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Handlers are pluggable components, that contain custom processing logic for handling resources. All handlers extend an abstract class named Handler, which provides default implementations for resource handling methods as well as a few utilities useful for concrete handler implementations.

Handler implementations can provide alternative behaviors for basic resource related operations, by overwriting one or more methods in the Handler class. At this point, it is useful to look at the Handler class listed below.

Note

Here some details are omitted for clarity.

Here is a description of how each of these methods works.

Method

Important parameters (To extract from Request Context)

Return value

Description

get

requestContext.getResourcePath() // path, the resource is getting

Resource // the resource at the path

Retrieves a resource in a given path.

put

requestContext.getResourcePath() // path to put
requestContext.getResource() // the resource to store

-

Stores a resource in a given path.

importResource

requestContext.getResourcePath() // path to put
requestContext.getSourceURL() // the URL of the importing resource

-

Imports a resource from a URL.

move

requestContext.getSourcePath() // source to move from
requestContext.getTargetPath() // target to move to

String // the new path

Moves a resource from one to another.

copy

requestContext.getSourcePath() // source to copy from
requestContext.getTargetPath() // target to copy to

String // the new path

Copies a resource from one to another.

rename

requestContext.getSourcePath() // source of the resource
requestContext.getTargetPath() // the new name

String // the new path

Changes a name of a resource.

createLink

requestContext.getResourcePath() // the path of the link is creating
requestContext.getTargetPath() // the target path or the target registry url
requestContext.getTargetSubPath() // the target sub path if the target is a remote url

-

Creates a sym-link or a remote link.

removeLink

requestContext.getResourcePath() // the path of the link to remove

-

Removes a link.

delete

requestContext.getResourcePath() // the path of the resource to remove

-

Deletes a resource. If this is a collection, all the children will also be removed.

putChild Deprecated.

requestContext.getResourcePath() // the path resource is putting
requestContext.getResource() // the resource to put

String // the path of the resource

Called when putting a resource to any path except root.

importChild

requestContext.getResourcePath() // the path resource is importing to
requestContext.getSourceURL() // the URL of the importing resource

String // the path of the resource

Called when importing a resource to any path except root.

invokeAspect

requestContext.getResource() // the resource to invoke the aspect
requestContext.getAspect() // the Aspect object to be invoked
requestContext.getAction() // the action of the Aspect

-

Triggered when invoking an aspect (Aspects are described in detail in following sections).

addAssociation

requestContext.getSourcePath() // left branch of the association
requestContext.getTargetPath() // right branch of the association
requestContext.getAssociationType() // the type of the association

-

Triggered when adding an association.

removeAssociation

requestContext.getSourcePath() // left branch of the association
requestContext.getTargetPath() // right branch of the association
requestContext.getAssociationType() // the type of the association

-

Triggered when removing an association.

getAllAssociations

requestContext.getResourcePath() // the path of the resource

Association[]

Returns all the associations of a given resource.

getAssociations

requestContext.getResourcePath() // the path of the resource
requestContext.getAssociationType() // the type of the association

Association[]

Returns associations of a give association type of a given resource.

applyTag

requestContext.getResourcePath() // the path of the resource
requestContext.getTag() // the tag to be added

-

Applies a tag to a particular path.

removeTag

requestContext.getResourcePath() // the path of the resource
requestContext.getTag() // the tag to be removed

-

Removes a tag in a particular path.

rateResource

requestContext.getResourcePath() // the path of the resource
requestContext.getRating() // the value of the rating

-

Triggered when Rating a resource.

restoreVersion

requestContext.getVersionPath() // the path + version of the resource

-

Triggered when restoring a version-ed resource.

createVersion

requestContext.getResourcePath() // Create a version of a resource

-

Triggered when creating a resource.

This is triggered when you create a snapshot (but not a new version) of an asset. It is related to the Repository aspect of WSO2 G-Reg.

editComment

requestContext.getCommentPath() // The path of the comment of a resource
requestContext.getComment() // The comment

-

Edits a comment in a given path.

addComment

requestContext.getResourcePath() // The path of the resource
requestContext.getComment() // The comment

String // the comment path

Adds a comment to the given path.

removeComment

requestContext.getCommentPath() // The path of the comment of a resource
requestContext.getComment() // The comment

-

Removes a comment in a given path.

getComments

requestContext.getResourcePath() // The path of the resource

Comment[]

Gets all comments in a given path.

getAverageRating

requestContext.getResourcePath() // The path of the resource

float

Gets the average rating of a resource.

getRating

requestContext.getResourcePath() // The path of the resource
requestContext.getUserName() // The path of the resource

int

Gets the rating given by a user to a given resource.

getVersions

requestContext.getResourcePath() // The path of the resource

String[]

Returns version paths of a given resource.

getTags

requestContext.getResourcePath() // The path of the resource

Tag[]

Returns tags of a given resource.

getResourcePathWithTag

requestContext.getResourcePath() // The path of the resource
requestContext.getTag() // The value of the tag

TaggedResourcePath[]

Returns resource paths with a given tag.

executeQuery

requestContext.getResourcePath() // The path of the query
requestContext.getQueryParameters() // The query parameters

Collection

Returns collection (paths as the content) queried in the given query.

searchContent

requestContext.getKeywords() // The search keywords

Collection

Returns collection (paths as the content) found as a result of search operation.

resourceExists

requestContext.getResourcePath() // The path of the resource

boolean

Returns whether the resource in the given path exists.

dump

requestContext.getResourcePath() // The path of the resource
requestContext.getDumpingWriter() // The writer that requested in dumping

-

Dumps a particular path.

restore

requestContext.getResourcePath() // The path of the resource
requestContext.getDumpingReader() // The reader that used with restoring

-

Restores a dump.

Handlers can be engaged and configured using the registry configuration file (registry.xml). Here is an example of using registry.xml to declare a handler.

<handler class="org.wso2.carbon.registry.extensions.handlers.WSDLMediaTypeHandler">
        <property name="schemaLocationConfiguration" type="xml">
            <locationType>absolute</locationType>
            <location>/governance/schemas/</location>
        </property>
        <property name="wsdlLocationConfiguration" type="xml">
            <locationType>absolute</locationType>  <!-- absolute or relative -->
            <location>/governance/wsdls/</location>
        </property>
        <filter class="org.wso2.carbon.registry.core.jdbc.handlers.filters.MediaTypeMatcher">
            <property name="mediaType">application/wsdl+xml</property>
        </filter>
    </handler>

Here are the important parameters you can provide in the handler configuration.

  • Handler class - The class name of the handler. Provided in the class attribute in the Handler. For example:
<handler class="org.wso2.carbon.registry.extensions.handlers.WSDLMediaTypeHandler">
       ...
    </handler>
  • Handler properties - Custom properties that will be used in handler processing logic. For example:
<property name="wsdlLocationConfiguration" type="xml">

The attributes in the property element:

  • name - The name of the property. In order to store the property value, you should have an setter method in the particular handler class. The method name should be set + property name with the first letter capitalized. The method name for the above property would be:
setWsdlLocationConfiguration
  • type - The type of the property. Possible values are xml and null. If the type is xml, the handler method should have an method argument of the type org.apache.axiom.om.OMElement. If the type attribute is not given, the method argument will be of the type java.lang.String. So the method signature for the above example property is:
public void setWsdlLocationConfiguration(OMElement locationConfiguration) throws RegistryException {
}
  • Filter is associated with the handler. You can refer a filter inside a handler which would provide the filter functionality to that particular handler. The handler for a particular method is invoked only if the filter is returning true for the corresponding method. For more details about filters, see Configuring Filters .
Common steps in writing a handler.

1. Extend the Handler class and overwrite necessary methods.

2. Implement whatever custom behaviors in overwritten methods. You may use information provided in the RequestContext instance, in your custom implementation.

3. Once the custom behavior is completed, it is usually required to perform the actual requested operation (for example, add the resource in put(...) method).

Tip

Use the Repository instance provided in the RequestContext to perform the actual operation. If it is required to version the resource in put operation, use VersionRepository instance.

Note

It is not recommended to use the Registry instance to perform resource related operations (get, put, import, delete) inside a handler as it may cause infinite loops as the Registry tries to invoke all handlers again.

See also Handlers.

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