The middleware (WebFlow)

Example of slave_test.conf: slave WebFlow server configuration file.

slave_test.conf
ServerName=slave_test
File=none 
URL=http://osprey4.npac.syr.edu:8001/IOR/testmaster.txt
PARENT=master_test
WEBFLOW_IDL=/npac/home/webflow/WEBFLOW/BeanContext_2.2.2
Modules:===================

To configure your slave server, please edit this file and set the values of URL and WEBFLOW_IDL attributes.

testing WebFlow servers

1. customize WebFlow servers configuration files
2. open a new window (Command Prompt window on WindowsNT)
3. execute command: java WebFlow.Server master_test.conf
   • a lot of cryptic text will be generated in the window. Among the last lines you should be able to find:

     GATEWAY SERVER:exist:true
     SERVER IS READY FOR ACCEPTING USER COMMANDS.....
     FactoryImpl: createProxy: after new proxy()_usermaster_test
     

     They can come in a different order, as they are generated by three different processes. Be patinet, starting a server takes time. It depends on speed of your machine. It may take serveral seconds.
   • any error messages, java exceptions, etc. are signatures of a failure. Double check configuration files and $CLASSPATH, and restart. If you cannot make it running please save the output, and send it with your *.conf files to T. Haupt
4. once the master server is up and running, make sure that your Web Server is up
5. open a new window
6. execute command: java WebFlow.Server slave_test.conf
   • a lot of cryptic text will be generated in the window, also you will see new messages printed to the master WebFlow server window. The last line should read

     ERVER IS READY FOR ACCEPTING USER COMMANDS.....
     GATEWAY SERVER:exist:true
     Slave Webflow: sent addWFServer request

     They can come in a different order, as they are generated by three different processes. Be patinet, starting a server takes time. It depends on speed of your machine. It may take several sececonds.
   • any error messages, java exceptions, etc. are signatures of a failure. Double check configuration files and $CLASSPATH, and restart. If you cannot make it running please save the output, and send it with your *.conf files to T. Haupt
7. once both master and slave server are running, you may run the test client code
8. open a new window (third one) and execute command java WebFlow.client url of the master ior file. The url is identical to that you specified in the save_test.conf file
9. the client will connect to your slave server, create a new context within the slave context, shut down both slave and master servers, and finally write to the output stream message "TEST COMPLETED".
   Example output:

   osprey4:/project/gateway/WebFlow/Releases/WebFlow_2.2.1% java WebFlow.Client http://osprey4.npac.syr.edu:8001/IOR/testmaster.txt
   Slave WebFlow is getting IOR from url:http://osprey4.npac.syr.edu:8001/IOR/testmaster.txt
   IOR:000000000000001f49444c3a576562466c6f772f576562466c6f77436f6e746578743a312e30000000000001000000000000003400010000000000156f7370726579342e6e7061632e7379722e6564750000aef0000000100000000037b096a80006ca4800000001
   Client: Connected to the Master Server
   Client: Connected to the Slave Server
   create a subContext
   Failure? false
   Client: SubContext created
   TEST COMPLETED
   

   Note: there should be no null pointer exceptions. If you got one, please double check your configuration files and $CLASSPATH
10. this concludes the test. Slave_server, and master_server should be shut down at this time (you should have the prompt at their windows).

java WebFlow.Server master.conf

You cannot instantiate a master server more than once (it will fire an exception if you do). To run two master servers concurrently, you must set different names in their configuration files (as well as the file attribute, otherwise one server will overwrite the IOR of the other).

Slave server: You start the slave server using command

java WebFlow.Server slave.conf

That is, the procedure of starting a slave server is identical to that of starting the master server. The only difference is different configuration file.

You can start and arbitrary number of slaves of a given master, as long as you assign them different names in their configuration files.

In addition, you can start a slave of a slave, by specifing accordingly the PARENT atribute in its configuration file. Say, if the master server name is "master", slave server name is "slave", you can start "slave-slave" by specifying its PARENT as master/slave, and slave-slave-slave by setting its PARENT to /master/slave/slave-slave.

WebFlow Contexts

A WebFlow context can be started as a separate process (then we call it a WebFlow server) or be added as a child to an existing contexts. Starting the server is described in section Starting a WebFlow Server above. You can add a new context to existing one by invoking a method of the WebFlowContext class:

org.omg.CORBA.Object addNewContext("context_name");

org.omg.CORBA.Object o = addNewContext("context_name");
WebFlowContext c = WebFlowContextHelper.narrow(o);

WebFlowContext c = WebFlowContextHelper.narrow(addNewContext("context_name"));

accessing a WebFlow context

You can access all existing WebFlow contexts (both servers and "internal") through the master server. To access the master server:

• read the master's IOR from your Web server
• using ORB method, convert IOR to an CORBA object
• narrow it

       String ior = readIORfromURL(url);
       try {  
       org.omg.CORBA.Object MasterObj=orb.string_to_object(ior);
       WebFlowContext Master = WebFlowContextHelper.narrow(MasterObj);  
       }
       catch (Exception e) {System.out.println("connection failure "+e);}

String orb.object_to_string(org.omg.CORBA.Object o);

Once you have acccess to the master server, you can use its methods to access other contexts by invoking

org.omg.CORBA.Object o = Master.getContext("context_name");
WebFlowContext slave = WebFlowContextHelper.narrow(o);

org.omg.CORBA.Object o = Master.getContext("master/slave/slave-slave/slave-slave-slave");

Selected methods of the WebFlowContext class

The full list of WebFlowContext class can be found in JavaDoc for BeanContext_2.2.2. Here we list a few most commonly used ones:

String c.getObjectID();

retuns the name of the context c

org.omg.CORBA.Object[] c.toArray();

returns all children of a givent context c (child contexts and modules)

org.omg.CORBA.Object c.getParent();

returns the parent context

org.omg.CORBA.Object c.getKeyedChild(String name);

returns child object (context or module) named "name" (but not grandchildren!)

void c.removeMyself();

removes itself together with all hierarchy of objects pending on it; if the context is a server, it terminates the process together with all processes pending on it, such as ir (interface depository).

org.omg.CORBA.Object c.addNewModule(String name);

add a new module to the context (see section WebFlow modules for details

void c.removeModule(String name);

removes the module from the context (see section WebFlow modules for details

void c.attachPullEvent(org.omg.CORBA.Object s, String eventName,org.omg.CORBA.Object d, String methodName);

attaches a pull event (see section WebFlow events for details

void c.attachPushEvent(org.omg.CORBA.Object s, String eventName,org.omg.CORBA.Object d, String methodName);

attaches a push event (see section WebFlow events for details

void c.detachPullEvent(org.omg.CORBA.Object s, String eventName,org.omg.CORBA.Object d, String methodName);

detaches a pull event (see section WebFlow events for details

void c.detachPushEvent(org.omg.CORBA.Object s, String eventName,org.omg.CORBA.Object d, String methodName);

detaches a push event (see section WebFlow events for details

to be written

WebFlow Events

to be written

WebFlow clients

to be written

Java Applets

to be written