Why do I get ClassNotFoundException when I call it from outside class?

Question

Below is the code that works perfectly fine when it is executed from main (ie in eclipse RunAs java application). However if I call Statement getStatement from outside ( meaning a servlet calling it via a put ) in the same package I get java.lang.ClassNotFoundException: com.mysql.jdbc.Driver. Any pointers to why ?

public class DBConnectivity {

    private static Statement getStatement(String username, String password) throws SQLException, ClassNotFoundException {
        Properties prop = new Properties();
        prop.put("user", "root");
        prop.put("password", "password");

        Class.forName("com.mysql.jdbc.Driver");

        Connection conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/keeptrack", prop);
        Statement stmt = conn.createStatement();

        return stmt;
    }

    public void put(String username, String password, String table,
            String name, String exercise, String wsj, String food)
            throws SQLException, ClassNotFoundException {
        Statement stmt = getStatement(username, password);
        // checkIfTableExists(stmt, table);     
        stmt.executeUpdate(
                "insert into " + table +
                " " +
                "values(\'" + name + "\', \'" +  exercise + "\', \'" + wsj + "\', \'" + food + "\')");
    }   


    public List<String> get(String username, String password, String table)
            throws SQLException, ClassNotFoundException {
        Statement stmt = getStatement(username, password);
        //checkIfTableExists(stmt, table);      
        ResultSet rs = stmt.executeQuery("select FOOD from " + table);

        List<String> foodData = new ArrayList<String>();

        while(rs.next()) {
            String output = rs.getString("FOOD");
            foodData.add(output);
        //  System.out.println("wohoo: " + output);
        }

        return foodData;
    }   

    public static void main(String[] args) throws SQLException, ClassNotFoundException {
        DBConnectivity conn = new DBConnectivity();
        conn.put("root", "password", "trackTable", "D", "B", "C", "D");
        conn.get("root", "password", "trackTable");
    }
}

Here is the servlet which calls the database:

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String username = request.getParameter("firstname");
        String password = request.getParameter("lastname");
        String firstname  = username;
        String exercise = request.getParameter("exerise");
        String wsj = request.getParameter("wsj");
        String food = request.getParameter("food");


        try {
            new DBConnectivity().put(username, password, "trackTable", firstname, exercise, wsj, food);
        } catch (ClassNotFoundException | SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

The new DBConnectivity().put call results in ClassNotFoundException.

Stack trace is :

java.lang.ClassNotFoundException: com.mysql.jdbc.Driver
at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1295)
at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1147)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:190)
at org.ameya.dynasty.DBConnectivity.getStatement(DBConnectivity.java:27)
at org.ameya.dynasty.DBConnectivity.get(DBConnectivity.java:63)
at org.ameya.dynasty.ServletIndex.doGet(ServletIndex.java:39)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:618)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:725)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:291)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:219)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:501)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:142)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:610)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:537)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1085)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:658)
at org.apache.coyote.http11.Http11NioProtocol$Http11ConnectionHandler.process(Http11NioProtocol.java:222)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1556)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1513)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:744)

I notice it's `private`, how do you call `getStatement` outside the class? — Elliott Frisch, Dec 03 '14 at 08:08
`private` means exactly that: you cannot use it outside the class — vefthym, Dec 03 '14 at 08:09
`however if I call Statement getStatement from outside ` you said . what do you mean by that? — Secondo, Dec 03 '14 at 08:13
Your code leaks `Connection` instances when `getStatement` is invoked. There are lots of good and free connection pools. I strongly urge that you use one. — Elliott Frisch, Dec 03 '14 at 08:14
@javadeveloper Try to use Singleton Pattern. for you to be sure that only one instance is created. — Secondo, Dec 03 '14 at 08:15
Can you post exception stack trace. You should not get 'ClassNotFoundException' unless the jar is not available. — janasainik, Dec 03 '14 at 08:17

score 4 · Accepted Answer · answered Dec 03 '14 at 08:29

Your error:

java.lang.ClassNotFoundException: com.mysql.jdbc.Driver

If it works running from Eclipse, that means you have the MySql jdbc dirver jar in the classpath of your project, but it is not available to your web application.

The project class path (build path) is not the same as the class path of your web application when deployed. Not all jars being on your project class path get exported automatically.

Usually jars in the WEB-INF/lib will be available for the web application, but jars outside of that will not.

You should either place the MySql jdbc driver jar in WEB-INF/lib, or add it to the lib folder of your Servlet container (Tomcat in your case judging by the exception stack trace).

add it to the lib folder of your Servlet container -- worked :) — JavaDeveloper, Dec 03 '14 at 16:40

score 0 · Answer 2 · answered Dec 03 '14 at 08:26

0

You have to include mysql-connector-java-5.1.24-bin.jar library file into your project. Then it will not give the error class not found. this file located inside C:\Program Files\MySQL\Connector J 5.1.20.0 folder.

answered Dec 03 '14 at 08:26

Sush

307
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score 0 · Answer 3 · answered Dec 03 '14 at 08:29

0

Add mysql-conneter jar in your project library. You can download it from below link

Download Connector Jar file

answered Dec 03 '14 at 08:29

Altmish-E-Azam

1,561
1
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score 0 · Answer 4 · answered Dec 03 '14 at 08:35

make sure that the packager you are using for creating war file (it could just as well be eclipse), is putting the mysql driver jar file in the war's web-inf lib.

typically, in eclipse you ensure above by going to project properties->deployment assembly and making sure your driver jar is included

score -1 · Answer 5 · edited Dec 03 '14 at 08:56

-1

If you execute the same method (main) in other class inside the project, must be executed perfectly.

The classloader is the same, but you can't access to the method getStatement outside the class DBConnectivity because the method is private.

You could execute this method by reflection.

edited Dec 03 '14 at 08:56

Bas Peeters

3,269
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answered Dec 03 '14 at 08:29

Sergio Gutiérrez Jiménez

1
2

Why do I get ClassNotFoundException when I call it from outside class?

5 Answers5