[hibernate-dev] A framework JDBC code change suggestion...

[Joseph Weinstein]

Hi all.

In debugging a JDBC-related issue with hibernate and
WebLogic I found a file:

org.springframework.jdbc.datasource.DriverManagerDataSource.

There is a part of this file that hurts JDBC concurrency
in multithreaded applications like WebLogic, and I have a
solution. I would like to suggest a better alternative that
would probably be named DriverDataSource.
   The problem is that *all* java.sql.DriverManager calls are
class-synchronized. This include getConnection() and some very
simple methods like DriverManager.println() which every driver
may be calling continually at runtime (whether or not there is
a DriverManager log stream). The constructor for SQLException
calls this method.
   This means that one slow call to DriverManager.getConnection()
can temporarily block all other JDBC in the whole JVM. In some
cases we have even seen deadlocks where one thread that holds the
DriverManager lock calls another thread that wants to do JDBC.
   The solution is to remove all calls to DriverManager.getConnection()
and replace them with a simple call to Driver.connect(). In fact,
this is what the DriverManager itself does, except that for every
getConnection() call, the DriverManager goes through it's list of
every registered driver in the JVM, trying each one with your URL
and properties until it finds one that doesn't throw an exception
and returns a connection. I decompiled and altered the
DriverManagerDataSource to do that, for a customer to try, and I
have attached it to this email as a suggestion for your consideration.
HTH,
Joe Weinstein at BEA Systems_______________________________________________________________________
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// Decompiled by Jad v1.5.8e2. Copyright 2001 Pavel Kouznetsov.
// Jad home page: http://kpdus.tripod.com/jad.html
// Decompiler options: packimports(3) 
// Source File Name:   DriverManagerDataSource.java

package org.springframework.jdbc.datasource;

import java.sql.*;
import java.util.Properties;
import org.apache.commons.logging.Log;
import org.springframework.jdbc.CannotGetJdbcConnectionException;
import org.springframework.util.ClassUtils;
import org.springframework.util.StringUtils;

// Referenced classes of package org.springframework.jdbc.datasource:
//            AbstractDataSource

public class DriverManagerDataSource extends AbstractDataSource
{

    public DriverManagerDataSource()
    {
    }

    public DriverManagerDataSource(String driverClassName, String url, String username, String password)
        throws CannotGetJdbcConnectionException
    {
        setDriverClassName(driverClassName);
        setUrl(url);
        setUsername(username);
        setPassword(password);
    }

    public DriverManagerDataSource(String url, String username, String password)
        throws CannotGetJdbcConnectionException
    {
        setUrl(url);
        setUsername(username);
        setPassword(password);
    }

    public DriverManagerDataSource(String url)
        throws CannotGetJdbcConnectionException
    {
        setUrl(url);
    }

    public void setDriverClassName(String driverClassName)
        throws CannotGetJdbcConnectionException
    {
        if(!StringUtils.hasText(driverClassName))
            throw new IllegalArgumentException("driverClassName must not be empty");
        this.driverClassName = driverClassName;
        try
        {
            d = (Driver)ClassUtils.forName(this.driverClassName).newInstance();
        }
        catch(ClassNotFoundException ex)
        {
            throw new CannotGetJdbcConnectionException("Could not load JDBC driver class [" + this.driverClassName + "]", ex);
        }
        catch(Exception ex2)
        {
            throw new CannotGetJdbcConnectionException("Could not load JDBC driver class [" + this.driverClassName + "]", new SQLException(ex2.getMessage()) );
        }
        if(logger.isInfoEnabled())
            logger.info("Loaded JDBC driver: " + this.driverClassName);
    }

    public String getDriverClassName()
    {
        return driverClassName;
    }

    public void setUrl(String url)
    {
        if(!StringUtils.hasText(url))
        {
            throw new IllegalArgumentException("url must not be empty");
        } else
        {
            this.url = url;
            return;
        }
    }

    public String getUrl()
    {
        return url;
    }

    public void setUsername(String username)
    {
        this.username = username;
    }

    public String getUsername()
    {
        return username;
    }

    public void setPassword(String password)
    {
        this.password = password;
    }

    public String getPassword()
    {
        return password;
    }

    public void setConnectionProperties(Properties connectionProperties)
    {
        this.connectionProperties = connectionProperties;
    }

    public Properties getConnectionProperties()
    {
        return connectionProperties;
    }

    public Connection getConnection()
        throws SQLException
    {
        return getConnectionFromDriverManager();
    }

    public Connection getConnection(String username, String password)
        throws SQLException
    {
        return getConnectionFromDriverManager(username, password);
    }

    protected Connection getConnectionFromDriverManager()
        throws SQLException
    {
        return getConnectionFromDriverManager(getUsername(), getPassword());
    }

    protected Connection getConnectionFromDriverManager(String username, String password)
        throws SQLException
    {
        Properties props = new Properties(getConnectionProperties());
        if(username != null)
            props.setProperty("user", username);
        if(password != null)
            props.setProperty("password", password);
        return getConnectionFromDriverManager(getUrl(), props);
    }

    protected Connection getConnectionFromDriverManager(String url, Properties props)
        throws SQLException
    {
        if(logger.isDebugEnabled())
            logger.debug("Creating new JDBC Connection to [" + url + "]");

        if (d == null)
          throw new SQLException("Have not successfully loaded "
                              + driverClassName + " as a java.sql.Driver");

        if (!d.acceptsURL(url))
          throw new SQLException("Failed to make a JDBC connection with "
                              + driverClassName + " which does not accept URL " + url);

        Connection c = d.connect(url, props);

        if (c == null)
          throw new SQLException("Failed to make a JDBC connection with "
                              + driverClassName + " and URL " + url + " and properties " + props);

        return c;

    }

    private String driverClassName;
    private String url;
    private String username;
    private String password;
    private Properties connectionProperties;
    private Driver d;
}