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How to delete row from bound JTable?

I have a JTable bound to MySQL. I already have done code to insert data.
But i don't know how to delete.
I have this sample delete method that works in other simple projects.
public String deleteItem(String name) {
String answer = "";
try {
Connection con = Connect.getConnection();
String sql = "Delete FROM item where name = ?";
PreparedStatement ps = con.prepareStatement(sql);
ps.setString(1, name);
ps.executeUpdate();
ps.close();
con.close();
answer = "OK";
} catch (Exception e) {
answer = e.toString();
}
return answer;
}
Even when I worked with an unbound table I have done this remove row from jtable that did well for me.
But now its a table bound to MySQL and I can't find a way to delete row... already searched on the internet. Found nothing.
PS: i'm using netbeans. i right-clicked jtable > bind > elements , to bind table.

Oh, I found a way!
First, I changed my deleteItem method, to delete by id
ItemDAO.java
public String deleteItem(int ID_item) {
String answer = "";
try {
Connection con = Connect.getConnection();
String sql = "Delete FROM item where ID_Item = ?";
PreparedStatement ps = con.prepareStatement(sql);
ps.setInt(1, ID_item);
ps.executeUpdate();
ps.close();
con.close();
answer = "OK";
} catch (Exception e) {
answer = e.toString();
}
return answer;
}
Then the action in delete button goes like this.
Form.java
private void btnDeleteActionPerformed(java.awt.event.ActionEvent evt) {
int column = 0; // get the first column which is ID_Item
int row = tableItem.getSelectedRow(); //get row selected by user
int value = (int) tableItem.getModel().getValueAt(row, column); // store ID_Item value
String answer = new ItemDAO().deleteItem(value); // call up deleteItem method
if(answer.equals("OK")) {
System.out.println("OK"); // just for test
itemList.clear(); // this is needed to update the bound table after Insert/Delete/Update etc
itemList.addAll(itemQuery.getResultList()); // same as above comment
}else{
System.out.println("ERROR"); // just for test.
}
Maybe isn't the most beautiful way to do it, but it works.

Java SQL Server Application Stuck On statement.executeUpdate()

I have a rather annoying issue. In the piece of code below, I am trying to insert a new row to the "RevisionDispersion" table in my database. However, whenever I call stmt.executeUpdate() the program freezes and there ends up being no transaction to the database. No matter how long I wait; the database just won't be updated. Below is the code of interest:
private static final String INSERT_DISPERSION = "insert into RevisionDispersion("
+ Assignments.ID + ", "
+ Persons.EMAIL + ", "
+ Handins.ID + ")"
+ " values(?, ?, ?)";
public static void disperse(DataSource source, Assignment assignment) throws Exception
{
List<String> handins = assignment.getHandins();
//used to decide who checks which assignment
int maxRNG = Math.max(1, handins.size() / assignment.getPeerCount());
int rng = new Random().nextInt(maxRNG);
PreparedStatement stmt = null;
Connection con = null;
try{
//Get the connection, set it to TRANSACTION_SERIALIZABLE and set autocommit to false
con = source.getConnection();
configureConnection(con);
//Prepare the statement to insert the new dispersion
stmt = con.prepareStatement(INSERT_DISPERSION);
stmt.setString(1, assignment.getID());
//Iterate over all hand-ins and decide from which peer a peer receives feedback
for(int i = 0; i < handins.size(); i++)
{
HandIn handin = new HandIn(source.getConnection(), handins.get(i));
String student = handin.getEmail();
stmt.setString(2, student);
for(int j = 1; j <= assignment.getPeerCount(); j++)
{
HandIn otherHandin = new HandIn(source.getConnection(), handins.get(j * rng));
stmt.setString(3, otherHandin.getId());
stmt.executeUpdate();
}
}
con.commit();
}catch(Exception e){
throw e;
}finally{
closeQuietly(con, stmt);
}
}
//This method is originally in the DBAO class, but I put it here for you folks.
protected static void configureConnection(Connection connection) throws SQLException
{
connection.setAutoCommit(false);
connection.setTransactionIsolation(Connection.TRANSACTION_SERIALIZABLE);
}
This problem occurs in no other places in the application. Whenever I run the SQL statement in SQL Server Management Studio, with identical parameters, it does not get stuck and it inserts the new rows just fine. After deleting the rows and trying the same in the application, it gets stuck.
Can anyone point me in the right direction of what is going wrong? I've been trying for 3 hours straight now...
Stuff I already tried
-use stmt.addBatch() rather than executeUpdate() (did not make a difference. It would get stuck at executeBatch())
-Check if all connections are being closed properly; they are.
-Check if other statements/resultsets are still open that use RevisionDispersion table (there are none still open. Even if there were, should not make a difference I think?)
-Completely delete the database and set it back up

I solved the issue...
In a different piece of code I had the following:
private static final String GET_NOT_DISPERSED = "select * from Assignments where "
+ Assignments.CLOSE_DATE + "<=? and "
+ Assignments.PEER_START_DATE + ">=? and "
+ Assignments.ID + " not in(select " + Assignments.ID + " from RevisionDispersion)";
private void makeMailDispersion() throws Exception
{
DateTime currentDate = DateTime.getCurrentDateTime();
PreparedStatement assignmentsStmt = null;
ResultSet assignments = null;
Connection con = null;
try{
con = source.getConnection();
configureConnection(con);
assignmentsStmt = con.prepareStatement(GET_NOT_DISPERSED);
assignmentsStmt.setString(1, currentDate.toString());
assignmentsStmt.setString(2, currentDate.toString());
assignments = assignmentsStmt.executeQuery();
ArrayList<Assignment> requiresDispersion = new ArrayList<>();
assignments.close();
assignmentsStmt.close();
while(assignments.next())
{
Assignment assignment = new Assignment(source.getConnection(), assignments.getString(Assignments.ID));
AssignmentDisperser.disperse(source, assignment);
}
}catch(Exception e){
throw e;
}finally{
closeQuietly(con, assignmentsStmt, assignments);
}
}
In this piece of code, I closed the variables 'assignments' and 'assignmentsStmt'. I thought this would be sufficient to unlock the table after having used the GET_NOT_DISPERSED query. Apparently it was not: the table was still locked.
What I had to do in order to fix it: aside from calling assignments.close() and assignmentsStmt.close() I also had to call con.close(). That completely unlocked the table and allowed the code to run properly.

SQLITE_BUSY the database is locked java

I have create a java software which make use of sqlite database. The whole database works smoothly however after some time of running the application I am reveiving the following message (from a try catch block):
java.sql.SQLException: [SQLITE_BUSY] The database file is locked (database is locked)
I ve solved my problems by closing the software every time the exception rising. However is there a way to close my database instead so as not to close the software every time?
I ve got plenty of queries however my prob arises always in a specific point:
try {
String query = "select * from StudentsSession where userId=? and course=? and level=?";
PreparedStatement pst = connectionUsers.prepareStatement(query);
pst.setString(1, saveUser.getText());
pst.setString(2, textSubjectQTest);
st.setString(3, showCurrentLevelLabel.getText());
ResultSet rs = pst.executeQuery();
while (rs.next()) {
count = count + 1;
}
pst.close();
rs.close();
} catch (Exception a) {
System.out.println(a);
}
try {
String countS, tmpS;
countS = String.valueOf(count);
sessionId.setText(countS);
long unixTime = System.currentTimeMillis() / 1000L;
tmpS = String.valueOf(unixTime);
date.setText(tmpS);
course.setText(textSubjectQTest);
String query = "insert into StudentsSession (userId,date,course,level,trial,score) values (?,?,?,?,?,-1)";
PreparedStatement pst = connectionUsers.prepareStatement(query);
pst.setString(1, saveUser.getText());
pst.setString(2, tmpS);
pst.setString(3, textSubjectQTest);
pst.setString(4, showCurrentLevelLabel.getText());
pst.setString(5, countS);
pst.executeUpdate();
pst.close();
} catch (Exception a) {
System.out.println(a);
System.exit(0);
}
String file1 = "";
ResultSet ts4;
try {
sessionId3 = "";
String query3 = "select * from studentssession where userid = ? and course = ? and level = ?";
PreparedStatement pst__1 = connectionUsers.prepareStatement(query3);
pst__1.setString(1, saveUser.getText());
pst__1.setString(2, textSubjectQTest);
pst__1.setString(3, showCurrentLevelLabel.getText());
ts4 = pst__1.executeQuery();
while (ts4.next()) {
sessionId3 = ts4.getString("sessionId");
}
pst__1.close();
ts4.close();
obj = new CaptureVideoFromWebCamera();
file1 = "videos/" + userTextFieldS.getText();
file1 = file1 + "_" + sessionId3;
file1 = file1 + ".wmv";
obj.start(file1);
} catch (Exception e4) {
e4.getCause();
}
Sometimes this code rise the exception.

Every time you open a connection with the SQLite database, make sure to close the database connection after you process the results or etc. if you already have an open connection to the database and if you try to get the connection again and try some Update or Insert queries, the system will not give the permission and will raise an error.

Your try catch are wrong, you try to close the ResultSet and Statemnt in the try block instead of a finally block. This could lead to leaks.
You should do it like this, in the finally.
PreparedStatement pst = null;
ResultSet rs = null;
try {
pst = connectionUsers.prepareStatement(query);
...
rs = pst.executeQuery();
...
} catch (Exception a) {
a.printStackTrace();
} finally {
if(rs != null){
try{
rs.close();
} catch(Exception e){
e.printStackTrace();
}
}
if(pst != null){
try{
pst.close();
} catch(Exception e){
e.printStackTrace();
}
}
}
Or you could look to the Try-with-resource.
This could be a reason.

Sorta duplicate of existing question, but this is a good starting point. Because SQLite is just a library that reads and writes to a file on the file system, not a full SQL database, you should really only have one connection open to it at a time. Otherwise it is pretty easy to get into a race condition.
For local testing, it should be fine, but for a system of any complexity expecting multiple users, you should be using something like Postgre or MySQL.

Mysql+JDBC+Linux: executeQuery returns empty result set when it shouldn't

I have following code:
public boolean updateDatabase(long houseValue, List<Users> userList)
{
boolean result = false;
Connection conn = null;
PreparedStatement stmtUpdateUsers = null;
PreparedStatement stmtQueryHouse = null;
PreparedStatement stmtUpdateHouse = null;
ResultSet rs = null;
String updateUsers = "UPDATE users SET money = ? WHERE username = ?";
String queryHouse = "SELECT * FROM house WHERE house_id = ?";
String updateHouse = "UPDATE house SET house_money = ? WHERE house_id = ?";
try
{
conn = getConnectionPool().getConnection();
conn.setAutoCommit(false);
stmtUpdateUsers = conn.prepareStatement(updateUsers);
...
// Here is some code that updates Users table in a short loop
...
stmtQueryHouse = conn.prepareStatement(queryHouse);
stmtQueryHouse.setInt(1, 1);
rs = stmtQueryHouse.executeQuery();
if(rs.next())
{
long houseMoney = rs.getLong("house_money");
houseMoney += houseValue;
stmtUpdateHouse = conn.prepareStatement(updateHouse);
stmtUpdateHouse.setLong(1, houseMoney);
stmtUpdateHouse.setInt(2, 1);
stmtUpdateHouse.executeUpdate();
}
else
{
throw new SQLException("Failed to update house: unable to query house table");
}
conn.commit();
result = true;
}
catch(SQLException e)
{
logger.warn(getStackTrace(e));
try{conn.rollback();}catch(SQLException excep)
{
logger.warn(getStackTrace(excep));
}
}
finally
{
DbUtils.closeQuietly(rs);
DbUtils.closeQuietly(stmtQueryHouse);
DbUtils.closeQuietly(stmtUpdateUsers);
DbUtils.closeQuietly(stmtUpdateHouse);
try { conn.setAutoCommit(true); } catch (SQLException e) { /* quiet */ }
DbUtils.closeQuietly(conn);
}
return result
}
This method can be called from multiple threads, house table is just a one row table which holds total earned money. It gets updated by different threads.
Problem is that stmtQueryHouse.executeQuery() returns empty set, and it should not happen, because house table always have (since database creation) one single row that gets updated (only house_money column is updated).
When I run this code on windows (JDBC driver + mysql 5.5.13) it works fine, but when I run it on CentOS (same JDBC driver + mysql 5.1.57) it returns empty result set very often (if not always). Any idea what is going wrong or how could I check where is the problem? Maybe I should use select for update, but then why it works on windows and not on linux? I appreciate any help. Thanks in advance.

Look in the mysql general query log for any errors?
I realize this isnt your question per se, but if you have another table with just a single row for each House, it sounds to me that it would make more sense to move house_money into your main house table

I'd say this one method is doing far too much.
I'd pass in the Connection to three separate methods and manage the transaction outside all of them.
I'd wonder if there's an optimization that would eliminate one of the UPDATES.
I'd want to batch all these so I didn't do a round trip for each and every user. It'll perform poorly as the # of users increases.

Java crash when database is empty

I am using the SQLite JDBC driver to access a database, for some reason the application terminates if there are no rows in the database with little explanation as to why it happened.
If the database is not empty it works perfectly fine;
This is where the termination occurs:
public static CustomFillTable Select(String table, String[] column, Object operand) throws SQLException
{
Connection connection = null;
PreparedStatement ps = null;
try
{
StringBuilder query = new StringBuilder();
query.append("select ");
for(int i = 0; i < column.length; i++)
{
query.append(column[i]);
if(i < column.length -1)
{
query.append(",");
}
}
query.append(" from ");
query.append(table);
//Verify usage of where clause
if(operand != null)
{
query.append(" where ");
query.append(operand);
}
//Termination occurs here
connection = DriverManager.getConnection(_connectionString);
connection.setAutoCommit(false);
ps = connection.prepareStatement(query.toString());
ResultSet rs = ps.executeQuery();
connection.commit();
CustomFillTable model = new CustomFillTable(rs);
while(rs.next())
{
System.out.println("id = " + rs.getString("id"));
System.out.println("name = " + rs.getString("name"));
}
return model;
}
The application closes at the DriverManager.getConnection line, something I don't find to be related to whether the database is populated or not.
Does anybody know how to fix this problem? I've posted the log dump information here.
Edit:
Connection String -
"jdbc:sqlite:D:\Documents\Uni\Semester 2\Languages, Platforms and Tools\Assignment\Java\SQLiteAssignment\mydatabasefile.db"

After looking at the vendors website it seems it is something that has been addressed in a later build. I ended up changing driver anyway but I thought this might be of some use to people.