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SMILA/Documentation/HowTo/How to implement a crawler

< SMILA‎ | Documentation‎ | HowTo
Revision as of 11:33, 18 September 2008 by (Talk | contribs) (Java implementations)

Java implementations

  • Create a new eclipse Project using the Plug-in Project Wizard and select "Equinox" as OSGi framework
  • name the project using the prefix org.eclipse.eilf.connectivity.framework.crawler.
  • edit the manifest and add the follwing to Imported Packages
    • org.eclipse.eilf.connectivity.framework
    • org.eclipse.eilf.connectivity.framework.utils
    • org.eclipse.eilf.datamodel.record
    • com.sun.xml.bind.v2;version="2.1.6"
    • javax.xml.bind;version="2.1.0"
    • javax.xml.bind.annotation;version="2.1.0"
    • javax.xml.bind.annotation.adapters;version="2.1.0"
    • org.apache.commons.logging;version="1.1.1"
  • edit the manifest and add the follwing to <tt>Require-Bundle: (it MUST be imported via reguire bundle instead of package import)</tt>
    • org.eclipse.eilf.connectivity.framework.indexorder
  • After edit the manifest, this looks like:
Require-Bundle: org.eclipse.eilf.connectivity.framework.indexorder
Import-Package: com.sun.xml.bind.v2;version="2.1.6",
  • Compile schema into JAXB classes (see main section on the top)
  • Add "code/gen" to source folders ( : source.. = code/src/,code/gen/)
    • click right on your bundle
    • go to the menu item New
    • click on Source folder
    • folder name: code/gen
  • Copy content of the folder "schema-compile-runtime\schema-pattern\" into your crawler bundle folder
  • Complile schema into JAXB classes by running schema.cmd ( "schema-compile-runtime" folder should be located on the projects level - it will be used for compilation )
    • start schema.cmd from cmd console, to see the result or error messages
  • Implement XSD schema for crawler configuration using template "schemas\TemplateIndexOrder.xsd"
    • Index Order Configaration based on XSD schema redefinition of abstract "RootIndexOrderConfiguration" schema
    • Developer should define redefinition of "Process" and "Attribute" nodes for crawler specific information.
<xs:schema elementFormDefault="qualified" attributeFormDefault="unqualified" xmlns:xs="">
	<xs:redefine schemaLocation="RootIndexOrderConfiguration.xsd">
		<xs:complexType name="Process">
				<xs:documentation>Process Specification</xs:documentation>
				<xs:extension base="Process">
					<\!--define process here -->
		<xs:complexType name="Attribute">
				<xs:extension base="Attribute">
					<\!--define attribute here -->
  • Add schema location reference in plug-in implementation (return "schemas/TemplateIndexOrder.xsd")
    • create a new class (IndexOrderSchemaImpl) which implements interface IndexOrderSchema
    • use method String getSchemaLocation() to return "schemas/TemplateIndexOrder.xsd"
package org.eclipse.eilf.connectivity.framework.crawler.filesystem;
import org.eclipse.eilf.connectivity.framework.indexorder.IndexOrderSchema;
 * The Class IndexOrderSchemaImpl.
public class IndexOrderSchemaImpl implements IndexOrderSchema {
   * {@inheritDoc}
   * @see org.eclipse.eilf.connectivity.framework.indexorder.IndexOrderSchema#getSchemaLocation()
  public String getSchemaLocation() {
    return "schemas/filesystemIndexOrder.xsd";

  • Implement extension for "org.eclipse.eilf.connectivity.framework.indexorder.schema" with the bundle name used as ID and NAME
    • check schema class and change if it is necessary
  • Note: if you renamed schema file name, it should be fixed inside
    • plug-in implementation
    • TemplateIndexOrder.jxb (it also should be also renamed with the same name as schema)
    • schema.cmd

OSGi and Declarative Service requirements

  • it is not required to implement a BundleActivator (this may change if SCA Nodes are used, then it may be required to register the Crawler)
  • create a top level folder OSGI-INF
  • create a Component Description file in OSGI-INF. You can name the file as you like, but it is good practice to name it like the Crawler. Therein you have to provide a unique component name, it should be the same as the Crawler's name followed by DS (for DeclarativeService). Then you have to provide your implementation class and the service interface class, which is always org.eclipse.eilf.connectivity.framework.Crawler.


<?xml version="1.0" encoding="UTF-8"?>
<component name="FileSystemCrawlerDS" immediate="true">
    <implementation class="org.eclipse.eilf.connectivity.framework.crawler.filesystem.FileSystemCrawler" />
         <provide interface="org.eclipse.eilf.connectivity.framework.Crawler"/>
    <property name="org.eclipse.eilf.connectivity.framework.crawler.type" value="filesystemcrawler"/>
  • add a Service-Component entry to your manifest file, e.g.
Service-Component: OSGI-INF/filesystemcrawler.xml

SCA requirements

Most requirements for SCA are already handled by the base class org.eclipse.eilf.connectivity.framework.AbstractCrawler. You should annotate your implementation with @AllowsPassByReference, to allow SCA to pass service parameters by reference when service interactions are within the same adress space. Here is an example:

public class FileSystemCrawler extends AbstractCrawler {
// implementation goes here ...

For SCA, make sure to set attribute "immediate" of tag "component" to false and attribute "servicefactory" of tag "service " to true in your xml-file. This is required to let SCA dynamically create ServiceReferences. Finally you have to provide a value for the property org.eclipse.eilf.connectivity.framework.crawler.type. This is used by SCA to find the correct OSGi Declarative Service during runtime. The value has to be unique (it is used in SCA contribution files) and should be named like the Crawler. Here is an example:


<?xml version="1.0" encoding="UTF-8"?>
<component name="FileSystemCrawlerDS" immediate="false">
    <implementation class="org.eclipse.eilf.connectivity.framework.crawler.filesystem.FileSystemCrawler" />
    <service servicefactory="true">
         <provide interface="org.eclipse.eilf.connectivity.framework.Crawler"/>
    <property name="org.eclipse.eilf.connectivity.framework.crawler.type" value="filesystemcrawler"/>
  • implement your crawler in a new Class extending org.eclipse.eilf.connectivity.framework.AbstractCrawler
  • Enjoy

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