Heading ##I have problem with my java application with database in mySQL and swing GUI.
When I've used localhost everything worked properly. But now I would like to share project with my friend and we decided to use server hosting.
And here is a problem:
Now application works very slow, after pressing a button I have to wait a few seconds for the program to respond. Also the connection is lost from time to time. I have no idea where can I find reason for the problem... Do somebody now what is the reason of this problem?
private static Connection connection = null;
Boolean error = false;
private static String jdbcURL = "jdbc:mysql://host_name:3306/db_name";
private static String user = "user";
private static String password = "password";
MakeConnection(Connection connection) throws SQLException{
this.connection = connection;
try {
getConnection();
System.out.print("Connected to the data base in MakeConnection");
}
catch(Exception e) {
error = true;
System.out.print("Error in connection in MakeConnection consturctor" + e.getMessage());
}
finally{
if(connection!=null) connection.close();
if(error) System.out.print("Problem with connection");
else System.out.print("Program finished");
}
}
public Connection getConnection() throws SQLException {
try {
Class.forName("com.mysql.cj.jdbc.Driver");
connection = DriverManager.getConnection(jdbcURL,user,password);
} catch (Exception e) {
e.printStackTrace();
}
return connection;
}
}
Also sometimes application shows this error:
The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server.
I don't see any problem in your code. The problem is probably with your server hosting. You should check the country of the host provider and measure the time required to send a request to the server. Also you should use logger instead of System.out.println so you can examine required time for actions like db access, application logic and find a bottleneck.
Related
I got to use MariaDB for my University Project.
it's my first time doing it, so I dont't know well how to use and code JDBC Driver and mariaDB.
Now I'm implementing the code in many places while looking at examples.
As I see, All the examples seems to creating Statement and making connection by using "DriverManager.getConnection"
Now I have a question.
I'm going to create a DBmanager Class that can connect, create tables, execute queries, and execute the code that updates data on tables in a single line.
I thought all the examples would run alone in one method and came from different places, so I could only try a new connection and create a code that would not close. But I have a gut feeling that this will be a problem.
Is there any way I can leave a connection connected at a single connection to send a command, and disconnect it to DB.disconnect()? And I'd appreciate it if you could tell me whether what I'm thinking is right or wrong.
The code below is the code I've written so far.
I am sorry if you find my English difficult to read or understand. I am Using translator, So, my English could not be display as I intended.
import java.sql.*;
import java.util.Properties;
public class DBManager {
/*********INNITIAL DEFINES********/
final static private String HOST="sumewhere.azure.com";//Azure DB URL
final static private String USER="id#somewhere";//root ID
final static private String PW="*****";//Server Password
final static private String DRIVER="org.mariadb.jdbc.Driver";//DB Driver info
private String database="user";
/***************API***************/
void setDB(String databaseinfo){
database=databaseinfo;
}
private void checkDriver() throws Exception
{
try
{
Class.forName("org.mariadb.jdbc.Driver");
}
catch (ClassNotFoundException e)
{
throw new ClassNotFoundException("MariaDB JDBC driver NOT detected in library path.", e);
}
System.out.println("MariaDB JDBC driver detected in library path.");
}
public void checkOnline(String databaseinfo) throws Exception
{
setDB(databaseinfo);
this.checkDriver();
Connection connection = null;
try
{
String url = String.format("jdbc:mariadb://%s/%s", HOST, database);
// Set connection properties.
Properties properties = new Properties();
properties.setProperty("user", USER);
properties.setProperty("password", PW);
properties.setProperty("useSSL", "true");
properties.setProperty("verifyServerCertificate", "true");
properties.setProperty("requireSSL", "false");
// get connection
connection = DriverManager.getConnection(url, properties);
}
catch (SQLException e)
{
throw new SQLException("Failed to create connection to database.", e);
}
if (connection != null)
{
System.out.println("Successfully created connection to database.");
}
else {
System.out.println("Failed to create connection to database.");
}
System.out.println("Execution finished.");
}
void makeCcnnection() throws ClassNotFoundException
{
// Check DB driver Exists
try
{
Class.forName("org.mariadb.jdbc");
}
catch (ClassNotFoundException e)
{
throw new ClassNotFoundException("MariaDB JDBC driver NOT detected in library path.", e);
}
System.out.println("MariaDB JDBC driver detected in library path.");
Connection connection = null;
}
public void updateTable(){}
public static void main(String[] args) throws Exception {
DBManager DB = new DBManager();
DB.checkOnline("DB");
}
}
For a studying project it's okay to give a connection from your DB Manager to client code and close it there automatically using try-with-resources construction.
Maybe you will find it possible to check Connection Pool tools and apply it further in your project or use as example (like HikariCP, here is a good introduction).
Read about Java try with resources. I think that this link could be usefull for your problem.
JDBC with try with resources
I am trying to connect to my database by JDBC on localhost. Connecting via windows authentication is no problem, but I want to connect via SQL authentication. Therefore, I created a login and a user corresponding to this login in my database. I can normally log in SSMS:
My connection string for JDBC:
jdbc:sqlserver://localhost:1433;databaseName=TestBazyDanych;user=doszke;password=doszke123
Thrown exception:
com.microsoft.sqlserver.jdbc.SQLServerException: Login failed for user 'doszke'. ClientConnectionId:b7005fe3-904d-40c5-a89e-af0cb61250d6
at com.microsoft.sqlserver.jdbc.SQLServerException.makeFromDatabaseError(SQLServerException.java:254)
at com.microsoft.sqlserver.jdbc.TDSTokenHandler.onEOF(tdsparser.java:258)
at com.microsoft.sqlserver.jdbc.TDSParser.parse(tdsparser.java:104)
at com.microsoft.sqlserver.jdbc.SQLServerConnection.sendLogon(SQLServerConnection.java:4772)
at com.microsoft.sqlserver.jdbc.SQLServerConnection.logon(SQLServerConnection.java:3581)
at com.microsoft.sqlserver.jdbc.SQLServerConnection.access$000(SQLServerConnection.java:81)
at com.microsoft.sqlserver.jdbc.SQLServerConnection$LogonCommand.doExecute(SQLServerConnection.java:3541)
at com.microsoft.sqlserver.jdbc.TDSCommand.execute(IOBuffer.java:7240)
at com.microsoft.sqlserver.jdbc.SQLServerConnection.executeCommand(SQLServerConnection.java:2869)
at com.microsoft.sqlserver.jdbc.SQLServerConnection.connectHelper(SQLServerConnection.java:2395)
at com.microsoft.sqlserver.jdbc.SQLServerConnection.login(SQLServerConnection.java:2042)
at com.microsoft.sqlserver.jdbc.SQLServerConnection.connectInternal(SQLServerConnection.java:1889)
at com.microsoft.sqlserver.jdbc.SQLServerConnection.connect(SQLServerConnection.java:1120)
at com.microsoft.sqlserver.jdbc.SQLServerDriver.connect(SQLServerDriver.java:700)
at java.sql/java.sql.DriverManager.getConnection(DriverManager.java:677)
at java.sql/java.sql.DriverManager.getConnection(DriverManager.java:251)
at main.Main.main(Main.java:38)
The username and password are the same, as those used for loging to SSMS.
Here my class code:
package main;
import java.sql.*;
public class Main {
private static ResultSet selectStan(Connection connection) throws SQLException {
String sql_stmt = "SELECT * FROM STAN;";
Statement statement = connection.createStatement();
ResultSet result = statement.executeQuery(sql_stmt);
System.out.println("Select executed");
return result;
}
public static void main(String[] args) {
try {
Class.forName("com.microsoft.sqlserver.jdbc.SQLServerDriver");
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
String userName = "doszke";
String password = "doszke123";
String url = "jdbc:sqlserver://localhost:1433;databaseName=TestBazyDanych;user=doszke;password=doszke123";
try (Connection con = DriverManager.getConnection(url)) {
if(con != null){
System.out.println("connected");
} else {
System.out.println("unable to connect");
}
}
catch (SQLException e) {
e.printStackTrace();
}
}
}
As Mark Rotteveel pointed out, I was trying to connect to a LocalDB instance with JDBC, which seemed undoable. (ref: here)
However, I installed jTDS and added to my classpath, changed my connection string to
jdbc:jtds:sqlserver://./TestBazyDanych;instance=LOCALDB#EB7165FD;namedPipe=true
create a connection by the use of this connection string, username and password and it worked. The instance pipe number was taken from cmd line via
sqllocaldb i MSSQLLocalDB
There are few things need to check:
Did you create doszke user under the database and SSMS?
Are you able to login with doszke/doszke123 credentials in SSMS?
Please check 1433 port are open or not in your inbound and outbound firewall.
Trying to telnet on localhost 1433. If it's getting failed change below setting:
Go to Configuration tools -> SQL Server Configuration Manager Select SQL Server Network Configuration -> Select protocol in the right side window enable tcp/ip and restart the services in services.
I have a simple database on my computer for testing purposed, and I'm trying to retrieve some information from the database, from my laptop. So I want my laptop to make a request to see the information inside my computers MySQL database. Below shows the java code I'm trying to run on my laptop to collect the first entry in the students table, which is located on my computer.
I have MySQL workbench installed on both my laptop and computer, is it necessary to be on both machines if the computer will store the data and the laptop only extracts data.
What I've learnt so far from researching is that the public ip should be used in the url instead of the ip for the computer, so I added that in but I received a CommunicationsException along with "Connection timed out" in the stack trace. I've read through this answer and this answer to a similar problem, but I'm having difficulty understanding both solutions, could someone refer me to a beginners guide to remotely accessing data from a database using MySQL.
public class TestRemote{
//JDBC variables
Connection connection;
Statement statement;
ResultSet resultSet;
//String variables
String url;
String user;
String password;
public static void main(String[] args) {
TestRemote sql = new TestRemote();
ArrayList<String> firstnames = sql.getColumn("students", "firstname", "studentid=4");
System.out.println(firstnames.get(0));
}
// Constructor
public TestRemote()
{
try {
Class.forName("com.mysql.jdbc.Driver");
} catch (ClassNotFoundException e) {
System.out.println("couldnt find class");
}
url = "jdbc:mysql://81.159.3.167:3306/test"; //?autoReconnect=true&useSSL=false";
user = "user";
password = "pass123";
connection = null;
statement = null;
resultSet = null;
}
private void closeConnection(){
try{
if(connection != null)
connection.close();
if(statement != null)
statement.close();
if(resultSet != null)
resultSet.close();
connection=null; resultSet=null; statement=null;
}catch(Exception e){
e.printStackTrace();
}
}
public ArrayList<String> getColumn(String table, String column, String where) {
ArrayList<String> resultsArray = new ArrayList<String>();
try {
connection = DriverManager.getConnection(url, user, password);
statement = connection.createStatement();
if(!where.equals(""))
resultSet = statement.executeQuery("SELECT "+column+" FROM "+table + " WHERE "+where);
else
resultSet = statement.executeQuery("SELECT "+column+" FROM "+table);
while(resultSet.next()) {
String val = resultSet.getString(1);
if(val==null)
resultsArray.add("");
else
resultsArray.add(val);
}
//resultsArray = (ArrayList<String>) resultSet.getArray(column);
} catch (SQLException ex) {
Logger lgr = Logger.getLogger(Model.class.getName());
lgr.log(Level.SEVERE, ex.getMessage(), ex);
}
closeConnection();
return resultsArray;
}
}
Your Java code is probably fine. But the question is, is on the other machine a MySQL server running and listening on port 3306 on the public IP? By default it should only listen on localhost, so you need to change your MySQL installation so that it listens to the public IP. Also make sure that no Firewall is blocking the access. Try connecting with the Workbench on the Laptop to reach the MySQL server on the other box. If you got this running, try your Java code again.
I have MySQL workbench installed on both my laptop and computer, is it
necessary to be on both machines if the computer will store the data
and the laptop only extracts data.
No what you call the "Computer" is your server here. it doesn't need mysql workbench. it only needs mysql server
the public ip should be used in the url instead of the ip for the
computer
A database should almost never be exposed on the public IP address. If you are having both computers on the LAN, the private network IP is what the server should listen on and that's what you should use on the connection string.
CommunicationsException along with "Connection timed out" in the stack
trace
Because the server is not running, not listening on that ip:port or firewalled to drop packets.
i have a database for practice at phpMyAdmin. i use XAMPP. I am in very early stages of learing about the conection with a database. I followa tutorial and i think i am understanding the concept and everything is cool. But i stepped on a problem that despite the fact that there are answers on the internet, i cant solve it. here is my code:
import java.sql.*;
public class DBConnect {
private Connection connection;
private Statement statement;
private ResultSet result;
public DBConnect(){
try {
Class.forName("com.mysql.jdbc.Driver");
connection = DriverManager.getConnection("jdbc:mysql://localhost:1234/practicedb"); //code stucks here and after some minutes it is throwing an exception
System.out.println("Connected");//this is never executed.
statement = connection.createStatement();
} catch (Exception ex) {
System.out.print("Error in Constractor: "+ex);
}
}
public void getData() {
try {
String query = "select * from cars";
result = statement.executeQuery(query);
while (result.next()) {
String name = result.getString("carName");
String id = result.getString("carID");
String modelNum = result.getString("modelNumber");
System.out.println("Car name: " + name + ", " + "Car ID: " + id + ", " + "Car model number: " + modelNum);
}
} catch (Exception ex) {
System.out.println(ex);
}
}
}
In the main class i create an instance of the class and then call the getData().
The code stucks in that line:
connection = DriverManager.getConnection("jdbc:mysql://localhost:1234/practicedb");
And it throws that:
com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure
The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server.java.lang.NullPointerException
This similar question was answered here: answer
But the suggestions are poor. I have tried flushing dns. I checked the URL and this is the one i connect to the database on phpmyadmin. i changed localhost to my ip adress. but all those just dont work.
I would really appreciate help. Is the first step on managing to receive that knowledge and i actually cant proceed at the moment. Thank you :)
i noticed that if i change the localhost:1234 to a random one like localhost:5432 it is throwing the error immediatelly. But when i have it on 1234(which i the port i have choosen through xampp config) then the programm runs for round about 5 minutes before it got terminated with the exception
Usually MySQL listens on the default port 3306.
If your database is named practicedb then your code should look like this:
private Connection connection;
try {
connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/practicedb");
System.out.println("Connected");
} catch (Exception ex) {
System.out.print("Error creating connection: "+ex);
}
I have a big problem and I do not know how to fix it:
I have a singleton instance of the database as follow:
public Connection getConnection() throws SQLException {
if (db_con == null)
db_con = createConnection();
return db_con;
}
And I have a code that as follow:
shortTextScoringComponent.scoreComponent( "RS",SelectDataBase.getBlogs(rightSarcastic));
shortTextScoringComponent.scoreComponent( "RNS",SelectDataBase.getBlogs(rightNonSarcasm));
shortTextScoringComponent.scoreComponent( "FNS",SelectDataBase.getBlogs(wrongNonSarcasm));
shortTextScoringComponent.scoreComponent( "FS",SelectDataBase.getBlogs(wrongSarcasm));
So as you can see I call the database 4 times and it is note worthy that between each call there is a long time of processing so after he second line is performed successfuly I mean this line:
SelectDataBase.getBlogs(rightNonSarcasm);
when it comes to the third line I get the following error:
com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: The last packet successfully received from the server was 79,547,948 milliseconds ago. The last packet sent successfully to the server was 79,547,964 milliseconds ago. is longer than the server configured value of 'wait_timeout'. You should consider either expiring and/or testing connection validity before use in your application, increasing the server configured values for client timeouts, or using the Connector/J connection property 'autoReconnect=true' to avoid this problem.
com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: No operations allowed after connection closed.
I searched a lot but there are many different answers which confuses me, do you have any idea what my exact problem is?
First of all as the exception says do add
autoReconnect=true
in your connectionString also add this as well
tcpKeepAlive=true
Secondly you can keep a polling thread to keep checking connection activeness
class PollingThread extends Thread
{
private java.sql.Connection connection;
PollingThread(int index, java.sql.Connection connection)
{
super();
this.connection = connection;
}
public void run()
{
Statement stmt = null;
while (!interrupted())
{
try
{
sleep(15 * 60 * 1000L);
stmt = connection.createStatement();
stmt.execute("do 1");
}
catch (InterruptedException e)
{
break;
}
catch (Exception sqle)
{
/* This thread should run even on DB error. If autoReconnect is true,
* the connection will reconnect when the DB comes back up. */
}
finally
{
if (stmt != null)
{
try
{
stmt.close();
} catch (Exception e)
{}
}
stmt = null;
}
}