[h2] H2 Environment Variable resolver

agharta82 Wed, 07 Aug 2013 00:22:53 -0700

Hi all,

Because my web applications runs in bot Windows and Linux, i have a 
problem: I need to create h2 database ALWAYS into LOCAL TOMCAT 
(catalina.home) directory in server (-tcpAllowOthers) mode.


So, this is not possibile, because h2 requires absolute path (or relative 
to running dir or user home), and this differs from linux to windows.


Following this suggestion relative to environment variables into tomcat's 
web.xml 
http://www.coderanch.com/t/79094/Websphere/environment-variable-referance-Web-xmli've
 created a custom listener (based on h2's DbStarter listener ).

*ATTENTION: this works only if web application and db are both in same 
machine and in same web server, because the variable resolver is system 
restricted.*


public class DbStarter implements ServletContextListener {

    private Connection conn;
    private Server server;

    public void contextInitialized(ServletContextEvent servletContextEvent) 
{
        try {
            org.h2.Driver.load();

            // This will get the setting from a context-param in web.xml if 
defined:
            ServletContext servletContext = 
servletContextEvent.getServletContext();
            String url = 
*resolveEnvironmentVariable(*getParameter(servletContext, 
"db.url", "jdbc:h2:~/test")*);*
            String user = getParameter(servletContext, "db.user", "sa");
            String password = getParameter(servletContext, "db.password", 
"sa");

            // Start the server if configured to do so
            String serverParams = getParameter(servletContext, 
"db.tcpServer", null);
            if (serverParams != null) {
                String[] params = StringUtils.arraySplit(serverParams, ' ', 
true);
                server = Server.createTcpServer(params);
                server.start();
            }

            // To access the database in server mode, use the database URL:
            // jdbc:h2:tcp://localhost/~/test
            conn = DriverManager.getConnection(url, user, password);
            servletContext.setAttribute("connection", conn);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    private String getParameter(ServletContext servletContext, String key, 
String defaultValue) {
        String value = servletContext.getInitParameter(key);
        return value == null ? defaultValue : value;
    }

   * /**
     * Converts ${something} into relative environment variable value.
     * 
     * 
     * @param value
     * @return
     */
    public static String resolveEnvironmentVariable(String value) {
        Properties props = System.getProperties();
        if (value == null) {
            return null;
        }
        String initialValue = null;
        final Pattern p = 
Pattern.compile("\\$\\{([\\p{Alnum}|\\.|\\-]*)\\}");
        while (!value.equals(initialValue)) {
            initialValue = value;
            final Matcher m = p.matcher(value);
            while (m.find()) {
                final String propName = m.group(1);
                final String propValue = props.getProperty(propName, null);
                if (propValue != null) {
                    value = value.replaceAll("\\$\\{" + propName + "\\}", 
Matcher.quoteReplacement(propValue));
                }
            }
        }
        return value;
    }*

    /**
     * Get the connection.
     *
     * @return the connection
     */
    public Connection getConnection() {
        return conn;
    }

    public void contextDestroyed(ServletContextEvent servletContextEvent) {
        try {
            Statement stat = conn.createStatement();
            stat.execute("SHUTDOWN");
            stat.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
        try {
            conn.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
        if (server != null) {
            server.stop();
            server = null;
        }
    }
}


Bold code is the added code.
In this mode, my web.xml h2 db.url context parameter looks like this:

<context-param>
        <param-name>db.url</param-name>
        <param-value>jdbc:h2:*${catalina.home}*
/AXLOGDB/axLogDB</param-value>
</context-param>


Now the db is created into tomcat's home /AXLOGDB/axLogDB !!!!

If i need to attach a connection pooling (like c3p0 or commons dbcp or 
tomcat dbcp), i can call the custom DbStarter's *resolveEnvironmentVariable 
*method, in this way:

somedbcp.setJdbcUrl(*DbStarter.resolveEnvironmentVariable*
("jdbc:h2:tcp://localhost/${catalina.home}/AXLOGDB/axLogDB"));


So, it works! 


I hope that a *resolveEnvironmentVariable *method* *could be included by 
default in h2 path resolver, to allow a standard way to include local 
variable resolver in h2 (and remote connection with remote variable 
resolver).


Feel free to post suggestions or comments about my methods. And CORRECT ME 
if i am wrong.

Best regards,

Agharta 



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[h2] H2 Environment Variable resolver

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