We Keep Coding

Is it possible to reuse a connection statement without closing it? [duplicate]

I've been working at this for almost a day and a half now and I can't seem to work this error out. I don't know why the ResultSet is being closed. Maybe some of you can help me out.
MySQLDatabase:
package net.gielinor.network.sql;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
public abstract class MySQLDatabase {
private String host;
private String database;
private String username;
private String password;
private Connection connection = null;
private Statement statement;
public MySQLDatabase(String host, String database, String username, String password) {
this.host = host;
this.database = database;
this.username = username;
this.password = password;
}
public abstract void cycle() throws SQLException;
public abstract void ping();
public void connect() {
try {
Class.forName("com.mysql.jdbc.Driver").newInstance();
connection = DriverManager.getConnection(String.format("jdbc:mysql://%s/%s", host, database), username, password);
statement = connection.createStatement();
} catch (Exception e) {
e.printStackTrace();
}
}
public void ping(String table, String variable) {
try {
statement.executeQuery(String.format("SELECT * FROM `%s` WHERE `%s` = 'null'", table, variable));
} catch (Exception e) {
connect();
}
}
public ResultSet query(String query) throws SQLException {
if (query.toLowerCase().startsWith("select")) {
return statement.executeQuery(query);
} else {
statement.executeUpdate(query);
}
return null;
}
public Connection getConnection() {
return connection;
}
}
MySQLHandler
package net.gielinor.network.sql;
import java.io.FileInputStream;
import java.util.ArrayList;
import java.util.List;
import java.util.Properties;
import net.gielinor.network.sql.impl.MySQLDonation;
public class MySQLHandler extends Thread {
private static final MySQLHandler mysqlHandler = new MySQLHandler();
public static MySQLHandler getMySQLHandler() {
return mysqlHandler;
}
private static List<MySQLDatabase> updateList;
private static String host;
private static String database;
private static String username;
private static String password;
#Override
public void run() {
while (true) {
for (MySQLDatabase database : updateList) {
try {
if (database.getConnection() == null) {
database.connect();
} else {
database.ping();
}
database.cycle();
} catch (Exception ex) {
ex.printStackTrace();
}
try {
Thread.sleep(10000);
} catch (Exception ex) {
}
}
}
}
private static void loadProperties() {
Properties p = new Properties();
try {
p.load(new FileInputStream("./sql.ini"));
host = p.getProperty("host");
database = p.getProperty("database");
username = p.getProperty("username");
password = p.getProperty("password");
} catch (Exception ex) {
System.out.println("Error loading MySQL properties.");
}
}
public static String getHost() {
return host;
}
static {
loadProperties();
updateList = new ArrayList<MySQLDatabase>();
updateList.add(new MySQLDonation(host, database, username, password));
}
}
MySQLDonation
package net.gielinor.network.sql.impl;
import java.sql.ResultSet;
import java.sql.SQLException;
import net.gielinor.game.model.player.Client;
import net.gielinor.game.model.player.PlayerHandler;
import net.gielinor.game.model.player.PlayerSave;
import net.gielinor.network.sql.MySQLDatabase;
public final class MySQLDonation extends MySQLDatabase {
public MySQLDonation(String host, String database, String username, String password) {
super(host, database, username, password);
}
#Override
public void cycle() throws SQLException {
ResultSet results = query("SELECT * FROM `gieli436_purchases`.`donations`");
if (results == null) {
return;
}
while (results.next()) {
String username = results.getString("username").replace("_", " ");
System.out.println("name=" + username);
Client client = (Client) PlayerHandler.getPlayer(username.toLowerCase());
System.out.println(client == null);
if (client != null && !client.disconnected) {
int creditamount = results.getInt("creditamount");
if (creditamount <= 0) {
continue;
}
handleDonation(client, creditamount);
query(String.format("DELETE FROM `gieli436_purchases`.`donations` WHERE `donations`.`username`='%s' LIMIT 1", client.playerName.replaceAll(" ", "_")));
}
}
}
#Override
public void ping() {
super.ping("donations", "username");
}
private void handleDonation(Client client, int creditamount) throws SQLException {
client.credits = (client.credits + creditamount);
client.sendMessage("Thank you for your purchase. You have received " + creditamount + " store credits.");
PlayerSave.save(client);
}
}
The exception occurs here: in the while loop within MySQLDonation and the actual stacktrace is this:
java.sql.SQLException: Operation not allowed after ResultSet closed
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1055)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:956)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:926)
at com.mysql.jdbc.ResultSetImpl.checkClosed(ResultSetImpl.java:794)
at com.mysql.jdbc.ResultSetImpl.next(ResultSetImpl.java:7077)
at net.gielinor.network.sql.impl.MySQLDonation.cycle(Unknown Source)
at net.gielinor.network.sql.MySQLHandler.run(Unknown Source)
With this information let me say that this does work, I get my message and what not in-game but it repeats, like the user is never removed from the query so it gives them infinite rewards. If you need any more information feel free to ask.

When you run the Delete query, you use the same Statement that was used in the Select query. When you re-execute on the same Statement, the previous ResultSet gets closed.
To avoid this, you should create a new Statement everytime you execute a query. So remove statement = connection.createStatement(); from the connect() method in MySQLDatabase class, and replace all statement in that class to connection.createStatement(). You may also choose to delete the private variable statement altogether.
You can read more about it here.

this error is some time occur when we use same statement object for diff. types
check Statement objectsss;

Netbeans MySQL Connection - not to do with jbdc

I have a login app that needs to connect to a server to check the username and password. I am using netbeans and the jbdc is installed and working in the services tab(thanks stack overflow!). By the jbdc is work I mean that i can execute SQL script through it.
I have set this up with MS Server 16 and MySQL so I am convied it is the code:
Connection method:
package dbUtil;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
public class dbConnection {
private static final String USERNAME = "root";
private static final String PASSWORD = "mess";
private static final String SQCONN = "jdbc:mysql://localhost:1434/MessyLogin?zeroDateTimeBehavior=convertToNull";
public static Connection getConnection()throws SQLException{
try {
Class.forName("com.mysql.jdbc.Driver");
return DriverManager.getConnection(SQCONN, USERNAME, PASSWORD);
}catch (ClassNotFoundException e) {
}
return null;
}
}
loginmodel:
package LogIn;
import dbUtil.dbConnection;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.logging.Level;
import java.util.logging.Logger;
public class LogInModel {
Connection connection;
public LogInModel() {
try{
this.connection = dbConnection.getConnection();
}catch(SQLException e){
}
if(this.connection == null){
System.out.println("here");
// System.exit(1);
}
}
public boolean isDatabaseConnected(){
return this.connection != null;
}
public boolean isLogin(String username, String password) throws Exception{
PreparedStatement pr = null;
ResultSet rs = null;
String sql = "SELECT * FROM MessyLogin where username = ? and Password = ?";
try{
pr = this.connection.prepareStatement(sql);
pr.setString(1, username);
pr.setString(2, password);
rs = pr.executeQuery();
boolean bool1;
if(rs.next()){
return true;
}
return false;
}
catch(SQLException ex){
return false;
}
finally {
{
pr.close();
rs.close();
}
}
}
}
I believe the issue is the return null; from the dbConnection file. The if(this.connection==Null) comes back true and the system is exiting.
Thank you in advance.

Your dbConnection class is a bad idea. Why hard wire those values when you can pass them in?
Your application will only have one Connection if you code it this way. A more practical solution will use a connection pool.
Learn Java coding standards. Your code doesn't follow them; it makes it harder to read and understand.
Here's a couple of recommendations:
package dbUtil;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
public class dbConnection {
public static final String DRIVER = "com.mysql.jdbc.Driver";
public static final String USERNAME = "root";
public static final String PASSWORD = "mess";
public static final String URL = "jdbc:mysql://localhost:1434/MessyLogin?zeroDateTimeBehavior=convertToNull";
public static Connection getConnection(String driver, String url, String username, String password) throws ClassNotFoundException, SQLException {
Class.forName(driver);
return DriverManager.getConnection(url, username, password);
}
}
I might write that LogInModel this way:
package LogIn;
import dbUtil.dbConnection;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.logging.Level;
import java.util.logging.Logger;
public class LogInModel {
private static final String sql = "SELECT * FROM MessyLogin where username = ? and Password = ?";
private Connection connection;
public LogInModel(Connection connection) {
this.connection = connection;
}
public boolean isLogin(String username, String password) {
boolean isValidUser = false;
PreparedStatement pr = null;
ResultSet rs = null;
try {
pr = this.connection.prepareStatement(sql);
pr.setString(1, username);
pr.setString(2, password);
rs = pr.executeQuery();
while (rs.hasNext()) {
isValidUser = true;
}
} catch (SQLException ex) {
e.printStackTrace();
isValidUser = false;
} finally {
dbUtils.close(rs);
dbUtils.close(pr);
}
return isValidUser;
}
}
Here's my guess as to why your code fails: You don't have the MySQL JDBC driver JAR in your runtime CLASSPATH. There's an exception thrown when it can't find the driver class, but you didn't know it because you swallowed the exception.

Writing data into MySQL table with JavaFX

I have linked up a database to my Java application using the JDBC in Netbeans.
But whenever I try to write something from a TextField to a MySQL table, it doesn't work.
I have a pre-made class to make the database connection.
Here is my database class:
package testswitch;
import java.sql.Connection;
import java.sql.Driver;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.Enumeration;
import java.util.logging.Level;
import java.util.logging.Logger;
/**
*
* #author Maarten
*/
public class Database {
public final static String DB_DRIVER_URL = "com.mysql.jdbc.Driver";
public final static String DB_DRIVER_PREFIX = "jdbc:mysql://";
private Connection connection = null;
public Database(String dataBaseName, String serverURL, String userName, String passWord) {
try {
// verify that a proper JDBC driver has been installed and linked
if (!selectDriver(DB_DRIVER_URL)) {
return;
}
if (serverURL == null || serverURL.isEmpty()) {
serverURL = "localhost:3306";
}
// establish a connection to a named Database on a specified server
connection = DriverManager.getConnection(DB_DRIVER_PREFIX + serverURL + "/" + dataBaseName, userName, passWord);
} catch (SQLException eSQL) {
logException(eSQL);
}
}
private static boolean selectDriver(String driverName) {
// Selects proper loading of the named driver for Database connections.
// This is relevant if there are multiple drivers installed that match the JDBC type.
try {
Class.forName(driverName);
// Put all non-prefered drivers to the end, such that driver selection hits the first
Enumeration<Driver> drivers = DriverManager.getDrivers();
while (drivers.hasMoreElements()) {
Driver d = drivers.nextElement();
if (!d.getClass().getName().equals(driverName)) {
// move the driver to the end of the list
DriverManager.deregisterDriver(d);
DriverManager.registerDriver(d);
}
}
} catch (ClassNotFoundException | SQLException ex) {
logException(ex);
return false;
}
return true;
}
public void executeNonQuery(String query) {
try (Statement statement = connection.createStatement()) {
statement.executeUpdate(query);
} catch (SQLException eSQL) {
logException(eSQL);
}
}
public ResultSet executeQuery(String query) {
Statement statement;
try {
statement = connection.createStatement();
ResultSet result = statement.executeQuery(query);
return result;
} catch (SQLException eSQL) {
logException(eSQL);
}
return null;
}
private static void logException(Exception e) {
System.out.println(e.getClass().getName() + ": " + e.getMessage());
e.printStackTrace();
}
}
And here's my JavaFX controller.
What I want is that when the "handle" button is pressed, that the data filled in the TextField gets inserted into the database.
package testswitch;
import java.io.IOException;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import javafx.event.ActionEvent;
import javafx.fxml.FXML;
import javafx.scene.control.Button;
import javafx.scene.control.CheckBox;
import javafx.scene.control.TextField;
import javafx.stage.Stage;
import testswitch.Database;
/**
*
* #author Maarten
*/
public class gebruikerToevoegenController {
//TextFields
#FXML
private TextField FXVoornaam, FXTussenvoegsel, FXAchternaam, FXGebruikersnaam;
#FXML
private TextField FXWachtwoord, FXEmail, FXTelefoonnummer;
//Boolean checkbox positie
#FXML
private CheckBox ManagerPosition;
#FXML
private Button gebruikerButton;
public final String DB_NAME = "testDatabase";
public final String DB_SERVER = "localhost:3306";
public final String DB_ACCOUNT = "root";
public final String DB_PASSWORD = "root";
Database database = new Database(DB_NAME, DB_SERVER, DB_ACCOUNT, DB_PASSWORD);
public void handle(ActionEvent event) throws SQLException {
String query = "INSERT INTO testDatabase.Gebruikers (Voornaam) VALUES " + FXVoornaam.getText();
try {
database.executeQuery(query);
} catch (Exception e) {
}
}
}
Thanks in advance

The string in your SQL query doesn't seem to be properly quoted. It's best to use PreparedStatement for this scenario:
public class Database {
public PreparedStatement prepareStatement(String query) throws SQLException {
return connection.prepareStatement(query);
}
...
public void handle(ActionEvent event) throws SQLException {
String query = "INSERT INTO testDatabase.Gebruikers (Voornaam) VALUES (?);";
PreparedStatement statement = database.prepareStatement(query);
try {
statement.setString(1, FXVoornaam.getText());
statement.executeUpdate();
} catch (Exception e) {
// log info somewhere at least until it's properly tested/
// you implement a better way of handling the error
e.printStackTrace(System.err);
}
}

You have to add like this in JavaFx :
String query = "INSERT INTO testDatabase.Gebruikers (Voornaam) VALUES ('{FXVoornaam.getText()}') ";

String query = "INSERT INTO testDatabase.Gebruikers(Voornaam)
VALUES('" + FXVoornaam.getText() + "')";

How to update a table using values from java ArrayList?

I'm working on my application where I want to update my table after email has been sent. I created function that connect sql database and java, also in other class I created function that updates table but what I need is these two classes together. I want to use my array-list after execution for updating of my table.
Here is my code for connection and sending emails:
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;
import java.util.Properties;
import javax.mail.Message;
import javax.mail.MessagingException;
import javax.mail.PasswordAuthentication;
import javax.mail.Session;
import javax.mail.Transport;
import javax.mail.internet.InternetAddress;
import javax.mail.internet.MimeMessage;
public class TestSendEmails {
private String emailTo;
private String emailSubject;
private String emailBody;
private String emailAttachments;
private Integer RecordId;
public TestSendEmails(){
}
public TestSendEmails(String emailTo, String emailSubject, String emailBody, String emailAttachments, Integer RecordId){
super();
this.emailTo = emailTo;
this.emailSubject = emailSubject;
this.emailBody = emailBody;
this.emailAttachments = emailAttachments;
this.RecordId = RecordId;
}
public String getEmailTo(){
return emailTo;
}
public void setEmailTo(String emailTo){
this.emailTo = emailTo;
}
public String getEmailSubject(){
return emailSubject;
}
public void setEmailSubject(String emailSubject){
this.emailSubject = emailSubject;
}
public String getEmailBody(){
return emailBody;
}
public void setEmailBody(String emailBody){
this.emailBody = emailBody;
}
public String getEmailAttachments(){
return emailAttachments;
}
public void setEmailAttachments(String emailAttachments){
this.emailAttachments = emailAttachments;
}
public Integer getRecordId(){
return RecordId;
}
public void setRecordId(Integer RecordId){
this.RecordId = RecordId;
}
}
class TestSendEmailD{
private Connection con;
private static final String GET_EMAILS = "Select* From Emails";
private void connect() throws InstantiationException, IllegalAccessException, ClassNotFoundException, SQLException{
Class.forName("com.microsoft.sqlserver.jdbc.SQLServerDriver").newInstance();
con = DriverManager.getConnection("jdbc:sqlserver://100.000.000.00\\:3333;databaseName=Test;user=mmmm;password=1234");
}
public List<TestSendEmails> getTestSendEmails() throws Exception{
connect();
PreparedStatement ps = con.prepareStatement(GET_EMAILS);
ResultSet rs = ps.executeQuery();
List<TestSendEmails> result = new ArrayList<TestSendEmails>();
while(rs.next()){
result.add(new TestSendEmails(rs.getString("emailTo"), rs.getString("emailSubject"),rs.getString("emailBody"),rs.getString("emailAttachments",rs.getInt("RecordId"))));
}
disconnect();
return result;
}
private void disconnect() throws SQLException{
if(con != null){
con.close();
}
}
}
class EmailSender{
private Session session;
private void init(){
Properties props = new Properties();
props.put("mail.smtp.auth", "true");
props.put("mail.smtp.starttls.enable", "true");
props.put("mail.smtp.host", "100.000.000.00");
props.put("mail.smtp.port", "678");
session = Session.getInstance(props,
new javax.mail.Authenticator() {
protected PasswordAuthentication getPasswordAuthentication() {
return new PasswordAuthentication("test#gmail.com", "123");
}
});
}
public void sendEmail(TestSendEmails s) throws MessagingException{
init();
Message message = new MimeMessage(session);
message.setFrom(new InternetAddress("test#gmail.com"));
message.setRecipients(Message.RecipientType.TO, InternetAddress.parse(s.getEmailTo().replace(";", ",")));
message.setSubject(s.getEmailSubject());
message.setText(s.getEmailBody());
message.setContent(s.getEmailBody(),"text/html");
Transport.send(message);
System.out.println("Done");
}
public void sendEmail(List<TestSendEmails> emails) throws MessagingException{
for(TestSendEmails TestSendEmails:emails ){
sendEmail(TestSendEmails);
}
}
}
Here is my Update code:
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.util.Date;
public class UpdateEmail {
public static Connection getConnection() throws Exception {
String driver = "com.microsoft.sqlserver.jdbc.SQLServerDriver";
String url = "jdbc:sqlserver://100.000.000.00\\:3333;databaseName=Test";
String username = "mmmm";
String password = "1234";
Class.forName(driver);
Connection conn = DriverManager.getConnection(url, username, password);
return conn;
}
public static void main(String[] args) throws Exception {
java.util.Date date = new Date();
Connection conn = null;
PreparedStatement pstmt = null;
try {
conn = getConnection();
String query = "update Emails set SentOn = ? where Id = ? ";
pstmt = conn.prepareStatement(query); // create a statement
pstmt.setTimestamp(1, new java.sql.Timestamp(date.getTime()));
pstmt.setInt(2, 200); // In this line I want to use my array-list to update my table.
pstmt.executeUpdate(); // execute update statement
} catch (Exception e) {
e.printStackTrace();
System.exit(1);
} finally {
pstmt.close();
conn.close();
}
}
}
I'm not sure if I have to create new connection for my update in my second program and where I should implement my update code. If you know what I should change please let me know. Thanks in advance.
Main.java code:
import java.util.List;
public class Main {
public static void main(String[] args) throws Exception {
TestSendEmailD dao=new TestSendEmailD();
List<TestSendEmails> list=dao.getTestSendEmails();
EmailSender sender=new EmailSender();
sender.sendEmail(list);
}
}

I guess you have an ArrayList() called yourList. The following code goes before
String query ...
StringBuilder ids = "";
String prefix ="";
for (Integer id: yourList) {
append(prefix);
prefix = ",";
ids.append(String.valueOf(id));
}
change your query to:
String query = "update Emails set SentOn =? where Id in (" + ids.toString() + ")";
and send only the SentOn as parameter:
pstmt.setTimestamp(1, new java.sql.Timestamp(date.getTime()));

Connection conn = null;
PreparedStatement pstmt = null;
conn = getConnection();
java.util.Date date = new Date();
message.setFrom(new InternetAddress("test#gmail.com"));
String query = "update Emails set SentOn = ? where Id = ? ";
pstmt = conn.prepareStatement(query); // create a statement
String str[]=String.valueOf(s.getRecordId()).split(";");//id1;id;id3;....
for(int i=0;i<str.length();i++)
{
message.setRecipients(Message.RecipientType.TO, InternetAddress.parse(s.getEmailTo().replace(";", ",")[i]));
message.setSubject(s.getEmailSubject());
message.setText(s.getEmailBody());
message.setContent(s.getEmailBody(),"text/html");
Transport.send(message);
System.out.println("Done");
pstmt.setTimestamp(1, new java.sql.Timestamp(date.getTime()));
pstmt.setInt(2, str[i]); // In this line I want to use my array-list to update my table.
pstmt.executeUpdate(); // execute update statement
System.out.println(str[i]+" "+s.getEmailTo().replace(";", ",")[i]+" "+new java.sql.Timestamp(date.getTime()));//to check whether its working or not.
}
Its exactly not an exact answer. check whether its working or not. Here you must take care of exceptions also. I didn't written that code here.

Java getter methods returning null instead of the string

When I call getName from MyServ class, I get null, but when I call them locally from DBClass they return strings. anyone know what I'm doing wrong?
package DB;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;
public class DBClass{
private Statement stmt;
private Connection conn;
private ResultSet result;
public String name, surname;
public DBClass(){
}
public Connection dbConnect(final String db_connect_string,
final String db_userid,
final String db_password){
try{
DriverManager.registerDriver(new oracle.jdbc.OracleDriver());
conn =
DriverManager.getConnection(db_connect_string, db_userid,
db_password);
stmt = conn.createStatement();
result = stmt.executeQuery("Select * from .....etc");
if(result.next()){
name = result.getString(1).toString();
surname = result.getString(2).toString();
}
return conn;
} catch(final Exception e){
e.printStackTrace();
return null;
}
}
public String getName(){
return name;
}
public String getSurname(){
return surname;
}
}
package DB;
import java.io.IOException;
import java.sql.Connection;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
* Servlet implementation class MyServ
*/
public class MyServ extends HttpServlet{
private static final long serialVersionUID = 1L;
private final DBClass dbclass;
private final String name, surname;
private final Connection conn;
public MyServ(){
dbclass = new DBClass();
final DBClass db = new DBClass();
conn =
db.dbConnect("jdbc:oracle:thin:#elanweb:1510:xxxxx", "xxxxx",
"xxxxxx");
name = dbclass.getName();
surname = dbclass.getSurname();
}
#Override
protected void doGet(final HttpServletRequest request,
final HttpServletResponse response) throws ServletException,
IOException{
}
#Override
protected void doPost(final HttpServletRequest request,
final HttpServletResponse response) throws ServletException,
IOException{
System.out.println("MyServer -- " + name + " " + surname);
response.sendRedirect("http://localhost:8080/DWP/");
}
}

Surely you mean:
name = db.getName();
instead of:
name = dbclass.getName();
You seem to be referencing the wrong variable within the constructor, the one without an open connection (dbclass).

Simply because the value is null (which is a String, kind of).
Look at the relevant bits of the code. In your MyServ constructor, you do:
dbclass = new DBClass();
According to the DBClass constructor, this initialises all fields to default values (which for a String is null).
Then you don't use this variable again until you call:
dbclass.getName();
which correctly goes and looks up the name variable - which is null, because it was implicitly assigned null when the object was constructed - and returns this to you.
Perhaps a better question is, what did you expect it to return, and why?