You should try to avoid as much as possible mixing server-side code with client-side code.
Your client-side code should only offer a nice and rich user interface, by manipulating the data which is provided by the server. The server-side code should only process the data - coming from different calls, or taken from a storage, usually a database.
Usually the comunication( asynchrounous or not) from a client and a server goes like that :
- client sends a request to the server
- server process the request and it gives a response, usually some html or json/xml
- client process the response from the server
Ok, now lets move our attention to your specific problem.
Your ajax call : xmlHttpReq.open('GET', "RTMonitor?rtype=groups&groupname="+temp, true); should send the request to the servlet and expect some data back to process and render in a nice way to the user. Your servlet should handle the request, by querying the database( you should definitely change your code so it uses prepared statements as they are preventing SQL injection). By doing so, you've separate your client-side code from server-side code.
private List<YourObject> loadObjectsBySomeLogic() throws SQLException{
String sql ="SELECT a.vehicleno,a.lat,a.lng,a.status,a.rdate,a.rtime FROM latlng a,vehicle_details b WHERE a.vehicleno=b.vehicleno AND b.clientid= ? AND b.groupid in(select groupid from group_details where groupname= ? and clientid= ?)";
List<YourObject> list = new ArrayList<YourObject>();//new ArrayList<>(); for Java versions > 1.7
PreparedStatement ps = null;
ResultSet rs = null;
try{
ps = connection.prepareStatement(sql);
ps.setLong(1, clientId);
ps.setString(2, gname);
ps.setLong(3, clientId);
rs = ps.executeQuery();
while(rs .next())
{
//load data from ResultSet into an object/list of objects
}
}finally{
closeResources(rs , ps);
}
return list;
}
private static final void closeResources(final ResultSet rs , final PreparedStatement ps){
if (rs != null) {
try {
rs.close();
} catch (SQLException e) {
//nasty rs. log the exception?
LOGGER.error("Could not close the ResultSet!" , e);
}
}
if (ps != null) {
try {
ps.close();
} catch (SQLException e) {
//nasty ps. log the exception?
LOGGER.error("Could not close the PreparedStatement!" , e);
}
}
}
You could delegate this method to a different object, which handles the business/aplication domain logic, but that's not our point in this case.
You can use Json for your data format, because it has a nice, and easy to understand way to format data, and it is more lightweight compared to XML. You can use any Java library to encode data as Json. I'll provide an example which uses Gson library.
List<YourObject> list = loadObjectsBySomeLogic();
String json = new Gson().toJson(list);
response.setContentType("application/json");
response.setCharacterEncoding("UTF-8");
response.getWriter().write(json);
Now your Ajax request, should handle the Json data coming from server( I recommend you to use jQuery to make Ajax calls as it's been tested and it works great on all major browsers).
$.get('RTMonitor', function(responseJson) {
//handle your json response by rendering it using html + css.
});
