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=5&revisedVersion=6
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{note:title=Under development}
Note that binding.corba is still under development and may not be yet available
in Tuscany releases.
{note}
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 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}
{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 \\ || 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 |
| 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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