Java Collection - 如何将地图转换为只读地图

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;

public class Main {
  public static void main(String[] argv) throws Exception {

    Map map = new HashMap();
    map = Collections.unmodifiableMap(map);


    try {
      map.put("key","new value");
    } catch (UnsupportedOperationException e) {
      System.out.println(e.getMessage());
    }

  }
}