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From conflue...@apache.org
Subject [CONF] Apache Tuscany: SCA Java binding.corba (page edited)
Date Fri, 01 Aug 2008 12:18:01 GMT
SCA Java binding.corba (TUSCANY) edited by Wojtek Janiszewski
      Page: http://cwiki.apache.org/confluence/display/TUSCANY/SCA+Java+binding.corba
   Changes: http://cwiki.apache.org/confluence/pages/diffpagesbyversion.action?pageId=91234&originalVersion=2&revisedVersion=3

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h3. <binding.corba>

The Tuscany Java SCA runtime supports CORBA using the <binding.corba> SCDL extension.
New CORBA based service can be provided using a <binding.corba> element within a SCA
<service>, existing CORBA object can be accessed using a <binding.corba> element
within a SCA <reference>.

h3. Using CORBA binding


h4. Configuring CORBA service/reference

Both service and reference CORBA binding can be configured by:

1. *Name*, *host*, *port* parameters, where *host* and *port* points to name service, and
*name* points to object within name service.


(i) Example service declaration:
{code}
<service name="ScenarionOneServiceGenerated" promote="ScenarionOneServiceGenerated">

    <interface.java interface="org.apache.tuscany.sca.test.corba.generated.ScenarioOneOperations"/>

    <tuscany:binding.corba host="localhost" port="5060" name="ScenarioOne/TuscanyGenerated"/>

</service>
{code}
2. Corbaname URI.

(i) Example reference declaration:
{code}
<reference name="scenarioOne">

    <tuscany:binding.corba uri="corbaname::localhost:5060#NamedWithURI"/>

</reference>
{code}

h4. Providing interface

For both service and reference side you can use one of two types of Java interface:

1. Generated by idlj compiler from \*.idl file.

2. Created by user according to rules for Java to CORBA mapping.

In both cases interfaces are almost the same. Difference is that generated interfaces extends/implements
CORBA types which are ignored by binding. Mapping rules are available under: [Java2IDL|http://www.omg.org/docs/formal/08-01-14.pdf],
[IDL2Java|http://www.omg.org/docs/formal/08-01-11.pdf]. Samples of CORBA bindings can be found
in *sca/itest/corba* module.
 
{note:title=Overloading, case collisions}
When using Tuscany service/reference binding to communicate with traditional CORBA objects:

1. Don't overload method names in Java interface.

2. Don't create methods with names which differs only by case, ie. you shouldn't declare both
methods: caseSensitive() and CaseSensitive().

You can ignore above rules if you are using Tuscany CORBA binding&nbsp; to communicate
with other Tuscany CORBA binding. Those constraints results from differences between IDL and
Java. More details can be found in "*Method/operation mapping rules"* section.
{note}&nbsp;
{note:title=Declaring exceptions}
Exceptions declared by user should be named to match remote exception ID.

Example: if in reference binding remote object throws exception with ID "IDL:org/apache/tuscany/sca/test/corba/generated/WrongColor:1.0"
then you should declare exception class named "org.apache.tuscany.sca.test.corba.generated.WrongColor".

The same in service bindings. SCA component exception will be thrown with ID created from
Java name.
{note}

h4. Method/operation mapping rules

IDL rules are different than rules in Java programming language - Java method names can't
be always directly mapped to CORBA operations. Following table shows used mapping rules:
|| Mapping type \\ || Description&nbsp; \\ || Examples: Java method - translated CORBA
operation ||
| 1. Getters and setters \\ | If user declared valid pair of getter and setter then those
methods would be translated to operations which are responsible for getting/setting objects
attribute. \\ | 1. getName() - \_get_name \\
2. setName(String newName) - \_set_name \\
3. isName() - \_get_name&nbsp; |
| 2. Overloaded names \\ | CORBA does not support overloading method names - Java does.. Some
mapping rules were applied to allow using overloaded names in Java interfaces using CORBA
binding. Final operation name is created by taking method name and appending it by CORBA parameters
type names separated by '_' chars. \\ | 1. overloadedMethod() - overloadedMethod_\_ \\
2. overloadedMethod(String arg1) - overloadedMethod__CORBA_WStringValue \\
3. overloadedMethod(String arg1, int arg2) - overloadedMethod\__CORBA_WStringValue_\_long
|
| 3. Names with case collisions | CORBA is not case sensitive - Java is. CORBA ie. doesn't
distinguish methods caseDifferent() and CaseDifferent(), so some mapping rules are fixing
it. Final operation name is created by taking method name and appending it by indexes of characters
which are capitals. | 1. caseDifferent() - caseDifferent_4 \\
2. CaseDifferent() - CaseDifferent_0_4 |

h4. Usage of additional "id" attribute in CORBA service bindings

User can also provide *id* attribute for service binding. It's not required, but helpfull
if we want to publish service which will be consumed by some idlj generated code. This generated
code contains \*Helper classes with narrow(...) methods. Narrow(...) method compares obtained
CORBA reference ID to some local (which was generated). CORBA service binding provide this
ID automatically basing on user provided Java interface name. Providing *id* attribute is
the only way to provide custom identifier.

(i) Example of using "id" attribute:
{code}
<service name="ScenarionOneServiceGenerated" promote="ScenarionOneServiceGenerated">

    <interface.java interface="org.apache.tuscany.sca.test.corba.generated.ScenarioOneOperations"/>

    <tuscany:binding.corba host="localhost" port="5060" name="ScenarioOneTuscanyGenerated"
id="IDL:org/apache/tuscany/sca/test/corba/generated/ScenarioOne:1.0"/>

</service>
{code}

h3. Host environment types

CORBA binding supports two hosting environments.

h4. host-corba-jdk

It is the standalone hosting environment where various ORBs could be used. You should provide
accessible name service and configure service/reference to point onto desired ORB.

(i) Usage: add *tuscany-host-jdk-<version>.jar* module to your class path.

h4. host-corba-jee

It is the JEE application server environment. In this case ORB is obtained from JNDI by *java:comp/ORB*
name and you do not need to provide name service.

(i) Usage: add *tuscany-host-jee-<version>.jar* module to your class path. 

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