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I'm trying to implement a TCP connection, everything works fine from the server's side but when I run the client program (from client computer) I get the following error:
java.net.ConnectException: Connection refused
at java.net.PlainSocketImpl.socketConnect(Native Method)
at java.net.PlainSocketImpl.doConnect(PlainSocketImpl.java:351)
at java.net.PlainSocketImpl.connectToAddress(PlainSocketImpl.java:213)
at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:200)
at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:432)
at java.net.Socket.connect(Socket.java:529)
at java.net.Socket.connect(Socket.java:478)
at java.net.Socket.<init>(Socket.java:375)
at java.net.Socket.<init>(Socket.java:189)
at TCPClient.main(TCPClient.java:13)
I tried changing the socket number in case it was in use but to no avail, does anyone know what is causing this error & how to fix it.
The Server Code:
//TCPServer.java
import java.io.*;
import java.net.*;
class TCPServer {
public static void main(String argv[]) throws Exception {
String fromclient;
String toclient;
ServerSocket Server = new ServerSocket(5000);
System.out.println("TCPServer Waiting for client on port 5000");
while (true) {
Socket connected = Server.accept();
System.out.println(" THE CLIENT" + " " + connected.getInetAddress()
+ ":" + connected.getPort() + " IS CONNECTED ");
BufferedReader inFromUser = new BufferedReader(
new InputStreamReader(System.in));
BufferedReader inFromClient = new BufferedReader(
new InputStreamReader(connected.getInputStream()));
PrintWriter outToClient = new PrintWriter(
connected.getOutputStream(), true);
while (true) {
System.out.println("SEND(Type Q or q to Quit):");
toclient = inFromUser.readLine();
if (toclient.equals("q") || toclient.equals("Q")) {
outToClient.println(toclient);
connected.close();
break;
} else {
outToClient.println(toclient);
}
fromclient = inFromClient.readLine();
if (fromclient.equals("q") || fromclient.equals("Q")) {
connected.close();
break;
} else {
System.out.println("RECIEVED:" + fromclient);
}
}
}
}
}
The Client Code:
//TCPClient.java
import java.io.*;
import java.net.*;
class TCPClient {
public static void main(String argv[]) throws Exception {
String FromServer;
String ToServer;
Socket clientSocket = new Socket("localhost", 5000);
BufferedReader inFromUser = new BufferedReader(new InputStreamReader(
System.in));
PrintWriter outToServer = new PrintWriter(
clientSocket.getOutputStream(), true);
BufferedReader inFromServer = new BufferedReader(new InputStreamReader(
clientSocket.getInputStream()));
while (true) {
FromServer = inFromServer.readLine();
if (FromServer.equals("q") || FromServer.equals("Q")) {
clientSocket.close();
break;
} else {
System.out.println("RECIEVED:" + FromServer);
System.out.println("SEND(Type Q or q to Quit):");
ToServer = inFromUser.readLine();
if (ToServer.equals("Q") || ToServer.equals("q")) {
outToServer.println(ToServer);
clientSocket.close();
break;
} else {
outToServer.println(ToServer);
}
}
}
}
}
This exception means that there is no service listening on the IP/port you are trying to connect to:
You are trying to connect to the wrong IP/Host or port.
You have not started your server.
Your server is not listening for connections.
On Windows servers, the listen backlog queue is full.
I would check:
Host name and port you're trying to connect to
The server side has managed to start listening correctly
There's no firewall blocking the connection
The simplest starting point is probably to try to connect manually from the client machine using telnet or Putty. If that succeeds, then the problem is in your client code. If it doesn't, you need to work out why it hasn't. Wireshark may help you on this front.
You have to connect your client socket to the remote ServerSocket. Instead of
Socket clientSocket = new Socket("localhost", 5000);
do
Socket clientSocket = new Socket(serverName, 5000);
The client must connect to serverName which should match the name or IP of the box on which your ServerSocket was instantiated (the name must be reachable from the client machine). BTW: It's not the name that is important, it's all about IP addresses...
I had the same problem, but running the Server before running the Client fixed it.
One point that I would like to add to the answers above is my experience-
"I hosted on my server on localhost and was trying to connect to it through an android emulator by specifying proper URL like http://localhost/my_api/login.php . And I was getting connection refused error"
Point to note - When I just went to browser on the PC and use the same URL (http://localhost/my_api/login.php) I was getting correct response
so the Problem in my case was the term localhost which I replaced with the IP for my server (as your server is hosted on your machine) which made it reachable from my emulator on the same PC.
To get IP for your local machine, you can use ipconfig command on cmd
you will get IPv4 something like 192.68.xx.yy
Voila ..that's your machine's IP where you have your server hosted.
use it then instead of localhost
http://192.168.72.66/my_api/login.php
Note - you won't be able to reach this private IP from any node outside this computer. (In case you need ,you can use Ngnix for that)
I had the same problem with Mqtt broker called vernemq.but solved it by adding the following.
$ sudo vmq-admin listener show
to show the list o allowed ips and ports for vernemq
$ sudo vmq-admin listener start port=1885 -a 0.0.0.0 --mountpoint /appname --nr_of_acceptors=10 --max_connections=20000
to add any ip and your new port. now u should be able to connect without any problem.
Hope it solves your problem.
Hope my experience may be useful to someone. I faced the problem with the same exception stack trace and I couldn't understand what the issue was. The Database server which I was trying to connect was running and the port was open and was accepting connections.
The issue was with internet connection. The internet connection that I was using was not allowed to connect to the corresponding server. When I changed the connection details, the issue got resolved.
In my case, I gave the socket the name of the server (in my case "raspberrypi"), and instead an IPv4 address made it, or to specify, IPv6 was broken (the name resolved to an IPv6)
In my case, I had to put a check mark near Expose daemon on tcp://localhost:2375 without TLS in docker setting (on the right side of the task bar, right click on docker, select setting)
i got this error because I closed ServerSocket inside a for loop that try to accept number of clients inside it (I did not finished accepting all clints)
so be careful where to close your Socket
I had same problem and the problem was that I was not closing socket object.After using socket.close(); problem solved.
This code works for me.
ClientDemo.java
public class ClientDemo {
public static void main(String[] args) throws UnknownHostException,
IOException {
Socket socket = new Socket("127.0.0.1", 55286);
OutputStreamWriter os = new OutputStreamWriter(socket.getOutputStream());
os.write("Santosh Karna");
os.flush();
socket.close();
}
}
and
ServerDemo.java
public class ServerDemo {
public static void main(String[] args) throws IOException {
System.out.println("server is started");
ServerSocket serverSocket= new ServerSocket(55286);
System.out.println("server is waiting");
Socket socket=serverSocket.accept();
System.out.println("Client connected");
BufferedReader reader=new BufferedReader(new InputStreamReader(socket.getInputStream()));
String str=reader.readLine();
System.out.println("Client data: "+str);
socket.close();
serverSocket.close();
}
}
I changed my DNS network and it fixed the problem
You probably didn't initialize the server or client is trying to connect to wrong ip/port.
Change local host to your ip address
localhost
//to you local ip
192.168.xxxx
I saw the same error message ""java.net.ConnectException: Connection refused" in SQuirreLSQL when it was trying to connect to a postgresql database through an ssh tunnel.
Example of opening tunel:
Example of error in Squirrel with Postgresql:
It was trying to connect to the wrong port. After entering the correct port, the process execution was successful.
See more options to fix this error at: https://stackoverflow.com/a/6876306/5857023
In my case, with server written in c# and client written in Java, I resolved it by specifying hostname as 'localhost' in the server, and '[::1]' in the client. I don't know why that is, but specifying 'localhost' in the client did not work.
Supposedly these are synonyms in many ways, but apparently, not not a 100% match. Hope it helps someone avoid a headache.
For those who are experiencing the same problem and use Spring framework, I would suggest to check an http connection provider configuration. I mean RestTemplate, WebClient, etc.
In my case there was a problem with configured RestTemplate (it's just an example):
public RestTemplate localRestTemplate() {
Proxy proxy = new Proxy(Proxy.Type.HTTP, new InetSocketAddress("localhost", <some port>));
SimpleClientHttpRequestFactory clientHttpReq = new SimpleClientHttpRequestFactory();
clientHttpReq.setProxy(proxy);
return new RestTemplate(clientHttpReq);
}
I just simplified configuration to:
public RestTemplate restTemplate() {
return new RestTemplate(new SimpleClientHttpRequestFactory());
}
And it started to work properly.
There is a service called MySQL80 that should be running to connect to the database
for windows you can access it by searching for services than look for MySQL80 service and make sure it is running
It could be that there is a previous instance of the client still running and listening on port 5000.
How do you connect to a MySQL database in Java?
When I try, I get
java.sql.SQLException: No suitable driver found for jdbc:mysql://database/table
at java.sql.DriverManager.getConnection(DriverManager.java:689)
at java.sql.DriverManager.getConnection(DriverManager.java:247)
Or
java.lang.ClassNotFoundException: com.mysql.jdbc.Driver
Or
java.lang.ClassNotFoundException: com.mysql.cj.jdbc.Driver
Here's a step by step explanation how to install MySQL and JDBC and how to use it:
Download and install the MySQL server. Just do it the usual way. Remember the port number whenever you've changed it. It's by default 3306.
Download the JDBC driver and put in classpath, extract the ZIP file and put the containing JAR file in the classpath. The vendor-specific JDBC driver is a concrete implementation of the JDBC API (tutorial here).
If you're using an IDE like Eclipse or Netbeans, then you can add it to the classpath by adding the JAR file as Library to the Build Path in project's properties.
If you're doing it "plain vanilla" in the command console, then you need to specify the path to the JAR file in the -cp or -classpath argument when executing your Java application.
java -cp .;/path/to/mysql-connector.jar com.example.YourClass
The . is just there to add the current directory to the classpath as well so that it can locate com.example.YourClass and the ; is the classpath separator as it is in Windows. In Unix and clones : should be used.
Create a database in MySQL. Let's create a database javabase. You of course want World Domination, so let's use UTF-8 as well.
CREATE DATABASE javabase DEFAULT CHARACTER SET utf8 COLLATE utf8_unicode_ci;
Create a user for Java and grant it access. Simply because using root is a bad practice.
CREATE USER 'java'#'localhost' IDENTIFIED BY 'password';
GRANT ALL ON javabase.* TO 'java'#'localhost' IDENTIFIED BY 'password';
Yes, java is the username and password is the password here.
Determine the JDBC URL. To connect the MySQL database using Java you need an JDBC URL in the following syntax:
jdbc:mysql://hostname:port/databasename
hostname: The hostname where MySQL server is installed. If it's installed at the same machine where you run the Java code, then you can just use localhost. It can also be an IP address like 127.0.0.1. If you encounter connectivity problems and using 127.0.0.1 instead of localhost solved it, then you've a problem in your network/DNS/hosts config.
port: The TCP/IP port where MySQL server listens on. This is by default 3306.
databasename: The name of the database you'd like to connect to. That's javabase.
So the final URL should look like:
jdbc:mysql://localhost:3306/javabase
Test the connection to MySQL using Java. Create a simple Java class with a main() method to test the connection.
String url = "jdbc:mysql://localhost:3306/javabase";
String username = "java";
String password = "password";
System.out.println("Connecting database...");
try (Connection connection = DriverManager.getConnection(url, username, password)) {
System.out.println("Database connected!");
} catch (SQLException e) {
throw new IllegalStateException("Cannot connect the database!", e);
}
If you get a SQLException: No suitable driver, then it means that either the JDBC driver wasn't autoloaded at all or that the JDBC URL is wrong (i.e. it wasn't recognized by any of the loaded drivers). Normally, a JDBC 4.0 driver should be autoloaded when you just drop it in runtime classpath. To exclude one and other, you can always manually load it as below:
System.out.println("Loading driver...");
try {
Class.forName("com.mysql.jdbc.Driver");
System.out.println("Driver loaded!");
} catch (ClassNotFoundException e) {
throw new IllegalStateException("Cannot find the driver in the classpath!", e);
}
Note that the newInstance() call is not needed here. It's just to fix the old and buggy org.gjt.mm.mysql.Driver. Explanation here. If this line throws ClassNotFoundException, then the JAR file containing the JDBC driver class is simply not been placed in the classpath.
Note that you don't need to load the driver everytime before connecting. Just only once during application startup is enough.
If you get a SQLException: Connection refused or Connection timed out or a MySQL specific CommunicationsException: Communications link failure, then it means that the DB isn't reachable at all. This can have one or more of the following causes:
IP address or hostname in JDBC URL is wrong.
Hostname in JDBC URL is not recognized by local DNS server.
Port number is missing or wrong in JDBC URL.
DB server is down.
DB server doesn't accept TCP/IP connections.
DB server has run out of connections.
Something in between Java and DB is blocking connections, e.g. a firewall or proxy.
To solve the one or the other, follow the following advices:
Verify and test them with ping.
Refresh DNS or use IP address in JDBC URL instead.
Verify it based on my.cnf of MySQL DB.
Start the DB.
Verify if mysqld is started without the --skip-networking option.
Restart the DB and fix your code accordingly that it closes connections in finally.
Disable firewall and/or configure firewall/proxy to allow/forward the port.
Note that closing the Connection is extremely important. If you don't close connections and keep getting a lot of them in a short time, then the database may run out of connections and your application may break. Always acquire the Connection in a try-with-resources statement. Or if you're not on Java 7 yet, explicitly close it in finally of a try-finally block. Closing in finally is just to ensure that it get closed as well in case of an exception. This also applies to Statement, PreparedStatement and ResultSet.
That was it as far the connectivity concerns. You can find here a more advanced tutorial how to load and store fullworthy Java model objects in a database with help of a basic DAO class.
Using a Singleton Pattern for the DB connection is a bad approach. See among other questions: Is it safe to use a static java.sql.Connection instance in a multithreaded system?. This is a #1 starters mistake.
DriverManager is a fairly old way of doing things. The better way is to get a DataSource, either by looking one up that your app server container already configured for you:
Context context = new InitialContext();
DataSource dataSource = (DataSource) context.lookup("java:comp/env/jdbc/myDB");
or instantiating and configuring one from your database driver directly:
MysqlDataSource dataSource = new MysqlDataSource();
dataSource.setUser("scott");
dataSource.setPassword("tiger");
dataSource.setServerName("myDBHost.example.org");
and then obtain connections from it, same as above:
Connection conn = dataSource.getConnection();
Statement stmt = conn.createStatement();
ResultSet rs = stmt.executeQuery("SELECT ID FROM USERS");
...
rs.close();
stmt.close();
conn.close();
Initialize database constants
Create constant properties database username, password, URL and drivers, polling limit etc.
// init database constants
// com.mysql.jdbc.Driver
private static final String DATABASE_DRIVER = "com.mysql.cj.jdbc.Driver";
private static final String DATABASE_URL = "jdbc:mysql://localhost:3306/database_name";
private static final String USERNAME = "root";
private static final String PASSWORD = "";
private static final String MAX_POOL = "250"; // set your own limit
Initialize Connection and Properties
Once the connection is established, it is better to store for reuse purpose.
// init connection object
private Connection connection;
// init properties object
private Properties properties;
Create Properties
The properties object hold the connection information, check if it is already set.
// create properties
private Properties getProperties() {
if (properties == null) {
properties = new Properties();
properties.setProperty("user", USERNAME);
properties.setProperty("password", PASSWORD);
properties.setProperty("MaxPooledStatements", MAX_POOL);
}
return properties;
}
Connect the Database
Now connect to database using the constants and properties initialized.
// connect database
public Connection connect() {
if (connection == null) {
try {
Class.forName(DATABASE_DRIVER);
connection = DriverManager.getConnection(DATABASE_URL, getProperties());
} catch (ClassNotFoundException | SQLException e) {
// Java 7+
e.printStackTrace();
}
}
return connection;
}
Disconnect the database
Once you are done with database operations, just close the connection.
// disconnect database
public void disconnect() {
if (connection != null) {
try {
connection.close();
connection = null;
} catch (SQLException e) {
e.printStackTrace();
}
}
}
Everything together
Use this class MysqlConnect directly after changing database_name, username and password etc.
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.Properties;
public class MysqlConnect {
// init database constants
private static final String DATABASE_DRIVER = "com.mysql.cj.jdbc.Driver";
private static final String DATABASE_URL = "jdbc:mysql://localhost:3306/database_name";
private static final String USERNAME = "root";
private static final String PASSWORD = "";
private static final String MAX_POOL = "250";
// init connection object
private Connection connection;
// init properties object
private Properties properties;
// create properties
private Properties getProperties() {
if (properties == null) {
properties = new Properties();
properties.setProperty("user", USERNAME);
properties.setProperty("password", PASSWORD);
properties.setProperty("MaxPooledStatements", MAX_POOL);
}
return properties;
}
// connect database
public Connection connect() {
if (connection == null) {
try {
Class.forName(DATABASE_DRIVER);
connection = DriverManager.getConnection(DATABASE_URL, getProperties());
} catch (ClassNotFoundException | SQLException e) {
e.printStackTrace();
}
}
return connection;
}
// disconnect database
public void disconnect() {
if (connection != null) {
try {
connection.close();
connection = null;
} catch (SQLException e) {
e.printStackTrace();
}
}
}
}
How to Use?
Initialize the database class.
// !_ note _! this is just init
// it will not create a connection
MysqlConnect mysqlConnect = new MysqlConnect();
Somewhere else in your code ...
String sql = "SELECT * FROM `stackoverflow`";
try {
PreparedStatement statement = mysqlConnect.connect().prepareStatement(sql);
... go on ...
... go on ...
... DONE ....
} catch (SQLException e) {
e.printStackTrace();
} finally {
mysqlConnect.disconnect();
}
This is all :) If anything to improve edit it! Hope this is helpful.
String url = "jdbc:mysql://127.0.0.1:3306/yourdatabase";
String user = "username";
String password = "password";
// Load the Connector/J driver
Class.forName("com.mysql.jdbc.Driver").newInstance();
// Establish connection to MySQL
Connection conn = DriverManager.getConnection(url, user, password);
Here's the very minimum you need to get data out of a MySQL database:
Class.forName("com.mysql.jdbc.Driver").newInstance();
Connection conn = DriverManager.getConnection
("jdbc:mysql://localhost:3306/foo", "root", "password");
Statement stmt = conn.createStatement();
stmt.execute("SELECT * FROM `FOO.BAR`");
stmt.close();
conn.close();
Add exception handling, configuration etc. to taste.
you need to have mysql connector jar in your classpath.
in Java JDBC API makes everything with databases. using JDBC we can write Java applications to
1. Send queries or update SQL to DB(any relational Database)
2. Retrieve and process the results from DB
with below three steps we can able to retrieve data from any Database
Connection con = DriverManager.getConnection(
"jdbc:myDriver:DatabaseName",
dBuserName,
dBuserPassword);
Statement stmt = con.createStatement();
ResultSet rs = stmt.executeQuery("SELECT a, b, c FROM Table");
while (rs.next()) {
int x = rs.getInt("a");
String s = rs.getString("b");
float f = rs.getFloat("c");
}
You can see all steps to connect MySQL database from Java application here. For other database, you just need to change the driver in first step only. Please make sure that you provide right path to database and correct username and password.
Visit http://apekshit.com/t/51/Steps-to-connect-Database-using-JAVA
MySQL JDBC Connection with useSSL.
private String db_server = BaseMethods.getSystemData("db_server");
private String db_user = BaseMethods.getSystemData("db_user");
private String db_password = BaseMethods.getSystemData("db_password");
private String connectToDb() throws Exception {
String jdbcDriver = "com.mysql.jdbc.Driver";
String dbUrl = "jdbc:mysql://" + db_server +
"?verifyServerCertificate=false" +
"&useSSL=true" +
"&requireSSL=true";
System.setProperty(jdbcDriver, "");
Class.forName(jdbcDriver).newInstance();
Connection conn = DriverManager.getConnection(dbUrl, db_user, db_password);
Statement statement = conn.createStatement();
String query = "SELECT EXTERNAL_ID FROM offer_letter where ID =" + "\"" + letterID + "\"";
ResultSet resultSet = statement.executeQuery(query);
resultSet.next();
return resultSet.getString(1);
}
Short and Sweet code.
try {
Class.forName("com.mysql.jdbc.Driver");
System.out.println("Driver Loaded");
conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/testDB","root","");
//Database Name - testDB, Username - "root", Password - ""
System.out.println("Connected...");
} catch(Exception e) {
e.printStackTrace();
}
For SQL server 2012
try {
String url = "jdbc:sqlserver://KHILAN:1433;databaseName=testDB;user=Khilan;password=Tuxedo123";
//KHILAN is Host and 1433 is port number
Class.forName("com.microsoft.sqlserver.jdbc.SQLServerDriver");
System.out.println("Driver Loaded");
conn = DriverManager.getConnection(url);
System.out.println("Connected...");
} catch(Exception e) {
e.printStackTrace();
}
Connection I was using some time ago, it was looking like the easiest way, but also there were recommendation to make there if statement- exactly
Connection con = DriverManager.getConnection(
"jdbc:myDriver:DatabaseName",
dBuserName,
dBuserPassword);
if (con != null){
//..handle your code there
}
Or something like in that way :)
Probably there's some case, while getConnection can return null :)
HOW
To set up the Driver to run a quick sample
1. Go to https://dev.mysql.com/downloads/connector/j/, get the latest version of Connector/J
2. Remember to set the classpath to include the path of the connector jar file.
If we don't set it correctly, below errors can occur:
No suitable driver found for jdbc:mysql://127.0.0.1:3306/msystem_development
java.lang.ClassNotFoundException: com.mysql.jdbc:Driver
To set up the CLASSPATH
Method 1: set the CLASSPATH variable.
export CLASSPATH=".:mysql-connector-java-VERSION.jar"
java MyClassFile
In the above command, I have set the CLASSPATH to the current folder and mysql-connector-java-VERSION.jar file. So when the java MyClassFile command executed, java application launcher will try to load all the Java class in CLASSPATH.
And it found the Drive class => BOOM errors was gone.
Method 2:
java -cp .:mysql-connector-java-VERSION.jar MyClassFile
Note: Class.forName("com.mysql.jdbc.Driver"); This is deprecated at this moment 2019 Apr.
Hope this can help someone!
MySql JDBC Connection:
Class.forName("com.mysql.jdbc.Driver");
Connection con=DriverManager.getConnection("jdbc:mysql://localhost:3306/DatabaseName","Username","Password");
Statement stmt=con.createStatement();
stmt = con.createStatement();
ResultSet rs=stmt.executeQuery("Select * from Table");
Short Code
public class DB {
public static Connection c;
public static Connection getConnection() throws Exception {
if (c == null) {
Class.forName("com.mysql.jdbc.Driver");
c =DriverManager.getConnection("jdbc:mysql://localhost:3306/DATABASE", "USERNAME", "Password");
}
return c;
}
// Send data TO Database
public static void setData(String sql) throws Exception {
DB.getConnection().createStatement().executeUpdate(sql);
}
// Get Data From Database
public static ResultSet getData(String sql) throws Exception {
ResultSet rs = DB.getConnection().createStatement().executeQuery(sql);
return rs;
}
}
Download JDBC Driver
Download link (Select platform independent): https://dev.mysql.com/downloads/connector/j/
Move JDBC Driver to C Drive
Unzip the files and move to C:\ drive. Your driver path should be like C:\mysql-connector-java-8.0.19\mysql-connector-java-8.0.19
Run Your Java
java -cp "C:\mysql-connector-java-8.0.19\mysql-connector-java-8.0.19\mysql-connector-java-8.0.19.jar" testMySQL.java
testMySQL.java
import java.sql.*;
import java.io.*;
public class testMySQL {
public static void main(String[] args) {
// TODO Auto-generated method stub
try
{
Class.forName("com.mysql.cj.jdbc.Driver");
Connection con=DriverManager.getConnection(
"jdbc:mysql://localhost:3306/db?useSSL=false&useUnicode=true&useJDBCCompliantTimezoneShift=true&useLegacyDatetimeCode=false&serverTimezone=UTC","root","");
Statement stmt=con.createStatement();
ResultSet rs=stmt.executeQuery("show databases;");
System.out.println("Connected");
}
catch(Exception e)
{
System.out.println(e);
}
}
}
I'm building a desktop app that needs to communicate with a MS Access database. Now, unless I want to register the DSN for the database on every computer that's going to use the desktop app, I need a way to connect to the database in a DSN-less fashion.
I've searched alot and found some useful links on how to create connection strings and based on that I tried modifying my program based on that but without success.
The code below fails. If i switch the string in the getConnection to "jdbc:odbc:sampleDB" it works, but that's using DSN and not what I want to achieve.
How do I write and use a connection string in java to make a DSN-less connection to a MS Access database?
private Connection setupConnection() throws ClassNotFoundException,
SQLException {
Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
Connection con = DriverManager.getConnection("Driver={Microsoft Access Driver (*.mdb)} &_ Dbq=c:\\as\\sampleDB.mdb");
return con;
}
Addition: I'd also like to point out that if anyone has an idea of a way to achieve what I asked for WITH a DSN-connection I'll gladly listen to it!
JDBC connection string shouls start with jdbc: like:
jdbc:odbc:Driver={Microsoft Access Driver (*.mdb)};DBQ=c:\\Nwind.mdb
so try with:
Connection con = DriverManager.getConnection("jdbc:odbc:Driver={Microsoft Access Driver (*.mdb)};Dbq=c:\\as\\sampleDB.mdb");
If you configure DSN then you can connect to it using simplier connect string: jdbc:odbc:[alias], example:
jdbc:odbc:northwind
I also had this problem and tried many of the suggestions here and on various forums. Finally, I discovered a snippet from one place which led to success connecting and also explains why many of these posts do not work. See http://www.coderanch.com/t/295299/JDBC/databases/jdbc-odbc-DSN-connection-MS
The issue is that there must be a semicolon after the colon at the end of odbc as in jdbc:odbc:;Driver= . This made sense after reading the Oracle documentation on the JdbcOdbc bridge which states that the syntax is jdbc:odbc:dsn; attributes....... Since we are not supplying a DSN, then we need to end with ; before adding attributes.
I am showing below the tests I ran with different connection strings on a Windows 7 Ultimate 32bit machine:
driver= (Driver)Class.forName("sun.jdbc.odbc.JdbcOdbcDriver").newInstance();
//jdbc:odbc:Driver={Microsoft Access Driver (*.mdb, *.accdb)};DBQ= does lookup to ODBC.ini to find matching driver
try {
connstr= "jdbc:odbc:;Driver={Microsoft Access Driver (*.mdb, *.accdb)};DBQ=" + fileURI; //64 bit ?? (*.mdb,*.accdb)
conn= DriverManager.getConnection(connstr, "", "");
stmt= conn.createStatement();
}
catch (Exception e){}
try {
connstr= "jdbc:odbc:;Driver={Microsoft Access Driver (*.mdb)};DBQ=" + fileURI; //64 bit ?? (*.mdb,*.accdb)
conn1= DriverManager.getConnection(connstr, "", "");
stmt1= conn1.createStatement();
dbmeta1=conn1.getMetaData();
}
catch (Exception e){}
try {
connstr= "jdbc:odbc:MS Access Database;DBQ=" + fileURI; //64 bit ?? (*.mdb,*.accdb)
conn2= DriverManager.getConnection(connstr, "", "");
stmt2= conn2.createStatement();
dbmeta2=conn2.getMetaData();
}
catch (Exception e){}
try {
connstr= "jdbc:odbc:Driver={Microsoft Access Driver (*.mdb)};DBQ=" + fileURI; //64 bit ?? (*.mdb,*.accdb)
conn3= DriverManager.getConnection(connstr, "", "");
stmt3= conn3.createStatement();
dbmeta3=conn3.getMetaData();
}
catch (Exception e){}
stmt1 and stmt3 are null since the connections are null. stmt and stmt2 work. stmt2 uses a connection string I found in the documentation for IBM Tivoli. It works because "MS Access Database" is a valid title in the ODBC registry as a User DSN on my computer.
I am having some problems with getting my OSGI programs to recognzie/utilize the mysql jdbc driver.
I have a bundle that is speficcally for entering data into a mysql database. I have copied over all the same methods as in a test program (non-OSGI). I am not able to create a connection suing DriverManager.getConnection().
I have added the driver to the class path andhave tried all the solutions on this site such as using Class.forName(). Possibly I am inputting the wrong string arg into forName().
public void createConn(String URL, String DBName, String username, String password){
try {
Class.forName("mysql-connector-java-5.1.14-bin.jar");
} catch (ClassNotFoundException e1) {
e1.printStackTrace();
}
try {
conn = DriverManager.getConnection(URL + DBName,username,password);
System.out.println("Connection Created");
stmt = conn.createStatement();
System.out.println("Statement Created");
//data = new ApplianceData();
//flag = true;
//this.writeThread = new Thread();
//writeThread.start();
} catch (SQLException e) {
System.err.println(e.getMessage());
}
}
Can someone tell me the argument they used in Class.forName();
Does anybody have a solution to this problem or encountered this?
Thanks, that took care of the classNotFound Exception. Now I have an error stating that the driver is not suitable. I know OSGI has some issues with drivers etc. Can someone recommend a way to circumvent this?
I have placed the jdbc jar in the java installation bin folders, and in the bin folder of the bundle.
ClassLoader DBHCL = ClassLoader.getSystemClassLoader();
DBHCL.loadClass("com.mysql.jdbc.Driver");
Class.forName("com.mysql.jdbc.Driver", true, DBHCL).newInstance();
System.out.println("Class Loaded");
//DriverManager.getDriver("jdbc:mysql://localhost/timedb");
//System.out.println("Driver Gotten");
conn = DriverManager.getConnection(URL + DBName,username,password);
System.out.println("Connection Created");
stmt = conn.createStatement();
System.out.println("Statement Created");
connFlag = true;
Console Output, Error:
osgi> start 7
Data Base Service (MYSQL) Starting
Class Loaded
No suitable driver found for jdbc:mysql://localhost/timedb
Exception in thread "Thread-1" INSERT INTO appliance1...
Does anybody have any insight into this problem?
Thanks
Class.forName(String) takes a fully qualified class name, not a jar file. You should use something like
Class.forName("com.mysql.jdbc.Driver");
i know this has 3 years but i'm answering just in case someone googles it.
so the problem is that the bundle does not see the jar from the classloade, so you need to import its packages in the manifest.
the way i did, is i created a separate bundle containing mysql connector jar.
newProject> plugin from existing jar; then i added all of its packages to "exported packages" in its manifest file. Then in my first bundle i added all the packages of the connector to "imported packages" and it worked.
I am new to JDBC and I am trying to make a connection to a MySQL database.
I am using Connector/J driver, but I cant find the JDBC connection string for my Class.forName() method.
Assuming your driver is in path,
String url = "jdbc:mysql://localhost/test";
Class.forName ("com.mysql.jdbc.Driver").newInstance ();
Connection conn = DriverManager.getConnection (url, "username", "password");
Here's the documentation:
https://dev.mysql.com/doc/connector-j/en/connector-j-reference-configuration-properties.html
A basic connection string looks like:
jdbc:mysql://localhost:3306/dbname
The class.forName string is "com.mysql.jdbc.Driver", which you can find (edit: now on the same page).
"jdbc:mysql://localhost"
From the oracle docs..
jdbc:mysql://[host][,failoverhost...]
[:port]/[database]
[?propertyName1][=propertyValue1]
[&propertyName2][=propertyValue2]
host:port is the host name and port number of the computer hosting your database. If not specified, the default values of host and port are 127.0.0.1 and 3306, respectively.
database is the name of the database to connect to. If not specified, a connection is made with no default database.
failover is the name of a standby database (MySQL Connector/J supports failover).
propertyName=propertyValue represents an optional, ampersand-separated list of properties. These attributes enable you to instruct MySQL Connector/J to perform various tasks.
It is very simple :
Go to MySQL workbench and lookup for Database > Manage Connections
you will see a list of connections. Click on the connection you wish to connect to.
You will see a tabs around connection, remote management, system profile. Click on connection tab.
your url is jdbc:mysql://<hostname>:<port>/<dbname>?prop1 etc.
where <hostname> and <port> are given in the connection tab.It will mostly be localhost : 3306. <dbname> will be found under System Profile tab in Windows Service Name. Default will mostly be MySQL5<x> where x is the version number eg. 56 for MySQL5.6 and 55 for MySQL5.5 etc.You can specify ur own Windows Service name to connect too.
Construct the url accordingly and set the url to connect.
For Mysql, the jdbc Driver connection string is com.mysql.jdbc.Driver. Use the following code to get connected:-
class DBConnection {
private static Connection con = null;
private static String USERNAME = "your_mysql_username";
private static String PASSWORD = "your_mysql_password";
private static String DRIVER = "com.mysql.jdbc.Driver";
private static String URL = "jdbc:mysql://localhost:3306/database_name";
public static Connection getDatabaseConnection(){
Class.forName(DRIVER);
return con = DriverManager.getConnection(URL,USERNAME,PASSWORD);
}
}
As the answer seems already been answered, there is not much to add but I would like to add one thing to the existing answers.
This was the way of loading class for JDBC driver for mysql
com.mysql.jdbc.Driver
But this is deprecated now. The new driver class is now
com.mysql.cj.jdbc.Driver
Also the driver is automatically registered via the SPI and manual loading of the driver class is generally unnecessary.
update for mySQL 8 :
String jdbcUrl="jdbc:mysql://localhost:3306/youdatabase?useSSL=false&serverTimezone=UTC";
Here is a little code from my side :)
needed driver:
com.mysql.jdbc.Driver
download: here (Platform Independent)
connection string in one line:
jdbc:mysql://localhost:3306/db-name?user=user_name&password=db_password&useSSL=false
example code:
public static void testDB(){
try {
Class.forName("com.mysql.jdbc.Driver");
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
try {
Connection connection = DriverManager.getConnection(
"jdbc:mysql://localhost:3306/db-name?user=user_name&password=db_password&useSSL=false");
if (connection != null) {
Statement statement = connection.createStatement();
if (statement != null) {
ResultSet resultSet = statement.executeQuery("select * from test");
if (resultSet != null) {
ResultSetMetaData meta = resultSet.getMetaData();
int length = meta.getColumnCount();
while(resultSet.next())
{
for(int i = 1; i <= length; i++){
System.out.println(meta.getColumnName(i) + ": " + resultSet.getString(meta.getColumnName(i)));
}
}
resultSet.close();
}
statement.close();
}
connection.close();
}
} catch (Throwable throwable) {
throwable.printStackTrace();
}
}
update for mySQL 8 :
String jdbcUrl="jdbc:mysql://localhost:3306/youdatabase?useSSL=false&serverTimezone=UTC";
Check whether your Jdbc configurations and URL correct or wrong using the following code snippet.
import java.sql.Connection;
import java.sql.DriverManager;
public class TestJdbc {
public static void main(String[] args) {
//db name:testdb_version001
//useSSL=false (get rid of MySQL SSL warnings)
String jdbcUrl = "jdbc:mysql://localhost:3306/testdb_version001?useSSL=false";
String username="testdb";
String password ="testdb";
try{
System.out.println("Connecting to database :" +jdbcUrl);
Connection myConn =
DriverManager.getConnection(jdbcUrl,username,password);
System.out.println("Connection Successful...!");
}catch (Exception e){
e.printStackTrace();
//e.printStackTrace();
}
}
}
The method Class.forName() is used to register the JDBC driver. A connection string is used to retrieve the connection to the database.
The way to retrieve the connection to the database is shown below. Ideally since you do not want to create multiple connections to the database, limit the connections to one and re-use the same connection. Therefore use the singleton pattern here when handling connections to the database.
Shown Below shows a connection string with the retrieval of the connection:
public class Database {
private String URL = "jdbc:mysql://localhost:3306/your_db_name"; //database url
private String username = ""; //database username
private String password = ""; //database password
private static Database theDatabase = new Database();
private Connection theConnection;
private Database(){
try{
Class.forName("com.mysql.jdbc.Driver"); //setting classname of JDBC Driver
this.theConnection = DriverManager.getConnection(URL, username, password);
} catch(Exception ex){
System.out.println("Error Connecting to Database: "+ex);
}
}
public static Database getDatabaseInstance(){
return theDatabase;
}
public Connection getTheConnectionObject(){
return theConnection;
}
}
String url = "jdbc:mysql://localhost:3306/dbname";
String user = "user";
String pass = "pass";
Class.forName ("com.mysql.jdbc.Driver").newInstance ();
Connection conn = DriverManager.getConnection (url, user, pass);
3306 is the default port for mysql.
If you are using Java 7 then there is no need to even add the Class.forName("com.mysql.jdbc.Driver").newInstance (); statement.Automatic Resource Management (ARM) is added in JDBC 4.1 which comes by default in Java 7.
The general format for a JDBC URL for connecting to a MySQL server is as follows, with items in square brackets ([ ]) being optional:
jdbc:mysql://[host1][:port1][,[host2][:port2]]...[/[database]] ยป
[?propertyName1=propertyValue1[&propertyName2=propertyValue2]...]
protocol//[hosts][/database][?properties]
If you don't have any properties ignore it then it will be like
jdbc:mysql://127.0.0.1:3306/test
jdbc:mysql is the protocol
127.0.0.1: is the host and 3306 is the port number
test is the database
it's depends on what service you're using.
if you use MySQL Workbench it wold be some thing like this :
jdbc:mysql://"host":"port number"/
String url = "jdbc:mysql://localhost:3306/";
And of course it will be different if you using SSL/SSH.
For more information follow the official link of Jetbriens (intelliJ idea) :
Connecting to a database #
https://www.jetbrains.com/help/idea/connecting-to-a-database.html
Configuring database connections #
https://www.jetbrains.com/help/idea/configuring-database-connections.html
Check if the Driver Connector jar matches the SQL version.
I was also getting the same error as I was using the
mySQl-connector-java-5.1.30.jar
with MySql 8