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}
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{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.
{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*|#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}
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}
{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 \\ || 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 |
| 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.
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