Programming Forums > Application Development > Java

paulchwd · Mar 2nd, 2007, 11:59 PM

Hello:

Im a new to working with servlets so please bear with me:

I have 2 classes, one that reads database connection details from a file and establishes a database connection with a mysql database. and a second class (a servlet) that for now just does a simple query on the database and returns the result.

2 problems with the servlet code (no problems with the other class):

1. from the init method of the servlet, i call a method in my EstablishDBConnetion class to establish the connection. The compiler says i cannot reference this no-static method from a static context(Must it be static for my to reference it by Class.method ?)

2. The compiler doesnt seem to recognize its a servlet.

errors:

(Toggle Plain Text)

CustomQuery.java:12: non-static method establishConnection() cannot be referenced from a static context
                EstablishDBConnetion.establishConnection();
                                    ^
CustomQuery.java:19: package response does not exist
                PrintWriter printer = new response.getWriter();
                                                  ^
CustomQuery.java:23: cannot find symbol
symbol  : variable establishConnection
location: class EstablishDBConnetion
                Statement stmt = EstablishDBConnetion.establishConnection.con.createStatement();
                                                     ^
CustomQuery.java:40: cannot find symbol
symbol  : variable con
location: class CustomQuery
                con.close();
                ^
4 errors

Servlet Code

(Toggle Plain Text)

import java.io.*;
import java.sql.*;
import java.util.*;
import javax.servlet.*;
import javax.servlet.http.*;

public class CustomQuery extends HttpServlet
{

	public void init() throws ServletException
	{
		EstablishDBConnetion.establishConnection();
		
	}

	public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException
	{
		response.setContentType("text/html");
		PrintWriter printer = new response.getWriter();

		String title = "Result from custom query";

		Statement stmt = EstablishDBConnetion.establishConnection.con.createStatement();

		ResultSet rs = stmt.executeQuery("select customerID from customer");

		
		
		while(rs.next())
		{
			
			printer.println("<html> <head><title>" + title + "</title><br><br><table border=\"0\"> <tr><td>" + rs.getString(1) +"</td></tr></table></body></html>");
			
                
				                
		}

		rs.close();
		stmt.close();
		con.close();
	}

}

Establish Connection Code

(Toggle Plain Text)

import java.io.*;
import java.sql.*;
import java.util.StringTokenizer;

class EstablishDBConnetion
{

   public void establishConnection()
	{
	   		
	   	try
		{
			String dbDriver ="";
			String dbUrl="";
			String dbName="";
			String dbUser="";
			String dbPassword = "";
			String newLine = "";

			BufferedReader fileRead = new BufferedReader(new FileReader("connection.txt"));
			boolean readerStatus = fileRead.ready();
			
			newLine = fileRead.readLine();

			while (readerStatus)
			{

				StringTokenizer st = new StringTokenizer(newLine,",");

				while (st.hasMoreTokens())
				{
					dbDriver   = st.nextToken();
					dbUrl      = st.nextToken();
					dbName     = st.nextToken();
					dbUser     = st.nextToken();
					dbPassword = st.nextToken();
				}
								
				readerStatus = fileRead.ready();

			}

			Class.forName(dbDriver);
			String url = dbUrl + dbName;
			Connection con = DriverManager.getConnection(url, dbUser, dbPassword);

			
		}

		catch (IOException e)
		{
			System.out.println("IO exception in establishConnection()");

			e.printStackTrace();
		}

		catch (java.lang.Exception ex)
		{
			System.out.println("General exception in establishConnection()");
			ex.printStackTrace();
		}
  }

}

My Classpath:

.;C:\Program Files\QuickTime\QTSystem\QTJava.zip;"X:\Documents and Settings\Paul\My Documents\java\Code\servlets\invoice";"C:\Program Files\Apache Software Foundation\Tomcat 6.0\lib\servlet-api.jar"

Again, many thanks

paulchwd · Mar 3rd, 2007, 2:02 AM

pls ignore above code and errors, and see correct below

Errors

CustomQuery.java:4: package javax.servlet does not exist
import javax.servlet.*;
^
CustomQuery.java:5: package javax.servlet.http does not exist
import javax.servlet.http.*;
^
CustomQuery.java:7: cannot find symbol
symbol: class HttpServlet
public class CustomQuery extends HttpServlet
^
CustomQuery.java:10: cannot find symbol
symbol : class ServletException
location: class CustomQuery
public void init() throws ServletException
^
CustomQuery.java:16: cannot find symbol
symbol : class HttpServletRequest
location: class CustomQuery
public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException
^
CustomQuery.java:16: cannot find symbol
symbol : class HttpServletResponse
location: class CustomQuery
public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException
^
CustomQuery.java:16: cannot find symbol
symbol : class ServletException
location: class CustomQuery
public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException
^
CustomQuery.java:12: non-static method establishConnection() cannot be referenced from a static context
EstablishDBConnetion.establishConnection();
^
CustomQuery.java:19: package response does not exist
PrintWriter printer = new response.getWriter();
^
CustomQuery.java:23: cannot find symbol
symbol : variable establishConnection
location: class EstablishDBConnetion
Statement stmt = EstablishDBConnetion.establishConnection.con.createStatement();
^
CustomQuery.java:40: cannot find symbol
symbol : variable establishConnection
location: class EstablishDBConnetion
EstablishDBConnetion.establishConnection.con.close();
^
11 errors

Code

(Toggle Plain Text)

import java.io.*;
import java.sql.*;
import java.util.*;
import javax.servlet.*;
import javax.servlet.http.*;

public class CustomQuery extends HttpServlet
{

	public void init() throws ServletException
	{
		EstablishDBConnetion.establishConnection();
		
	}

	public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException
	{
		response.setContentType("text/html");
		PrintWriter printer = new response.getWriter();

		String title = "Result from custom query";

		Statement stmt = EstablishDBConnetion.establishConnection.con.createStatement();

		ResultSet rs = stmt.executeQuery("select customerID from customer");

		
		
		while(rs.next())
		{
			
			printer.println("<html> <head><title>" + title + "</title><br><br><table border=\"0\"> <tr><td>" + rs.getString(1));
			
                
				                
		}

		rs.close();
		stmt.close();
		EstablishDBConnetion.establishConnection.con.close();
	}

}

db Connection code

(Toggle Plain Text)

import java.io.*;
import java.sql.*;
import java.util.StringTokenizer;

class EstablishDBConnetion
{

   public void establishConnection()
	{
	   		
	   	try
		{
			String dbDriver ="";
			String dbUrl="";
			String dbName="";
			String dbUser="";
			String dbPassword = "";
			String newLine = "";

			BufferedReader fileRead = new BufferedReader(new FileReader("connection.txt"));
			boolean readerStatus = fileRead.ready();
			
			newLine = fileRead.readLine();

			while (readerStatus)
			{

				StringTokenizer st = new StringTokenizer(newLine,",");

				while (st.hasMoreTokens())
				{
					dbDriver   = st.nextToken();
					dbUrl      = st.nextToken();
					dbName     = st.nextToken();
					dbUser     = st.nextToken();
					dbPassword = st.nextToken();
				}
								
				readerStatus = fileRead.ready();

			}

			Class.forName(dbDriver);
			String url = dbUrl + dbName;
			Connection con = DriverManager.getConnection(url, dbUser, dbPassword);

			
		}

		catch (IOException e)
		{
			System.out.println("IO exception in establishConnection()");

			e.printStackTrace();
		}

		catch (java.lang.Exception ex)
		{
			System.out.println("General exception in establishConnection()");
			ex.printStackTrace();
		}
  }

}

Arevos · Mar 3rd, 2007, 5:29 AM

Quote:

Originally Posted by paulchwd

CustomQuery.java:4: package javax.servlet does not exist
import javax.servlet.*;

Check your classpath. Also, what are you using to compile the code?

paulchwd · Mar 3rd, 2007, 11:25 AM

AS far as I understand the classpath should have :

., my development directory and the location of the servlet jar file.

X:\Documents and Settings\Paul\My Documents\java\Code\servlets\invoice" is the exact directory where my class and java files are.

To compile I am using the command line (javac command)

Any thoughts?

paulchwd · Mar 3rd, 2007, 1:41 PM

I ensured my Classpath is correct, and it still wont work, but if i use the -classpath option at the commandline when compiling it recognizes that i am importing the servlet packages, but i still get these errors:

CustomQuery.java:19: package response does not exist
PrintWriter printer = new response.getWriter();
^
CustomQuery.java:24: cannot find symbol
symbol : variable establishConnection
location: class EstablishDBConnetion
Statement stmt = EstablishDBConnetion.establishConnection.con.createStatement();
^
CustomQuery.java:39: cannot find symbol
symbol : variable establishConnection
location: class EstablishDBConnetion
EstablishDBConnetion.establishConnection.con.close();
^
3 errors

For starters, it doesn't understand what the response object is
and then it doesxnt like the way i call Statement stmt = EstablishDBConnetion.establishConnection.con.createStatement();,

(FYI: con is in the establishConnection method of the EstablishDBConnetion class)

Mar 2nd, 2007, 11:59 PM	#1
paulchwd Hobbyist Programmer Join Date: Mar 2005 Posts: 139 Rep Power: 4	Servlet problems Hello: Im a new to working with servlets so please bear with me: I have 2 classes, one that reads database connection details from a file and establishes a database connection with a mysql database. and a second class (a servlet) that for now just does a simple query on the database and returns the result. 2 problems with the servlet code (no problems with the other class): 1. from the init method of the servlet, i call a method in my EstablishDBConnetion class to establish the connection. The compiler says i cannot reference this no-static method from a static context(Must it be static for my to reference it by Class.method ?) 2. The compiler doesnt seem to recognize its a servlet. errors: (Toggle Plain Text) CustomQuery.java:12: non-static method establishConnection() cannot be referenced from a static context EstablishDBConnetion.establishConnection(); ^ CustomQuery.java:19: package response does not exist PrintWriter printer = new response.getWriter(); ^ CustomQuery.java:23: cannot find symbol symbol : variable establishConnection location: class EstablishDBConnetion Statement stmt = EstablishDBConnetion.establishConnection.con.createStatement(); ^ CustomQuery.java:40: cannot find symbol symbol : variable con location: class CustomQuery con.close(); ^ 4 errors CustomQuery.java:12: non-static method establishConnection() cannot be referenced from a static context EstablishDBConnetion.establishConnection(); ^ CustomQuery.java:19: package response does not exist PrintWriter printer = new response.getWriter(); ^ CustomQuery.java:23: cannot find symbol symbol : variable establishConnection location: class EstablishDBConnetion Statement stmt = EstablishDBConnetion.establishConnection.con.createStatement(); ^ CustomQuery.java:40: cannot find symbol symbol : variable con location: class CustomQuery con.close(); ^ 4 errors Servlet Code (Toggle Plain Text) import java.io.; import java.sql.; import java.util.; import javax.servlet.; import javax.servlet.http.; public class CustomQuery extends HttpServlet { public void init() throws ServletException { EstablishDBConnetion.establishConnection(); } public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setContentType("text/html"); PrintWriter printer = new response.getWriter(); String title = "Result from custom query"; Statement stmt = EstablishDBConnetion.establishConnection.con.createStatement(); ResultSet rs = stmt.executeQuery("select customerID from customer"); while(rs.next()) { printer.println("<html> <head><title>" + title + "</title><br><br><table border=\"0\"> <tr><td>" + rs.getString(1) +"</td></tr></table></body></html>"); } rs.close(); stmt.close(); con.close(); } } import java.io.; import java.sql.; import java.util.; import javax.servlet.; import javax.servlet.http.; public class CustomQuery extends HttpServlet { public void init() throws ServletException { EstablishDBConnetion.establishConnection(); } public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setContentType("text/html"); PrintWriter printer = new response.getWriter(); String title = "Result from custom query"; Statement stmt = EstablishDBConnetion.establishConnection.con.createStatement(); ResultSet rs = stmt.executeQuery("select customerID from customer"); while(rs.next()) { printer.println("<html> <head><title>" + title + "</title><br><br><table border=\"0\"> <tr><td>" + rs.getString(1) +"</td></tr></table></body></html>"); } rs.close(); stmt.close(); con.close(); } } Establish Connection Code (Toggle Plain Text) import java.io.; import java.sql.; import java.util.StringTokenizer; class EstablishDBConnetion { public void establishConnection() { try { String dbDriver =""; String dbUrl=""; String dbName=""; String dbUser=""; String dbPassword = ""; String newLine = ""; BufferedReader fileRead = new BufferedReader(new FileReader("connection.txt")); boolean readerStatus = fileRead.ready(); newLine = fileRead.readLine(); while (readerStatus) { StringTokenizer st = new StringTokenizer(newLine,","); while (st.hasMoreTokens()) { dbDriver = st.nextToken(); dbUrl = st.nextToken(); dbName = st.nextToken(); dbUser = st.nextToken(); dbPassword = st.nextToken(); } readerStatus = fileRead.ready(); } Class.forName(dbDriver); String url = dbUrl + dbName; Connection con = DriverManager.getConnection(url, dbUser, dbPassword); } catch (IOException e) { System.out.println("IO exception in establishConnection()"); e.printStackTrace(); } catch (java.lang.Exception ex) { System.out.println("General exception in establishConnection()"); ex.printStackTrace(); } } } import java.io.; import java.sql.; import java.util.StringTokenizer; class EstablishDBConnetion { public void establishConnection() { try { String dbDriver =""; String dbUrl=""; String dbName=""; String dbUser=""; String dbPassword = ""; String newLine = ""; BufferedReader fileRead = new BufferedReader(new FileReader("connection.txt")); boolean readerStatus = fileRead.ready(); newLine = fileRead.readLine(); while (readerStatus) { StringTokenizer st = new StringTokenizer(newLine,","); while (st.hasMoreTokens()) { dbDriver = st.nextToken(); dbUrl = st.nextToken(); dbName = st.nextToken(); dbUser = st.nextToken(); dbPassword = st.nextToken(); } readerStatus = fileRead.ready(); } Class.forName(dbDriver); String url = dbUrl + dbName; Connection con = DriverManager.getConnection(url, dbUser, dbPassword); } catch (IOException e) { System.out.println("IO exception in establishConnection()"); e.printStackTrace(); } catch (java.lang.Exception ex) { System.out.println("General exception in establishConnection()"); ex.printStackTrace(); } } } My Classpath: .;C:\Program Files\QuickTime\QTSystem\QTJava.zip;"X:\Documents and Settings\Paul\My Documents\java\Code\servlets\invoice";"C:\Program Files\Apache Software Foundation\Tomcat 6.0\lib\servlet-api.jar" Again, many thanks

Mar 3rd, 2007, 2:02 AM	#2
paulchwd Hobbyist Programmer Join Date: Mar 2005 Posts: 139 Rep Power: 4	pls ignore above code and errors, and see correct below Errors CustomQuery.java:4: package javax.servlet does not exist import javax.servlet.; ^ CustomQuery.java:5: package javax.servlet.http does not exist import javax.servlet.http.; ^ CustomQuery.java:7: cannot find symbol symbol: class HttpServlet public class CustomQuery extends HttpServlet ^ CustomQuery.java:10: cannot find symbol symbol : class ServletException location: class CustomQuery public void init() throws ServletException ^ CustomQuery.java:16: cannot find symbol symbol : class HttpServletRequest location: class CustomQuery public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException ^ CustomQuery.java:16: cannot find symbol symbol : class HttpServletResponse location: class CustomQuery public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException ^ CustomQuery.java:16: cannot find symbol symbol : class ServletException location: class CustomQuery public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException ^ CustomQuery.java:12: non-static method establishConnection() cannot be referenced from a static context EstablishDBConnetion.establishConnection(); ^ CustomQuery.java:19: package response does not exist PrintWriter printer = new response.getWriter(); ^ CustomQuery.java:23: cannot find symbol symbol : variable establishConnection location: class EstablishDBConnetion Statement stmt = EstablishDBConnetion.establishConnection.con.createStatement(); ^ CustomQuery.java:40: cannot find symbol symbol : variable establishConnection location: class EstablishDBConnetion EstablishDBConnetion.establishConnection.con.close(); ^ 11 errors Code (Toggle Plain Text) import java.io.; import java.sql.; import java.util.; import javax.servlet.; import javax.servlet.http.; public class CustomQuery extends HttpServlet { public void init() throws ServletException { EstablishDBConnetion.establishConnection(); } public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setContentType("text/html"); PrintWriter printer = new response.getWriter(); String title = "Result from custom query"; Statement stmt = EstablishDBConnetion.establishConnection.con.createStatement(); ResultSet rs = stmt.executeQuery("select customerID from customer"); while(rs.next()) { printer.println("<html> <head><title>" + title + "</title><br><br><table border=\"0\"> <tr><td>" + rs.getString(1)); } rs.close(); stmt.close(); EstablishDBConnetion.establishConnection.con.close(); } } import java.io.; import java.sql.; import java.util.; import javax.servlet.; import javax.servlet.http.; public class CustomQuery extends HttpServlet { public void init() throws ServletException { EstablishDBConnetion.establishConnection(); } public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setContentType("text/html"); PrintWriter printer = new response.getWriter(); String title = "Result from custom query"; Statement stmt = EstablishDBConnetion.establishConnection.con.createStatement(); ResultSet rs = stmt.executeQuery("select customerID from customer"); while(rs.next()) { printer.println("<html> <head><title>" + title + "</title><br><br><table border=\"0\"> <tr><td>" + rs.getString(1)); } rs.close(); stmt.close(); EstablishDBConnetion.establishConnection.con.close(); } } db Connection code (Toggle Plain Text) import java.io.; import java.sql.; import java.util.StringTokenizer; class EstablishDBConnetion { public void establishConnection() { try { String dbDriver =""; String dbUrl=""; String dbName=""; String dbUser=""; String dbPassword = ""; String newLine = ""; BufferedReader fileRead = new BufferedReader(new FileReader("connection.txt")); boolean readerStatus = fileRead.ready(); newLine = fileRead.readLine(); while (readerStatus) { StringTokenizer st = new StringTokenizer(newLine,","); while (st.hasMoreTokens()) { dbDriver = st.nextToken(); dbUrl = st.nextToken(); dbName = st.nextToken(); dbUser = st.nextToken(); dbPassword = st.nextToken(); } readerStatus = fileRead.ready(); } Class.forName(dbDriver); String url = dbUrl + dbName; Connection con = DriverManager.getConnection(url, dbUser, dbPassword); } catch (IOException e) { System.out.println("IO exception in establishConnection()"); e.printStackTrace(); } catch (java.lang.Exception ex) { System.out.println("General exception in establishConnection()"); ex.printStackTrace(); } } } import java.io.; import java.sql.; import java.util.StringTokenizer; class EstablishDBConnetion { public void establishConnection() { try { String dbDriver =""; String dbUrl=""; String dbName=""; String dbUser=""; String dbPassword = ""; String newLine = ""; BufferedReader fileRead = new BufferedReader(new FileReader("connection.txt")); boolean readerStatus = fileRead.ready(); newLine = fileRead.readLine(); while (readerStatus) { StringTokenizer st = new StringTokenizer(newLine,","); while (st.hasMoreTokens()) { dbDriver = st.nextToken(); dbUrl = st.nextToken(); dbName = st.nextToken(); dbUser = st.nextToken(); dbPassword = st.nextToken(); } readerStatus = fileRead.ready(); } Class.forName(dbDriver); String url = dbUrl + dbName; Connection con = DriverManager.getConnection(url, dbUser, dbPassword); } catch (IOException e) { System.out.println("IO exception in establishConnection()"); e.printStackTrace(); } catch (java.lang.Exception ex) { System.out.println("General exception in establishConnection()"); ex.printStackTrace(); } } }

Mar 3rd, 2007, 1:41 PM	#5
paulchwd Hobbyist Programmer Join Date: Mar 2005 Posts: 139 Rep Power: 4	Updated I ensured my Classpath is correct, and it still wont work, but if i use the -classpath option at the commandline when compiling it recognizes that i am importing the servlet packages, but i still get these errors: CustomQuery.java:19: package response does not exist PrintWriter printer = new response.getWriter(); ^ CustomQuery.java:24: cannot find symbol symbol : variable establishConnection location: class EstablishDBConnetion Statement stmt = EstablishDBConnetion.establishConnection.con.createStatement(); ^ CustomQuery.java:39: cannot find symbol symbol : variable establishConnection location: class EstablishDBConnetion EstablishDBConnetion.establishConnection.con.close(); ^ 3 errors For starters, it doesn't understand what the response object is and then it doesxnt like the way i call Statement stmt = EstablishDBConnetion.establishConnection.con.createStatement();, (FYI: con is in the establishConnection method of the EstablishDBConnetion class)

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Mar 3rd, 2007, 11:25 AM	#4
paulchwd Hobbyist Programmer Join Date: Mar 2005 Posts: 139 Rep Power: 4	AS far as I understand the classpath should have : ., my development directory and the location of the servlet jar file. X:\Documents and Settings\Paul\My Documents\java\Code\servlets\invoice" is the exact directory where my class and java files are. To compile I am using the command line (javac command) Any thoughts?

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