JDBC can't connect to mysql database on opensh

问题:

I managed to set up MySQL database on OpenShift with phpMyAdmin and all. I was told the host name and port my for my database are $OPENSHIFT_MYSQL_DB_HOST and $OPENSHIFT_MYSQL_DB_PORT respectively, which I put in my context.xml file like this:

<context-param>
        <param-name>driver</param-name>
        <param-value>com.mysql.jdbc.Driver</param-value>
    </context-param>
    <context-param>
        <param-name>url</param-name>
        <param-value>jdbc:mysql://$OPENSHIFT_MYSQL_DB_HOST:$OPENSHIFT_MYSQL_DB_PORT/burgerjoint</param-value>
    </context-param>
    <context-param>
        <param-name>user</param-name>
        <param-value>admin******</param-value>
    </context-param>
    <context-param>
        <param-name>password</param-name>
        <param-value>*********</param-value>
    </context-param>

The code to set up the connection is:

public void contextInitialized(ServletContextEvent event) {
    // Connect
    String driver = event.getServletContext().getInitParameter(PARAM_DRIVER);
    String url = event.getServletContext().getInitParameter(PARAM_URL);
    String username = event.getServletContext().getInitParameter(PARAM_USERNAME);
    String password = event.getServletContext()
        .getInitParameter(PARAM_PASSWORD);

    try {
        Class.forName(driver);
        Connection connection = DriverManager.getConnection(url, username,
            password);

        event.getServletContext().setAttribute(ATTR_CONNECTION, connection);


    } catch (ClassNotFoundException e) {
        e.printStackTrace();
    } catch (SQLException e) {
        e.printStackTrace();
    }

    }

but the problem is that the connection is null on the server and I don't understand why. Did I do something wrong? The code works when I try it on localhost. And as far as I can tell, I have all necessary libraries:

Thanks for the help :)

Update

I've modified the Connection code as follows:

{
    if (connection != null) return connection;

    try
    {
        Properties dbProperties = new Properties();
        InputStream input = DatabaseUtil.class.getClassLoader().getResourceAsStream(DB_PROPERTIES_FILE);
        dbProperties.load(input);
        String url = "";
        if (appIsDeployed)
        {
        String host = System.getenv("$OPENSHIFT_MYSQL_DB_HOST");
        String port = System.getenv("$OPENSHIFT_MYSQL_DB_PORT");
        String name = "burgerjoint";
        url = "jdbc:mysql://" + host + ":" + port + "/" + name;
        } else
        {
        url = dbProperties.getProperty(PARAM_URL);
        }
        String driver = dbProperties.getProperty(PARAM_DRIVER);
        String username = dbProperties.getProperty(PARAM_USERNAME);
        String password = dbProperties.getProperty(PARAM_PASSWORD);

        Class.forName(driver);
        connection = DriverManager.getConnection(url, username, password);

but it still gives null connection. The values of System.getenv("$OPENSHIFT_MYSQL_DB_HOST") and System.getenv("$OPENSHIFT_MYSQL_DB_PORT") are null.

回答1:

This is incorrect:

jdbc:mysql://$OPENSHIFT_MYSQL_DB_HOST:$OPENSHIFT_MYSQL_DB_PORT/burgerjoint

That dollar sign suggests that you think a proper host and database name will be substituted, but that's not the case.

Code the host and database name to see that it works, then learn about .properties files to externalize it.

回答2:

Remove the Dollar signs :

   String host = System.getenv("OPENSHIFT_MYSQL_DB_HOST");
   String port = System.getenv("OPENSHIFT_MYSQL_DB_PORT");

And it will work great (I tested it on my machine and on my OpenShift) .

回答3:

Can you please try to start port-forwarding first.

rhc port-forward -a your-app-name

Once started don't kill this cmd & just use the generated local addresses/ports.

回答4:

If you are using the MySQL cartridge, the information to connect to the database are in the environment variables of the application. If you are using JDBC pure , you need to first retrieve the values​​. e.g.:

String host = System.getenv("OPENSHIFT_MYSQL_DB_HOST");
String port = System.getenv("OPENSHIFT_MYSQL_DB_PORT");
String username = System.getenv("OPENSHIFT_MYSQL_DB_USERNAME");
String password = System.getenv("OPENSHIFT_MYSQL_DB_PASSWORD");

String url = String.format(":mysql://%s:%s/jbossas", host, port);
Connection conn = DriverManager.getConnection(url, username, password);

The jbossas in the string url is the schema. Change with your schema (burgerjoint).