Ajay Ejantkar wrote:
> I am trying to run the following servlet.
>
> *************************************************************************
>
You must especify the driver Class, and the correct parameters to etstabilish
conection.
[]�s
Daniel A.
> config.getInitParameter("driverClassName");
> String url = config.getInitParameter("url");
> String username = config.getInitParameter("username");
> String password = config.getInitParameter("password");
>
> // Use those init params to establish a connection to the
> database
> // If anything goes wrong, log it, wrap the exception and
> re-throw it
> try {
> Class.forName(driverClassName);
> db = DriverManager.getConnection(url, username, password);
> }
> catch (Exception e) {
> log("Can't create DB connection", e);
> throw new ServletException("Query: can't initialize: " +
> e.getMessage(), e);
> }
> }
>
> /** Close the database connection when the servlet is unloaded */
> public void destroy() {
> try{ db.close(); } // Try to close the connection
> catch (SQLException e) {} // Ignore errors; at least we
> tried!
> }
>
> public void doGet(HttpServletRequest request, HttpServletResponse
> response) throws IOException, ServletException
> {
> response.setContentType("text/html"); // We'returnoutputting
> HTML
> PrintWriter out = response.getWriter(); // Where to output it
> to
>
> // Output document header and a form for entering SQL queries
> // When the form is submitted, this servlet is reloaded
> out.println("<HEAD><TITLE>DB Query</TITLE></HEAD>\n" +
> "<BODY BGCOLOR=white><H1>DB Query</H1>\n" +
> "<FORM><B>Query:</B><INPUT NAME='q'>" +
> "<INPUT TYPE=submit></FORM>");
>
> // See if a query was specified in this request.
> String query = request.getParameter("q");
> if (query != null) {
> // display the query text as a page heading
> out.println("<H1>" + query + "</H1>");
>
> // Now try to execute the query and display the results in
> a table
> Statement statement = null; // An object to execute the
> query
> try {
> // Create a statement to use
> statement = db.createStatement();
> // Use it to execute the specified query, and get the
> result set
> ResultSet results = statement.executeQuery(query);
> // Ask for extra information about the results
> ResultSetMetaData metadata = results.getMetaData();
> // How many columns are there in the results?
> int numcols = metadata.getColumnCount();
>
> // Begin a table, and output a header row of column
> names
> out.println("<TABLE BORDER=2><TR>");
> for(int i = 0; i < numcols; i++)
> out.print("<TH>" + metadata.getColumnLabel(i+1) +
> "</TH>");
> out.println("</TR>");
>
> // Now loop through the "rows of the result set
> while(results.next()){
> // For each row, display the values for each column
> out.print("<TR>");
> for(int i = 0; i < numcols; i++)
> out.print("<TH>" + results.getObject(i+1) +
> "</TD>");
> out.println("</TR>");
> }
> out.println("</TABLE>"); // end the table.
>
> }
> catch (SQLException e) {
> // If anything goes wrong (usually SQL error) display
> the
> // error to the user so they can correct it.
> out.println("SQL Error: " + e.getMessage());
> }
> finally { // Whatever happens, always close the Statement
> object
> try { statement.close();}
> catch (Exception e) {}
> }
> }
>
> // Finally, end the HTML output
> out.println("</BODY>");
> }
> }
>
> *************************************************************************
>
> When I load the servlet I get the following error:
>
> Error: 500
> Location: /myapp/query
> Internal Servlet Error:
>
> javax.servlet.ServletException: Query: can't initialize: null
> at Query.init(Query.java:31)
> at javax.servlet.GenericServlet.init(GenericServlet.java:258)
> at
> org.apache.tomcat.core.ServletWrapper.doInit(ServletWrapper.java:317)
> at org.apache.tomcat.core.Handler.init(Handler.java:215)
> at org.apache.tomcat.core.ServletWrapper.init(ServletWrapper.java:296)
> at org.apache.tomcat.core.Handler.service(Handler.java:254)
> at
> org.apache.tomcat.core.ServletWrapper.service(ServletWrapper.java:372)
> at
> org.apache.tomcat.core.ContextManager.internalService(ContextManager.java:797)
> at
> org.apache.tomcat.core.ContextManager.service(ContextManager.java:743)
> at
>
>org.apache.tomcat.service.http.HttpConnectionHandler.processConnection(HttpConnectionHandler.java:210)
> at
> org.apache.tomcat.service.TcpWorkerThread.runIt(PoolTcpEndpoint.java:416)
> at
> org.apache.tomcat.util.ThreadPool$ControlRunnable.run(ThreadPool.java:498)
> at java.lang.Thread.run(Thread.java:484)
>
> Root cause:
> java.lang.NullPointerException
> at java.lang.Class.forName0(Native Method)
> at java.lang.Class.forName(Class.java:120)
> at Query.init(Query.java:26)
> at javax.servlet.GenericServlet.init(GenericServlet.java:258)
> at
> org.apache.tomcat.core.ServletWrapper.doInit(ServletWrapper.java:317)
> at org.apache.tomcat.core.Handler.init(Handler.java:215)
> at org.apache.tomcat.core.ServletWrapper.init(ServletWrapper.java:296)
> at org.apache.tomcat.core.Handler.service(Handler.java:254)
> at
> org.apache.tomcat.core.ServletWrapper.service(ServletWrapper.java:372)
> at
> org.apache.tomcat.core.ContextManager.internalService(ContextManager.java:797)
> at
> org.apache.tomcat.core.ContextManager.service(ContextManager.java:743)
> at
>
>org.apache.tomcat.service.http.HttpConnectionHandler.processConnection(HttpConnectionHandler.java:210)
> at
> org.apache.tomcat.service.TcpWorkerThread.runIt(PoolTcpEndpoint.java:416)
> at
> org.apache.tomcat.util.ThreadPool$ControlRunnable.run(ThreadPool.java:498)
> at java.lang.Thread.run(Thread.java:484)
>
> ************************************************************************
>
> I have put the location of my jdbc driver in my classpath before I
> start up the tomcat server. I have also tried to put the zip file with
> the drivers in myapps/web-inf/lib/ directory. It still does not seem to
> be able to locate the jdbc driver. Following is my web.xml file :
>
> ************************************************************************
> <!DOCTYPE web-app
> PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.2//EN"
> "http://java.sun.com/j2ee/dtds/web-app_2_2.dtd";>
>
> <web-app>
>
> <display-name>Hello, World Application</display-name>
> <description>
> This is a simple web application with a source code organization
> based on the recommendations of the Application Developer's Guide.
> </description>
>
> <servlet>
> <servlet-name>HelloServlet</servlet-name>
> <servlet-class>Hello</servlet-class>
> </servlet>
>
> <servlet-mapping>
> <servlet-name>HelloServlet</servlet-name>
> <url-pattern>/hello</url-pattern>
> </servlet-mapping>
>
> <servlet>
> <servlet-name>MonkeyServlet</servlet-name>
> <servlet-class>Monkey</servlet-class>
> </servlet>
>
> <servlet-mapping>
> <servlet-name>MonkeyServlet</servlet-name>
> <url-pattern>/monkey</url-pattern>
> </servlet-mapping>
>
> <servlet>
> <servlet-name>ListManagerServlet</servlet-name>
> <servlet-class>ListManagerServlet</servlet-class>
> <init-param>
> <param-name>addressfile</param-name>
> <param-value>addressfile.txt</param-value>
> </init-param>
> </servlet>
>
> <servlet-mapping>
> <servlet-name>ListManagerServlet</servlet-name>
> <url-pattern>/list</url-pattern>
> </servlet-mapping>
>
> <servlet>
> <servlet-name>Query</servlet-name>
> <servlet-class>Query</servlet-class>
> <init-param>
> <param-name>driverClassName</param-name>
> <param-value>"com.sybase.jdbc.SybDriver"</param-value>
> <param-name>url</param-name>
> <param-value>"jdbc:sybase:Tds:localhost:2638"</param-value>
> <param-name>username</param-name>
> <param-value>"DBA"</param-value>
> <param-name>password</param-name>
> <param-value>"SQL"</param-value>
> </init-param>
> </servlet>
>
> <servlet-mapping>
> <servlet-name>Query</servlet-name>
> <url-pattern>/query</url-pattern>
> </servlet-mapping>
>
> </web-app>
> *************************************************************************
>
> Any help on this would be greatly appreciated.
>
> Ajay
>
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