如何在Java中的SQL查询中使用map.KeySet（）

Question

I have a LinkedHahMap map1 whcih holds key as my beam_current which is of double type and value as my logtime which is of string type. Now I want to use this map1.keySet() in my sql query as-

Set<Double> arr=    map1.keySet();
String vs2="select b.beam_current, b.beam_energy where
          b.logtime between '"+first+"' and '"+last+"' and b.beam_current in('"+arr+"')";

But when I use arr which holds value of map1 key ,**nothing is being displayed.**Can't we use map1.KeySet() method in sql query or I'm implemting it in wrong way??

Answer 1

First convert your map keys into comma separated string and then use it in your query.

  List<Double> slist = new ArrayList<Double>(map1.keySet());
  String s = StringUtils.join(slist, ',');


      String vs2="select b.beam_current, b.beam_energy where
                  b.logtime between '"+first+"' and '"+last+"' and    
                  b.beam_current in('"+s+"')";

Answer 2

If you don't want to depend on external libs (like StringUtils.join), you can do it manually:

public static void main(String[] args) {
    HashMap<Double, String> map1 = new HashMap<Double, String>();
    map1.put(1.5, "");
    map1.put(2.5, "");
    String first = "first";
    String last = "last";

    String query = buildQuery(map1, first, last);
    System.out.println(query);
}

private static String buildQuery(HashMap<Double, String> map1, String first, String last) {
    StringBuilder sb = new StringBuilder();
    sb.append("select b.beam_current, b.beam_energy where b.logtime between '");
    sb.append(first);
    sb.append("' and '");
    sb.append(last);
    sb.append("' and b.beam_current in (");
    String separator = "";
    for (Double val : map1.keySet()) {
        sb.append(separator);
        sb.append(val);
        separator = ", ";
    }
    sb.append(")");
    return sb.toString();
}