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How to check resultset is empty or null in java

I have a sql query to run in my java class (Servlet) what i am trying to do if there is no data in database for that query then want to do something else.
In simple terms i am checking if there is no data in resultset than want to do something else,but that's not working
What i have tried
String str = null;
Gson gson = new Gson();
LinkedHashMap<Object, Object> lhm = null;
LinkedList<LinkedHashMap<Object, Object>> mainList = new LinkedList<LinkedHashMap<Object, Object>>();
String sql;
try {
Connection con = DBConnection.createConnection();
Statement statement = con.createStatement();
sql = "select distinct a.DISPLAYCOUNTERNAME from DISPLAYCOUNTERNAMES a,DISPLAYCOUNTER b where a.DISPLAYCOUNTERCODE=b.DISPLAYCOUNTERCODE and USERNAME='"
+ userName + "'";
System.out.println(sql);
ResultSet resultSet = statement.executeQuery(sql);
if (!resultSet.isBeforeFirst()) { // if there is no data
lhm = new LinkedHashMap<Object, Object>();
lhm.put("outlet", "NoData");
mainList.add(lhm);
str = gson.toJson(mainList);
}
while (resultSet.next()) { // if there is data
lhm = new LinkedHashMap<Object, Object>();
counterName = resultSet.getString("DISPLAYCOUNTERNAME");
System.out.println("counternam"+counterName);
lhm.put("Counter name", counterName);
mainList.add(lhm);
str = gson.toJson(mainList);
}
System.out.println(str);
response.setContentType("application/json");
response.getWriter().write(str);
} catch (SQLException e) {
System.out.println("SQL Issues 2...");
e.printStackTrace();
}
The above code is throwing error as SQL Issues 2...
java.sql.SQLException: This method should only be called on ResultSet objects that are scrollable (type TYPE_SCROLL_INSENSITIVE).
I don't know what i am doing wrong here,any-kind of help will be appreciated

You can try modifying the line:
Statement statement = con.createStatement();
to
Statement statement = con.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE,
ResultSet.CONCUR_READ_ONLY);

You could use next but switch to use a do/while loop, if the first call to next returns true then the row pointer points to the first row in the result set so you must read it before calling next again
if (!resultSet.next()) {
// do no data stuff
} else {
do {
//handle result set data
} while (rs.next());
}

Problem with diacritic, getting data from database java

I have MySQL database, where I have saved data and some words have diacritics.
This is my function how to get data from database.
public List<RowType> getData(String query){
List<RowType> list = new ArrayList<>();
try{
connect();
Statement statement = connection.createStatement();
ResultSet resultSet = statement.executeQuery(query);
while(resultSet.next()){
StringBuilder str = new StringBuilder();
for(int i = 1; i <= getCountColumns(resultSet); i++){
if(i==1) str.append(resultSet.getString(i));
else str.append("," + resultSet.getString(i));
}
list.add(new RowType(str.toString()));
}
}
catch(Exception e){
System.out.println("Chyba při získavání údajů z databáze.");
System.out.println(e);
Console.print("Chyba při získavání údajů z databáze.");
Console.print(e.toString());
}
finally{
disconnect();
}
return list;
}
As parameter i send this query.
List<RowType> list = connection.getData("Select id from countries where name = 'Česko'");
But it doesn´t find anything, because i have diacritic in the query ("Česko"). I try it without diacritic and it works. So don´t you know how to fix it to work with accents too?

Can you try to add a few more queries before executing your main query?
so it will look something like:
connect();
Statement statement = connection.createStatement();
String query2 = "SET NAMES 'utf8'";
statement.execute(query2);
query2 = "SET CHARACTER SET 'utf8'";
statement.execute(query2);
ResultSet resultSet = statement.executeQuery(query);
if the above does not work for you, then maybe there is an issue with your database settings; if that's the case, you can refer to the answer here

Query data and pass as input for another function in a loop Java

I am writing an application that required to query data from oracle database and send each queried data as input to another function in java. I am not sure how to pass those queried data as input to another function. I am trying to use Arraylist but still could not able to pass as input. Any help will be appreciated. Hope to hear from you all.
String dbuserName = "";
String dbpassword = "";
String url = "jdbc:oracle:thin:#//xxxxxxxxxxxxxx";
String driverName = "oracle.jdbc.driver.OracleDriver";
Connection conn = null;
Session session = null;
try{
// Some Connection code to database here before below code
Statement stmt = conn.createStatement();
ResultSet rs = stat.executeQuery( "SELECT ..." );
ArrayList <String[]> result = new ArrayList<String[]>();
/*Queried data has only one column, that is useid, now need to
send each id as input to below try/catch statement*/
try {
userManager.enable(USER_LOGIN, true);
System.out.print("\n Enabled user Successfully");
} catch (ValidationFailedException e) {
e.printStackTrace();
logger.severe("ValidationFailedException: " + e ");
}

This will help you
while (rs.next()) {
int i = 1;
result.add(rs.getString(i++));
}
Then in the for loop
for(int i=0;i<result.size()-1;i++)
{
String USER_LOGIN=result.get(i);
userManager.enable(USER_LOGIN, true);
}

Displaying datatable from database

I am trying to display data from the database into a datatable and I am getting no results. I tested the queries with JDBC with exact select statement to see if it returns any row, and it always worked. But when I try to have the data from the database into my datatable I get no results. I even made a fake dummy data just to populate my datatable. I must be doing something wrong in the index.xhtml file that I don't know of. What could I doing wrong ? any help would be appreciated ?
edit: first I went to with Primefaces with their datatable example, and than I went with simple jsf style datatable like I have here and neither of those worked when I try to do it with the database
UserDAO.java
public class UserDAO {
private static final String USERNAME = "something";
private static final String PASSWORD = "something";
private static final String CONN_STRING =
"jdbc:sqlserver://petunia.arvixe.com.....something";
public List<Report> getUserList() {
List<Report> list = new ArrayList<Report>();
PreparedStatement ps = null;
Connection con = null;
ResultSet result = null;
try {
con = DriverManager.getConnection(CONN_STRING, USERNAME, PASSWORD);
String sql = "SELECT id, tag,asset_name, model, ser_no, value, \n" +
" asset_condition, asset_type FROM assets";
String sql1 = "SELECT name, address, city,state,zip, phone, district FROM location";
ps = con.prepareStatement(sql);
ps = con.prepareStatement(sql1);
result = ps.executeQuery();
while (result.next()) {
Report rep = new Report();
rep.setId(result.getInt("id"));
rep.setTag(result.getString("tag"));
rep.setName(result.getString("asset_name"));
rep.setModel(result.getString("model"));
rep.setSerial(result.getString("ser_no"));
rep.setValue(result.getFloat("value"));
rep.setCondition(result.getString("asset_condition"));
rep.setType(result.getString("asset_type"));
rep.setLocationName(result.getString("name"));
rep.setAddress(result.getString("address"));
rep.setCity(result.getString("city"));
rep.setState(result.getString("state"));
rep.setZip(result.getString("zip"));
rep.setPhone(result.getString("phone"));
rep.setDistrict(result.getInt("district"));
}
} catch (Exception e) {
e.printStackTrace();
} finally {
try {
con.close();
ps.close();
} catch (Exception e) {
e.printStackTrace();
}
}
return list;
}
}

Well, you are making a report:
Report rep = new Report();
...but not adding it to your list. Add this:
Report rep = new Report();
list.add(rep);

I suppose your problem is this code:
ps = con.prepareStatement(sql);
ps = con.prepareStatement(sql1);
result = ps.executeQuery();
You are overwriting your sql statement immediately with the statement sql1.
I think, you probably want to select the assets with THEIR locations. In SQL you can use a JOIN to achieve that.

If you use this syntax
String sql = "SELECT id, tag,asset_name, model, ser_no, value, \n" +
" asset_condition, asset_type FROM assets";
String sql1 = "SELECT name, address, city,state,zip, phone, district FROM location";
ps = con.prepareStatement(sql);
ps = con.prepareStatement(sql1);
result = ps.executeQuery();
You will get as a result only the execution of the second query. I think that in your case you are trying to get a result from both tables assets and location so you should use a join between the 2 tables.

A lock could not obtained within the time requested issue

The title is the error I'm getting, when I click load my program freezes. I assume it's because I'm doing a statement inside a statement, but from what I see it's the only solution to my issue. By loading, I want to just repopulate the list of patients, but to do so I need to do their conditions also. The code works, the bottom method is what I'm trying to fix. I think the issue is that I have 2 statements open but I am not sure.
load:
public void DatabaseLoad()
{
try
{
String Name = "Wayne";
String Pass= "Wayne";
String Host = "jdbc:derby://localhost:1527/Patients";
Connection con = DriverManager.getConnection( Host,Name, Pass);
PatientList.clear();
Statement stmt8 = con.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE,
ResultSet.CONCUR_UPDATABLE);
String SQL8 = "SELECT * FROM PATIENTS";
ResultSet rs8 = stmt8.executeQuery( SQL8 );
ArrayList<PatientCondition> PatientConditions1 = new ArrayList();
while(rs8.next())
{
PatientConditions1 = LoadPatientConditions();
}
Statement stmt = con.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE,
ResultSet.CONCUR_UPDATABLE);
String SQL = "SELECT * FROM PATIENTS";
ResultSet rs = stmt.executeQuery( SQL );
while(rs.next())
{
int id = (rs.getInt("ID"));
String name = (rs.getString("NAME"));
int age = (rs.getInt("AGE"));
String address = (rs.getString("ADDRESS"));
String sex = (rs.getString("SEX"));
String phone = (rs.getString("PHONE"));
Patient p = new Patient(id, name, age, address, sex, phone,
PatientConditions1);
PatientList.add(p);
}
UpdateTable();
UpdateAllViews();
DefaultListModel PatientListModel = new DefaultListModel();
for (Patient s : PatientList) {
PatientListModel.addElement(s.getAccountNumber() + "-" + s.getName());
}
PatientJList.setModel(PatientListModel);
}
catch(SQLException err)
{
System.out.println(err.getMessage());
}
}
This is the method that returns the ArrayList of patient conditions
public ArrayList LoadPatientConditions()
{
ArrayList<PatientCondition> PatientConditionsTemp = new ArrayList();
try
{
String Name = "Wayne";
String Pass= "Wayne";
String Host = "jdbc:derby://localhost:1527/Patients";
Connection con = DriverManager.getConnection( Host,Name, Pass);
Statement stmt = con.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE,
ResultSet.CONCUR_UPDATABLE);
String SQL = "SELECT * FROM PATIENTCONDITIONS";
ResultSet rs5 = stmt.executeQuery( SQL );
int e = 0;
while(rs5.next())
{
e++;
String ConName = (rs5.getString("CONDITION"));
PatientCondition k = new PatientCondition(e,ConName);
PatientConditionsTemp.add(k);
}
}
catch(SQLException err)
{
System.out.println(err.getMessage());
}
return PatientConditionsTemp;
}

I had a similar problem.
I was connecting to derby db hosted on local server.
I created 2 simultaneous connections:
With squirrel
With ij tool
When a connection makes a modification on a table, it first gets a lock for the particular table.
This lock is released by the connection only after committing the transaction.
Thus if the second connection tries to read/write the same table, a msg prompts saying:
ERROR 40XL1: A lock could not be obtained within the time requested
To fix this, the connection which modified the table has to commit its transaction.
Hope this helps !

Here is a good place to start: http://wiki.apache.org/db-derby/LockDebugging

You need to close your statement and result set as well so that when you restart your program they won't be open. Add stmt.close(); and rs.close(); at the end of your lines of code within the try and catch statement.

Why could you not use the same connection object to do both the queries?
Like pass that connection object to the LoadPatientConditions() as a parameter and use it there.