Here's how I'm trying to connect:
try {
Class.forName("com.mysql.jdbc.Driver").newInstance();
} catch (Exception e) {
throw new DbConnectionException();
}
try {
connection = DriverManager.getConnection(url,username,password);
} catch (SQLException e) {
e.printStackTrace();
throw new DbConnectionException();
}
I'm 100% sure that the url, username, password strings are correct. I've already connected successfully using an external tool (MySQL query browser).
This is the error I receive:
com.mysql.jdbc.CommunicationsException:
Communications link failure due to
underlying exception:
** BEGIN NESTED EXCEPTION **
java.net.SocketException MESSAGE:
java.net.ConnectException: Connection
refused
...
Possibly a url issue. If your code is pointing to MySQL localhost, try changing localhost to 127.0.0.1 on your url.
E.g.:
jdbc:mysql://localhost:3306/MY_DB
to
jdbc:mysql://127.0.0.1:3306/MY_DB
And see if this works.
did you run the mysql browser from the same machine where the code is running? What I am getting at is the permissions in mysql can be host-specific, and depending on how you set them up you might not be able to connect from the machine where the code is running.
Also, you might want to double check the url, name, pword again, perhaps with log statements or a debugger to make sure there are no typos, trailing whitespaces, etc...
Double check the format of your url. It should start with "jdbc:mysql:". Make sure you are using a current version for the driver as well.
Check that you can connect to the database from the mysql admin tool, that will drive out whether your mysql is running and that the port is open.
In my case the problem was that I was using a connection from emulator to localhost.
If you use emulator to localhost don't use localhost value in connection String but use 10.0.2.2 instead:
jdbc:mysql://10.0.2.2:3306/MY_DB
Hope this helps.
Related
Dear StackOverFlowers,
I was trying event-driven LISTENER/NOTIFY on Postgres 9.6 (Windows 10).
I followed PGJDBC example given by Steve Taylor at https://www.openmakesoftware.com/postgresql-listen-notify-events-example/.
I started by downloading pgjdbc-ng-0.7-complete.jar and have put that in my CLASSPATH replacing standard JDBC driver.
When I am trying to connect to Postgres database using pgjdbc driver, I am getting an error:
connection received: host=127.0.0.1 port=50325
connection authorized: user=postgres database=scott
could not receive data from client: An existing connection was forcibly closed by the remote host.
Here are my system variables:
DBHost: localhost
DBName: scott
DBPort: 5432
DBUserName: postgres
DBPassword: postgres
I am not getting past the first hurdle, rest looks like Mount Everest. Please help me. Should you be needing the code, I am following Steve's code ditto.
Further to Joseph Larson's answer, the database is always running. I have connected to Postgres database from PGADMIN and Java successfully. I think issue is with the connect string. From Java when I am using standard JDBC which is provided by Postgres I am using URL like jdbc:postgresql://localhost:5432/dbname but PGJDBC suggests a different connect string like JDBC:PGSQL://localhost:5432/dbname. I tried to connect with that string (forcibly), it did not work. There is no method in PGJDBC PGDataSource for providing URL directly. I had to go through:
dataSource.setHost(DBHost);
dataSource.setPort(5432);
dataSource.setDatabase(DBName);
dataSource.setUser(DBUserName);
dataSource.setPassword(DBPassword);
And what URL it is sending to Database I am not able to figure out. Please suggest me a connect string and this problem is solved.
thanks
Thanks very much for asking me to post error messages:
Exception in thread "main" java.lang.NullPointerException
at com.impossibl.postgres.system.BasicContext.loadLocale(BasicContext.java:294)
at com.impossibl.postgres.system.BasicContext.init(BasicContext.java:273)
at com.impossibl.postgres.jdbc.PGConnectionImpl.init(PGConnectionImpl.java:251)
at com.impossibl.postgres.jdbc.ConnectionUtil.createConnection(ConnectionUtil.java:182)
at com.impossibl.postgres.jdbc.AbstractDataSource.createConnection(AbstractDataSource.java:723)
at com.impossibl.postgres.jdbc.PGDataSource.getConnection(PGDataSource.java:66)
at com.impossibl.postgres.jdbc.PGDataSource.getConnection(PGDataSource.java:58)
at PGListenNotify.<init>(PGListenNotify.java:26)
at PGListenNotify.main(PGListenNotify.java:37)
Here is source code:
import java.sql.SQLException;
import java.sql.Statement;
import com.impossibl.postgres.api.jdbc.PGConnection;
import com.impossibl.postgres.jdbc.PGDataSource;
public class PGListenNotify
{
PGConnection connection;
public PGListenNotify()
{
String DBHost = System.getenv("DBHost");
String DBName = System.getenv("DBName");
String DBUserName = System.getenv("DBUserName");
String DBPassword = System.getenv("DBPassword");
try
{
PGDataSource dataSource = new PGDataSource();
dataSource.setHost(DBHost);
dataSource.setPort(5432);
dataSource.setDatabase(DBName);
dataSource.setUser(DBUserName);
dataSource.setPassword(DBPassword);
connection = (PGConnection) dataSource.getConnection();
Statement statement = connection.createStatement();
}
catch (SQLException e)
{
e.printStackTrace();
}
}
public static void main(String[] args)
{
PGListenNotify ln = new PGListenNotify();
}
}
This looks like the Windows locale bug in pgjbdc-ng. It has been addressed, try the latest version 0.8.1.
The latest releases have detailed documentation related to asynchronous notifications here.
If it still fails to execute on your Windows system, please create an issue here.
Did you actually start a database server? I didn't know PostgreSQL server could run on Windows, but I've never tried.
I would simplify your problem a little. I know nothing about psql on Windows, but on Mac, I would start the server and then use the psql command (it's part of PostgreSQL) to ensure the server was up and running.
If you're to connecting, then the problems can be:
-There is no server at all
-The server isn't running on the port you're attempting
-The server isn't listening for connections on host 127.0.0.1 but could be listening on the actual IP address of your machine
-I'm not sure about that particular error, but username, password, or database may not exist.
I'd use psql to figure out which of those possible reasons is the real problem. That isolates out your program as being part of the problem, and it becomes entirely one of managing your database server.
Ok first of all i'm french so sorry for the possible incomprehension or bad translate of error messages.
I have a Raspberry, with a Tomcat server on. Also, i use Postgresql too.
On my website, The server side connect to the localhost to access to the database with the JDBC plugin, all works great.
But now i'm trying to developp a Java Program, which one need to connect to the sql database.
But the program have as target to being deployed. So, I can't use "localhost" to connect to the database. On my computer, i'm trying to connect to my Raspberry's database with the JDBC and the few following code :
<code>
public class DB {
Connection co;
PreparedStatement ps;
public DB() {
try {
Class.forName("org.postgresql.Driver");
co = DriverManager.getConnection("jdbc:postgresql://192.168.1.47:5432/database?sslmode=require", "username", "password");
}
catch (ClassNotFoundException e) {System.out.println(e);}
catch (SQLException e) {System.out.println(e);}
}
}
</code>
But when i try to connect, i get the following error :
" org.postgresql.util.PSQLException: FATAL: aucune entr?e dans pg_hba.conf pour l'h?te << 192.168.1.73 >>, utilisateur << username >>,
base de donn?es << database >>, SSL actif "
Which means "No entries in pg_hba.conf for the host..." but i tried to add entries in pg_hba.conf, like this :
host all postgres 192.168.0.0/24 trust
host databaseName userName 192.168.0.0/24 md5
host all all 0.0.0.0/24 md5
but this didn't worked (maybe bad row ? how can i just authorize the user "username" with a password ?)
I added the listen_addresses='*' in postgres.conf too.
Someone know how i need to configure all ?
My computer is on the same WIFI than my Raspberry. Does i need to connect with an external computer on an external WIFI ?
Maybe i did another mistake ?
Thanks for your attention.
OK I solved it by myself, i added these line to pg_hba.conf :
host all all 0.0.0.0/0 md5
now i have to work on the security. Thanks by the way.
I am learning Java and trying to put together a simple App containing a few jTables connected to database that can be updated etc. To do this I have created a database with a few tables through Netbeans which I understand (and wish) to be embedded in the final distributable app.
I am following the Programming Knowledge tutorials on Youtube to create most of the GUI. Everting is OK as long as I open the Services tab on Netbeans and manually right-click my database(testDB) and click Start Server. Then when I run the following code I get a successful connection:
private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {
try{
//Register JDBC driver
Class.forName("org.apache.derby.jdbc.ClientDriver");
//Open a connection
String DB_URL = "jdbc:derby://localhost:1527/testDB";
String u_name = jTextField1.getText();
String p_word = jPasswordField1.getText();
conn = DriverManager.getConnection("jdbc:derby://localhost:1527/testDB",u_name,p_word);
JOptionPane.showMessageDialog(null,"Details Correct - Connection established");
Close_me();
Open_Table_GUI(u_name,p_word);
}
catch(ClassNotFoundException | SQLException e){
System.out.println(e);
}
}
However if I run that code WITHOUT manually clicking on start server I get the following:
java.sql.SQLNonTransientConnectionException: java.net.ConnectException : Error connecting to server localhost on port 1,527 with message Connection refused.
I have read the apache documentation and due to my level of inexperience I am not getting anywhere.
I have also checked out the answers to similar connection questions on here but again I can't seem to relate the issue in a way that works.
The ultimate goal for me is to have an app I can distribute to run on windows machines that will have the database/tables all included individually editable etc. I would hope to eventually create a database that resides on a shared drive and each individual can connect to automatically - but that's way down the line for now.
My request here is that someone can help me understand what I need to change in my code so that the "Start Server" is automatically done.
Thanks in advance for nay response.
OK guys so I found code that seems to work for me from a question asked on here by LMS
private void setup(){
try{
Class.forName("org.apache.derby.jdbc.EmbeddedDriver");
connection=DriverManager.getConnection("jdbc:derby:sheet;create=true","test","1234");
statement=connection.createStatement();
}
catch(ClassNotFoundException cnf){
System.out.println("class error");
}
catch(SQLException se){
System.out.println(se);
}
}
If anyone cares to link me to a reason why this in fact works that would be great, I'm assuming the Embedded driver doesn't go through the port and just looks within the project??
Anyway initially this seems to be solved!!
Please check your Server setting i.e.
-username and pwd in your program
and check that did you start the Derby server and is it listening at port 1527?
I’m trying to connect to a MySQL database on my website from java.
Currently I’m getting a exception that says
Must specify port number after:”
I Google stack overflow and found the default MySQL port is 3306.
But I can't find any information about how I add it to my url, which now looks like
jdbc:mysql://http://www.findmeontheweb.biz/database name"+
“user=findmeon_bitcoin&password=password
code:
try {
// this will load the MySQL driver, each DB has its own driver
Class.forName("com.mysql.jdbc.Driver");
// setup the connection with the DB.
Connection connect = DriverManager.getConnection("jdbc:mysql://http: //www.findmeontheweb.biz//findmeon_bitcoin//"+ "user=findmeon_bitcoin&password=oreo8157");
} catch (Exception e) {
System.out.println("Exception...." );
}
1) Hope the space in your code was only a copy/paste error here
2) You need to remove the http in the mysql uri
Connection connect = DriverManager.getConnection("jdbc:mysql://http: //www.findmeontheweb.biz//findmeon_bitcoin//"+ "user=findmeon_bitcoin&password=oreo8157");
will be
Connection connect = DriverManager.getConnection("jdbc:mysql://findmeontheweb.biz/findmeon_bitcoin/"+ "user=findmeon_bitcoin&password=oreo8157");
And just in case you are running it on a custom port, you can specify port by
Connection connect = DriverManager.getConnection("jdbc:mysql://findmeontheweb.biz:3306/findmeon_bitcoin/"+ "user=findmeon_bitcoin&password=oreo8157");
replace 3306 with your custom port.
Also I hope that is not your real username and password!
I've been using java on a computer (lets call it PC1) to connect to a database on a server, and until recently it was working with no errors.
By working, I mean I could connect to the server using java on PC1, and access the info I needed from the tables using select statements.
The only changes that have been made are the ip addresses on PC1 and the server.
After changing the IP addresses, I then updated the grant table in mysql, and yet, I get the following error:
java.sql.SQLException: Access denied for user 'robot'#'aa-PC' (using password: YES)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:946)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:2985)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:885)
at com.mysql.jdbc.MysqlIO.secureAuth411(MysqlIO.java:3421)
at com.mysql.jdbc.MysqlIO.doHandshake(MysqlIO.java:1247)
at com.mysql.jdbc.Connection.createNewIO(Connection.java:2775)
at com.mysql.jdbc.Connection.<init>(Connection.java:1555)
at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:285)
at java.sql.DriverManager.getConnection(DriverManager.java:664)
at java.sql.DriverManager.getConnection(DriverManager.java:247)
at WriteToMySql.connection1(WriteToMySql.java:26)
at WriteToMySql.main(WriteToMySql.java:259)
The strange part however, is that I am able to connect to the server's database using the mySQL workbench and access all data on them.
here's the java code:
String host = "jdbc:mysql://PC1IPAdress:3306/users";
String user= "robot";
String password="mypassword";
public void connect()
{
try {
Class.forName("com.mysql.jdbc.Driver");
System.out.println("worked"); //this gets printed
connect = DriverManager.getConnection(host, user, password);
System.out.println("works"); // this does not get printed due to error
stmt = connect.createStatement();
} catch (ClassNotFoundException e) {
e.printStackTrace();
} catch (SQLException e) {
e.printStackTrace();
}
}
note: "users" is the name of the database
Any help will be greatly appreciated.
Thank you.
EDIT:
for testing purposes I tried turning off the firewall, but it did not help.
I think there may be an error in the code sample - it connects to PC1IPAddress when you mention that PC1 should be connecting to a server earlier in the post. Just want to make sure before we continue that it was a typo, as otherwise PC1 would be connecting to itself.
If you have administrative access to the server, connect to MySQL as root and use this query to show configured users and ensure the host field is correct: SELECT user, host FROM mysql.user WHERE user='robot';
If the above checks out, I would suggest looking into Windows user authentication. The fact that MySQL returned the Windows computer name ('aa-PC') and not its IP address seems to indicate it may be attempting to authenticate using Windows domain credentials: http://dev.mysql.com/doc/refman/5.5/en/windows-authentication-plugin.html
If you change the ip address of the client (PC1) make sure that you updated the host field as well when granting new rights to user "robot". Check the table "db", "user" and "host".