2001: JNDI Its all in the Context

transcript

JNDI, It’s All in the Context

Russell CastagnaroChief Mentor 4Charity.comrussell@4charity.com

Introduction• Presenter

– Russell Castagnaro

– Chief Mentor • 4Charity.com • SyncTank Solutions, Inc

– russell@4charity.com

– Experience

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…

Why JNDI?You can:• Develop networked application.• Find remote objects.• Interface with distributed systems.• Interact with non-Java, networked

systems

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.

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.

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

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.

Naming

JNDI Tree lives in the Server as a collection of

Named Object References

Object/ Service

Reference

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.

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;”

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”

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”);

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

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 ) {}

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.

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

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 &

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..

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,..)

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

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);

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);

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”);

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");

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!

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.

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);}

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

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

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());

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.

Other Features• Removing Items from the JNDI Tree

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) ..

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

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>

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”);

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){}

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);

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.

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.

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.

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);

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

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();

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

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"));

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.

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.

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

– russell@4charity.com

• Aloha!

2001: JNDI Its all in the Context

Technology