Developer's Guide

Accessor Development Kit (ADK) Guide

This guide is intended to help a developer to extend the GI-cat architecture with a new customized accessor. For example if you have metadata stored on a custom database and wish to make it available through GI-cat.

The ADK is a package (jar) that contains the core classes and interfaces on which all other accessors are based. Specific accessors (e.g. WMS, WFS, ...) are in fact subclass of the abstract class "Accessor" that is included in the ADK.

The rules

The rules to implement a new accessor are:

1. Create the new accessor class by extending the class "Accessor"
2. Put in the classpath a file called conf/accessorBindings.properties. This file will contain a string like the following: [New accessor type]=[New accessor class qualified name], needed to support the pluggable extension system and put the new accessor in the system (e.g. the WMS accessor: WMS=it.cnr.imaa.essi.sdi.accessor.WMSAccessor).
   
3. Implement the Accessor interfaces (see below).
   

The new accessor may implement the Java interfaces (a more detailed description can be found in this document) :

• IDiscovery to discover resources metadata, either by means of catalog browsing or through a query operation.
• IAccess to get binary datablock associated to a resource or a resource preview.
• ISession to abort a running query or to get feedback on a query status.

Discovery interface operations

GetResource	Retrieve the resource with the given id
GetRootResource	Retrieve the catalog root resource
GetContent	Browse the children resources of a resource
Query	To perform a query on the catalog

Access interface operations

GetAccessParameters	Retrieve the XForms fields needed by GI-cat to access a given resource
GetDataURL	Gets the URL to use for subsequent data access
GetData	Gets the binary data block associated to a resource
GetPreview	Gets a preview of the given resource

Session interface operations

Close/Cancel	To terminate a previous query operation
Status	To retrieve feedback on a previous request

Step-by-step example

This section will guide you in the creation and integration of a new customized accessor into GI-cat. To create the new accessor, you must implement the corresponding class following the above rules. Here we provide an exampleAccessor implementation to be taken as an example during the development. This accessor discovers a single example resource and gives a sample preview.

Install GI-cat

Install the latest stable version of GI-cat with the automatic package installer. Download it from the download page

Since now on we will refer to GI-cat installation directory as to [GI-cat HomeDir]

Compile the new Accessor

After installing GI-cat and implementing your customized accessor, you will have to compile the new classess, create a jar with the new package and add it to the GI-cat classpath. Then the automatic plugin mechanism will recognize the accessor in the framework. To understand the necessary steps try first to integrate this example accessor. Download the exampleAccessor package^?. Unzip, the file and copy the directory (with all of its content) to the GI-cat lib directory . An "exampleAccessor" directory will be created and inside of it the sources of the new accessor are present.

Go to the GI-cat lib directory

$ cd [GI-cat HomeDir]/webapps/gi-cat-[version]/WEB-INF/lib/

run the following command (Linux, Mac OS X; if you use a Windows system replace the ":" with ";") (This requires to have Java v.1.6 last update pre installed on your system)

$ javac -classpath FastInfoset-1.2.3.jar:XmlSchema-1.4.5.jar:activation-1.1.jar:ant-1.7.0.jar:ant-launcher-1.7.0.jar:antlr-2.7.6.jar:aopalliance-1.0.jar:asm-2.2.3.jar:axiom-api-1.2.7.jar:axiom-impl-1.2.7.jar:axis2-1.4.jar:backport-util-concurrent-3.1.jar:bcel-5.1.jar:bcprov-jdk15-140.jar:commons-beanutils-1.7.0.jar:commons-beanutils-core-1.8.0.jar:commons-codec-1.2.jar:commons-collections-3.2.1.jar:commons-configuration-1.6.jar:commons-digester-1.8.jar:commons-discovery-0.2.jar:commons-httpclient-3.1.jar:commons-lang-2.4.jar:commons-logging-1.0.4.jar:commons-pool-1.2.jar:cxf-api-2.2.1.jar:cxf-common-schemas-2.2.1.jar:cxf-common-utilities-2.2.1.jar:cxf-rt-bindings-soap-2.2.1.jar:cxf-rt-bindings-xml-2.2.1.jar:cxf-rt-core-2.2.1.jar:cxf-rt-databinding-jaxb-2.2.1.jar:cxf-rt-frontend-jaxws-2.2.1.jar:cxf-rt-frontend-simple-2.2.1.jar:cxf-rt-transports-http-2.2.1.jar:cxf-rt-ws-addr-2.2.1.jar:cxf-rt-ws-security-2.2.1.jar:cxf-tools-common-2.2.1.jar:dom4j-1.6.1.jar:exist-1.2.jar:exist-modules-1.2.jar:ezmorph-1.0.6.jar:filter-v_1_0_0-schema-1.0.0.jar:geoapi-2.3-M1.jar:geoapi-pending-2.3-M1.jar:geronimo-activation_1.1_spec-1.0.2.jar:geronimo-annotation_1.0_spec-1.1.1.jar:geronimo-javamail_1.4_spec-1.6.jar:geronimo-jaxws_2.1_spec-1.0.jar:geronimo-stax-api_1.0_spec-1.0.1.jar:geronimo-ws-metadata_2.0_spec-1.1.2.jar:gml-v_2_1_2-schema-1.0.0.jar:gml-v_3_1_1-schema-0.1.jar:gt-api-2.6.0.jar:gt-main-2.6.0.jar:gt-metadata-2.6.0.jar:gt-referencing-2.6.0.jar:jaxb-api-2.1.jar:jaxb-impl-2.1.9.jar:jaxen-1.1.1.jar:jcl-over-slf4j-1.5.8.jar:jdom-1.0.jar:jgroups-all-2.2.9.1.jar:json-lib-2.2.3-jdk15.jar:jsr-275-1.0-beta-2.jar:jsyntaxpane-0.9.5-b29.jar:jta-1.0.1B.jar:jts-1.10.jar:lablib-jaxb-1.2.8.jar:lablib-nxd-1.2.3.jar:lablib-opensearch-1.0.jar:lablib-publisher-server-1.0.3.jar:lablib-utils-2.6.jar:lablib-xforms-2.1.5.jar:lablib-xml-1.5.jar:log4j-1.2.14.jar:mail-1.4.1.jar:neethi-2.0.4.jar:ogc-csw-2.0.2-2.0.1.jar:ogc-csw-2.0.2-apiso-1.0.0-2.0.1.jar:ogc-csw-2.0.2-ebrim-1.0-2.0.1.jar:ogc-filter-1.1.0-2.0.1.jar:ogc-gml-3.2.0-2.0.1.jar:ogc-org-purl-dc-1-2.0.1.jar:ogc-ows-1.0.0-1.1.0.jar:ogc-ows-1.1.0-1.1.3.jar:ogc-services-2.0.jar:ogc-wcs-1.1.0-1.0.3.jar:ows-v_1_0_0-schema-1.0.0.jar:quartz-1.5.1.jar:regexp-1.3.jar:saaj-api-1.3.jar:saaj-impl-1.3.2.jar:saxon-8.7.jar:saxon-dom-8.7.jar:sdi-accessor-cdi-2.1.5.jar:sdi-accessor-cswcore-2.1.5.jar:sdi-accessor-cswebrim-2.1.5.jar:sdi-accessor-cswebrim-cim-2.1.5.jar:sdi-accessor-cswebrim-eo-2.1.5.jar:sdi-accessor-cswiso-2.1.5.jar:sdi-accessor-download-2.1.5.jar:sdi-accessor-gbif-2.1.5.jar:sdi-accessor-gi-cat-2.1.5.jar:sdi-accessor-nxd-2.1.5.jar:sdi-accessor-opensearch-2.1.5.jar:sdi-accessor-thredds-2.1.5.jar:sdi-accessor-wcs-2.1.5.jar:sdi-accessor-wfs-2.1.5.jar:sdi-accessor-wms-2.1.5.jar:sdi-adk-4.0.4.jar:sdi-atom-rss-mapper-4.0.4.jar:sdi-chain-4.0.4.jar:sdi-core-mapper-4.0.4.jar:sdi-datamodel_6-4.0.4.jar:sdi-dclite4g-mapper-4.0.4.jar:sdi-eo-cim-mapper-4.0.4.jar:sdi-messages_6-4.0.4.jar:sdi-profiler-cswcore-1.1.7.jar:sdi-profiler-cswebrim-1.1.7.jar:sdi-profiler-cswebrim-cim-1.1.7.jar:sdi-profiler-cswebrim-eo-1.1.7.jar:sdi-profiler-cswiso-1.1.7.jar:sdi-profiler-genesi-dr-1.1.7.jar:sdi-profiler-gi-cat-1.1.7.jar:serializer-2.7.1.jar:slf4j-api-1.5.8.jar:slf4j-log4j12-1.5.8.jar:spring-beans-2.5.5.jar:spring-context-2.5.5.jar:spring-core-2.5.5.jar:spring-web-2.5.5.jar:stax-api-1.0-2.jar:sunxacml-1.2.jar:thredds-datamodel-1.0.2-1.2.jar:vecmath-1.3.2.jar:wcs-1.1.0-response-reader-1.0.5.jar:wcs-v_1_0_0-schema-0.1.jar:wfs-v_1_0_0-schema-1.0.0.jar:woden-api-1.0M8.jar:wsdl4j-1.6.1.jar:wss4j-1.5.7.jar:wstx-asl-3.2.8.jar:xalan-2.7.1.jar:xercesImpl-2.6.2.jar:xml-apis-1.3.04.jar:xml-resolver-1.2.jar:xmlParserAPIs-2.6.2.jar:xmldb-api-1.4.2.jar:xmlrpc-1.2-b1.jar:xmlsec-1.4.2.jar:xom-1.1.jar exampleAccessor/it/cnr/imaa/essi/sdi/accessor/ExampleAccessor.java

At this point you should have compiled your custom accessor.

Create a JAR with the new Accessor package

Enter the exampleAccessor directory

$ cd [GI-cat HomeDir]/webapps/gi-cat-[version]/WEB-INF/lib/exampleAccessor

Run the following command (you must have administrator permission)

$ jar cvf exampleAccessor.jar *

You should have the exampleAccessor.jar file in the current directory ([GI-cat HomeDir]/webapps/gi-cat-[version]/WEB-INF/lib/exampleAccessor)

Add the JAR to GI-cat classpath

Copy the created jar to the GI-cat lib directory (you must have administrator permission)

$ cp exampleAccessor.jar ../

Now, you can re-start GI-cat.

Test the Example Accessor

To check you have correctly plugged the new accessor, configure GI-cat adding a new resource of type EXAMPLE

Open GI-conf and press the Edit federated resources button

To add a new resource press the Add button

Source Code

If you are interested in the source code or want let us know about your custom accessor, please contact us. You are encouraged to provide some information/background of your project (we like to know developers who are interested in GI-cat and perhaps having their achievements listed under the success stories section!).