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Connecting to MySQL using servlet

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Connecting to MySQL using servlet Java Help forum discussing all Java platforms - J2ME, J2SE and J2EE - as well as relevant standards, APIs and frameworks such as Swing, Servlets, JSPs, Applets, Struts, Spring, Hibernate, ANT, EJB, and other Java-related topics.

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  #1  
Old May 26th, 2003, 03:44 AM
Sthir Sthir is offline
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Connecting to MySQL using servlet
Hi,
I am trying to connect to the MySql database using a servlet. I have been downloaded the mysql-connector-java-3.0.7-stable-bin.jar file into my Lib directory in my WEb-INF dir.

I am getting the following compilations errors.

Connection.java:28: incompatible types
found : java.sql.Connection
required: Connection
con = DriverManager.getConnection("jdbc:mysql://localhost/work");
^
Connection.java:29: cannot resolve symbol
symbol : method prepareStatement (java.lang.String)
location: class Connection
PreparedStatement pstmt = con.prepareStatement("
SELECT * FROM employee");
^
Connection.java:42: cannot resolve symbol
symbol : method close ()
location: class Connection
try {con.close();}
^

Can anyone please tell me why I am getting this error.
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  #2  
Old May 26th, 2003, 07:35 AM
jaffadan jaffadan is offline
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Well without the rest of your code we can not see if you are importing java.sql.*

You should also check and see if this type of database connection is really what you want to do. Creating and using a datasource would be a safer route to go.

What app server are you using. So that i could help you more
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  #3  
Old May 26th, 2003, 03:13 PM
Nemi Nemi is offline
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If I had to guess, I would say you named your class "Connection", correct? And you likely have a line like this
Code:
Connection con;
...

con = DriverManager.getConnection("jdbc:mysql://localhost/work");

It thinks the Connection con; is the class you created, not the java.sql.Connection class. Rename your class or qualify the con variable like this
Code:
java.sql.Connection con;
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  #4  
Old May 26th, 2003, 09:05 PM
Sthir Sthir is offline
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Thanks Nemi. I got rid of the compilation errors. But I when try to run the program it gives me the following error(list). I have checked my web.xml file. Changed my class Connection to SConnection (so that there is no confusion). Could you please help me out again.

Thanks a lot

The server encountered an internal error () that prevented it from fulfilling this request.

exception

java.lang.NullPointerException
at SConnection.doGet(SConnection.java:44)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:743)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:856)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:288)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:263)
at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:151)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:561)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:1018)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:196)
at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:151)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:561)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:1018)
at org.apache.catalina.core.StandardContext.invoke(StandardContext.java:2748)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:186)
at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:151)
at org.apache.catalina.valves.ErrorDispatcherValve.invoke(ErrorDispatcherValve.java:171)
at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:149)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:172)
at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:149)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:561)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:1018)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:163)
at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:151)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:561)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:1018)
at org.apache.coyote.tomcat5.CoyoteAdapter.service(CoyoteAdapter.java:199)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:630)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.processConnection(Http11Protocol.jav a:463)
at org.apache.tomcat.util.net.TcpWorkerThread.runIt(PoolTcpEndpoint.java:568)
at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:631)
at java.lang.Thread.run(Unknown Source)

I am also attaching my code
Attached Files
File Type: java sconnection.java (1.3 KB, 274 views)
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  #5  
Old May 27th, 2003, 09:27 AM
Nemi Nemi is offline
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The reason you are likely getting a null pointer exception is because you are encountering a problem connecting to the database and 'con' never gets set to anything. Was there a "Error Occured" output to the browser?

In your finally block, since the code execution can reach it and the con variable may not be set, you should always check that the con variable is not null before trying to close it. Somehting like this:
Code:
public void doGet(HttpServletRequest request, HttpServletResponse response)
				throws  IOException, ServletException
		{
					
					response.setContentType("text/html");
					PrintWriter out = response.getWriter();
					java.sql.Connection con = null;
					out.println("<html> <head> <title> Connection Successful");
					out.println(" </title> </head> <body>");
					
			try { 
				
				Class.forName("com.mysql.jdbc.Driver");
			        con = DriverManager.getConnection("jdbc:mysql://localhost/work");
				PreparedStatement pstmt = con.prepareStatement("SELECT * FROM employee");
				ResultSet results = pstmt.executeQuery();
			    }
			catch (Exception ex) 
			{
			 out.println("<h2> Error Occured </h2>");
			}	
			
		
						
			
			finally 
			{
				try {
					if(con != null) con.close();
				} 
				catch (SQLException e)
				{
				out.println("<h2> Error in closing the connection <h2>");
				e.printStackTrace();
				}
			} 
			out.println("</body></html>");
					
		}

}

After fixing that you will need to figure out why you are not connecting to the database. Probably because you are not using a username and password.
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  #6  
Old May 28th, 2003, 12:32 PM
Sthir Sthir is offline
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Thanks a lot!!
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