Why does runtime loaded MySQL driver output "No suitable driver found"? - java

I tried to load MySQL driver when my application is running. So I made jar file loading method as "loadJobJars" to that be creating URLClassLoader object with given jar file list. And I was call Class.forName method and then DriverManager.getConnection method. But it was output "No suitable driver found" on terminal.
Is there anyone know why this be happened?
My code is below.
public DBConnectionManager(Path jarPath) throws MalformedURLException {
this.urlClassLoader = loadJobJars(listJarFiles(jarPath));
}
public Connection createConnection(String dbName, String host, int port, String db, String user,
String password) throws NoSuchFieldException, SecurityException, IllegalArgumentException,
IllegalAccessException, ClassNotFoundException, SQLException, InstantiationException {
dbName = dbName.toLowerCase();
String url = "jdbc:" + dbName + "://" + host + ":" + port + "/" + db;
String driverName = DBDriver.getDriverName(dbName.toUpperCase());
Logger.getInstance().info("connection url: "+url+" driver: "+driverName);
Class.forName(driverName, true, this.urlClassLoader);
Connection conn = DriverManager.getConnection(url, user, password); //Here is it was happened code line.
return conn;
}
public URLClassLoader loadJobJars(File[] jarFiles) throws MalformedURLException {
URL[] urls = Arrays.asList(jarFiles).stream().map(f -> {
try {
System.out.println(f.getAbsolutePath());
return f.toURI().toURL();
} catch (MalformedURLException e) {
e.printStackTrace();
}
return null;
}).filter(u -> u != null).toArray(URL[]::new);
return URLClassLoader.newInstance(urls, ClassLoader.getPlatformClassLoader());
}
public File[] listJarFiles(Path jarPath) {
return jarPath.toFile().listFiles(new FilenameFilter() {
#Override
public boolean accept(File dir, String name) {
return name.endsWith(".jar");
}
});
}
Console output is below.
[INFO][DBConnectionManager:77][20210119152004] connection url: jdbc:mysql://localhost:3306/mysql driver: com.mysql.jdbc.Driver
Exception in thread "main" java.sql.SQLException: No suitable driver found for jdbc:mysql://192.168.1.157:3306/mysql
at java.sql/java.sql.DriverManager.getConnection(DriverManager.java:702)
at java.sql/java.sql.DriverManager.getConnection(DriverManager.java:251)
at com.innotree.innoquartz.iqjobgen.DBConnectionManager.createConnection(DBConnectionManager.java:35)
at com.innotree.innoquartz.iqjobgen.DBConnectionManager.main(DBConnectionManager.java:77)

The way DriverManager creates connections is sensitive to the class loader of the calling code. The Driver used to create the connection must be visible to the class loader of the calling class (or when the calling code has no class loader, the context class loader). The driver you loaded is not visible to the class loader of the calling code, so DriverManager will not use the driver to create a connection.
You must create the connection using code that uses the same class loader (or at least where the class loader with the driver is visible). Alternatively, you need to use the java.sql.Driver directly, skipping DriverManager altogether.

Thank for your kind answer.
I saw your answer and finally figure out the problem by direct loading MySQL driver. Your help was very useful to solve that. Solution code is down below.
String url = "jdbc:mysql://localhost:3306/mysql";
URLClassLoader loader = new URLClassLoader(urls, ClassLoader.getSystemClassLoader());
Class cls = loader.loadClass("com.mysql.jdbc.Driver");
Driver driver = (Driver)cls.newInstance();
Properties info = new Properties();
info.put("user", "admin");
info.put("password", "1234");
Connection conn = driver.connect(url, info);

Related

java.sql.SQLException: No suitable driver found for jdbc://localhost:3306/twitch

I was trying to connect to MySQL "twitch" database using java with this code below:
import java.sql.*;
public class App {
public static void main(String[] args) throws Exception {
try {
Class.forName("com.mysql.jdbc.Driver");
//Class.forName("com.mysql.cj.jdbc.Driver");
String url = "jdbc://localhost:3306/twitch";
String username = "root";
String pass = "nfreal-yt10";
Connection con=DriverManager.getConnection(url,username,pass);
Statement stmt=con.createStatement();
ResultSet rs=stmt.executeQuery("select distinct creator_id from twitch.information where creator_id > 40;");
while (rs.next()) {
System.out.println(rs.getString(1));
}
con.close();
}
catch(Exception e) {
System.out.println(e);
}
}
}
when I executed the code my console throws (Full error):
Loading class `com.mysql.jdbc.Driver'.
This is deprecated. The new driver class is `com.mysql.cj.jdbc.Driver'. The driver is automatically registered via the SPI and manual loading of the driver
class is generally unnecessary.
java.sql.SQLException: No suitable driver found for jdbc://localhost:3306/twitch
I have added MySQL connector on my directory folder and all stuff which required to be added, yet the error still occurred, why?
When you communicate with your database (located at /localhost:3306/twitch), you must precise the protocol used (eg. your browser use http or https protocol followed with the adress).
JDBC is a driver that can interface with MySQL, but can't directly access to your database. Hence your URL should be:
String url = "jdbc:mysql://localhost:3306/twitch";
EDIT : Class.forName("com.mysql.cj.jdbc.Driver"); is no more needed in general. Details here.

Setting up a remote Derby DB: "No suitable driver found" error

I am trying to set up a remote Derby database just for practice. The following code works without a problem whenever I access the DB on my harddrive:
class Test{
public static void main(String[] args) {
String protocol = "jdbc:derby:";
// String dbPath = "C:/Java_Practice/derbyDB"; // this dbPath works...
String dbPath = "//108.167.141.127/derbyDB"; // and this one doesn't
String url = protocol + dbPath;
try( Connection conn = DriverManager.getConnection(url) )
{
System.out.println(conn);
}
catch(SQLException e){
System.out.println(e.getMessage());
}
}
}
I then uploaded the whole derbyDB directory to my Hostgator-hosted website, obtained its IP by pinging the server and edited the dbPath var accordingly. The code stopped working as if it can't even see the DB. What am I missing?
Looks like your driver class not loaded.
Try loading it before calling DriverManager.getConnection, and see if it works.
String driver = "org.apache.derby.jdbc.ClientDriver";
Class.forName(driver).newInstance();
String protocol = "jdbc:derby:";
String dbPath = "//108.167.141.127/derbyDB"+";create=true";
String url = protocol + dbPath;
Connection conn = DriverManager.getConnection(url);
Answering my own question after some digging.
This is what I found in the official Apache Derby documentation (https://db.apache.org/derby/docs/10.0/manuals/develop/develop14.html):
You can specify only databases that are local to the machine on which
the JVM is running.
Looks like what I wanted to accomplish cannot be done...

Still getting ClassNotFoundException with com.mysql.jdbc.Driver [duplicate]

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);
}
}
}

Loading jars at runtime

I am trying to add jar file to classpath at runtime. I use this code
public static void addURL(URL u) throws IOException {
URLClassLoader sysloader = (URLClassLoader) ClassLoader
.getSystemClassLoader();
Class<URLClassLoader> sysclass = URLClassLoader.class;
try {
Method method = sysclass.getDeclaredMethod("addURL", parameters);
method.setAccessible(true);
method.invoke(sysloader, new Object[] { u });
System.out.println(u);
} catch (Throwable t) {
t.printStackTrace();
throw new IOException("Error");
}
}
System out prints this url:
file:/B:/Java/Tools/mysql-connector-java-5.1.18/mysql-connector-java-5.1.18/mysql-connector-java-5.1.18-bin.jar
I was check this path carefully, this jar exist. Even this test show that com.mysql.jdbc.
Driver class exists.
javap -classpath "B:\Java\Tools\mysql-connector-java-5.1.18\
mysql-connector-java-5.1.18\mysql-connector-java-5.1.18-bin.jar" com.mysql.jdbc.
Driver
Compiled from "Driver.java"
public class com.mysql.jdbc.Driver extends com.mysql.jdbc.NonRegisteringDriver i
mplements java.sql.Driver{
public com.mysql.jdbc.Driver() throws java.sql.SQLException;
static {};
}
But I still get java.lang.ClassNotFoundException when I use this Class.forName(driver).
What is wrong with this code?
The URL is ok, nevertheless you try to load a jar from classpath, so it means that yo need to have the file in cp first.
In your case you want to load a jar that is not in classpath so you have to use
URLClassLoader and for JAR you can use also the JARClassLoader
If you want some sample lesson on it:
http://docs.oracle.com/javase/tutorial/deployment/jar/jarclassloader.html
Here a sample I ran by myself see if helps you. It search the Logger class of Log4j that is not in my classpath, of course i got exception on invocation of the constructor since i did not pass the right params to the constructor
package org.stackoverflow;
import java.io.File;
import java.net.URL;
import java.net.URLClassLoader;
public class URLClassLoaderSample
{
public static void main(String[] args) throws Exception
{
File f = new File("C:\\_programs\\apache\\log4j\\v1.1.16\\log4j-1.2.16.jar");
URLClassLoader urlCl = new URLClassLoader(new URL[] { f.toURL()},System.class.getClassLoader());
Class log4jClass = urlCl.loadClass("org.apache.log4j.Logger");
log4jClass.newInstance();
}
}
Exception in thread "main" java.lang.InstantiationException: org.apache.log4j.Logger
at java.lang.Class.newInstance0(Class.java:357)
at java.lang.Class.newInstance(Class.java:325)
at org.stackoverflow.URLClassLoaderSample.main(URLClassLoaderSample.java:19)
Exception due to the wrong invocation, nevertheless at this stage we already found the class
Ok try the alternative approach with DataSource and not directly the Driver
Below is the code (working with oracle driver, i don't have my sql db, but the properties are the same)
Generally using the DataSource interface is the preferred approach since JDBC 2.0
The DataSource jar was not in the classpath neither for the test below
public static void urlCLSample2() throws Exception
{
File f = new File("C:\\_programs\\jdbc_drivers\\oracle\\v11.2\\ojdbc6.jar");
URLClassLoader urlCl = new URLClassLoader(new URL[] { f.toURL() }, System.class.getClassLoader());
// replace the data source class with MySQL data source class.
Class dsClass = urlCl.loadClass("oracle.jdbc.pool.OracleDataSource");
DataSource ds = (DataSource) dsClass.newInstance();
invokeProperty(dsClass, ds, "setServerName", String.class, "<put your server here>");
invokeProperty(dsClass, ds, "setDatabaseName", String.class, "<put your db instance here>");
invokeProperty(dsClass, ds, "setPortNumber", int.class, <put your port here>);
invokeProperty(dsClass, ds, "setDriverType",String.class, "thin");
ds.getConnection("<put your username here>", "<put your username password here>");
System.out.println("Got Connection");
}
// Helper method to invoke properties
private static void invokeProperty(Class dsClass, DataSource ds, String propertyName, Class paramClass,
Object paramValue) throws Exception
{
try
{
Method method = dsClass.getDeclaredMethod(propertyName, paramClass);
method.setAccessible(true);
method.invoke(ds, paramValue);
}
catch (Exception e)
{
throw new Exception("Failed to invoke method");
}
}

Loading JDBC Driver at Runtime

I'm using the following code to load a driver class:
public class DriverLoader extends URLClassLoader {
private DriverLoader(URL[] urls) {
super(urls);
File driverFolder = new File("driver");
File[] files = driverFolder.listFiles();
for (File file : files) {
try {
addURL(file.toURI().toURL());
} catch (MalformedURLException e) {
}
}
}
private static DriverLoader driverLoader;
public static void load(String driverClassName) throws ClassNotFoundException {
try {
Class.forName(driverClassName);
} catch (ClassNotFoundException ex) {
if (driverLoader == null) {
URL urls[] = {};
driverLoader = new DriverLoader(urls);
}
driverLoader.loadClass(driverClassName);
}
}
}
Although the class loads fine I can't establish a Database connection (No suitable driver found for ...) no matter which driver I try.
I assume this is because I'm not loading the driver class using Class.forName (which wouldn't work since I'm using my own ClassLoader). How can I fix this?
You need to create an instance of the driver class before you can connect:
Class drvClass = driverLoader.loadClass(driverClassName);
Driver driver = drvClass.newInstance();
Once you have the instance you can either use that instance to connect:
Properties props = new Properties();
props.put("user", "your_db_username");
props.put("password", "your_db_password");
Connection con = driver.connect("jdbc:postgresql:...", props);
As an alternative, if you want to keep using DriverManager you must register the driver with the DriverManager manually:
DriverManager.registerDriver(driver);
Then you should be able to use the DriverManager to establis a connection.
If I recall it correctly there was a problem with the DriverManager refusing to connect if the driver itself was not loaded by the same classloader as the DriverManager. If that (still) is the case, you need to use Driver.connect() directly.
You should establish connection in a class loaded by your DriverLoader. So, load the connection establishment code using DriverLoader and then call JDBC from it.
You need to add a Classpath reference in the manifest. Follow these simple steps:
add a folder "lib" to your application
place "mysql-connector-java-5.1.18-bin" in lib
now open your "MANIFEST.MF" and go to tab "RUNTIME"
on bottom right, you would see "classpath" ; click "Add"
now add the folder lib [created in step 1] along with the jar file
in this way, whenever a runtime EclipseApplication /OSGi Application is started this jar file is exported along too. So the connectivity would then be available there too.

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