I have following code,
private void trans_tabMouseClicked(java.awt.event.MouseEvent evt) {
try{
con = DriverManager.getConnection("jdbc:mysql://localhost:3306/online_store","poornima","mit1234");
if(con != null){
String query = "SELECT * FROM bill";
rs = stmt.executeQuery(query);
System.out.println("fffgg");
ResultSetMetaData rsmt = rs.getMetaData();
int c = rsmt.getColumnCount();
Vector row = new Vector();
DefaultTableModel model = (DefaultTableModel)expense_table.getModel();
while(rs.next())
{
row = new Vector(c);
for(int i = 1; i <= c; i++)
{
row.add(rs.getString(i));
}
model.addRow( row );
}
}
}catch(Exception ex){
System.out.println(ex);
}
}
in the above code query is not executed. Fired null pointer exception at rs = stmt.executeQuery(query); line. I tried hours, but I can't figure out where the issue is. Please help.
because stmt is null.
use this
String query = "SELECT * FROM bill";
stmt = con.createStatement();
rs = stmt.executeQuery(query);
instead of this
String query = "SELECT * FROM bill";
rs = stmt.executeQuery(query);
refer this
currently I have data in MySQL server and I am calling the datas onto the JTable through JDBC. However there are 1369 rows and it seems that it has too much data for it to load. It usually takes 5 minutes to load. Are there anyways to optimize the process? This is my code(I apologize in advance for a messy code):
public class DataTable {
private String databaseName = "*****";
private String tableName = "******";
public void showDatabase(){
Connection conn = null;
DatabaseMetaData meta = null;
Statement stmt = null;
ResultSet rs = null;
int k = 0;
try{
Class.forName("com.mysql.jdbc.Driver").newInstance();
String connectionUrl = "jdbc:mysql://localhost:3306/" + databaseName;
String connectionUser = "*****";
String connectionPassword = "*****";
conn = DriverManager.getConnection(connectionUrl, connectionUser, connectionPassword);
stmt = conn.createStatement();
meta = conn.getMetaData();
dataSets(stmt, meta);
}catch(Exception e){
e.printStackTrace();
} finally{
try { if (rs != null) rs.close(); } catch (SQLException e) { e.printStackTrace(); }
try { if (stmt != null) stmt.close(); } catch (SQLException e) { e.printStackTrace(); }
try { if (conn != null) conn.close(); } catch (SQLException e) { e.printStackTrace(); }
}
}
//return the column size of the table
public int getColumnNumber(DatabaseMetaData meta, Statement stmt) throws SQLException
{
//ResultSet rs = meta.getColumns(null, null, "practiceexample", null);
ResultSet rs = stmt.executeQuery("SELECT * FROM " + tableName);
ResultSetMetaData rsmd = rs.getMetaData();
int columnsNumber = rsmd.getColumnCount();
return columnsNumber;
}
//return the rowNumber of the tables
public int getRowNumber(Statement stmt) throws SQLException
{
ResultSet rs = stmt.executeQuery("SELECT COUNT(*) FROM " + tableName);
int rowCount = 0;
while(rs.next()){
rowCount = rs.getInt(1);
}
return rowCount;
}
public void dataSets(Statement stmt, DatabaseMetaData meta) throws SQLException
{
String[] columnNames = new String[getColumnNumber(meta, stmt)];
String[][] dataSets = new String[getRowNumber(stmt)][columnNames.length];
ResultSet column = meta.getColumns(null, null, tableName, null);
int i = 0;
while(column.next())
{
columnNames[i] = column.getString("COLUMN_NAME");
//columnNames.add(i, column.getString("COLUMN_NAME"));
i++;
}
for(int j = 0; j < dataSets.length; j++)
{
String[] singleRowData = new String[columnNames.length];
ResultSet data = null;
for(int k = 0; k < columnNames.length; k++)
{
String columnName = columnNames[k];
data = stmt.executeQuery("SELECT " + columnName +
" FROM " + tableName + " LIMIT " + j + ", " + 1);
while(data.next())
{
singleRowData[k] = data.getString(columnName);
}
}
dataSets[j] = singleRowData;
}
SimpleTable table = new SimpleTable(columnNames, dataSets);
javax.swing.SwingUtilities.invokeLater(new Runnable() {
public void run() {
table.createAndShowGUI();
}
});
}
class SimpleTable{
String[] columns;
String[][] dataSets;
public SimpleTable(String[] columns, String[][] dataSets){
this.columns = columns;
this.dataSets = dataSets;
}
public void createAndShowGUI(){
JPanel gui = new JPanel(new BorderLayout(3, 3));
final JTable table = new JTable(new DefaultTableModel(dataSets, columns));
final JScrollPane scrollPane = new JScrollPane(table, JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED
, JScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED);
Dimension dimension = table.getPreferredSize();
scrollPane.setPreferredSize(new Dimension(dimension.width, table.getRowHeight() * 30));
JPanel navigation = new JPanel(new FlowLayout(FlowLayout.CENTER));
JButton next = new JButton(">");
next.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent e)
{
int height = table.getRowHeight() * (20-1);
JScrollBar bar = scrollPane.getVerticalScrollBar();
bar.setValue(bar.getValue() + height);
}
});
JButton previous = new JButton("<");
previous.addActionListener( new ActionListener(){
public void actionPerformed(ActionEvent ae) {
int height = table.getRowHeight()*(20-1);
JScrollBar bar = scrollPane.getVerticalScrollBar();
bar.setValue( bar.getValue()-height );
}
} );
navigation.add(previous);
navigation.add(next);
gui.add(scrollPane, BorderLayout.CENTER);
gui.add(navigation, BorderLayout.SOUTH);
JOptionPane.showMessageDialog(null, gui);
}
}
}
IMHO the root of the bad permormance is you unnecessarily query the database mutliple times to get the data (columns, rows, rows number, columns number, etc) you need:
To get columns number:
ResultSet rs = stmt.executeQuery("SELECT * FROM " + tableName);
To get rows number:
ResultSet rs = stmt.executeQuery("SELECT COUNT(*) FROM " + tableName);
To get rows (this is the worst beacuse it's inside a loop):
data = stmt.executeQuery("SELECT " + columnName + " FROM " + tableName + " LIMIT " + j + ", " + 1);
How to solve it
Just query the database once. A single ResultSet and its associated ResultSetMetaData should be enough to accomplish your goal. Additionaly, and as already suggested, use a SwingWorker to do database calls in a separate thread. For example:
final JTable table = new JTable();
SwingWorker<Void, TableModel> worker = new SwingWorker<Void, TableModel> () {
#Override
protected Void doInBackground() throws Exception {
ResultSet resultSet = stmt.executeQuery("SELECT * FROM " + tableName);
ResultSetMetaData metaData = resultSet.getMetaData();
int columnCount = metaData.getColumnCount(); // columns number
String[] columnNames = new String[columnCount];
for (int i = 1; i <= columnCount; i++) {
columnNames[i] = metaData.getColumnName(i); // fill columns names
}
resultSet.last();
int rowCount = resultSet.getRow(); // get rows number
resultSet.beforeFirst();
Object[][] data = new Object[rowCount][columnCount];
int currentRow = 0;
while (resultSet.next()) {
for (int currentColumn = 1; currentColumn <= columnCount; currentColumn++) {
data[currentRow][currentColumn - 1] = resultSet.getObject(currentColumn); // fill data set
}
currentRow++;
}
TableModel model = new DefaultTableModel(data, columnNames);
publish(model);
return null;
}
#Override
protected void process(List<TableModel> chunks) {
TableModel model = chunks.get(0);
table.setModel(model);
}
}
worker.execute();
I am using PhpMyAdmin to save my data in database. I have a SWT table to populate with database content.
here is my code..
public static void fetchDatafromDB(String StartIndex, String FinalIndex) {
try {
Class.forName(GlobalVariables.SQL_driver).newInstance();
Connection conn = DriverManager.getConnection(GlobalVariables.DB_url + GlobalVariables.DB_name, GlobalVariables.DB_Username, GlobalVariables.DB_password);
Statement st = conn.createStatement();
String query = "SELECT `From`, `To`, `IDno`, `TimeStamp` FROM `callsheet` WHERE TimeStamp BETWEEN '" + StartIndex + "' AND '" + FinalIndex + "'";
ResultSet rs = st.executeQuery(query);
java.sql.ResultSetMetaData rsmd = rs.getMetaData();
int columnsNumber = rsmd.getColumnCount();
while (rs.next()) {
for (int i = 1; i <= columnsNumber; i++) {
// System.out.print(rs.getString(i));
item.setText(i, rs.getString(i));
}
// System.out.println();
}
} catch (Exception P) {
P.printStackTrace();
}
}
it worked.
Now I am getting some problem with tabling the DB content in my swt table. What my program does, is that, it sets the selected (defined by limit in program above) content of DB in one row (one by one manner) but I want the next row of DB table to be tabled in next row of SWT table. Could you suggest something about this? ! Screenshot of my swtTable
It should look something like this:
public static void fetchDatafromDB(String startIndex, String finalIndex) {
try {
Class.forName(GlobalVariables.SQL_driver).newInstance();
Connection conn = DriverManager.getConnection(GlobalVariables.DB_url + GlobalVariables.DB_name, GlobalVariables.DB_Username, GlobalVariables.DB_password);
Statement st = conn.createStatement();
String query = "SELECT `FROM`, `To`, `IDno`, `TimeStamp` FROM `callsheet` WHERE TimeStamp BETWEEN '" + startIndex + "' AND '" + finalIndex + "'";
ResultSet rs = st.executeQuery(query);
java.sql.ResultSetMetaData rsmd = rs.getMetaData();
int columnsNumber = rsmd.getColumnCount();
TableItem item;
while (rs.next()) {
// Create a new TableItem for each entry in the result set (each row)
item = new TableItem(table, SWT.NONE);
for (int i = 1; i <= columnsNumber; i++) {
// Populate the item (mind the index!!)
item.setText(i - 1, rs.getString(i));
}
}
} catch (Exception e) {
e.printStackTrace();
}
}
i'm doing my first applications using JDBC/Oracle...
Today i had a problem and i can't find out what's wrong.
That's my code (some parts)
My global variables:
public class Esercizio02_GestioneDB {
public Esercizio02_GestioneDB(){
}
public Connection conn = null;
public Statement s = null;
public ResultSet rs = null;
public ResultSet rs1 = null;
ResultSetMetaData rsmd = null;
ResultSetMetaData rsmd1 = null;
[...]
My connection method:
public void connetti(String user, String pwd) throws ClassNotFoundException, SQLException {
//DRIVER
Class.forName("oracle.jdbc.driver.OracleDriver");
//URL
String url = "jdbc:oracle:thin:#//localhost:1521/xe";
//CONNECTION
conn = DriverManager.getConnection(url, user, pwd);
//AUTOCOMMIT
conn.setAutoCommit(true);
//STATEMENT
s = conn.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE, ResultSet.CONCUR_UPDATABLE);
}
So, i have a method to delete a row in a table:
private void eliminaPrenotazione() {
try {
String message1 = "Scegli la prenotazione da cancellare:\n\n";
String query = "SELECT * FROM camere_prenotate";
rs1 = s.executeQuery(query);
rsmd1 = rs1.getMetaData();
message1 += "INDICE ";
for (int i=1; i<=rsmd1.getColumnCount(); i++) {
message1 += rsmd1.getColumnName(i);
message1 += " \t ";
}
message1 += "\n_______________________________\n";
int rowIndex = 1;
String columnType = "";
while (rs1.next()) {
message1 += "["+rowIndex+"]. ";
rowIndex++;
for (int i=1; i<=rsmd1.getColumnCount(); i++) {
columnType = rsmd1.getColumnTypeName(i);
if(columnType.substring(0, 3).equalsIgnoreCase("num")) message1 += rs1.getInt(i);
if(columnType.substring(0, 3).equalsIgnoreCase("var") || columnType.substring(0, 3).equalsIgnoreCase("dat"))
message1 += rs1.getString(i);
message1 += " \t ";
}
message1 +="\n";
}
message1 +="\n";
String scelta = JOptionPane.showInputDialog(null, message1);
int sceltaInt = Integer.parseInt(scelta);
rs1.absolute(sceltaInt);
rs1.deleteRow();
} catch (Exception e) {
JOptionPane.showMessageDialog(null, "Errore: " + e.getMessage());
}
}
deleteRow() returns me an error... it says me that my ResultSet is read only, but in my statement it's delcared as
s = conn.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE, ResultSet.CONCUR_UPDATABLE);
so, what's wrong?
sry for the noobish code and the bad english -.-'''
select * makes the Resultset instance readonly.
select COLUMNNAME makes it updatable.
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");
}
}