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From conflue...@apache.org
Subject [CONF] Apache Tuscany: SCA Java binding.corba (page edited)
Date Mon, 18 Aug 2008 11:06:00 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=13&revisedVersion=14

Comment:
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added guide to CORBA arrays and unions

Change summary:
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added guide to CORBA arrays and unions

Change summary:
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added guide to CORBA arrays and unions

Change summary:
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added guide to CORBA arrays and unions

Change summary:
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added guide to CORBA arrays and unions

Content:
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{section:border=false}
{column:width=15%}
{include: SCA Java Subproject Menu}
{include: Java SCA Menu New}
{column}
{column:width=85%}
{note:title=Under development}
Note that binding.corba is 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>.
* [*Configuring CORBA service/reference*|#Location]
* [*Providing interface*|#ProvidingInterface]
* [*CORBA arrays and unions mapping*|#ArraysUnions]
* [*Methods to operations mapping*|#MethodMapping]
* [*Usage of additional "id" attribute in CORBA service bindings*|#IdAttribute]
* [*Host environment types*|#Hosts]

h3. Using CORBA binding

{anchor:Location}

h4. Configuring CORBA service/reference

Location for 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}
{anchor:ProvidingInterface}

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.
&nbsp;
{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*|#MethodMapping] 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}{anchor:ArraysUnions}

h4. CORBA arrays and unions mapping

CORBA arrays and unions cannot be directly mapped so additional metadata should be used.

*1. Arrays mapping*

To declare CORBA array you should declare Java array and annotate it by *org.apache.tuscany.sca.binding.corba.meta.CorbaArray*
annotation.

Annotation *org.apache.tuscany.sca.binding.corba.meta.CorbaArray* has one default attribute
(array of integers) which declares lengths of following array dimensions. Objects you can
annotate are:
* binding interface methods arguments
* binding interface methods, which will refer to return type
* structure fields

(i) Example:
{code}
import org.apache.tuscany.sca.binding.corba.meta.CorbaArray;

public interface SampleInterface {

    @CorbaArray( {2, 2}) // this annotation makes return array to be CORBA array
    public String[][] passStringArray(@CorbaArray( {2, 2})String[][] arg); // this annotation
makes mehods argument to be CORBA array

}
{code}
&nbsp;You can also annotate fields in CORBA structures.

(i) Example:
{code}
import org.apache.tuscany.sca.binding.corba.meta.CorbaArray;

public final class SampleStruct {

    @CorbaArray( {2, 2}) // following field is two dimensional CORBA array, which has 2 elements
in both first and second dimension
    public String[][] stringArray;

    public SampleStruct() {

    }

    public SampleStruct(String[][] stringArray) {
        this.stringArray = stringArray;
    }

}
{code}
*2. Unions mapping*

To declare CORBA union you should create final Java class which contains:
* private field for every union option
* private field of int, which will be discriminator

Union options as well as discriminator should be annotated with *org.apache.tuscany.sca.binding.corba.meta.CorbaUnionElement*,
which has two attributes:
* CorbaUnionElementType type(), which can take following values:
** CorbaUnionElementType.option for member, additional optionNumber attribute is required
** CorbaUnionElementType.defaultOption for default union member
** CorbaUnionElementType.discriminator for discriminator field
* int optionNumber() - can be used only with CorbaUnionElementType.option

(i) Example:

Following IDL declaration:
{code}
union SampleUnion switch (long) {
    case 1: long x;
    case 2: float y;
    default: string z;
};
{code}
is equal to Tuscany CORBA binding declaration:
{code}
import org.apache.tuscany.sca.binding.corba.meta.CorbaUnionElement;
import org.apache.tuscany.sca.binding.corba.meta.CorbaUnionElementType;

public final class SampleUnion {

    @CorbaUnionElement(type = CorbaUnionElementType.option, optionNumber = 1)
    // this is union member, id = 1
    private int x;

    @CorbaUnionElement(type = CorbaUnionElementType.option, optionNumber = 2)
    // this is union member, id = 2
    private float y;

    @CorbaUnionElement(type = CorbaUnionElementType.defaultOption)
    // this is default union member
    private String z;

    @CorbaUnionElement(type = CorbaUnionElementType.discriminator)
    private int discriminator;

    public int getX() {
        return x;
    }

    public void setX(int x) {
        discriminator = 1;
        this.x = x;
    }

    public float getY() {
        return y;
    }

    public void setY(float y) {
        discriminator = 2;
        this.y = y;
    }

    public float getZ() {
        return z;
    }

    public void setZ(float z) {
        discriminator = -1;
        this.z = z;
    }

}
{code}
&nbsp;{anchor:MethodMapping}

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 wouldbe 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 |
{anchor:IdAttribute}

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}
{anchor:Hosts}

h3. Host environment types

CORBA binding supports two hosting environments.

h4. host-corba-jse

It is the standalone hosting environment where various ORBs could be used. Note that you have
to provide name service by yourself and configure service/reference to point onto desired
ORB.
(i) Usage: add *tuscany-host\-*{*}jse{*}*\-<version>.jar* module to your class path.

h4. host-corba-jse-tns

This hosting environment extends *host-corba-jse*. For every configured service CORBA binding
which points to localhost Transient Name Service will be created and name servers for bindings
using the same port will be shared.
(i) Usage: add *tuscany-host-jse-tns-<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 don't need to provide name service. Also *host* and *port* (or their equivalent
contained in corbaname URI) parameters are ignored.
(i) Usage: add *tuscany-host-jee-<version>.jar* module to your class path.
{column}
{section}

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