CORBA版HelloWorld
 
CORBA,是一个很古老的技术,甚至诞生于Java之前,不过随着WebService、SOA、RMI等等技术的出现,CORBA由于过于复杂而渐渐淡出了人们的视线,不过在一些交互性很强的系统异构应用领域,CORBA似乎很重要,比如中国联通、移动、美国的数字电视系统应用领域,是CORBA把整个系统核心部分集成起来的。如果没有异构的、需要预留标准接口的、交互性很强的应用,你不应该考虑使用COBRA。
 
CORBA目前的最近版本规范是3.2,Java1.5、1.6均支持该版本。
 
CORBA比较亲和C++,对Java程序员来说,开始CORBA应用难度比较大,以至于网上找一个真正能跑的HelloWorld都很难。
 
下面是我经过阅读SUN的CORBA文档,所做的一个完整的HelloWorld实例:
 
一、定义IDL
 
module HelloApp{
        interface Hello{
                string sayHello();
                oneway void shutdown();
        };
};
 
没有IDL的专门的开发工具,写起来容易出错,而且不美观,IDEA勉强支持语法高亮,但不支持格式化和语法校验!
 
二、从IDL生成存根
 
进入IDL文件存放目录,然后执行:idlj -fall Hello.idl
 
会生成一批Java文件:
 
helloCorba\src\HelloApp
HelloPOA.java
_HelloStub.java
HelloHolder.java
HelloHelper.java
Hello.java
HelloOperations.java
 
三、实现IDL接口,开发服务端程序
 
import HelloApp.Hello;
import HelloApp.HelloHelper;
import HelloApp.HelloPOA;
import org.omg.CORBA.ORB;
import org.omg.CosNaming.NameComponent;
import org.omg.CosNaming.NamingContextExt;
import org.omg.CosNaming.NamingContextExtHelper;
import org.omg.PortableServer.POA;
import org.omg.PortableServer.POAHelper;

class HelloImpl extends HelloPOA {
        private ORB orb;

        public void setORB(ORB orb_val) {
                orb = orb_val;
        }

        // implement sayHello() method
        public String sayHello() {
                return "\nHello world !!\n";
        }

        // implement shutdown() method
        public void shutdown() {
                orb.shutdown(false);
        }
}

public class HelloServer {

        public static void main(String args[]) {
                try {
                        //创建一个ORB实例
                        ORB orb = ORB.init(args, null);

                        //得到一个RootPOA的引用,并激活POAManager
                        POA rootpoa = POAHelper.narrow(orb.resolve_initial_references("RootPOA"));
                        rootpoa.the_POAManager().activate();

                        // create servant and register it with the ORB
                        //创建一个HelloImpl实例(servant),并注册到ORB上
                        HelloImpl helloImpl = new HelloImpl();
                        helloImpl.setORB(orb);

                        //从服务中得到对象的引用
                        org.omg.CORBA.Object ref = rootpoa.servant_to_reference(helloImpl);
                        Hello href = HelloHelper.narrow(ref);

                        //得到一个根名称的上下文
                        org.omg.CORBA.Object objRef = orb.resolve_initial_references("NameService");
                        // Use NamingContextExt which is part of the Interoperable
                        // Naming Service (INS) specification.
                        NamingContextExt ncRef = NamingContextExtHelper.narrow(objRef);

                        //在命名上下文中绑定这个对象
                        String name = "Hello";
                        NameComponent path[] = ncRef.to_name(name);
                        ncRef.rebind(path, href);

                        System.out.println("HelloServer ready and waiting ...");

                        //启动线程服务,等待客户端的调用
                        orb.run();
                }catch (Exception e) {
                        System.err.println("ERROR: " + e);
                        e.printStackTrace(System.out);
                }
                System.out.println("HelloServer Exiting ...");
        }
}
 
四、实现CORBA的客户端
 
import HelloApp.Hello;
import HelloApp.HelloHelper;
import org.omg.CORBA.ORB;
import org.omg.CosNaming.NamingContextExt;
import org.omg.CosNaming.NamingContextExtHelper;

public class HelloClient {
        static Hello helloImpl;

        public static void main(String args[]) {
                try {
                        //创建一个ORB实例
                        ORB orb = ORB.init(args, null);

                        //获取根名称上下文
                        org.omg.CORBA.Object objRef = orb.resolve_initial_references("NameService");
                        // Use NamingContextExt instead of NamingContext. This is
                        // part of the Interoperable naming Service.
                        NamingContextExt ncRef = NamingContextExtHelper.narrow(objRef);

                        //从命名上下文中获取接口实现对象
                        String name = "Hello";
                        helloImpl = HelloHelper.narrow(ncRef.resolve_str(name));

                        //调用接口对象的方法
                        System.out.println("Obtained a handle on server object: " + helloImpl);
                        System.out.println(helloImpl.sayHello());
                        helloImpl.shutdown();

                } catch (Exception e) {
                        System.out.println("ERROR : " + e);
                        e.printStackTrace(System.out);
                }
        }
}
 
五、运行
 
1)运行CORBA服务
orbd -ORBInitialPort 1050 -ORBInitialHost 192.168.14.117
 
2)运行CORBA应用的服务端
java HelloServer -ORBInitialPort 1050
 
输出:
HelloServer ready and waiting ...
HelloServer Exiting ...
 
3)运行CORBA应用的客户端
java HelloClient -ORBInitialHost 192.168.14.117 -ORBInitialPort 1050
 
Obtained a handle on server object: IOR:000000000000001749444c3a48656c6c6f4170702f48656c6c6f3a312e30000000000001000000000000008a000102000000000f3139322e3136382e31342e313137000006db000000000031afabcb00000000206d3bb80000000001000000000000000100000008526f6f74504f410000000008000000010000000014000000000000020000000100000020000000000001000100000002050100010001002000010109000000010001010000000026000000020002

Hello world !!
 
呵呵,很垃圾吧,但是客户要,我们就做!
 
太费劲了,如果做一个接口很复杂,参数很多,自定义类型不少的CORBA应用,复杂度将很好,如果经常改,那就更加郁闷了。