) {
        try (BufferedWriter writer = Files.newBufferedWriter(path, Charset.forName("ISO-8859-1"));) {
            for (String key : map.keySet()) {
                String line = key + "=" + toHex(map.get(key));
                writer.write(line);
                writer.newLine();
            }
        } catch (IOException ex) {
            Logger.getLogger(PropertiesSample.class.getName()).log(Level.SEVERE, null, ex);
        }
    }
    private static String toHex(String val) {
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < val.length(); i++) {
            char c = val.charAt(i);
            if (!isEacapeTarget(c)){
                sb.append(c);
            } else {
                sb.append("\\u");
                sb.append(hexDigit[((c >> 12) & 0xF)]);
                sb.append(hexDigit[((c >> 8) & 0xF)]);
                sb.append(hexDigit[((c >> 4) & 0xF)]);
                sb.append(hexDigit[(c & 0xF)]);
            }
        }
        return sb.toString();
    }
    
    private static boolean isEacapeTarget(char c) {
        if (String.valueOf(c).equals("¥")){
            return false;
        }
        if (c < 128){
            return false;
        }
        return true;
    }

    private static final char[] hexDigit = {
        '0','1','2','3','4','5','6','7','8','9','A','B','C','D','E','F'
    };

}