mysql jdbc Query from a Servlet (tomcat server)

I'm confused with a little code of mine.

I wrote a function, that executes a query on a mySQL database and returns the content as a string. I have a Class for testing purposes.

public static void main(String[] args) {    
    System.out.println(funct());
}
public static String funct(){
    DBOps dbops=new DBOps();
    String s=(dbops.read("select * from db.table"));
    return s;
}

Executing main() works absolutely fine and returns the desired String But if I want to execute funkt() in a Servlet, shit hits the fan.

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    PrintWriter out = response.getWriter();
    out.println(HTML_START + "<h2>Hello!</h2><br></br><h2> " + Test.funct() + " </h2>" +HTML_END);
}

The Servlet is executed on a tomcat Server. Tomcat starts up just fine. From the errors that are appearing it seems to be some kind of JDBC problem, what should not be the possible, since the JDBC runs fine, when funct() is not executed in the Servlet. This is the part with the jdbc actions in it:

String url="jdbc:mysql://localhost:3306/db"; 
String username ="root";
String password ="pass";

private ResultSet getDB(String q){ //q is the input query
    try {
          Class.forName("com.mysql.jdbc.Driver");
          connect = DriverManager.getConnection(url, username, password);
          statement = connect.createStatement();
          resultSet = statement.executeQuery(q);
          System.out.println(writeResults(resultSet));
     }

Then I get this bunch of errors:

java.lang.ClassNotFoundException: com.mysql.jdbc.Driver
at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1720)
at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1571)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Unknown Source)
at mainPackage.DBOps.getDB(DBOps.java:27)
at mainPackage.DBOps.read(DBOps.java:144)
at mainPackage.Test.funct(Test.java:18)
at mainPackage.Main.doGet(Main.java:73)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:620)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:220)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:503)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:170)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:950)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:421)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1070)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:611)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:314)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Unknown Source)
Mär 05, 2015 12:06:59 AM org.apache.catalina.core.StandardWrapperValve invoke
SCHWERWIEGEND: Servlet.service() for servlet [mainPackage.Main] in context with path [/NozPrototyp01] threw exception
java.lang.NullPointerException
at mainPackage.DBOps.writeResults(DBOps.java:105)
at mainPackage.DBOps.read(DBOps.java:144)
at mainPackage.Test.funct(Test.java:18)
at mainPackage.Main.doGet(Main.java:73)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:620)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:220)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:503)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:170)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:950)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:421)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1070)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:611)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:314)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Unknown Source)

I really hope someone can help me, since I'm staring to get a little frustrated over here >.<