2001: jndi its all in the context
DESCRIPTION
Back in 2001 I was giving talks on how to use Java Naming and Directory Interface effectively.TRANSCRIPT
1
Copyright 2000 SyncTank Solutions, Inc.
JNDI, It’s All in the Context
Russell CastagnaroChief Mentor [email protected]
Copyright 2000 SyncTank Solutions, Inc.
Introduction• Presenter
– Russell Castagnaro
– Chief Mentor • 4Charity.com • SyncTank Solutions, Inc
– Experience
2
Copyright 2000 SyncTank Solutions, Inc.
Introduction• 4Charity.com
– Application Service Provider for the Non-Profit industry
– Pure Java development– Http://www.4charity.com– Locations:
• San Francisco,CA • Honolulu, HI
– We’re Hiring…
Copyright 2000 SyncTank Solutions, Inc.
Why JNDI?You can:• Develop networked application.• Find remote objects.• Interface with distributed systems.• Interact with non-Java, networked
systems
3
Copyright 2000 SyncTank Solutions, Inc.
Presentation Goals• Review of basic JNDI.• Using JNDI for local service resolution.• JNDI as an alternative to static
constants.• Using Custom Contexts with JNDI.• Implementing Singletons.• Using RMI and IIOP.• Using Events in JNDI.
Copyright 2000 SyncTank Solutions, Inc.
Who needs JNDI?• If you want to use J2EE, you need
JNDI.• JNDI is the standard way to access
distributed and local resources for enterprise applications.
4
Copyright 2000 SyncTank Solutions, Inc.
What is JNDI?• JNDI is a set of interfaces.• Provides a programming interface,
allowing for Discovery and Registration.• Standards-based approach, providing
common API to a searchable structure of objects.
• Naming Services• Directory Services
Copyright 2000 SyncTank Solutions, Inc.
What is a Naming Service?• Provides the ability to map a name or
identifier to objects or services.• A tree-like structure, nodes can be
associated with other nodes or objects.• Objects are bound into the JNDI tree.• Objects can be resolved by performing
a lookup using the composite name.
5
Copyright 2000 SyncTank Solutions, Inc.
Naming
JNDI Tree lives in the Server as a collection of
Named Object References
Object/ Service
Reference
Copyright 2000 SyncTank Solutions, Inc.
What is a Directory Service?• Provides a structure containing objects.• Allows access to object attributes.• Enables searching the structure using
these attributes.• Think of a computer’s file system or an
SQL database.• Simple JNDI has one attribute, the
object’s name.
6
Copyright 2000 SyncTank Solutions, Inc.
JNDI is Like a Database• Start with a database instance.• Use a tablespace or ownership area.• Access a table in the tablespace.• Access a row in the table.• Access a column in the row.
sqlplus scott@beq-local
“SELECT name FROM scott.emp;”
Copyright 2000 SyncTank Solutions, Inc.
JNDI is Like a File System
• Start with a mounted drive.• Use a subdirectory.• Access a subdirectory.• Access a file.
“C:/data/your_client/financials.xls”
7
Copyright 2000 SyncTank Solutions, Inc.
Using JNDI• Start with an Initial Context.• Navigate to a Sub-Context.• Drill-down through other sub-contexts.• Access the object or service.
new InitialContext().lookup(“name”);
Copyright 2000 SyncTank Solutions, Inc.
Comparisons
JNDI File System RDBMS
Initial Context Mount Point (c:\)Database instance
SubContext Subdirectory TablespaceSubContext Subdirectory TableObject File Data (row)rmi://myserver:8080/myobjects.example.object
c:\data\your_client\financials.xls
SELECT * FROM Demo.Employee
8
Copyright 2000 SyncTank Solutions, Inc.
JNDI Examplepackage com.synctank.labs.jndi;import javax.naming.*;public class TestJNDI {
public static void main(String _arg[]){Object o = null; InitialContext ctx= null;try{
ctx = new InitialContext(System.getProperties());o = ctx.lookup("myobjects.example.object");String s = (String)o; System.out.println("Found a string: "+s);
} catch (ClassCastException e) {System.out.println("Found a "+o.getClass().getName() +": "+o.toString() );
} catch (NamingException ne) {System.out.println("We have a problem!"); ne.printStackTrace();
} finally {try { ctx.close(); }catch (Exception e ) {}
}} }
Copyright 2000 SyncTank Solutions, Inc.
JNDI Example• Primary classes are located in the
javax.naming package.• Primarily use Context objects:
– javax.naming.Context
– javax.naming.InitialContext
– javax.naming.directory.InitialDirContext
– javax.naming.ldap.InitialLdapContext
• Use a context that matches your needs.
9
Copyright 2000 SyncTank Solutions, Inc.
JNDI Providers• JNDI Providers are the services that will be
accessed.
• More on the Service Provider Interface Later.
• Most application servers come with some Naming service.
• J2SDK v. 1.3 includes code for many interfaces.
• Many are downloadable, for free, at http://java.sun.com/products/jndi/serviceproviders.html#12
Copyright 2000 SyncTank Solutions, Inc.
Starting the Service• FS service doesn’t need to be started!• RMI Registry (JNDI Service)
– start rmiregistry.exe OR– java.rmi.registry.LocateRegistry.createRegistry(port);
• Weblogic JNDI service– start startWebLogic.cmd OR – ./startWebLogic.sh &
10
Copyright 2000 SyncTank Solutions, Inc.
Getting the Initial Context
• Similar to JDBC. Use a Hashtable object.• Two required properties:
– Context.INITIAL_CONTEXT_FACTORY– Context.PROVIDER_URL
• Other optional properties:– Context.SECURITY_PRINCIPAL
– Context.SECURITY_CREDENTIALS
– And many, many more..
Copyright 2000 SyncTank Solutions, Inc.
Getting the Initial Context• Context.INITIAL_CONTEXT_FACTORY
– Actually “java.naming.factory.initial”– Name of the Factory that creates Initial Contexts.
• Context.PROVIDER_URL
– Actually “java.naming.provider.url”– Tells JNDI where to find the service.
• Context.SECURITY_PRINCIPAL
– Who is the connecting?
• Context.SECURITY_CREDENTIALS
– What is authentication object (password, certificate,..)
11
Copyright 2000 SyncTank Solutions, Inc.
Getting the Initial Context• Place the correct properties in a
Hashtable or Properties object.• Call the constructor for the InitialContext
class, pass the Hashtable as a parameter.
• Catch (throw) any Naming Exceptions!• Remember to close() the context when
done.
Copyright 2000 SyncTank Solutions, Inc.
Getting the Initial Context
public static InitialContext getInitialContext() throws NamingException {// use the factory and url supported by your providerString factory = "weblogic.jndi.WLInitialContextFactory";String url = "t3://localhost:7001"; // “http://localhost:7001”; String user = null; String password = null;java.util.Hashtable p = new java.util.Properties();p.put(Context.INITIAL_CONTEXT_FACTORY, factory);p.put(Context.PROVIDER_URL, url);if (user != null && password != null ) {
p.put(Context.SECURITY_PRINCIPAL, user);p.put(Context.SECURITY_CREDENTIALS, password);
}return new InitialContext(p);
}
12
Copyright 2000 SyncTank Solutions, Inc.
Getting the Initial Context (file system)
public static void main(String[] args) {Hashtable env = new Hashtable(11);env.put(Context.INITIAL_CONTEXT_FACTORY,
"com.sun.jndi.fscontext.RefFSContextFactory");String root = "file:/jdk1.3"; if (args != null && args.length > 0) root = args[0];
env.put(Context.PROVIDER_URL, "file:/jdk1.3");try {
Context ctx = new InitialContext(env); String start = ""; if (args != null && args.length > 0) start = args[0];
listBindings(ctx,start);ctx.close();
} catch (NamingException e) {System.out.println("List Bindings failed: " + e);
}}
Copyright 2000 SyncTank Solutions, Inc.
EJSkin LookupProperties p = new Properties();p.put(Context.INITIAL_CONTEXT_FACTORY,
“com.ejskin.context.SkinnyInitialContextFactory");p.put(Context.PROVIDER_URL,
“ejs://ejs.ejs.com:666");Context ctx = new InitialContext(p);SkinnyAppp app = (SkinnyApp)ctx.lookup(“SkinyApp.fore”);
13
Copyright 2000 SyncTank Solutions, Inc.
Resolving Objects• Once you have a context any lookup is a relative search.• user.russell.castagnaro.wallet can be resolved from:
– The initial context as ctx.lookup(“user.russell.castagnaro.wallet”);
– A subcontext “user.russell” as ctx.lookup(“castagnaro.wallet”);
• Access a sub-context using the lookup method from any context.Context ctx = new InitialContext(p); Context sub = ctx.lookup("user");sub = sub.lookup("russell"); sub = sub.lookup(”castagnaro");Object o = sub.lookup("wallet");
Copyright 2000 SyncTank Solutions, Inc.
JNDI Perusal• It is possible to dynamically access all of
the objects bound into the JNDI tree with two overloaded methods:– public abstract NamingEnumeration list(java.lang.String) throws
NamingException;– public abstract NamingEnumeration list(javax.naming.Name) throws
NamingException;– public abstract NamingEnumeration listBindings(java.lang.String) throws
NamingException;– public abstract NamingEnumeration listBindings(javax.naming.Name)
throws NamingException;
• There is a very large difference between the two methods!
14
Copyright 2000 SyncTank Solutions, Inc.
JNDI Perusal
• listBindings()– Returns an enumeration of Binding objects.– Bindings contain the actual object* from the tree!– May take a long time!
• list()– Returns an Enumeration of NameClassPair objects.– Access to the Name and class, but not the object.– Faster than the alternative, like a ‘shallow get.’
* Remote objects are an exception.
Copyright 2000 SyncTank Solutions, Inc.
JNDI Perusal Example Codepublic static void list(Context ctx,StringBuffer sb) {
try {NamingEnumeration enum = ctx.listBindings("");while (enum.hasMore()) {
Binding binding = (Binding)enum.next();Object obj = (Object)binding.getObject();if (obj instanceof Context) {
sb.append("---> "); sb.append(binding.getName());sb.append("."); list((Context)obj,_sb);
} else {sb.append(binding.getName()); sb.append("\n"); }
}} catch (NamingException e) {
System.out.println(e);}
}
15
Copyright 2000 SyncTank Solutions, Inc.
JNDI Perusal Output---> javax.--->
jts.UserTransaction
---> transaction.UserTransaction
--->jms.QueueConnectionFactory
TopicConnectionFactory
PrePackagedSessionEJB_EO
---> weblogic.
---> fileSystem.
---> ejb.EJBManager---> common.T3Services---> jdbc.JdbcServices
---> connectionPool.ejbpoolcs1demoPoolcs--->jts.CoordinatorFactory[]CoordinatorFactory---> server.myserverWebLogic---> rmi.--->jms.ServerSessionPoolFactory---> jndi.---> internal.RemoteContextFactoryRemoteContextFactory
Copyright 2000 SyncTank Solutions, Inc.
Adding Objects• You can use the bind() or rebind() methods to
add objects to the tree. • If an object extends java.io.Serializable, it is
copied and placed into the tree.• If an object extends java.rmi.Remote, a copy of
the stub is placed into the tree.• rebind() will automatically overwrite an existing
object.• bind() throws a javax.naming.NamingException
16
Copyright 2000 SyncTank Solutions, Inc.
Adding Objectspublic static void main(String args[]) throws java.rmi.RemoteException{
Hashtable ht = new Hashtable();ht.put(Context.INITIAL_CONTEXT_FACTORY, "weblogic.jndi.WLInitialContextFactory");ht.put(Context.PROVIDER_URL, "t3://localhost:7001");try {
Context ic = new InitialContext(ht);//serializable, an actual copy put into the treeic.bind("Object1",new String("Object1"));ic = ic.createSubContext(“foo”);//remote, a copy of the stub placed in the treeic.bind("Trivial",new TrivialImpl("Trivial!"));
} catch (NamingException e){System.out.println(e.getMessage());
}}
Copyright 2000 SyncTank Solutions, Inc.
Other Features• Use unbind() to remove an object from the
tree.• Use rename() to change its registered
name.• Use custom startup classes to bind
objects into the tree upon start up.• Use custom properties to automatically
bind objects into the tree.
17
Copyright 2000 SyncTank Solutions, Inc.
Other Features• Removing Items from the JNDI Tree
try {
Context ic = new InitialContext(ht);
ic.unbind(data);System.out.println(data+ " successfully unbound.");
} catch (NamingException e) ..
• Renamingtry {
Context ic = new InitialContext(ht);
ic.rename(oldName, newName);} catch (NamingException e) ..
Copyright 2000 SyncTank Solutions, Inc.
Local Data Access• Accessing local data using constants
requires recompilation to change those values
public static String SOME_VALUE=“foo”;
• Using JNDI gives you the freedom to pin values that need to be shared, without access to:– System properties– File Systems– Custom Classes
18
Copyright 2000 SyncTank Solutions, Inc.
Local Data Access• Enterprise Java Beans require the use of
this JNDI for deployment values.• Allows deployment specialists to change
values without recompilation.• EJB deployment descriptor snippet:
<env-entry>
<env-entry-name>foo</env-entry-name>
<env-entry-type>String</env-entry-type>
<env-entry-value>bar</env-entry-value>
</env-entry>
Copyright 2000 SyncTank Solutions, Inc.
Local Data Access• Use a local context and lookup the object
by prepending “java:comp/env”ctx = new InitialContext();String foo = (String)ctx.lookup(“java:comp/env.foo”);
19
Copyright 2000 SyncTank Solutions, Inc.
Using Custom Startup Classes
• Using a custom WebLogic startup Classpublic String startup(String _name, java.util.Hashtable
_args) throws Exception {TrivialImpl o = new TrivialImpl(); System.out.println("TrivialImpl instanciated..");Context context = getInitialContext(); context.rebind(_name, o);System.out.println("Bound..");
return ("TrivialImpl bound to the name "+_name);}public void setServices(weblogic.common.T3ServicesDef
services){}
Copyright 2000 SyncTank Solutions, Inc.
Using a Startup Servlet
public void init(ServletConfig config) throws ServletException {super.init(config);String className = config.getInitParameter("CLASS_NAME");String jndiName = config.getInitParameter("JNDI_NAME");if (className != null && jndiName != null) {try{
Object o = Class.forName(className).newInstance();Context ctx = new InitialContext();ctx.rebind(jndiName,o);log("StartupServlet has bound "+ className +" into”+ the JNDI tree as "+ jndiName);
} catch (Exception ne) {throw new ServletException(ne);
}}
20
Copyright 2000 SyncTank Solutions, Inc.
Singletons• You need one and only one instance of
a particular class.• You want to provide access to
distributed applications/ services.• Don’t make static methods! Make the
class an RMI object.• Bind the object’s implementation into
the JNDI tree.• Essentially what happens for EJBHome
interfaces.
Copyright 2000 SyncTank Solutions, Inc.
CORBA Objects• When accessing CORBA objects, things
used to be more complicated.• RMI over IIOP, included in Java 2,
solves this problem.• Narrowing the object maps it from a
CORBA object to a Java object auto-magically.
21
Copyright 2000 SyncTank Solutions, Inc.
Narrowing• If you access services using RMI over
IIOP (WebSphere, Iona, etc.).• If you use HomeHandle or Handle
objects (EJB 1.1). • Use PortableObject.narrow()• Pass an Object and the class you
expect from the remote method call.
Copyright 2000 SyncTank Solutions, Inc.
Class NarrowingObjectOutputStream stream = ...;Account account = ...;Handle handle = account.getHandle();stream.writeObject(handle);// A client can read the handle from stable storage, and use the
// handle to resurrect an object reference to the
// account entity object.
//
ObjectInputStream stream = ...;Handle handle = (Handle) stream.readObject(handle);Account account = (Account)javax.rmi.PortableRemoteObject.narrow(handle.getEJBObject(), Account.class);account.debit(100.00);
22
Copyright 2000 SyncTank Solutions, Inc.
JDBC and JNDI• It is possible to use JNDI to store JDBC
connection objects:SampleDataSource sds = new SampleDataSource();
sds.setServerName(“BEQ-LOCAL”);
sds.setDatabaseName(“demo”);
Context ctx = new InitialContext();
ctx.bind(“EmployeeDB”, sds);
• Application servers typically feature datasource publishing:weblogic.jdbc.TXDataSource.ejbDataSource=ejbPool
weblogic.jdbc.DataSource.ejbPool=ejbPool
Copyright 2000 SyncTank Solutions, Inc.
JDBC and JNDI• Use them later to avoid prior knowledge of
driver information:Context ctx = new InitialContext();
DataSource ds = (DataSource)ctx.lookup(“ejbDataSource”);
Connection con = ds.getConnection();
23
Copyright 2000 SyncTank Solutions, Inc.
Events• JNDI Events provide local or remote
callback functionality.• Similar to the event model used in Swing.• Uses subclasses of the
javax.naming.NamingListener interface.• NamingListeners:
– NamespaceChangeListener– ObjectChangeListener– UnsolicitedNotificationListener
Copyright 2000 SyncTank Solutions, Inc.
Events• JNDI Events require the use of a different
type of context.• New Context interfaces:
– EventContext for standard naming services
– EventDirContext for LDAP service
• Access Contexts in a familiar way:EventDirContext edc = (EventDirContext)
(new InitialDirContext(env).lookup("ou=People"));
24
Copyright 2000 SyncTank Solutions, Inc.
JNDI Gotchas• Use rebind() wisely.
• Know the URL and InitialContextFactory class name.
• When using advanced features (LDAP, etc.) place the correct resources in your classpath..\lib\rmiregistry.jar;.\lib\providerutil.jar;
.\lib\jndi.jar;.\lib\jaas.jar;.\lib\ldap.jar;
.\lib\ldapbp.jar;.\lib\fscontext.jar
• J2EE has made deploying JNDI services much easier, look for vendors to support advanced features 2Q 2000.
Copyright 2000 SyncTank Solutions, Inc.
Review• JNDI is used for all advanced J2EE
features.• JNDI provides an easy method of accessing
remote or local resources.• Use bind() or rebind() to register objects.• Use lookup() to resolve objects.• Use your server vendors startup facilities for
initial JNDI registration.
25
Copyright 2000 SyncTank Solutions, Inc.
Finally• Thanks for attending.• Live in Hawaii or Bay Area? Do you like
this stuff? Email your resume to us!• Source Code Available:
– http://www.synctank.com/softwaresummit
• Aloha!