The Community OpenORB - TradingObjectService

The Trading Object Server is composed of 2 parts: the trader, and the service type repository

To start the trader, execute the Java class org.openorb.trader.Server. You can apply several options when you start the trader:

The service type repository can be used as embedded into the trader or in a stand alone mode. ( In this case, you have to start the trader and specifying the CORBA URL for the stand alone service type repsitory ).

To start the service type repository, execute the following Java class org.openorb.trader.repository.Server. Several options are available :

The Easy Trader System is an exclusive mechanism provided by the OpenORB Trading Object Service. The OMG Trading Service is a very interesting service that provides powerful features. However, it is often very difficult to use it, because it requires a lot of code to develop a simple application.

This is the reason why the OpenORB Trading Object Service provides a Service Type compiler that generates some Java classes ( fully portables ) to facilitate the Trading Service usage.

To describe a Service Type, you have to use the following grammar :

            service <ServiceTypeName> [ : <BaseServiceTypeName>
            [ , <BaseServiceTypeName> ]* ]
            {
            interface <InterfaceTypeName>;
            [ [ mandatory ] [ readonly ] property <IDLType>
            <PropertyName> ; ]*
            };
            

Each service type description must be defined in a file that uses the ".st" extension. This file could include IDL descriptions ( via #include ), and could use comments ( /* .. */ ).

This description must be compiled with the OpenORB Service Type compiler ( see next chapter to get more information about this compiler ).

When a ServiceType description is compiled, a file is generate <ServiceTypeName>Helper.java. This class provides the following operations :

Plus, if you use the -export flag with the service type compiler, another class is generated with the following name : <ServiceTypeName>.java

This class contains several operations :

The OpenORB Trading Object Service provides a service type compiler to generate Java classes that provide an easy way to use the trader.

The compiler class is: java org.openorb.trader.compiler.StdlCompiler

In addition to the standard IDL compiler flags, the STDL compiler provides :

OpenORB provides an Ant task that eases the use of OpenORB STDL compiler. The Ant task can be easily included in your projects by using the taskdef tag. The task does additionnal uptodate checks and only compiles idl files which are more recent than the target Java files. This is done using a cache (in a file called stdl2java.cache by default) which is updated every time the compiler is run.

             <project name="myproject">
               <taskdef resource="stdl2java.properties">
               ...
           

You only need to reference the openorb_tools-<version>.jar and openorb_trader-<version>.jar in the classpath of your build. The source files are set using a nested FileSet task which means that it possible to specify a whole tree of files to be compiled. It is possible to refine the set of files that are being compiled. This can be done with the includes, includesfile, excludes, and excludesfile attributes. With the includes or includesfile attribute, you specify the files you want to have included. The exclude or excludesfile attribute is used to specify the files you want to have excluded. In both cases, the list of files can be specified by either the filename, relative to the directory(s) specified in the srcdir attribute or nested <src> element(s), or by using wildcard patterns. See the section on Ant Manual,directory-based tasks, for information on how the inclusion/exclusion of files works, and how to write wildcard patterns.

Example:

<stdl2java destdir="${gensrc.dir}/examples"
           includepath="${examples.dir}/org/openorb/trader/examples/bank"
           srcdir="${examples.dir}/org/openorb/trader/examples/bank"
           includes="Bank.st" />

This tutorial explains how to use the OpenORB Trading Service and in a more generic way how to use a trader. The source code used by this tutorial is available into the "examples" directory of the OpenORB Trading Service distribution.

The source code for the steps 1 to 4 is available inside the "example/bank" directory.

To access the trader server, the TradingService key word must be resolved. A Lookup interface reference is returned :

                org.omg.CosTrading.Lookup lookup = null;
                try
                {
                    org.omg.CORBA.Object obj =
                    orb.resolve_initial_references("TradingService");
                    lookup = org.omg.CosTrading.LookupHelper.narrow( obj );
                }
                catch ( org.omg.CORBA.ORBPackage.InvalidName ex )
                {
                    System.out.println("Unknown service :" + ex.toString() );
                    System.exit(1);
                }
                

The Lookup interface provides all attributes and operations to use and manage the Trading Service.

There are two solutions to describe a service type :

Here, we are going to explain the two methods, but we will begin by the second solution, which is really easier !

We would like to describe a service type that corresponds to a bank. This service type provides a bank name and a property that indicates if this bank object supports the transactions. Thus, we create a file named "Bank.st" where we describe the following service :

                #include "bank.idl"
                service BankService
                {
                    interface Bank;
                    mandatory property string bank_name;
                    mandatory property boolean transactional;
                };
                

Now, we have to compile this description : java org.openorb.trader.compiler.StdlCompiler bank.st -export

Two files are generated :

In the Bank server, to create the BankService description creation into the trader, we have to write:

                BankServiceHelper.create_service( lookup );
                

And that's all !

The second solution to create a service type description is a little bit more complicated. First, we have to describe each properties, then the interface type, then the inheritance ( if any ) as shown in the following source code we have :

First, we create the list of properties ( here 2 : bank name + transactional ) :

                org.omg.CosTradingRepos.ServiceTypeRepositoryPackage.PropStruct []
                properties = new org.omg.CosTradingRepos.
                ServiceTypeRepositoryPackage.PropStruct[2];
                

Then, we describe the two properties ( name / mode / type ) :

                // Property bank_name
                properties[0] = new org.omg.CosTradingRepos.ServiceTypeRepositoryPackage.PropStruct();
                properties[0].name = "bank_name";
                properties[0].value_type = orb.get_primitive_tc( org.omg.CORBA.TCKind.tk_string );
                properties[0].mode =org.omg.CosTradingRepos.ServiceTypeRepositoryPackage.PropertyMode.PROP_MANDATORY_READONLY;

                // Property transactionnal
                properties[1] = new org.omg.CosTradingRepos.ServiceTypeRepositoryPackage.PropStruct();
                properties[1].name = "transactional";
                properties[1].value_type = orb.get_primitive_tc( org.omg.CORBA.TCKind.tk_boolean );
                properties[1].mode = org.omg.CosTradingRepos.ServiceTypeRepositoryPackage.PropertyMode.PROP_MANDATORY;
                

Now, we describe the inheritance ( here no inheritance ) :

                String [] inherited = new String[0];
                

Then, to finish we create the new description ( first, we have to get access to the repository ) :

                try
                {
                    org.omg.CosTradingRepos.ServiceTypeRepository repository =
                    org.omg.CosTradingRepos.ServiceTypeRepositoryHelper.narrow( lookup.type_repos() );
                    org.omg.CosTradingRepos.ServiceTypeRepositoryPackage.IncarnationNumber incarnation = null;
                    incarnation = repository.add_type( "BankService", "::Bank", properties, inherited );
                }
                catch ( java.lang.Exception ex )
                {
                    System.out.println("Unable to create the service type description !");
                    System.exit(1);
                }
                

Now, this is finished ! We suggest you always use the Service Type compiler, because it generates portable source code that could be reused by another trading service !

To export an offer, two approaches are also available !

The first one is as usual the most simple, it uses the generated files from the service type description. If you use the -export flag with the compiler, it also generates a class which has the same name than the service type. The following piece of code explains how to use this class :

                BankService bank_service = new BankService( orb, lookup );
                

The previous line uses the constructor to create a new instance of the BankService. This class contains an accessor to set the value for each property :

                bank_service.bank_name( "Barclays" );
                bank_service.transactional( false );
                

When the values are set, the last thing to do is to export the offer :

                if ( bank_service.export( bank._this( orb ) ) == null )
                {
                    System.out.println("Unable to export offer...");
                }
                

The second approach ( the standard approach ) is more complicated as shown above :

                org.omg.CosTrading.Property [] properties = new org.omg.CosTrading.Property[2];

                properties[0] = new org.omg.CosTrading.Property();
                properties[0].name = "bank_name";
                properties[0].value = orb.create_any();
                properties[0].value.insert_string( "barclays" );

                properties[1] = new org.omg.CosTrading.Property();
                properties[1].name = "transactional";
                properties[1].value = orb.create_any();
                properties[1].value.insert_boolean( false );

                try
                {
                    return register.export( bank._this( orb ), "BankService", properties );
                }
                catch ( java.lang.Exception ex )
                { }
                

To find a service, again, two solutions :

                org.omg.CosTrading.Offer [] offers =
                    BankServiceHelper.resolve_service( orb, lookup, "transactional == FALSE", "" );
                

In the previous line, we ask for a BankService offer, by providing the ORB instance, the Lookup reference, the constraint and the preference.

                // -- Check for errors --
                if ( offers == null )
                {
                    System.out.println("An error occured during query...");
                    System.exit(0);
                }
                // -- Check if there are some compliant offers --
                if ( offers.length == 0 )
                {
                    System.out.println("No compliant Bank found...");
                    System.exit(0);
                }
                // -- Access to a compliant offer --
                Bank bank = BankHelper.narrow( offers[ 0 ].reference );
                

The second possibility ( standard way ) :

                org.omg.CosTrading.OfferSeqHolder offers =
                    new org.omg.CosTrading.OfferSeqHolder();
                org.omg.CosTrading.OfferIteratorHolder iterator =
                    new org.omg.CosTrading.OfferIteratorHolder();
                org.omg.CosTrading.PolicyNameSeqHolder limits =
                    new org.omg.CosTrading.PolicyNameSeqHolder();

                try
                {
                    org.omg.CosTrading.Policy [] policies =
                    new org.omg.CosTrading.Policy[3];

                    policies[0] = new org.omg.CosTrading.Policy();
                    policies[0].name = "exact_type_match";
                    policies[0].value = orb.create_any();
                    policies[0].value.insert_boolean( true );
                    policies[1] = new org.omg.CosTrading.Policy();
                    policies[1].name = "use_dynamic_properties";
                    policies[1].value = orb.create_any();
                    policies[1].value.insert_boolean( true );
                    policies[2] = new org.omg.CosTrading.Policy();
                    policies[2].name = "use_proxy_offers";
                    policies[2].value = orb.create_any();
                    policies[2].value.insert_boolean( true );

                    org.omg.CosTrading.LookupPackage.SpecifiedProps
                    desired_properties = new org.omg.CosTrading.LookupPackage.SpecifiedProps();
                    desired_properties.all_dummy((short)0);

                    lookup.query( "BankService", "transactional == FALSE", "",
                        policies, desired_properties, 10, offers, iterator, limits );

                    return offers.value;
                }
                catch ( java.lang.Exception ex )
                {
                    System.out.println("An error occured during query...");
                    System.exit(0);
                }
                // -- Check if there are some compliant offers --
                if ( offers.value.length == 0 )
                {
                    System.out.println("No compliant Bank found...");
                    System.exit(0);
                }
                // -- Access to a compliant offer --
                Bank bank = BankHelper.narrow( offers.value[ 0 ].reference );
                

A property can be dynamic. It means that you don't have to provide a value for the property, but you have to register an external evaluator that is invoked when you want to get the dynamic property value.

The source code of this example is available in example/task. In this section we only explain the most simple way which uses the OpenORB TOS extension ( the service type compiler and its generated files ).

The example Task shows this kind of properties. In this example, we are looking for a task executor which provides in its offer the quantity of memory available to run the task. The memory quantity is evaluted via a dynamic property :

                service TaskService
                {
                    interface Task;
                    mandatory property string host_name;
                    mandatory property long long memory;
                };
                

As you see in the previous description, the memory property is not marked as dynamic. Indeed, any property can be dynamic ! The compiler generates two kind of accessors for each property :

Example :

                public class TaskService
                {
                    // ...
                    public void memory( long value )
                    {
                        // ...
                    }
                    public void memory( org.omg.CosTradingDynamic.DynamicPropEval eval )
                    {
                        // ...
                    }
                }
                

An evaluator is simple to develop :

                public class MemoryEval
                    extends org.omg.CosTradingDynamic.DynamicPropEvalPOA
                {
                    private org.omg.CORBA.ORB orb;
                    public MemoryEval( org.omg.CORBA.ORB orb )
                    {
                        this.orb = orb;
                    }
                    public org.omg.CORBA.Any evalDP(
                                java.lang.String name,
                                org.omg.CORBA.TypeCode returned_type,
                                org.omg.CORBA.Any extra_info )
                        throws org.omg.CosTradingDynamic.DPEvalFailure
                    {
                        if ( ! name.equals("memory") )
                            throw new org.omg.CosTradingDynamic.DPEvalFailure( name,
                                            returned_type, extra_info );
                        long free = java.lang.Runtime.getRuntime().freeMemory();
                        org.omg.CORBA.Any any = orb.create_any();
                        any.insert_longlong( free );
                        return any;
                    }
                }
                

Now to export the offer :

                TaskService task_service = new TaskService( orb, lookup );
                String name = java.net.InetAddress.getLocalHost().getHostName();
                task_service.host_name( name );
                task_service.memory( eval._this( orb ) );
                // -- And to finish, export the offer --
                if ( task_service.export( task._this( orb ) ) == null )
                {
                    System.out.println("Unable to export offer...");
                }