Connecting to a database

[tom davies]

I am trying to establish a connection to a HSQL database using jdbc.
I am loosely following an example from Horstmann's book, Big Java.

I have my properties file database.properties, where i am pretty sure the problem lies. I am not sure what i want to add to the jdbc.url line for it to connect.

jbdc.url=jdbc:hsqldb:file:myHSQLDB
jbdc.username=sa
jbdc.password=
jbdc.driver=org.hsqldb.jdbcDriver

The other files include SimpleDataSource which reads the properties from the properties file

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.io.FileInputStream;
import java.io.IOException;
import java.util.Properties;

public class SimpleDataSource 
{
    private static String url;
    private static String username;
    private static String password;
    
    public static void init(String database)
            throws IOException, ClassNotFoundException
    {
        Properties props = new Properties();
        FileInputStream in = new FileInputStream(database);
        props.load(in);
        
        String driver = props.getProperty("jdbc.driver");
        url = props.getProperty("jdbc.url");
        username = props.getProperty("jdbc.username");
        if(username == null) 
        {
            username = "";
        }
        password = props.getProperty("jdbc.password");
        if(password == null) 
        {
            password = "";
        }
        
        
    }
    
    public static Connection getConnection() throws SQLException
    {
        return DriverManager.getConnection(url, username, password);
    }
    
}

And then i attempt to establish a connection to the database.

import java.sql.Connection;
public class TestDB 
{
    public static void main(String[] args) throws Exception
    {
        Connection conn = SimpleDataSource.getConnection();
        conn.close();
    }
}

When i run this test file i get this error

Exception in thread "main" java.sql.SQLException: The url cannot be null
	at java.sql.DriverManager.getConnection(DriverManager.java:564)
	at java.sql.DriverManager.getConnection(DriverManager.java:221)
	at SimpleDataSource.getConnection(SimpleDataSource.java:48)
	at TestDB.main(TestDB.java:18)
Java Result: 1

[Jesper de Jong]

In the properties file, you typed jbdc instead of jdbc - look carefully, the b and the d have been exchanged, for the keys.

[Paul Clapham]

The "url" variable is null, which is what the error message says.

That's because nothing ever assigns it a value. And that's because the only code which might assign it a value, the code in your init() method, is never called.

[tom davies]

I didn't spot the spelling mistake, changed it now, it made no differene to the result though.
"Paul Clapham"
I thought i was assigning the string url the property of jbdc.url, and then in TestDB i am calling the getConnection() method which uses the url in it. Or am i missing something?

[Paul Clapham]

tom davies wrote:I thought i was assigning the string url the property of jbdc.url

Well, no, you're not doing that. The init() method would be doing it, if it were ever called. But nothing ever calls the init() method, so none of the code in it ever runs.

[tom davies]

Paul Clapham wrote:

tom davies wrote:I thought i was assigning the string url the property of jbdc.url

Well, no, you're not doing that. The init() method would be doing it, if it were ever called. But nothing ever calls the init() method, so none of the code in it ever runs.

Ahh, I see the problem now, i might re write the SimpleDataSource file as well, so i will write back if i have any further problems.
Thank you!

[tom davies]

I thought i had the answer.
I added this line

SimpleDataSource.init("database.properties");

Into the TestDB file, so that it actually reads the file first. I still get the same error message though.