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Unlike recipe 1.1, you cannot create only the default InitialContext instance and be able to invoke a remote EJB. You must pass in some properties that let the context find the Java Naming and Directory Interface (JNDI) system used for the remote EJBs. For example, the private method in listing 1.2 looks up a remote EJB home object in a Weblogic EJB container.
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Listing 1.2 A lookup method using an initialized InitialContext
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private EquityHome getEquityHome() { try { // Get an InitialContext Properties props = new Properties(); props.put( Context.INITIAL_CONTEXT_FACTORY,
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Creates an InitialContext instance with environment properties
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Invoking a remote EJB from another EJB
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"weblogic.jndi.WLInitialContextFactory" ); props.put( Context.PROVIDER_URL, "http://MyRemoteHost:7001" ); Context ic = new InitialContext( props ); equityHome = ( EquityHome ) ic.lookup( "ejbAccess.equityHome" ); equityHome = ( EquityHome ) Narrows the PortableRemoteObject.narrow( equityHome, return value EquityHome.class ); return equityHome; } catch (NamingException ne) { return null; } } EquityHome
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With a home reference in hand, you can find or create a new EJB. The following code locates an existing instance of the EquityBean entity bean:
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//remote interface of the EJB Equity equity = null; String symbol = getSymbol(); try{ //Use previously acquired home reference //to find an entity instance equity = equityHome.findByPrimaryKey( symbol ); } catch(Exception e){ e.printStackTrace(); throw new RemoteException("Error Finding Symbol:"+symbol); }
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This recipe shows how one EJB might contact a remote EJB (in a different EJB container). The solution provided here is similar to recipe 1.1 (contacting local EJBs) except that the JNDI InitialContext object must be provided with some properties in order to find the other EJB container. In this example, we provided the InitialContext instance with the correct properties to find a remote Weblogic EJB container using the following code:
props.put( Context.INITIAL_CONTEXT_FACTORY, "weblogic.jndi.WLInitialContextFactory" ); props.put( Context.PROVIDER_URL, "http://MyRemoteHost:7001" );
Client code
Consult your application server s documentation for the exact properties you need to provide. In addition, to make your beans more portable (and maintainable), you should read the property values in from an environment variable (or similar mechanism). Notice also that the example EJB uses the javax.rmi.PortableRemoteObject class to retrieve the EJB s stub for use. You must always use this class s narrow() method when retrieving a remote stub to ensure that the remote stub conforms to the IIOP protocol used now by Java RMI.
See also
1.1 Invoking a local EJB from another EJB 1.12 Improving your client-side EJB lookup code 2.1 Generating home, remote, local, and local home interfaces 4.1 Retrieving an environment variable
1.3 Accessing EJBs from a servlet
Problem
You want to contact an EJB from a servlet.
Background
With the recent push to use web applications for enterprise solutions, servlets have started to perform important roles in business applications. While servlets control the flow and validation of page presentation, they also are the main access point to the back-end business logic contained in EJBs.
Recipe
When using a servlet as an EJB client, you might need to contact a local or remote EJB container, so we provide separate recipes for local and remote EJBs. Also, you need to write portable servlets that don t contain hard-coded values for creating the JNDI initial context environment. Contacting EJBs from the same server When contacting an EJB in the same virtual machine, you need only make use of a default instance of the InitialContext class. For example, the servlet in listing 1.3 contacts a LoginBean EJB in order to process a user login.
Accessing EJBs from a servlet
Listing 1.3
LoginServlet.java
import javax.servlet.*; public class LoginServlet extends HttpServlet { //home interface for the EJB PasswordBean private LoginHome loginHome = null; public void init(ServletConfig conf) throws ServletException { super.init(conf); Looks up the EJB home try { from the servlet init lookupLoginHome(); } catch (NamingException e) { e.printStackTrace (); } } public void doGet( HttpServletRequest req, HttpServletResponse res ) { try { String name = getUserName( req ); String password = getUserPassword( req ); Login loginBean = loginHome.create( name ); Boolean valid = loginBean.login( password ); }catch( Exception e ) { //handle exception } //perform further work (not shown) } public void doPost( HttpServletRequest req, HttpServletResponse res ) { doGet( req ); } private void lookupLoginHome() throws NamingException { Context ctx = new InitialContext(); try { if( loginHome == null ) loginHome = ( LoginHome )3 ctx.lookup( "servletAccess.loginHome" ); }
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