How to sort Properties in java?

No, java.util.Properties extends java.util.Hashtable which doesn't define a predictable sort order for keys or values.

You could try dumping all values into something like java.util.TreeMap, which will impose a natural ordering on your keys.

all you have to do is create class which extends Properties. source: java2s.com

import java.io.FileOutputStream;
import java.util.Collections;
import java.util.Enumeration;
import java.util.Properties;
import java.util.Vector;

public class Main{
  public static void main(String[] args) throws Exception {
    SortedProperties sp = new SortedProperties();
    sp.put("B", "value B");
    sp.put("C", "value C");
    sp.put("A", "value A");
    sp.put("D", "value D");
    FileOutputStream fos = new FileOutputStream("sp.props");
    sp.store(fos, "sorted props");
  }

}
class SortedProperties extends Properties {
  public Enumeration keys() {
     Enumeration keysEnum = super.keys();
     Vector<String> keyList = new Vector<String>();
     while(keysEnum.hasMoreElements()){
       keyList.add((String)keysEnum.nextElement());
     }
     Collections.sort(keyList);
     return keyList.elements();
  }

}

it works for me.

Overriding keys works well with Java 8, but since Java 9, the new implementation of method store don't call the method keys any more but the method entrySet.

So, you have to override entrySet too to make your Properties sorted with Java 8/9/10 when stored.

Here an example with inline overriding:

Properties properties = new Properties() {

    private static final long serialVersionUID = 1L;

    @Override
    public Set<Object> keySet() {
        return Collections.unmodifiableSet(new TreeSet<Object>(super.keySet()));
    }

    @Override
    public Set<Map.Entry<Object, Object>> entrySet() {

        Set<Map.Entry<Object, Object>> set1 = super.entrySet();
        Set<Map.Entry<Object, Object>> set2 = new LinkedHashSet<Map.Entry<Object, Object>>(set1.size());

        Iterator<Map.Entry<Object, Object>> iterator = set1.stream().sorted(new Comparator<Map.Entry<Object, Object>>() {

            @Override
            public int compare(java.util.Map.Entry<Object, Object> o1, java.util.Map.Entry<Object, Object> o2) {
                return o1.getKey().toString().compareTo(o2.getKey().toString());
            }
        }).iterator();

        while (iterator.hasNext())
            set2.add(iterator.next());

        return set2;
    }

    @Override
    public synchronized Enumeration<Object> keys() {
        return Collections.enumeration(new TreeSet<Object>(super.keySet()));
        }
    };