urobo urobo - 1 month ago 21
Java Question

Class not found loading JDBC org.postgresql.Driver

I'm working on a web project and I recently installed postgres 9.1.1

The postgresql server is up and running. I can connect via psql as usual and everything is loaded and properly saved from a dump of the db I made from 8.5.

So I also downloaded the JDBC4 driver for 9.1 postgres version here:
http://jdbc.postgresql.org/download/postgresql-jdbc-9.1-901.src.tar.gz

I added it to the java build path using the project properties via eclipse.

This is the code I use to provide db connection to other classes (i.e. it's a singleton, I get a new connection only if the existing is either closed or null, from one object at a time only)

public abstract class DBConnection {
private static Connection connection = null;

public static void connect() {
try {
if (connection == null) {
String host = "127.0.0.1";
String database = "xxxxx";
String username = "xxxxx";
String password = "xxxxx";
String url = "jdbc:postgresql://" + host + "/" + database;
String driverJDBC = "org.postgresql.Driver";
Class.forName(driverJDBC);
connection = DriverManager.getConnection(url, username,
password); //line firing the class not found exception

} else if (connection.isClosed()) {
connection = null;
connect();
}
} catch (SQLException e) {
e.printStackTrace(System.err);
} catch (Exception e) {
e.printStackTrace(System.err);
}
}

public static void disconnect() {
if (connection != null) {
try {
connection.close();
} catch (SQLException e) {
Logger.getLogger(DBConnection.class.getName()).log(
Level.SEVERE, null, e);
}
}
}

public static Connection getConnection() {

try {
if (connection != null && !connection.isClosed()) {
return connection;
} else {
connect();
return connection;
}
} catch (SQLException e) {
Logger.getLogger(DBConnection.class.getName()).log(Level.SEVERE,
null, e);
return null;
}
}

@Override
public void finalize() {
if (connection != null) {
try {
connection.close();
} catch (SQLException e) {
Logger.getLogger(DBConnection.class.getName()).log(
Level.SEVERE, null, e);
}
}
}

}


As I wrote in the title when I run the project and a class asks for a connection to this class I always get a Class Not Found Exception, Since it apparently can't load the org.postgresql.Driver.class The driver is located in a subfolder of the project ~/lib/org.postgresql-9.1-901.jdbc4.jar and as I said added to the build path via eclipse project properties.

I'm also providing a sample query to let see the usual behavior of my classes to access the DBConnection:

public static final User validateUserCredentials(String id, String pswd) {
Connection connection = DBConnection.getConnection();
Logger.getLogger(Credentials.class.getName()).log(Level.SEVERE, (connection!=null)?"connection not null":"connection null");
Statement stmt = null;
Logger.getLogger(Home.class.getName()).log(Level.SEVERE, "validating credentials for user: username : " + id + " password : " + pswd);
String sql = "Select * from fuser where id = '" + id + "'";
ResultSet resultset = null;
try {
stmt = connection.createStatement();
resultset = stmt.executeQuery(sql);
Logger.getLogger(Credentials.class.getName())
.log(Level.SEVERE, sql);
resultset.next();
String password = resultset.getString("pswd");
if (pswd.equals(password))
return new User(id, pswd);
} catch (SQLException ex) {

Logger.getLogger(Credentials.class.getName()).log(Level.SEVERE,
null, ex);
} finally {
if (stmt != null)
stmt = null;

if (resultset != null)
resultset = null;
if (connection != null) {
try {
connection.close();
} catch (SQLException e) {

}
connection = null;
}
}
return null;
}

Answer

I'm working on a web project and I recently installed postgres 9.1.1

...

I added it to the java build path using the project properties via eclipse.

That's the wrong way. That JAR has to be dropped straight in /WEB-INF/lib folder of the web project without fiddling with the Build Path in the project's properties. That folder is standard part of webapp's runtime classpath.


Unrelated to the concrete problem: you've a major design flaw in your DBConnection class. You've declared Connection as static which essentially makes your connection not threadsafe. Use a connection pool and never assign the Connection (nor Statement nor ResultSet) as a class/instance variable. They should be created and closed in the very same try-finally block as where you're executing the query. Further you've there also a SQL injection hole. Use PreparedStatement instead of concatenating user-controlled variables in the SQL string.

See also: