使用Jet的JNDI查找失败与MySQL建立JDBC连接池？

Question

I'm using Jetty 9.2 (embedded) with the standard MySQL connector API and I'm very confused by how this is supposed to be setup. Currently, I have this in my web.xml file:

<webapp ...

    <resource-ref>
        <description>JDBC Data Source</description>
        <res-ref-name>jdbc/DataSource</res-ref-name>
        <res-type>javax.sql.DataSource</res-type>
        <res-auth>Container</res-auth>
    </resource-ref>
</webapp>

...and this in my jetty-env.xml:

<Configure class="org.eclipse.jetty.webapp.WebAppContext">

   <New id="DatabaseConnector" class="org.eclipse.jetty.plus.jndi.Resource">
        <Arg></Arg>
        <Arg>jdbc/DataSource</Arg>
        <Arg>
            <New class="com.mysql.jdbc.jdbc2.optional.MysqlConnectionPoolDataSource">
                <Set name="Url">jdbc:mysql://localhost:3306/DBName</Set>
                <Set name="User">user</Set>
                <Set name="Password">pass</Set>
            </New>
        </Arg>
    </New>

 </Configure>

...and this code to initialize:

Context envCtx = (Context) new InitialContext().lookup("java:comp/env");
DataSource datasource = (DataSource) envCtx.lookup("jdbc/DataSource");

When I try to fire up the server, I get the error javax.naming.NameNotFoundException; remaining name 'jdbc/DataSource' javax.naming.NameNotFoundException; remaining name 'jdbc/DataSource' . I've tried lots of different variations of the strings in the code initialization, like removing the lookup call on the InitialContext object, but I just keep getting variations of the same error with a different name value;

Both of the xml files are located in my /WAR/WEB-INF directory. I've looked at loads of previous questions and tutorials, blogs etc. but I'm getting nowhere.

Answer 1

It was a combination of problems specific to embedded Jetty.

First, my launcher code that was configuring and launching the web server was doing the JNDI lookup before I actually started the web server ie before calling server.start() , so the JNDI configuration was not initialized at that stage.

But even making this change didn't work, because the envCtx.lookup("jdbc/DataSource") needs to be called from a thread that's associated with the WebApp. So I moved that code to a static block that gets called the first time a database connection is requested by a web server request.

In the end, I ended up with something like this for my launcher code :

public static void main(String[] args) {
    Server server = new Server();

    //Enable parsing of jndi-related parts of web.xml and jetty-env.xml
    ClassList classlist = ClassList.setServerDefault(server);
    classlist.addAfter(
            "org.eclipse.jetty.webapp.FragmentConfiguration", 
            "org.eclipse.jetty.plus.webapp.EnvConfiguration", 
            "org.eclipse.jetty.plus.webapp.PlusConfiguration");
...
...
server.start();

The JNDI lookup cannot be made by this main thread, so put it somewhere like the init method of a servlet request, or like I did, a synchronized method of a static database accessor class that gets used by servlets eg

public class DatabaseUtils {

    private static DataSource datasource;

    private static synchronized Connection getDBConnection() throws SQLException {
        if (datasource == null) {
            initDataSource();
        }
        return datasource.getConnection();
    }

    public static void initDataSource() {
        try {
             datasource = (DataSource) new InitialContext().lookup("java:comp/env/jdbc/DataSource");
             LOG.info("Database connection pool initalized successfully");
        } catch (Exception e) {
            LOG.error("Error while initialising the database connection pool", e);
        }
    }