How do I load and store global variables in Jersey/Glassfish

Question

I am creating a RESTful Web Service that wraps an antiquated vendor API. Some external configuration will be required and will be stored on the server either in a file or rdbms. I'm using Jersey 1.11.1 in Glassfish 3.1.2. This configuration data is all in String key/value format.

My first question is this - where can I store global/instance variables in Jersey so that they will be persisted between requests and available to all resources? If this was a pure Servlet application I would use the ServletContext to accomplish this.

The second part to the question is how can I load my configuration once the Jersey server has loaded? Again, my Servlet analogy would be to find the equivalent to the init() method.

Answer 1

@Singleton @Startup EJB matches your requirements.

@Singleton
@Startup // initialize at deployment time instead of first invocation
public class VendorConfiguration {

    @PostConstruct
    void loadConfiguration() {
        // do the startup initialization here
    }

    @Lock(LockType.READ) // To allow multiple threads to invoke this method
                         // simultaneusly
    public String getValue(String key) {
    }
}


@Path('/resource')
@Stateless
public class TheResource {
    @EJB
    VendorConfiguration configuration;
    // ...
}

EDIT: Added annotation as per Graham's comment

Answer 2

You can use a listener for init the variables and set to the context as attribute before the web application start, something like the following:

package org.paulvargas.shared;

import java.util.HashMap;
import java.util.Map;

import javax.servlet.ServletContext;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;

public class LoadConfigurationListener implements ServletContextListener {

    public void contextInitialized(ServletContextEvent sce) {
        // read file or rdbms
        ...
        ServletContext context = sce.getServletContext();
        // set attributes
        ...
    }

    public void contextDestroyed(ServletContextEvent sce) {
        ServletContext context = sce.getServletContext();
        // remove attributes
        ...
    }

}

This listener is configured in the web.xml.

<listener>
    <listener-class>org.paulvargas.shared.LoadConfigurationListener</listener-class>
</listener>

You can use the @Context annotation for inject the ServletContext and retrieving the attribute.

package org.paulvargas.example.helloworld;

import java.util.*;

import javax.servlet.ServletContext;
import javax.ws.rs.*;
import javax.ws.rs.core.*;

@Path("/world")
public class HelloWorld {

    @Context
    private ServletContext context;

    @GET
    @Produces("text/plain; charset=UTF-8")
    public String getGreeting() {

        // get attributes
        String someVar = (String) context.getAttribute("someName")

        return someVar + " says hello!";
    }

}