java.lang.NullPointerException

[Craig Giles]

Trying to connect to a oracle database and display some data. Not sure where the "Parm" is coming from.

Here is the error:

Parm
Exception in thread "main" java.lang.NullPointerException
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:164)
at DatabaseExample.ConnectionManager.makeConnection(ConnectionManager.java:35)
at DatabaseExample.DatabaseService.getEmployee(DatabaseService.java:45)
at DatabaseExample.DatabaseService.main(DatabaseService.java:98)

The program uses 5 files, not sure how many I should post. Here is the one that outputs the records selected.

 package DatabaseExample;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;

/**
 * Class to communicate to the database
 * and display results.
 * @author Michael Jenkins
 *
 */

public abstract class DatabaseService {

	// static variable used for our select statement
	// helps to prevent sql injection
	private static final String SELECT_EMPLOYEES;
	
	/**
	 * Method to return an array list of employees
	 * @return
	 */
	public static ArrayList getEmployee() {
		
		// initializing connection
		Connection conn = null;
		// initializing statement
		PreparedStatement stmt = null;
		// initializing result set
		ResultSet rs = null;
		// initializing return value
		ArrayList returnVal = new ArrayList();
		
		try {
			// getting connection
			conn = ConnectionManager.makeConnection();
			// setting the statement
			stmt = conn.prepareStatement(SELECT_EMPLOYEES);
			// filling the result set with results from the query
			rs = stmt.executeQuery();
			// looping through the result set
			while (rs.next()) {
				// creating an employee object
				EmployeeWrapper ew = new EmployeeWrapper();
				// setting the first name in the object
				ew.setFirstName(rs.getString("FIRST_NAME"));
				// setting the last name in the object
				ew.setLastName(rs.getString("LAST_NAME"));
				// adding the object to the array list
				returnVal.add(ew);
			}
			// closing the statement
			stmt.close();
		} catch (SQLException esql) {
			System.out.println(esql.getMessage());
		} finally {
			try {
				if(conn != null) {
					conn.close();
					conn=null;
				}
			} catch (SQLException esql) {
				System.out.println(esql.getMessage());
			}
		}
		// returning the array list
		return returnVal;
		
	}
	
	// static block of code for the sql statement
	static {
		
	StringBuffer tempBuffer = null;
	
	tempBuffer = new StringBuffer();
	tempBuffer.append("SELECT LAST_NAME, FIRST_NAME FROM EMPLOYEES");
	SELECT_EMPLOYEES = tempBuffer.toString();
	
	}
	
	/**
	 * Main method to test our retrieval of data from the database
	 * @param args
	 */
	public static void main(String[] args) {
		// initializing an array list, filling it with a list 
		// of employee objects from the database.
		ArrayList e = DatabaseService.getEmployee();
		// looping through the array list
		for(int x=0; x<e.size(); x++) {
			// getting the employee object from the array list one at a time
			EmployeeWrapper ew = (EmployeeWrapper) e.get(x);
			// printing to the screen the employee first and last names
			System.out.println(ew.getFirstName() + " " + ew.getLastName());
		}
	}


}

   

[Ernest Friedman-Hill]

The stack trace indicates that the error happens in the ConnectionManager class, but you haven't shown us the code for that. It looks like you're passing "null" to Class.forName() on line 35. Presumably the database connection string is supposed to come from somewhere, but it's not getting initialized.

Incidentally, why do you have this:

     StringBuffer tempBuffer = null;         
     tempBuffer = new StringBuffer();  
     tempBuffer.append("SELECT LAST_NAME, FIRST_NAME FROM EMPLOYEES");  
     SELECT_EMPLOYEES = tempBuffer.toString();  

instead of simply

    SELECT_EMPLOYEES = "SELECT LAST_NAME, FIRST_NAME FROM EMPLOYEES";

[Balu Sadhasivam]

at DatabaseExample.ConnectionManager.makeConnection(ConnectionManager.java:35) 

This shows the error at ConnectionManager Class. show that please.

[Craig Giles]

Here is the Connection Manager class

  
package DatabaseExample;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;

/**
 * Class used to connect allow for connections
 * to the Oracle database
 * @author Michael Jenkins
 *
 */
public class ConnectionManager {
	// setting up static variables for use with the connection
	private static final String DRIVER = Parm.getSystemSetting("DB_DRIVER");
	private static final String CONN_URL = Parm.getSystemSetting("CONN_URL");
	private static final String USER_NAME = Parm.getSystemSetting("DB_USERNAME");
	private static final String PASSWORD = Parm.getSystemSetting("DB_PASSWORD");

	// empty constructor
	private ConnectionManager() {
	}
	
	/**
	 * Method to make a connection to the database
	 * @return
	 * @throws SQLException
	 */
	public static Connection makeConnection() throws SQLException {
		
		// initializing connection
		Connection conn = null;
		
		try {
			Class.forName(DRIVER);
			conn = DriverManager.getConnection(CONN_URL, USER_NAME, PASSWORD);
			conn.setAutoCommit(false);
		 } catch (ClassNotFoundException cnfe) {
			System.out.println(cnfe.getMessage());
		}
		
		return conn;
	}

}
  

Herer is the parm.properties file

   CONN_URL=jdbc:oracle:thin:@localhost:1521:xe
DB_USERNAME=hr
DB_PASSWORD=password
DB_DRIVER=oracle.jdbc.driver.OracleDriver
 

and the Parm.java

   
package DatabaseExample;

import java.io.FileNotFoundException;
import java.io.IOException;
import java.util.Properties;

/**
 * Class file to pull parameters from a file
 * @author Michael Jenkins
 *
 */
public class Parm {
	
	private static Properties props = null;
	
	static {
		
		try {
			props = new Properties();
			Class s = Class.forName("Parm");
			props.load(s.getResourceAsStream("/parm.properties"));
		} catch (FileNotFoundException fnfe) {
			System.out.println(fnfe.getMessage());
		} catch (IOException ioe) {
			System.out.println(ioe.getMessage());
		} catch (ClassNotFoundException cnfe) {
			System.out.println(cnfe.getMessage());
		}
	}
	// empty constructor
	private Parm() {		
	}
	
	public static String getSystemSetting(String pVariable) {
		if (props != null) {
			return ((String) props.getProperty(pVariable));
		} else {
			System.out.println("system variables were never initialized.");
			return null;
		}
	}
}


 

[Balu Sadhasivam]

Couple of things to check ,

Is your param.properties in loaded to Properties object properly ? because static initialiser is not recommended way and not sure if there is a exception , it reports where ??!? , so constructor or static method is pretty safe

DB_DRIVER=oracle.jdbc.driver.OracleDriver  

make sure there are no additional spaces or any other characaters after "OracleDriver" , some additional spaces may lead to such beahviour. you can use trim() to eliminate such behaviour.

(String) props.getProperty(pVariable)).trim();

[Rob Spoor]

Balu Sadhasivam wrote:it reports where ??!?

To System.out apparently, because that's where the caught exceptions are written out to.

Class s = Class.forName("Parm"); 

You do know that a) the class name is DatabaseExample.Parm, not just Parm, and b) you can simply use Parm.class?

Because you're using the wrong class name, a ClassNotFoundException is thrown, with message "Parm" - the class that could not be found. That's also where that printed Parm came from: System.out.println(cnfe.getMessage());

[Ernest Friedman-Hill]

... and that's also why the code never even attempts to load the properties file, so DRIVER is null, so you get the stack trace.

[Craig Giles]

thanks for all the help

[jittu goud]

you can actually check if the connection object is initialized properly by printing the connection object to console .....