Custom Maven Plugin for Drools Rules

When I start developing business rules with Drools, I can utilize Guvnor as a repository for storing those assets. This application will allow us to add and create rules or functions within the product, or to upload those to the server. I can then use Guvnor to create packages that I can deploy with our applications that will use these rules. The packages are usually compiled into a pkg file that is then included into a war, for instance, a war that utilizes a Spring context file with a bean definition to register a KnowledgeSession that imports the pkg file. There are multiple ways to configure the KnowledgeSeesion with a pkg file, either by pulling a pkg file from the classpath or by pulling a pkg file from a URL.

One of the complexities that occurs when dealing with rules and the concept of the Guvnor, is treating Guvnor as not just a repository but as the main build system for rules. This hinders the potential for rapid development as it complicates build/run/test by introducing an Application Server which will be used as the main source for compilation of the rules for verification that they were designed correctly. If developers are not familiar with JBoss Application Server or in the case I have been familiar with (don’t have access to the server), when rules fail to compile, they have no way to search the log files for why rules failed to compile. Also, I ran into situations with the product poorly performing because it was installed as a simplistic development server and then doesn’t match the required performance capabilities.

To move past this, I decided to utilize the capabilities of Maven to create a custom plugin that could load rule files and compile those into a pkg file, by doing this locally and not having to rely on Guvnor for doing developmental builds. The plugin would need to scan a maven resources directory, compile a list of all the files, and then process those files through a KnowledgeSession, and then compile them into the binary package. The next step is to utilize a better deployment unit than a pkg. Since I am using Nexus (like Artifactory), I want to be able to deploy the pkg without having to create a customized dependency type. I can do this by jaring the pkg file, since as long as the jar file is on the classpath of the war I am deploying (which uses our rules), the configured KnowledgeSession will be able to resolve the pkg file within the jar. So once our pkg is complete, I will jar the pkg file with the same name as the pkg.

In this case, I am going to write a Maven Mojo. In order to do this, I really need to understand the Maven properties I have available to us. Maven runs on Plexus and as IOC, it has the great ability to inject property values into class level fields that are configured via Java Annotations (those that match Maven Properties or configurations within the pom file). I find some of these properties through the following resources:

Sonatype Maven Reference – Properties
Maven Properties Guide

In order to begin doing the Mojo development and use some of the more advanced capabilities that Plexus gives us, I will need to add to our Maven POM file for the plugin:

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<dependency>
    <groupId>org.apache.maven</groupId>
    <artifactId>maven-plugin-api</artifactId>
</dependency>
<dependency>
        <groupId>org.apache.maven</groupId>
        <artifactId>maven-project</artifactId>
</dependency>
<dependency>
        <groupId>org.codehaus.plexus</groupId>
        <artifactId>plexus-utils</artifactId>
</dependency>

Sample Maven Properties

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    /**
     * This will inject the MavenProject object that exists in the current
     * POM in which the plugin is running.  We can access all the information
     * we need from this single object.
     *
     * @parameter default-value="$"
     * */

    private MavenProject mavenProject;

    /**
     * This is where the .pkg files are written.  This is the project outputDirectory
     * and we technically don't need this field since we have the mavenProject field.
     *
     * @parameter expression="${project.build.outputDirectory}"
     */

    private File targetDirectory;

    /**
     * This is the project resource directory (not test).  This way we don't have to
     * hard-code a path in our plugin to access the resources, and we will have the
     * unique path even if a resources/resource configuration is used to modify the
     * default location of resources.  We technically don't need this field since
     * we have the mavenProject field.
     *
     * @parameter expression="${project.resources}"
     * @required
     */

    private List resources;

    /**
     * This gives us the artifactId for the project so that we can use this to name
     * we will give the pkg as well as the jar file.  This can also be retrieved from
     * the mavenProject.
     *
     * @parameter expression="${project.artifactId}"
     * @required
     */

    private String artifactId;

    /**
     * This parameter will automatically map the excludes/exclude listings from the
     * configuration segment of the plugin.
     *
     * @parameter
     */

    private List<String> excludes;

    /**
     * This parameter will automatically map the includes/include listings from the
     * configuration segment of the plugin.
     *
     * @parameter
     */

    private List<String> includes;

I can then access the Resources by calling the mavenProject.getResources(). I also need to get the list of possible includes/excludes, but these must first be converted from a List to a comma separated list of values (in order for us to take advantage of Maven’s path wildcarding). One of the features I also add is to set a default include list incase one is not set through the plugin:

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private static final String DEFAULT_INCLUDES_TYPES = "**/*.drl,**/*.xls,**/*.rf";

   private String getExcludesList() {
        if (CollectionUtils.isNotEmpty(excludes)) {
            return convertListToCsv(excludes);
        } else {
            return null;
        }
    }

    private String getIncludesList() {
        if (CollectionUtils.isNotEmpty(includes)) {
            return convertListToCsv(includes);

        } else {
            return DEFAULT_INCLUDES_TYPES;
        }
    }

    private String convertListToCsv(List<String> includeList) {
        StringBuilder nameBuilder = new StringBuilder();
        for (String includeItem : includeList) {
            nameBuilder.append(includeItem).append(",");
        }

        nameBuilder.deleteCharAt(nameBuilder.length() - 1);
        return nameBuilder.toString();
    }

I will use the class from the Plexus API.

When then utilize one of the helper methods to build the list of files that I will loop through and add the rule file to the KnowledgeBuilder:

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List<File> listOfFiles = org.codehaus.plexus.util.FileUtils.getFiles(new File(resource.getDirectory()), getIncludesList(), getExcludesList(), true);

I will then loop get the KnowledgePackages and then stream those packages out to the pkg file:

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String targetPath = mavenProject.getBuild().getDirectory() + "/classes/";
Collection<KnowledgePackage> kpkgs = kbuilder.getKnowledgePackages();
for (KnowledgePackage kpkg : kpkgs) {
    Collection<Rule> rules = kpkg.getRules();
    FileOutputStream out = null;

    try {
        File targetFile = new File(targetPath);
        if (!targetFile.exists()) {
            FileUtils.forceMkdir(new File(targetPath));
        }
        File outFilePath = new File(targetPath + mavenProject.getArtifactId() + ".pkg");
        out = new FileOutputStream(outFilePath);
        DroolsStreamUtils.streamOut(out, ((KnowledgePackageImp) kpkg).pkg);
    } catch (IOException ex) {
        throw new RuntimeException(ex);
    } finally {
        IOUtils.closeQuietly(out);
    }

}

Once I complete this Mojo, I can then install it and configure the plugin through a master POM. When can then create Maven Projects and store our rules assets (like xls, drl, or rf) into the src/main/resources directory.

I will configure the master pom of our rules projects to reconfigure the jar plugin so that it will ignore all our rules files and just compile the built pkg file into the jar:

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    <build>
        <pluginManagement>
            <plugins>
                <plugin>
                    <groupId>org.apache.maven.plugins</groupId>
                    <artifactId>maven-jar-plugin</artifactId>
                    <configuration>
                        <includes>
                            <include>**/${project.artifactId}.pkg</include>
                        </includes>
                    </configuration>
                    <executions>
                        <execution>
                            <goals>
                                <goal>jar</goal>
                            </goals>
                        </execution>
                    </executions>
                </plugin>
            </plugins>
        </pluginManagement>
    </build>

I can then configure our plugin and the types of files I want to exclude (for example) as well as the dependencies I need to include in order to compile the rules.

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        <plugins>
            <plugin>
                <groupId>com.foo.tools</groupId>
                <artifactId>foo-rules-plugin</artifactId>
                <configuration>
                    <excludes>
                        <exclude>**/sample.xls</exclude>
                        <exclude>**/*.drl</exclude>
                    </excludes>
                </configuration>
                <dependencies>
                    <dependency>
                        <groupId>com.foo.services</groupId>
                        <artifactId>core-foo-service</artifactId>
                        <version>1.0.0-SNAPSHOT</version>
                    </dependency>
                </dependencies>
            </plugin>
        </plugins>

When I am all said and done…the completed Mojo looks like this:

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import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;

import java.util.Collection;
import java.util.Iterator;
import java.util.List;

import org.apache.commons.collections.CollectionUtils;
import org.apache.commons.io.IOUtils;
import org.apache.commons.lang.StringUtils;
import org.apache.maven.model.Resource;
import org.apache.maven.plugin.AbstractMojo;
import org.apache.maven.plugin.MojoExecutionException;
import org.apache.maven.plugin.MojoFailureException;
import org.apache.maven.project.MavenProject;

import org.codehaus.plexus.util.FileUtils;

import org.drools.builder.KnowledgeBuilder;
import org.drools.builder.KnowledgeBuilderConfiguration;
import org.drools.builder.KnowledgeBuilderFactory;
import org.drools.builder.ResourceType;
import org.drools.compiler.DroolsParserException;
import org.drools.core.util.DroolsStreamUtils;
import org.drools.decisiontable.InputType;
import org.drools.decisiontable.SpreadsheetCompiler;
import org.drools.definition.KnowledgePackage;
import org.drools.definition.rule.Rule;
import org.drools.definitions.impl.KnowledgePackageImp;
import org.drools.io.ResourceFactory;

public class DroolsRulesMojo extends AbstractMojo {

    private static final String DEFAULT_INCLUDES = "**/*.drl,**/*.xls,**/*.rf";

    /**
     * Maven Project
     *
     * @parameter default-value="$"
     * */

    private MavenProject mavenProject;

    /**
     * @parameter
     */

    private List<String> excludes;

    /**
     * @parameter
     */

    private List<String> includes;

    /**
     * Setup the options to pass to the code generator.
     *
     * @return the configured options.
     */

    public void execute() throws MojoExecutionException, MojoFailureException {
        try {
            compileRules(mavenProject);
        } catch (Exception e) {
            // Normally don't log when an exception is thrown.
            // This just helps debugging more quickly for rules errors.
            getLog().error(e);
            throw new RuntimeException(e);
        }

    }

    public void compileRules(MavenProject mavenProject) throws DroolsParserException, IOException {
        ClassLoader classLoader = null;
        KnowledgeBuilderConfiguration kbuilderConf = KnowledgeBuilderFactory.newKnowledgeBuilderConfiguration(null,
                classLoader);
        KnowledgeBuilder kbuilder = KnowledgeBuilderFactory.newKnowledgeBuilder(kbuilderConf);

        // This is the target directory for where the rules will be placed during
        // the build.
        String targetPath = mavenProject.getBuild().getDirectory() + "/classes/";

        // Depending on how the project is checked out or the maven pom
        // sometimes the getDirectory() will not have the name of the project/pom
        // but unnamed since it cannot determine the correct name.
        if (StringUtils.contains(targetPath, "Unnamed")) {
            throw new RuntimeException("The project was incorrectly checked out so that maven cannot determine the"
                    + " project name, therefore it creates a directory with Unnamed.  Fix the project or add the name"
                    + " property into the Maven pom.xml");
        }

        // Ask the mavenProject for all it's resource locations.
        List resources = mavenProject.getResources();
        getLog().debug("Target directory to write output file - " + targetPath);

        // Loop through the collection, even though we really could lock this down
        // to just be the /src/main/resources. We could also change the plugin
        // to differentiate between running against test rules and production
        // rules.
        for (Iterator i = resources.iterator(); i.hasNext();) {
            Resource resource = (Resource) i.next();
            getLog().debug("Resource directory to pull rules from - " + resource.getDirectory());

            // The following method call allows us to use the capabilities of
            // wildcarding like we see in most maven plugins. Where we can do
            // things such as **/*.xls. This call will also resolve any conflicting
            // includes and excludes.
            List<File> listOfFiles = org.codehaus.plexus.util.FileUtils.getFiles(new File(resource.getDirectory()),
                    getIncludesList(), getExcludesList(), true);

            if (CollectionUtils.isEmpty(listOfFiles)) {
                getLog().warn("No files were found to compile into package");
            } else {
                for (File file : listOfFiles) {

                    if (file.isFile()) {
                        String fileName = file.getName();

                        // Store the suffix so we can determine the rules type
                        String fileSuffix = StringUtils.substringAfterLast(fileName, ".");

                        if (StringUtils.endsWith(fileSuffix, "drl")) {
                            getLog().info("- Adding DRL: " + fileName + " to package");
                            kbuilder.add(ResourceFactory.newFileResource(file.getAbsolutePath()), ResourceType.DRL);
                        } else if (StringUtils.endsWith(fileSuffix, "xls")) {
                            // Decision tables have an extra step, so we provide additional
                            // output information.
                            SpreadsheetCompiler sc = new SpreadsheetCompiler();
                            String drlstr = sc.compile(ResourceFactory.newFileResource(file.getAbsolutePath())
                                    .getInputStream(), InputType.XLS);
                            getLog().debug("--- XLS compile details = " + drlstr);
                            getLog().info("- Adding Decision Table: " + fileName + " to package");
                            kbuilder.add(ResourceFactory.newFileResource(file.getAbsolutePath()), ResourceType.DTABLE);
                        } else if (StringUtils.endsWith(fileSuffix, "rf")) {
                            getLog().info("- Adding Rule Flow: " + fileName + " to package");
                            kbuilder.add(ResourceFactory.newFileResource(file.getAbsolutePath()), ResourceType.DRF);
                        }

                    }
                }
            }
        }

        // If any errors have occurred in the KnowledgeBuilder, then throw
        // the errors and stop the plugin process.
        if (kbuilder.hasErrors()) {
            getLog().error("Errors " + kbuilder.getErrors().toString());
            throw new RuntimeException(kbuilder.getErrors().toString());
        }

        int pkgCount = 0;
        Collection<KnowledgePackage> kpkgs = kbuilder.getKnowledgePackages();
        for (KnowledgePackage kpkg : kpkgs) {
            Collection<Rule> rules = kpkg.getRules();
            for (Object element : rules) {
                org.drools.definitions.rule.impl.RuleImpl rule = (org.drools.definitions.rule.impl.RuleImpl) element;
               
                //Providing additional debug information for rules within the KnowledgeBuilder
                getLog().debug(
                        "<RuleName> : <Activation-Group (null=non-existent)> : <Agenda-group>:   " + rule.getName()
                                + " : " + rule.getRule().getActivationGroup() + " : "
                                + rule.getRule().getRuleFlowGroup());
            }

            if (++pkgCount > 1) {
                getLog().warn(
                        "Your rules are being built into multiple packages, this is most likely an issue.");
            }

            //Create the pkg on the file system.
            FileOutputStream out = null;

            try {
                File targetFile = new File(targetPath);
                if (!targetFile.exists()) {
                    FileUtils.forceMkdir(new File(targetPath));
                }
                File outFilePath = new File(targetPath + mavenProject.getArtifactId() + ".pkg");
                out = new FileOutputStream(outFilePath);
                DroolsStreamUtils.streamOut(out, ((KnowledgePackageImp) kpkg).pkg);
                long filesize = outFilePath.length();
                long filesizeInKB = filesize / 1024;

                //Log information about the create package.
                getLog().info(
                        "- Package " + mavenProject.getArtifactId() + " built, putting pkg: " + targetPath
                                + mavenProject.getArtifactId() + ".pkg");

                getLog().info("- Size of " + mavenProject.getArtifactId() + ".pkg is: " + filesizeInKB + " KB");
            } catch (IOException ex) {
                throw new RuntimeException(ex);
            } finally {
                IOUtils.closeQuietly(out);
            }

        }
    }

    /**
     * Create the exclude list. If the maven plugin was configured with excludes, then convert the list into a Csv since
     * the Plexus utility needs a comma separated list, else return a null String.
     *
     * @return String containing the list of excludes.
     */

    private String getExcludesList() {
        if (CollectionUtils.isNotEmpty(excludes)) {
            return convertListToCsv(excludes);
        } else {
            return null;
        }
    }

    /**
     * Create the include list. If the maven plugin was configured with includes, then convert the list into a Csv since
     * the Plexus utility needs a comma separated list, else return the list of default rules types that will be
     * compiled.
     *
     * @return String containing the list of excludes.
     */

    private String getIncludesList() {
        if (CollectionUtils.isNotEmpty(includes)) {
            return convertListToCsv(includes);

        } else {
            return DEFAULT_INCLUDES;
        }
    }

    /**
     * Looks through a list of Strings and creates a comma separated String.
     *
     * @param includeList
     *            List of String values for include/exclude.
     * @return String that is a Csv of values.
     */

    private String convertListToCsv(List<String> includeList) {
        StringBuilder nameBuilder = new StringBuilder();
        for (String includeItem : includeList) {
            nameBuilder.append(includeItem).append(",");
        }

        nameBuilder.deleteCharAt(nameBuilder.length() - 1);
        return nameBuilder.toString();
    }
}

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