Develop Reference

Select query showing wrong result

I am tring to check whether a data is available or not in database table.if not it will insert the data. But in first button click it works perfectly. by when i try to click the button again with the same value it gets inserted into the table. please help someone
private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {
// TODO add your handling code here:
try {
// TODO add your handling code here:
DefaultTableModel model = (DefaultTableModel) jTable1.getModel();
ArrayList<String> list = new ArrayList<>();
Object obj[] = null;
Class.forName("com.mysql.jdbc.Driver");
java.sql.Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/cem?useSSL=false", "root", "123");
//here stu is database name, root is username and password
Statement stmt = con.createStatement();
String pn = "select gname from games where gname='" + jTextField1.getText() + "'";
ResultSet rsPn = stmt.executeQuery(pn);
System.out.println(rsPn.next());
if (rsPn.next() == false) {
String q = ("insert into games(gid,gname) values(NULL,'" + jTextField1.getText() + "')");
int i = 0;
i = stmt.executeUpdate(q);
if (i > 0) {
System.out.println("success");
list.add(jTextField1.getText());
obj = list.toArray();
model.addRow(obj);
} else {
System.out.println("stuck somewhere");
}
StudentDetails.details();
jTextField1.setForeground(Color.BLACK);
stmt.close();
con.close();
} else {
jTextField1.setForeground(Color.red);
System.out.println("Name Already exist");
}
} catch (SQLException ex) {
Logger.getLogger(InsertPanel.class.getName()).log(Level.SEVERE, null, ex);
} catch (ClassNotFoundException ex) {
Logger.getLogger(InsertPanel.class.getName()).log(Level.SEVERE, null, ex);
}
}

You're calling next() twice:
System.out.println(rsPn.next());
if (rsPn.next() == false) {
The second call will return false even if there's a row already (though it should work once there are two or more rows). Use a variable instead:
boolean hasNext = rdPn.next();
System.out.println(hasNext);
if (!hasNext) {

java - jTable database repeating values

I am trying to populate a java database with car brands, models, and if they are available but I have a big issue. When I enter multiple cars to the table, the new car prints to the table, but previous cars I have entered also reprint
[Issue.png][1]. So first I entered Ferrari Enzo, then I entered Tesla S but Ferrari Enzo is repeating.
I know the issue is not with adding the cars to the database because if I look in the database it only shows the two I entered [DatabasePic.png][2]. I know my problem is with how I am entering my cars into the JTable. My methods are below..
ButtonClickEvent:
private void refreshbtnMouseClicked(java.awt.event.MouseEvent evt) {
try {
String Brand = brandlbl.getText();
String Model = modellbl.getText();
Boolean Available = false;
switch (availabilitybox.getSelectedItem().toString()) {
case "True":
Available = true;
break;
case "False":
Available = false;
break;
}
InsertApp nw = new InsertApp();
nw.insert(Brand, Model, Available);
nw.refreshDatabase(jTable1);
} catch (SQLException ex) {
Logger.getLogger(Window.class.getName()).log(Level.SEVERE, null, ex);
}
}
Insert Method:
public void insert(String brand, String model, Boolean available) {
String sql = "INSERT INTO CARDATA(brand,model,available) VALUES(?,?,?)";
try (Connection conn = this.connect();
PreparedStatement pstmt = conn.prepareStatement(sql)) {
pstmt.setString(1, brand);
pstmt.setString(2, model);
pstmt.setBoolean(3, available);
pstmt.executeUpdate();
} catch (SQLException e) {
System.out.println(e.getMessage());
}
}
Refreshing my database:
public void refreshDatabase(JTable table) throws SQLException {
Connection con = connect();
String SQL = "SELECT * FROM CARDATA";
Statement stmt = con.createStatement();
ResultSet rs = stmt.executeQuery(SQL);
int col = rs.getMetaData().getColumnCount();
System.out.println(col);
while (rs.next()) {
Object[] rows = new Object[col];
for (int i = 1; i <= col; i++) {
rows[i - 1] = rs.getObject(i);
}
((DefaultTableModel) table.getModel()).insertRow(rs.getRow() - 1, rows);
}
con.close();
rs.close();
stmt.close();
}

When I enter multiple cars to the table, the new car prints to the table, but previous cars I have entered also reprint
You need to clear the data in the TableModel before you start adding data back into it.
The basic code should be something like:
DefaultTableModel model = (DefaultTableModel)table.getModel();
model.setRowCount(0);
while (rs.next())
{
...
model.addRow(...);
}
Or instead of retrieving all the data from the database every time you do an insert, just add the data to the table at the same time:
pstmt.executeUpdate();
model.addRow(...);

NullPointerException in Java TableRowSorter

I made a jtable for the list of chemicals in the inventory where I can sort each columns using the following code (chemicalTable is the name of the jTable):
chemicalTable.setAutoCreateRowSorter(true);
TableRowSorter<TableModel> sorter1
= new TableRowSorter<TableModel>(chemicalTable.getModel());
chemicalTable.setRowSorter(sorter1);
Then I used a jTextfield to create a searchbox with a keyTyped Listener so that whenever the user types a certain character the table refreshes. And it usually works.
I used this code in the keyTypedListener for the searchbox:
DefaultTableModel dm = (DefaultTableModel) chemicalTable.getModel();
str = searchChemicalText.getText();
try {
String url = "jdbc:mysql://localhost/chemical inventory";
Class.forName("com.mysql.jdbc.Driver").newInstance();
conn = DriverManager.getConnection(url, "root", "");
} catch (Exception e) {
JOptionPane.showMessageDialog(this, "Error Occurred.", "Error", JOptionPane.ERROR_MESSAGE);
}
int ctr = 0;
while (ctr < chemicalTable.getRowCount()) {
chemicalTable.getModel().setValueAt(null, ctr, 0);
chemicalTable.getModel().setValueAt(null, ctr, 1);
chemicalTable.getModel().setValueAt(null, ctr, 2);
ctr++;
}
int count = 0;
try {
Statement stmt = conn.createStatement();
String query = "Select * FROM chemicallist where name_of_reagent like '%" + str + "%'";
ResultSet rs = stmt.executeQuery(query);
if (rs.next()) {
rs = stmt.executeQuery(query);
while (rs.next()) {
String qty = null, qtyunit = null, chemstate = null, reagentName = null;
reagentName = rs.getString("name_of_reagent");
qty = rs.getString("quantity");
qtyunit = rs.getString("quantity_unit");
chemstate = rs.getString("state");
chemicalTable.getModel().setValueAt(reagentName, count, 0);
chemicalTable.getModel().setValueAt(qty + " " + qtyunit, count, 1);
chemicalTable.getModel().setValueAt(chemstate, count, 2);
if (count + 1 > chemicalTable.getRowCount() - 1) {
dm.setRowCount(chemicalTable.getRowCount() + 1);
dm.fireTableRowsInserted(0, 5);
}
count++;
}
}
} catch (Exception e) {
JOptionPane.showMessageDialog(this, "Error Occurred.", "Error", JOptionPane.ERROR_MESSAGE);
}
My problem is: Whenever I sort first any columns (col1, col2, or col3) and I insert a character in the searchbox, I got this error message:
"Exception occurred during event dispatching:
Java.lang.NullPointerException"

Although it's not possible to debug your code fragments, several things stand out:
In the same section, you reference the TableModel as dm and chemicalTable.getModel(); use a single reference or verify that they refer to the same instance.
Instead of meddling with setRowCount(), use one of the addRow() methods.
The DefaultTableModel methods that alter the model fire the correct event for you and the table will automatically update itself accordingly; you shouldn't have to do this yourself.

delete table if exists in Microsoft Access

I have one application in which I need to delete table if exit in Microsoft Access Database.
I saw the code here. The table name which I want to delete is data_table and the access database file name is local_entry
so where I need to change the code so it work for my application.
public void testDropTable () throws SQLException{
Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
Connection con = DriverManager.getConnection("jdbc:odbc:MsAccessDSN");
Statement stmt = con.createStatement();
ResultSet checkTable = con.getMetaData().getTables(null, null, "POI", null);
String tableName = null;
while (checkTable.next())
{
System.out.println("In here");
tableName = checkTable.getString("TABLE_NAME");
System.out.println(tableName);
}
if (tableName != null){
try {
String dropTable = "DROP TABLE ";
String[] tables = DB_TABLE;
for (int i = 0; i < tables.length; i++){
String stringCode = new String();
stringCode = stringCode + tables[i];
System.out.println(dropTable + tables[i]);
// Drop each table in the array.
int temp = stmt.executeUpdate(dropTable + tables[i]);
}
}
catch (Exception e) {
System.err.println("Exception in testDropTable (): \n"
+ "Drop Table testDropTable threw an exception: " +(e.getMessage()));
}
}
else{
con.close();
}
}
I think I need to change this two line:
String dropTable = "DROP TABLE ";
String[] tables = DB_TABLE;
can I change DROP TABLE to data_table and what about second line. What is this DB_TABLE
I change the whole code by this way but till problem is there:
public void testDropTable () throws SQLException{
try {
Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
} catch (ClassNotFoundException e1) {
e1.printStackTrace();
}
Connection con = DriverManager.getConnection("jdbc:odbc:MsAccessDSN");
Statement stmt = con.createStatement();
ResultSet checkTable = con.getMetaData().getTables(null, null, "POI", null);
String tableName = null;
while (checkTable.next())
{
System.out.println("In here");
tableName = checkTable.getString("data_table");
System.out.println(tableName);
}
if (tableName != null){
try {
String dropTable = "DROP TABLE ";
String[] tables = {"data_table"};
for (int i = 0; i < tables.length; i++){
String stringCode = new String();
stringCode = stringCode + tables[i];
System.out.println(dropTable + tables[i]);
// Drop each table in the array.
int temp = stmt.executeUpdate(dropTable + tables[i]);
}
}
catch (Exception e) {
System.err.println("Exception in testDropTable (): \n"
+ "Drop Table testDropTable threw an exception: " +(e.getMessage()));
}
}
else{
con.close();
}
}

try this code
Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
Connection con = DriverManager.getConnection("jdbc:odbc:MsAccessDSN");
Statement stmt = con.createStatement();
// Specify the type of object; in this case we want tables
String[] types = {"TABLE"};
ResultSet checkTable = con.getMetaData().getTables(null, null, "%", types);
String tableName = null;
while (checkTable.next())
{
System.out.println("In here");
tableName = checkTable.getString(3)
System.out.println(tableName);
// check if the table 'data_table' exist in your database
if (tableName.equals("data_table"){
try {
//drop the table if present
int temp = stmt.executeUpdate("DROP TABLE " + tableName);
break;
}
catch (Exception e) {
System.err.println("Exception in testDropTable (): \n"
+ "Drop Table testDropTable threw an exception: " +(e.getMessage()));
}
}
}
con.close;
for more information visit here Metadata

Drop table table name; is the command to drop the table in your database.
Try to replace the DB_TABLE with data_table.
String dropTable = "DROP TABLE ";
String[] tables = data_table;
try this
public void testDropTable () throws SQLException{
Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
Connection con = DriverManager.getConnection("jdbc:odbc:MsAccessDSN");
Statement stmt = con.createStatement();
ResultSet checkTable = con.getMetaData().getTables(null, null, "POI", null);
String tableName = null;
while (checkTable.next())
{
System.out.println("In here");
tableName = checkTable.getString("data_table");
System.out.println(tableName);
}
if (tableName != null){
try {
String dropTable = "DROP TABLE ";
String[] tables = tableName;
for (int i = 0; i < tables.length; i++){
String stringCode = new String();
stringCode = stringCode + tables[i];
System.out.println(dropTable + tables[i]);
// Drop each table in the array.
int temp = stmt.executeUpdate(dropTable + tables[i]);
}
}
catch (Exception e) {
System.err.println("Exception in testDropTable (): \n"
+ "Drop Table testDropTable threw an exception: " +(e.getMessage()));
}
}
else{
con.close();
}
}

For anybody interested in this question, i removed the while loop statement in the accepted answer and reduced the code to:
public void testDropTable() throws SQLException, ClassNotFoundException {
Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
Connection con = DriverManager.getConnection("jdbc:odbc:MsAccessDSN");
Statement stmt = con.createStatement();
String[] tables = {"data_table"};
for (String table : tables) {
try {
stmt.executeUpdate("DROP TABLE " + table);
} catch (SQLException e) {
System.err.println("Exception in testDropTable (): \n"
+ "Drop Table testDropTable threw an exception: " +(e.getMessage()));
}
}
con.close();
}

Retrieve column names from java.sql.ResultSet

With java.sql.ResultSet is there a way to get a column's name as a String by using the column's index? I had a look through the API doc but I can't find anything.

You can get this info from the ResultSet metadata. See ResultSetMetaData
e.g.
ResultSet rs = stmt.executeQuery("SELECT a, b, c FROM TABLE2");
ResultSetMetaData rsmd = rs.getMetaData();
String name = rsmd.getColumnName(1);
and you can get the column name from there. If you do
select x as y from table
then rsmd.getColumnLabel() will get you the retrieved label name too.

In addition to the above answers, if you're working with a dynamic query and you want the column names but do not know how many columns there are, you can use the ResultSetMetaData object to get the number of columns first and then cycle through them.
Amending Brian's code:
ResultSet rs = stmt.executeQuery("SELECT a, b, c FROM TABLE2");
ResultSetMetaData rsmd = rs.getMetaData();
int columnCount = rsmd.getColumnCount();
// The column count starts from 1
for (int i = 1; i <= columnCount; i++ ) {
String name = rsmd.getColumnName(i);
// Do stuff with name
}

You can use the the ResultSetMetaData (http://java.sun.com/javase/6/docs/api/java/sql/ResultSetMetaData.html) object for that, like this:
ResultSet rs = stmt.executeQuery("SELECT * FROM table");
ResultSetMetaData rsmd = rs.getMetaData();
String firstColumnName = rsmd.getColumnName(1);

This question is old and so are the correct previous answers. But what I was looking for when I found this topic was something like this solution. Hopefully it helps someone.
// Loading required libraries
import java.util.*;
import java.sql.*;
public class MySQLExample {
public void run(String sql) {
// JDBC driver name and database URL
String JDBC_DRIVER = "com.mysql.jdbc.Driver";
String DB_URL = "jdbc:mysql://localhost/demo";
// Database credentials
String USER = "someuser"; // Fake of course.
String PASS = "somepass"; // This too!
Statement stmt = null;
ResultSet rs = null;
Connection conn = null;
Vector<String> columnNames = new Vector<String>();
try {
// Register JDBC driver
Class.forName(JDBC_DRIVER);
// Open a connection
conn = DriverManager.getConnection(DB_URL, USER, PASS);
// Execute SQL query
stmt = conn.createStatement();
rs = stmt.executeQuery(sql);
if (rs != null) {
ResultSetMetaData columns = rs.getMetaData();
int i = 0;
while (i < columns.getColumnCount()) {
i++;
System.out.print(columns.getColumnName(i) + "\t");
columnNames.add(columns.getColumnName(i));
}
System.out.print("\n");
while (rs.next()) {
for (i = 0; i < columnNames.size(); i++) {
System.out.print(rs.getString(columnNames.get(i))
+ "\t");
}
System.out.print("\n");
}
}
} catch (Exception e) {
System.out.println("Exception: " + e.toString());
}
finally {
try {
if (rs != null) {
rs.close();
}
if (stmt != null) {
stmt.close();
}
if (conn != null) {
conn.close();
}
} catch (Exception mysqlEx) {
System.out.println(mysqlEx.toString());
}
}
}
}

SQLite 3
Using getMetaData();
DatabaseMetaData md = conn.getMetaData();
ResultSet rset = md.getColumns(null, null, "your_table_name", null);
System.out.println("your_table_name");
while (rset.next())
{
System.out.println("\t" + rset.getString(4));
}
EDIT: This works with PostgreSQL as well

import java.sql.*;
public class JdbcGetColumnNames {
public static void main(String args[]) {
Connection con = null;
Statement st = null;
ResultSet rs = null;
try {
Class.forName("com.mysql.jdbc.Driver");
con = DriverManager.getConnection(
"jdbc:mysql://localhost:3306/komal", "root", "root");
st = con.createStatement();
String sql = "select * from person";
rs = st.executeQuery(sql);
ResultSetMetaData metaData = rs.getMetaData();
int rowCount = metaData.getColumnCount();
System.out.println("Table Name : " + metaData.getTableName(2));
System.out.println("Field \tDataType");
for (int i = 0; i < rowCount; i++) {
System.out.print(metaData.getColumnName(i + 1) + " \t");
System.out.println(metaData.getColumnTypeName(i + 1));
}
} catch (Exception e) {
System.out.println(e);
}
}
}
Table Name : person
Field DataType
id VARCHAR
cname VARCHAR
dob DATE

while (rs.next()) {
for (int j = 1; j < columncount; j++) {
System.out.println( rsd.getColumnName(j) + "::" + rs.getString(j));
}
}

When you need the column names, but do not want to grab entries:
PreparedStatement stmt = connection.prepareStatement("SHOW COLUMNS FROM `yourTable`");
ResultSet set = stmt.executeQuery();
//store all of the columns names
List<String> names = new ArrayList<>();
while (set.next()) { names.add(set.getString("Field")); }
NOTE: Only works with MySQL

The SQL statements that read data from a database query return the data in a result set. The SELECT statement is the standard way to select rows from a database and view them in a result set. The **java.sql.ResultSet** interface represents the result set of a database query.
Get methods: used to view the data in the columns of the current row
being pointed to by the cursor.
Using MetaData of a result set to fetch the exact column count
ResultSet rs = stmt.executeQuery("SELECT a, b, c FROM TABLE2");
ResultSetMetaData rsmd = rs.getMetaData();
int numberOfColumns = rsmd.getColumnCount();
boolean b = rsmd.isSearchable(1);
http://docs.oracle.com/javase/7/docs/api/java/sql/ResultSetMetaData.html
and further more to bind it to data model table
public static void main(String[] args) {
Connection conn = null;
Statement stmt = null;
try {
//STEP 2: Register JDBC driver
Class.forName("com.mysql.jdbc.Driver");
//STEP 3: Open a connection
System.out.println("Connecting to a selected database...");
conn = DriverManager.getConnection(DB_URL, USER, PASS);
System.out.println("Connected database successfully...");
//STEP 4: Execute a query
System.out.println("Creating statement...");
stmt = conn.createStatement();
String sql = "SELECT id, first, last, age FROM Registration";
ResultSet rs = stmt.executeQuery(sql);
//STEP 5: Extract data from result set
while(rs.next()){
//Retrieve by column name
int id = rs.getInt("id");
int age = rs.getInt("age");
String first = rs.getString("first");
String last = rs.getString("last");
//Display values
System.out.print("ID: " + id);
System.out.print(", Age: " + age);
System.out.print(", First: " + first);
System.out.println(", Last: " + last);
}
rs.close();
} catch(SQLException se) {
//Handle errors for JDBC
se.printStackTrace();
} catch(Exception e) {
//Handle errors for Class.forName
e.printStackTrace();
} finally {
//finally block used to close resources
try {
if(stmt!=null)
conn.close();
} catch(SQLException se) {
} // do nothing
try {
if(conn!=null)
conn.close();
} catch(SQLException se) {
se.printStackTrace();
} //end finally try
}//end try
System.out.println("Goodbye!");
}//end main
//end JDBCExample
very nice tutorial here : http://www.tutorialspoint.com/jdbc/
ResultSetMetaData meta = resultset.getMetaData(); // for a valid resultset object after executing query
Integer columncount = meta.getColumnCount();
int count = 1 ; // start counting from 1 always
String[] columnNames = null;
while(columncount <=count) {
columnNames [i] = meta.getColumnName(i);
}
System.out.println (columnNames.size() ); //see the list and bind it to TableModel object. the to your jtbale.setModel(your_table_model);

#Cyntech is right.
Incase your table is empty and you still need to get table column names you can get your column as type Vector,see the following:
ResultSet rs = stmt.executeQuery("SELECT a, b, c FROM TABLE2");
ResultSetMetaData rsmd = rs.getMetaData();
int columnCount = rsmd.getColumnCount();
Vector<Vector<String>>tableVector = new Vector<Vector<String>>();
boolean isTableEmpty = true;
int col = 0;
while(rs.next())
{
isTableEmpty = false; //set to false since rs.next has data: this means the table is not empty
if(col != columnCount)
{
for(int x = 1;x <= columnCount;x++){
Vector<String> tFields = new Vector<String>();
tFields.add(rsmd.getColumnName(x).toString());
tableVector.add(tFields);
}
col = columnCount;
}
}
//if table is empty then get column names only
if(isTableEmpty){
for(int x=1;x<=colCount;x++){
Vector<String> tFields = new Vector<String>();
tFields.add(rsmd.getColumnName(x).toString());
tableVector.add(tFields);
}
}
rs.close();
stmt.close();
return tableVector;

ResultSet rsTst = hiSession.connection().prepareStatement(queryStr).executeQuery();
ResultSetMetaData meta = rsTst.getMetaData();
int columnCount = meta.getColumnCount();
// The column count starts from 1
String nameValuePair = "";
while (rsTst.next()) {
for (int i = 1; i < columnCount + 1; i++ ) {
String name = meta.getColumnName(i);
// Do stuff with name
String value = rsTst.getString(i); //.getObject(1);
nameValuePair = nameValuePair + name + "=" +value + ",";
//nameValuePair = nameValuePair + ", ";
}
nameValuePair = nameValuePair+"||" + "\t";
}

If you want to use spring jdbctemplate and don't want to deal with connection staff, you can use following:
jdbcTemplate.query("select * from books", new RowCallbackHandler() {
public void processRow(ResultSet resultSet) throws SQLException {
ResultSetMetaData rsmd = resultSet.getMetaData();
for (int i = 1; i <= rsmd.getColumnCount(); i++ ) {
String name = rsmd.getColumnName(i);
// Do stuff with name
}
}
});

U can get column name and value from resultSet.getMetaData();
This code work for me:
Connection conn = null;
PreparedStatement preparedStatement = null;
try {
Class.forName("com.mysql.cj.jdbc.Driver");
conn = MySQLJDBCUtil.getConnection();
preparedStatement = conn.prepareStatement(sql);
if (params != null) {
for (int i = 0; i < params.size(); i++) {
preparedStatement.setObject(i + 1, params.get(i).getSqlValue());
}
ResultSet resultSet = preparedStatement.executeQuery();
ResultSetMetaData md = resultSet.getMetaData();
while (resultSet.next()) {
int counter = md.getColumnCount();
String colName[] = new String[counter];
Map<String, Object> field = new HashMap<>();
for (int loop = 1; loop <= counter; loop++) {
int index = loop - 1;
colName[index] = md.getColumnLabel(loop);
field.put(colName[index], resultSet.getObject(colName[index]));
}
rows.add(field);
}
}
} catch (SQLException e) {
e.printStackTrace();
} finally {
if (preparedStatement != null) {
try {
preparedStatement.close();
}catch (Exception e1) {
e1.printStackTrace();
}
}
if (conn != null) {
try {
conn.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}
return rows;

I know, this question is already answered but probably somebody like me needs to access a column name from DatabaseMetaData by label instead of index:
ResultSet resultSet = null;
DatabaseMetaData metaData = null;
try {
metaData = connection.getMetaData();
resultSet = metaData.getColumns(null, null, tableName, null);
while (resultSet.next()){
String name = resultSet.getString("COLUMN_NAME");
}
}