Java Programming, Lecture Notes 628, Revised 08/22/99.
Students in Prof. Baldwin's Advanced Java Programming classes at ACC will be responsible for knowing and understanding all of the material in this lesson beginning with the spring semester of 1999.
This lesson was originally written on October 25, 1998. The sample program was tested using the JDK 1.2beta4 download package. The purpose of this lesson is to illustrate the changes required to the client and server code to accommodate an expansion of the IDL to include multiple modules and interfaces with multiple operations.
There is a great deal more technical information of a fairly complex nature that I need to present before we wrap up our studies of CORBA and Java. However, this lesson is not intended to provide any significant new technical material. Rather, this lesson is intended for the sole purpose of expanding the IDL to contain multiple modules having interfaces with multiple operations and showing you how you can organize your code to accommodate this expanded situation. As you add modules and operations to the IDL file, the overall structure of the program becomes more complex. Therefore, I wanted to present that expanded structure before getting into other complex technical issues.
Following this lesson, I will revert back to the simpler IDL cases for discussion of complex technical issues such as parameter passing, callback methods, and alternatives to the use of a name service.
This lesson builds directly upon the previous lessons, so it is important that you understand the material in those lessons before embarking on this lesson.
As you will recall, both the client code and the server code have access to an IDL file, which declares the methods that can be invoked remotely. This is the key to the whole process and is the glue that holds it all together.
As in the previous lessons, this application requires three separate source files and two utility programs to compile and execute. The source files are:
The two utility programs are:
I prefer to make the process semi-automatic by encapsulating the process in an MS-DOS batch file. If you are not running under Windows or NT, you will need to figure out how to produce an equivalent script file for the platform that you are running on.
I have a folder on my computer that contains the following four source files:
Only the last three files are required. The batch file is optional, but is useful for managing the whole process.
Initially, this folder doesn't have any sub folders. However, execution of the program idltojava in this case creates two packages that contain the source files that it generates. As you will recall, I force the packages to be part of a directory tree that begins with a folder named junk. As a result, a junk folder is automatically generated which contains one folder named TheLottoApp and another folder named TheDateApp. These are the actual package names..
Complete listings of all of the files for this application (except those that are automatically generated by the idltojava program) are available for you to view near the end of this lesson. Since the thing that triggered the major changes in this application relative to the applications in previous lessons was an expansion of the IDL file, a copy of the IDL file is also presented below for your convenience.
/*File Corba04.idl
**********************************************************/
module TheDateApp{
interface TheDate{
string getTheDate();
long getTheTemperature();
};//end interface TheDate
};//end module TheDateApp
//=======================================================//
module TheLottoApp{
interface TheLotto{
long getTheLotto();
};//end interface TheLotto
};//end module TheLottoAppp |
This IDL file specifies two modules named TheDateApp and TheLottoApp. Each of the modules results in a different package having the same name when the IDL file is converted to Java using the idltojava program.
Each module declares one interface. The module named TheDateApp declares an interface named TheDate, and the module named TheLottoApp declares an interface named TheLotto. Each interface results in an object having operations or methods that can be invoked remotely by clients. One of the objects has two methods and the other object has one method.
The interface named TheDate declares two operations named getTheDate() and getTheTemperature(). These are the two methods that can be invoked remotely on one of the objects by client code.
The other interface named TheLotto declares one operation named getTheLotto(). This is the one method that can be invoked remotely on the other object.
When this IDL file is processed against the program named idltojava, two packages are created having names that correspond to the names of the two modules. Each package contains five Java source files that are automatically generated by the idltojava program. If you examine the source code for the files in the package named TheDateApp, you will see that it contains material designed to deal with the fact that the interface in that module has two different operations.
The batch file for this application is named Corba04.bat. When you review it, you will see that I simplified it somewhat by allowing the name service to default to port 900 and by allowing the machine on which the name service runs to default to localhost. I also made similar simplifications in the server code and the client code. The simplified batch file is shown below.
rem File Corba04.bat idltojava -fno-cpp -p junk Corba04.idl javac Corba04*.java start tnameserv start java Corba04Server start java Corba04Client |
I also took advantage of the fact that the javac compiler will automatically compile all of the files in the packages generated by idltojava because the are referenced either directly or indirectly in either the server code or the client code. This resulted in simplification to the batch file as well.
The name of the file containing the server code is Corba04Server.java. I'm not going to make any attempt to explain or highlight the changes that were required to the code in this file due to the expansion of the IDL. Rather, I am providing this material so that you can study it on your own and identify those changes yourself. However, I felt that you would be able to do that more easily if you had an operational example to work with.
The file containing the client code is named Corba04Client.java. Similar to the server file, I'm not going to make any attempt to explain the changes to you. I will leave it up to you to study the expanded IDL file and the client code and determine for yourself what changes to the code were required to accommodate the expansion of the IDL file.
There are other ways to expand the IDL file as well. I recommend that as an experiment, you expand the IDL file to contain multiple interfaces having multiple operations in one of the modules and determine the changes that are required to the server and client code to accommodate the expansion.
Complete listings for the IDL file, the batch file and the source code files that you must create are provided in this section. Listings are not provided for the Java source code files that are automatically generated by the idltojava program.
/*File Corba04.idl
See Corba04Server.java for information on this program.
This is the IDL file for one servant object that provides
two operations and a second servant object that provides
one operation.
**********************************************************/
module TheDateApp{//creates package TheDateApp
interface TheDate{//one interface with two operations
string getTheDate();//one operation
long getTheTemperature();// a second operation
};//end interface TheDate
};//end module TheDateApp
//=======================================================//
module TheLottoApp{//creates package TheLottoApp
interface TheLotto{//one interface with one operation
long getTheLotto();//the operation
};//end interface TheLotto
};//end module TheLottoAppp |
.
rem File Corba04.bat rem Use default port 900 on localhost for name service rem See Corba04Server.java for description of program echo off echo Convert the idl file to the required set of java files idltojava -fno-cpp -p junk Corba04.idl echo Compile the java files javac Corba04*.java echo Start the transient name server as a new process start tnameserv echo Start the server as a new process. start java Corba04Server echo Start the client as a new process. start java Corba04Client |
.
/*File Corba04Server.java
This is a simple CORBA server that provides two servant
objects. One object provides two different operations and
the other object provides one operation. To reduce
complexity, the program was written to default to name
service port 900 on localhost.
**********************************************************/
import junk.TheDateApp.*;
import junk.TheLottoApp.*;
import org.omg.CosNaming.*;
import org.omg.CosNaming.NamingContextPackage.*;
import org.omg.CORBA.*;
import java.util.Date;
//Define the class for the servant object that provides
// two different operations.
class TheDateServant extends _TheDateImplBase{
public String getTheDate(){//one operation
return new Date().toString();
}//end getTheDate()
//-----------------------------------------------------//
public int getTheTemperature(){//another operation
return 91;
}//end getTheTemperature
}//end TheDateServant class
//=======================================================//
//Define the class for the servant object that provides
// one operation.
class TheLottoServant extends _TheLottoImplBase{
public int getTheLotto(){
return 123456789;
}//end getTheLotto()
}//end TheLottoServant class
//=======================================================//
//Define the class for the server
public class Corba04Server{
public static void main(String args[]){
try{
// create and initialize the ORB
ORB orb = ORB.init(args, null);
//Instantiate two servant objects and register them
// with the ORB
TheDateServant theDateRef = new TheDateServant();
orb.connect(theDateRef);
TheLottoServant theLottoRef = new TheLottoServant();
orb.connect(theLottoRef);
//Get the root naming context
org.omg.CORBA.Object objRef =
orb.resolve_initial_references("NameService");
NamingContext ncRef
= NamingContextHelper.narrow(objRef);
//Establish id values for and bind the servabt
// objects in the naming service
NameComponent ncDate = new NameComponent("TheDate", "");
NameComponent datePath[] = {ncDate};
ncRef.rebind(datePath, theDateRef);
NameComponent ncLotto = new NameComponent("TheLotto", "");
NameComponent lottoPath[] = {ncLotto};
ncRef.rebind(lottoPath, theLottoRef);
System.out.println("Server is running");
//Wait for invocations from clients
java.lang.Object sync = new java.lang.Object();
synchronized (sync) {
sync.wait();
}//end synchronized block
}catch (Exception e) {
System.err.println("ERROR: " + e);
e.printStackTrace(System.out);
}//end catch block
}//end main()
}//end Corba04Server class |
.
/*File Corba04Client.java
See Corba04Server.java for information on this program.
**********************************************************/
import junk.TheDateApp.*;
import junk.TheLottoApp.*;
import org.omg.CosNaming.*;
import org.omg.CORBA.*;
public class Corba04Client{
public static void main(String args[]){
try{
//Create and initialize the ORB
ORB orb = ORB.init(args, null);
//Get the root naming context
org.omg.CORBA.Object objRef =
orb.resolve_initial_references("NameService");
NamingContext ncRef =
NamingContextHelper.narrow(objRef);
//Resolve the Object Reference for the servant obj
// with the id of TheDate.
NameComponent ncDate =
new NameComponent("TheDate","");
NameComponent datePath[] = {ncDate};
TheDate theDateRef =
TheDateHelper.narrow(ncRef.resolve(datePath));
//Invoke methods on the servant object and display
// the returned value
String theDate = theDateRef.getTheDate();
System.out.println("theDate: " + theDate);
int theTemperature = theDateRef.getTheTemperature();
System.out.println("theTemperature: "
+ theTemperature);
//Now resolve the Object Reference for the servant
// obj with the id of TheLotto.
NameComponent ncLotto =
new NameComponent("TheLotto", "");
NameComponent lottoPath[] = {ncLotto};
TheLotto theLottoRef =
TheLottoHelper.narrow(ncRef.resolve(lottoPath));
//Invoke a method on the servant object and display
// the returned value
int theLotto = theLottoRef.getTheLotto();
System.out.println("theLotto: " + theLotto);
//Delay program termination so that the console
// won't disappear from the screen when running
// under control of a batch file.
int ch1 = '0';
System.out.println("Press Ctrl-z to terminate");
while( (ch1 = System.in.read() ) != -1);
}catch (Exception e) {
System.out.println("ERROR : " + e) ;
e.printStackTrace(System.out);
}//end catch block
}//end main() method
}//end Corba04Client class |
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