For complex rules like this, we use Drools Templates. You write a rule template with parameter expansions for fields to populate and you have much more flexibility in where the actual values come from to populate the skeleton rule.
This capability is built into Drools Guvnor, but writing the complex rule templates through the GUI is somewhat tedious. I have also written standalone Java to populate template drl files from lists of values pulled from properties files, and recently developed a SmartGWT web app that allows the user to populate rule values and generate DRL.
Edit: Adding sample program. DroolsTemplateBuilder creates a list of TestType objects, which have fields that map to the template keys in Test.drl. The generated DRL is printed and also compiled to a pkg which is written out to a file called Test.pkg.
Libraries: antlr-3.3.jar, antlr-runtime-3.3.jar, drools-compiler-5.2.0.Final.jar, drools-core-5.2.0.Final.jar, drools-templates-5.2.0.Final.jar, ecj-4.2.jar, knowledge-api-5.2.0.Final.jar, mvel2-2.1.0.drools.jar (these may not all be necessary).
Note: This example uses 5.2.0 libraries and some functionality may be different in newer releases. build.xml should make it clear how to structure your project.
DroolsTemplateBuilder.java:
package some.test.pkg;
import java.io.ByteArrayInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.ObjectOutputStream;
import java.io.OutputStream;
import java.io.Reader;
import java.io.StringReader;
import java.util.ArrayList;
import java.util.Collection;
import org.drools.builder.KnowledgeBuilder;
import org.drools.builder.KnowledgeBuilderError;
import org.drools.builder.KnowledgeBuilderFactory;
import org.drools.builder.ResourceType;
import org.drools.common.DroolsObjectOutputStream;
import org.drools.definitions.impl.KnowledgePackageImp;
import org.drools.io.ResourceFactory;
import org.drools.template.ObjectDataCompiler;
public class DroolsTemplateBuilder {
private String filePath;
private String drl;
public static void main(String[] args) {
DroolsTemplateBuilder test = new DroolsTemplateBuilder();
test.filePath = args[0] + File.separator + "Test.drl";
test.runTest();
}
public void runTest() {
buildPackage();
writeRulePackageToFile();
}
public void buildPackage() {
Collection<Object> templateList = new ArrayList<Object>();
templateList.add(new TestType(1, "John", "Manager"));
templateList.add(new TestType(2, "Peter", "CEO"));
templateList.add(new TestType(3, "Kate", "Engineer"));
try {
ObjectDataCompiler converter = new ObjectDataCompiler();
InputStream templateStream = new FileInputStream(filePath);
String myDrl = inputStreamToString(templateStream, 200);
// I use this ##### replacement instead of just a newline in the
// template
// because of windows/linux issues with newline and carriage return.
// Drools template
// builder, at least in 5.2.0, was very picky about the template
// structure, including
// where newlines are expected.
myDrl = myDrl.replaceAll("#####", "\n");
InputStream tempStream = new ByteArrayInputStream(myDrl.getBytes());
drl = converter.compile(templateList, tempStream);
System.out.println(drl);
} catch (Exception e) {
System.out.println("Exception: " + e.getMessage());
}
}
public void writeRulePackageToFile() {
try {
KnowledgeBuilder kBuilder = KnowledgeBuilderFactory
.newKnowledgeBuilder();
Reader rdr = new StringReader(drl);
kBuilder.add(ResourceFactory.newReaderResource(rdr),
ResourceType.DRL);
if (kBuilder.hasErrors()) {
System.out.println("Drools blew up on");
for (KnowledgeBuilderError err : kBuilder.getErrors()) {
System.out.println(err.getMessage());
}
} else {
String outFile = filePath.replaceFirst("\\.drl", ".pkg");
OutputStream os = new FileOutputStream(outFile);
ObjectOutputStream oos = new DroolsObjectOutputStream(os);
KnowledgePackageImp kPackage = (KnowledgePackageImp) kBuilder
.getKnowledgePackages().iterator().next();
oos.writeObject(kPackage);
oos.close();
}
} catch (Exception e) {
System.out.println("Exception " + e.getMessage());
}
}
public String inputStreamToString(final InputStream is, final int bufferSize) {
final char[] buffer = new char[bufferSize];
final StringBuilder out = new StringBuilder();
try {
final Reader in = new InputStreamReader(is, "UTF-8");
try {
for (;;) {
int rsz = in.read(buffer, 0, buffer.length);
if (rsz < 0)
break;
out.append(buffer, 0, rsz);
}
} finally {
in.close();
}
} catch (Exception ex) {
System.out.println("Something went wrong: " + ex.getMessage());
}
return out.toString();
}
}
Test.drl:
template header
id
name
title
#####
package some.test.pkg;
template "sampleTemplate"
rule "id filter_@{row.rowNumber}"
no-loop true
dialect "java"
when
$t : TestType(id=="@{id}")
then
System.out.println("Doing something special...");
end
end template
template "anotherSample"
rule "another rule_@{row.rowNumber}"
no-loop true
dialect "java"
when
$t : TestType((name=="@{name}") || (title=="@{title}"))
then
System.out.println("Doing something else...");
end
end template
TestType.java:
package some.test.pkg;
public class TestType {
private int id;
private String name;
private String title;
public TestType(int id, String name, String title) {
this.id = id;
this.name = name;
this.title = title;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getTitle() {
return title;
}
public void setTitle(String title) {
this.title = title;
}
}
build.xml:
<project name="TemplateTest" basedir="." default="jar">
<property name="src.dir" value="src" />
<property name="build.dir" value="build" />
<property name="drl.dir" value="${basedir}/drl" />
<property name="classes.dir" value="${build.dir}/classes" />
<property name="jar.dir" value="${build.dir}/jar" />
<property name="lib.dir" value="${basedir}/lib" />
<path id="compile.classpath">
<fileset dir="${lib.dir}" includes="*.jar" />
</path>
<path id="run.classpath">
<fileset dir="${jar.dir}" includes="*.jar" />
<fileset dir="${lib.dir}" includes="*.jar" />
</path>
<target name="clean">
<delete dir="${classes.dir}" />
<delete dir="${jar.dir}" />
</target>
<target name="compile" depends="clean">
<mkdir dir="${classes.dir}" />
<mkdir dir="${jar.dir}" />
<javac includeantruntime="false" srcdir="${src.dir}" classpathref="compile.classpath" destdir="${classes.dir}" />
</target>
<target name="jar" depends="compile">
<jar destfile="${jar.dir}/${ant.project.name}.jar" basedir="${classes.dir}">
</jar>
</target>
<target name="run" depends="jar" description="run">
<java classpathref="run.classpath" classname="some.test.pkg.DroolsTemplateBuilder" fork="true">
<arg value="${drl.dir}" />
</java>
</target>
</project>
