EJB works First, I want to talk about RMI's working principle, because EJB is based on RMI. There are not many nonsense, the essence of RMI is the call between different JVMs, the working principle is as follows: its implementation method is to open a Stub and Skeleton in two JVMs, both through Socket communication to implement parameters And the transfer of the return value. There are a lot of examples on RMI, but most of them are implemented through extende interface java.rmi.Remote, which has been installed very well, and it is inevitable that people feel in fog. The following example is I saw in "Enterprise Javabeans", although it is rough, but it is very intuitive, it is good to learn about its working principle. 1. Define a Person interface, two business methods, getage () and getname ()
Code: public interface person {public interface () throws throwable; public string getName () throws throwable;} 2. Person's implementation of the Personserver class
Code: public class PersonServer implements Person {int age; String name; public PersonServer (String name, int age) {this.age = age; this.name = name;} public int getAge () {return age;} public String getName () {RETURN Name;}} 3. Well, we now have to call Getage () and getName () on the Client machine, so we have to write the corresponding Stub (Client end) and SKELETON (SERVER) program. This is the implementation of Stub:
Code: import java.io.ObjectOutputStream; import java.io.ObjectInputStream; import java.net.Socket; public class Person_Stub implements Person {Socket socket; public Person_Stub () throws Throwable {// connect to skeleton socket = new Socket ( " computer_name ", 9000);} public int getAge () throws Throwable {// pass method name to skeleton ObjectOutputStream outStream = new ObjectOutputStream (socket.getOutputStream ()); outStream.writeObject (" age "); outStream.flush (); ObjectInputStream inStream = new ObjectInputStream (socket.getInputStream ()); return inStream.readInt ();} public String getName () throws Throwable {// pass method name to skeleton ObjectOutputStream outStream = new ObjectOutputStream (socket.getOutputStream ()); outStream .writeObject ("name"); outstream.flush (); ObjectInputStream Instream = new ObjectInputst Ream (socket.getinputStream ()); return (String) Instream.readObject ();}} Note, like Person_stub and PersonServer, both imports person. They all enable both business method, different is that PersonServer is real implementation, and Person_STub is a Socket connection to the Skeleton, and then call the Personserver by Skeleton, and finally receive the result of returned . 4. Skeleton implementation
Code: import java.io.ObjectOutputStream; import java.io.ObjectInputStream; import java.net.Socket; import java.net.ServerSocket; public class Person_Skeleton extends Thread {PersonServer myServer; public Person_Skeleton (PersonServer server) {// get reference of object server this.myServer = server;} public void run () {try {// new socket at port 9000 serverSocket serverSocket = new serverSocket (9000); // accept stub's request Socket socket = serverSocket.accept (); while ( ! socket = null) {// get stub's request ObjectInputStream inStream = new ObjectInputStream (socket.getInputStream ()); String method = (String) inStream.readObject (); // check method name if (method.equals ( "age" )) {// Execute Object Server's business method int Age = MyServer.getage () ; ObjectOutputStream outStream = new ObjectOutputStream (socket.getOutputStream ()); // return result to stub outStream.writeInt (age); outStream.flush ();} if (method.equals ( "name")) {// execute object server's business method String name = myServer.getName (); ObjectOutputStream outStream = new ObjectOutputStream (socket.getOutputStream ()); // return result to stub outStream.writeObject (name);
Outstream.flush ();}}} catch (throwable t) {T.PrintStackTrace (); system.exit (0);}} public static void main (string args []) {// new object server personServer person = new Personserver ("Richard", 34); Person_Skeleton Skel = New Person_skeleton (Person); Skel.Start ();}} Skeleton class Extends from Thread, which is running in the background, receives the client sent by Client. And call the corresponding business method according to the sending key. 5. Last, Client's implementation code: public class persid {public static void main (string [] args) {Try {person Person = new person_stub (); int Age = person.getage (); string name = person.getname (); System.out.println (Name "IS" Age "Years Old");} catch (throwable t) {T.PrintStackTrace ();}}} Client's nature is that it must know the Person interface Definition, and instance a person_stub, call Business Method via Stub, as for how to communicate with Server, and Client does not have to manage. Pay attention to it: Person Person = New Person_stub (); not Person_stub Person = new person_stub (); why? Because it is necessary to facilitate interface programming, huh, huh. About RMI, I want to say so much. Here is the EJB of each class
The EJB class will not be used by WebLogic, here is combined with WebSphere to talk about the call relationships of each class. Assuming that we want to create a sessionbean that reads User information, we need to write 3 files: 1. UserviceHome.java HOME interface 2. Uservice.java Remote interface 3. UserviceBean.java bean implementation WSAD will eventually generate 10 Class. What is the other 7? Let's have a number of: 4. _USERSERSERVICEHOME_STUB.JAVA This is of course the Home interface in the Client side (dynamically loaded) Stub class, it is IMPLEments UserviceHome. 5._ejsremotestatelessuserServiceHome_A940AA04_TIE.JAVA HOME Interface The SKELETON class in the Server side, "A940AA04" should be randomly generated, all other related CLASS names will have this flag string, Tie is called Skeleton. 6. EJSREMOTASTATASSERSERSERVICEHOME_A940AA04.Java Home Interface Implementation in Server end, of course, it also imports UserviceHome. 7. EJSSTATASSERSERSERVICEHOMEBEAN_A940AA04.JAVA is called by # 6, Create _userService_stub. (Why can't # 6 can't use directly _userService_stub?) After later.) 8. _USERSERSERVICE_STUB.JAVA Remote Interface The stub class of the Client side (dynamically). It imports Uservice. 9. _ejsRemotestateLessuserService_a940aa04_tie.java Remote Interface The Skeleton class in the Server end. 10. EJSREMOTESTATELESSUSERSERVICE_A940AA04.Java Remote Interface Implementation in the Server end, of course, it is also imports Uservice. Also, it is responsible for calling UserServiceBean - that is, the bean we wrote bean implementation class - the business method inside. So, what is the call relationship between the various classes? Simply put, it is two RMI cycles.
