Question

I’m working in a java project using eclipse, eclipseLink, java persistence API (JPA) and two databases (MYSQL and SQLServer) with the same structure (same tables). Sometimes I need to check the database that I’m using to apply conditional statements such as “if” or others. The question is:
How can i verify if I’m connected to a MySQL or SQLServer database using and use that information in a parameter?

Answer 1

I solved the problem reading the tag property and the Attribute name=”eclipselink.target-database” at the persistence.xml configuration file. I used these imports:

import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.DocumentBuilder;
import org.w3c.dom.Document;
import org.w3c.dom.NodeList;
import org.w3c.dom.Node;
import org.w3c.dom.Element;

And this is the function that I used to read the property:

public String DatabaseIdentifier() 
{
    String dbIdentifier=null ;
    try {
        //Creates a virtual file where is allowed for default the persistence.xml configurarion file
        File path= new File("src\\META-INF");

        //Using the xml libraries prepare the document to be read.
        DocumentBuilderFactory dbFactory = DocumentBuilderFactory.newInstance();
        DocumentBuilder dBuilder = dbFactory.newDocumentBuilder();
        Document doc = dBuilder.parse(new File(path+"\\persistence.xml"));
        doc.getDocumentElement().normalize();

        //Gets the list of properties  contained in the persistence.xml file
        NodeList listProperties= doc.getElementsByTagName("property");

        //We searching in the list of properties the attribute with the name 
        //eclipselink.target-database and there we get the database that 
        //is in use.
        for (int i = 0; i < listProperties.getLength(); i ++) {
            Node team = listProperties.item(i);

            if (team.getNodeType() == Node.ELEMENT_NODE)    
            {
                Element element = (Element) team;

            if (element.getAttribute("name").contains("eclipselink.target-database"))
                    {
                dbIdentifier=element.getAttribute("value").toString();
                System.out.println(element.getAttribute("value"));
                    }

            }
        }
    } catch (Exception e) 
    {e.printStackTrace();}
    return dbIdentifier;
}

In another class you should to assign to a String the return of this method. And that’s the answer, now you can use this information in a conditional statement like “if”.