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5.2. KnowledgeBuilder
5.2.1. The KnowledgeBuilder
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The KnowledgeBuilder is responsible for taking source files, such as a DRL file or an Excel file, and turning them into a Knowledge Package of rule and process definitions which a Knowledge Base can consume. An object of the class
ResourceType indicates the type of resource the builder is being asked to process.
Figure 5.2. Builder Chart
5.2.2. The ResourceFactory
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The
ResourceFactory provides capabilities to load resources from a number of sources: java.io.Reader, the classpath, a URL, a java.io.File, or a byte array. Binary files, such as decision tables (Excel's .xls files), should not be passed in with Reader, which is only suitable for text based resources.
Figure 5.3. KnowledgeBuilder Chart
5.2.3. Creating a new KnowledgeBuilder
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Procedure 5.2. Task
- Open the KnowledgeBuilderFactory.
- Create a new default configuration.
- Enter this into the configuration:
KnowledgeBuilder kbuilder = KnowledgeBuilderFactory.newKnowledgeBuilder();
KnowledgeBuilder kbuilder = KnowledgeBuilderFactory.newKnowledgeBuilder();Copy to Clipboard Copied! Toggle word wrap Toggle overflow The first parameter is for properties and is optional. If left blank, the default options will be used. The options parameter can be used for things like changing the dialect or registering new accumulator functions. - To add a KnowledgeBuilder with a custom ClassLoader, use this code:
KnowledgeBuilderConfiguration kbuilderConf = KnowledgeBuilderFactory.newKnowledgeBuilderConfiguration(null, classLoader ); KnowledgeBuilder kbuilder = KnowledgeBuilderFactory.newKnowledgeBuilder(kbuilderConf);
KnowledgeBuilderConfiguration kbuilderConf = KnowledgeBuilderFactory.newKnowledgeBuilderConfiguration(null, classLoader ); KnowledgeBuilder kbuilder = KnowledgeBuilderFactory.newKnowledgeBuilder(kbuilderConf);Copy to Clipboard Copied! Toggle word wrap Toggle overflow
5.2.4. Adding DRL Resources
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Procedure 5.3. Task
- Resources of any type can be added iteratively. Below, a DRL file is added. The Knowledge Builder can handle multiple namespaces, so you can combine resources regardless of their namespace:
kbuilder.add( ResourceFactory.newFileResource( "/project/myrules.drl" ), ResourceType.DRL);kbuilder.add( ResourceFactory.newFileResource( "/project/myrules.drl" ), ResourceType.DRL);Copy to Clipboard Copied! Toggle word wrap Toggle overflow - Check the compilation results after each resource addition. The KnowledgeBuilder can report compilation results of 3 different severities: ERROR, WARNING and INFO.
- An
ERRORindicates that the compilation of the resource failed. You should not add more resources or retrieve the Knowledge Packages if there are errors.getKnowledgePackages()returns an empty list if there are errors. WARNINGandINFOresults can be ignored, but are available for inspection nonetheless.
5.2.5. KnowledgeBuilder Result Inspection Methods
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The KnowledgeBuilder API offers several methods to check and retrieve the build results for a list of severities:
The KnowledgeBuilder API also has two helper methods to inspect for errors:
hasErrors() and getErrors():
if( kbuilder.hasErrors() ) {
System.out.println( kbuilder.getErrors() );
return;
}
if( kbuilder.hasErrors() ) {
System.out.println( kbuilder.getErrors() );
return;
}
5.2.6. Getting the KnowledgePackages
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When all the resources have been added and there are no errors, the collection of Knowledge Packages can be retrieved. It is a java.util.Collection because there is one KnowledgePackage per package namespace. These Knowledge Packages are serializable and often used as a unit of deployment.
The Knowledge Package can been seen below:
Collection<KnowledgePackage> kpkgs = kbuilder.getKnowledgePackages();
Collection<KnowledgePackage> kpkgs = kbuilder.getKnowledgePackages();
5.2.7. Extended KnowledgeBuilder Example
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This is what a complete KnowledgeBuilder package looks like:
5.2.8. Using KnowledgeBuilder in Batch Mode
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The KnowledgeBuilder has a batch mode with a fluent interface. It allows you to build multiple DRLs at once as in the following example:
5.2.9. Discard the Build of the Last Added DRL
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The KnowledgeBuilder (regardless if you are using the batch mode or not) also allows you to discard what has been added with the last DRL(s) build. This can be useful to recover from having added an erroneous DRL to the KnowledgeBuilder, as shown below:
kbuilder.add( ResourceFactory.newFileResource( "/project/wrong.drl" ), ResourceType.DRL );
if ( kbuilder.hasErrors() ) {
kbuilder.undo();
}
kbuilder.add( ResourceFactory.newFileResource( "/project/wrong.drl" ), ResourceType.DRL );
if ( kbuilder.hasErrors() ) {
kbuilder.undo();
}
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