Java infinite tree of recursive hyperpractical case

As follows:

 @Override 
  public String getEmployeeBysup(String employeeID) { 
    String str=""; 
    str = getEmployeeBysupSelas(employeeID, str); 
    return str.substring(0, str.lastIndexOf(",")); 
  } 
  @Override 
  public String getEmployeeBysupSelas(String employeeID, String str) { 
    str+="'"+employeeID+"',"; 
    System.out.println(str); 
    String sql="SELECT u.employeeID from tbl_system_user u where supervisorID='"+employeeID+"'"; 
    List<String> list= jdbcTemplate.queryForList(sql, String.class); 
    if(list!=null&&list.size()>0){ 
      for(int i=0;i<list.size();i++){ 
        str = getEmployeeBysupSelas(list.get(i), str); 
      } 
    } 
    return str; 
  }