Chapter 14. Android Integration

Drools Android integration comes in two flavors, with or without the drools-compiler dependency. Without the drools-compiler dependency the knowledge bases are pre-serialized at buildtime using the kie-maven-plugin. They can be then deserialized using the API, or directly injected using Roboguice. When using the drools-compiler dependency there are two options: (1) standard KieContainer API or (2) CDI-like injection with Roboguice.

14.1.1. Pre-serialized Rules

It is possible to use Drools without the drools-compiler dependency, which results in a smaller apk, by pre-serializing the compiled knowledge bases during build-time and then de-serializing them at runtime.

14.1.1.1. Maven Configuration

The KieBase must be serialized during build time using kie-maven-plugin.

Example 14.1. Pre-serialized KieBase Maven pom.xml

<dependencyManagement>
  <dependencies>
    <dependency>
      <groupId>org.drools</groupId>
      <artifactId>drools-bom</artifactId>
      <version>6.5.0.CR1</version>
      <type>pom</type>
      <scope>import</scope>
  </dependencies>
</dependencyManagement>
<dependencies>
  <dependency>
    <groupId>org.drools</groupId>
    <artifactId>drools-android</artifactId>
    <exclusions>
     <exclusion>
       <groupId>org.slf4j</groupId>
       <artifactId>slf4j-api</artifactId>
    </exclusions>
  </dependency>
  <dependency>
    <groupId>org.drools</groupId>
    <artifactId>drools-core</artifactId>
  </dependency>
</dependencies>
<build>
  <plugins>
    <plugin>
      <groupId>org.kie</groupId>
      <artifactId>kie-maven-plugin</artifactId>
      <version>6.5.0.CR1</version>
      <configuration>
        <kiebases>
        <kiebase>HelloKB</kiebase>
        </kiebases>
        <resDirectory>${basedir}/src/main/res/raw</resDirectory>
      </configuration>
        <executions>
          <execution>
            <id>touch</id>
            <goals>
              <goal>touch</goal>
            </goals>
            <phase>initialize</phase>
          </execution>
          <execution>
            <id>compile-kbase</id>
              <goals>
                <goal>build</goal>
              </goals>
              <phase>compile</phase>
          </execution>
          <execution>
            <id>serialize</id>
            <goals>
              <goal>serialize</goal>
            </goals>
            <phase>compile</phase>
          </execution>
        </executions>
     </plugin>
  </plugins>
</build>

14.1.1.2. Loading the KieBase

The KieBase must be de-serialized before creating the sessions.

Figure 14.1. Loading serialized KieBase

private class LoadKieBaseTask extends AsyncTask<InputStream, Void, KieBase> {
   @Override
   protected KieBase doInBackground(InputStream... params) {
      try {
         logger.debug("Loading knowledge base");
         final KnowledgeBase kbase = KnowledgeBaseFactory.newKnowledgeBase();
         kbase.addKnowledgePackages((List<KnowledgePackage>) DroolsStreamUtils.streamIn(params[0]));
         return kbase;
      }catch(Exception e) {
         logger.error("Drools exception", e);
         return null;
      }
   }
}

14.1.2. KieContainer API with drools-compiler dependency

With the drools-compiler dependency standard KieContainer API can be used. This comes at a cost of a larger apk. To avoid the 65K limit, multidex (or proguard) can be used.

14.1.2.1. Maven Configuration with drools-compiler and multidex

The kie-maven-plugin must be configured to build the kiebase. Multidex must be used to allow for the increased dependencies. There are also some settings for merging various Drools XML files within the apk.

Example 14.2. pom.xml with drools-compiler and multidex

<dependencyManagement>
  <dependencies>
    <dependency>
      <groupId>org.drools</groupId>
      <artifactId>drools-bom</artifactId>
      <version>6.5.0.CR1</version>
      <type>pom</type>
      <scope>import</scope>
  </dependencies>
</dependencyManagement>
<dependencies>
  <dependency>
    <groupId>org.drools</groupId>
    <artifactId>drools-android</artifactId>
    <exclusions>
      <exclusion>
        <groupId>org.slf4j</groupId>
        <artifactId>slf4j-api</artifactId>
      </exclusion>
    </exclusions>
  </dependency>
  <dependency>
    <groupId>org.drools</groupId>
    <artifactId>drools-compiler</artifactId>
    <exclusions>
      <exclusion>
         <groupId>org.slf4j</groupId>
         <artifactId>slf4j-api</artifactId>
      </exclusion>
      <exclusion>
         <groupId>xmlpull</groupId>
         <artifactId>xmlpull</artifactId>
      </exclusion>
      <exclusion>
         <groupId>xpp3</groupId>
         <artifactId>xpp3_min</artifactId>
      </exclusion>
      <exclusion>
         <groupId>org.slf4j</groupId>
         <artifactId>slf4j-api</artifactId>
      </exclusion>
      <exclusion>
         <groupId>org.eclipse.jdt.core.compiler</groupId>
         <artifactId>ecj</artifactId>
      </exclusion>
    </exclusions>
  </dependency>
</dependencies>
<build>
  <plugins>
    <plugin>
      <groupId>org.kie</groupId>
      <artifactId>kie-maven-plugin</artifactId>
      <version>6.5.0.CR1</version>
      <executions>
        <execution>
          <id>compile-kbase</id>
          <goals>
            <goal>build</goal>
          </goals>
          <phase>compile</phase>
        </execution>
      </executions>
    </plugin>
    <plugin>
      <groupId>com.simpligility.maven.plugins</groupId>
      <artifactId>android-maven-plugin</artifactId>
      <version>4.2.1</version>
      <extensions>true</extensions>
      <configuration>
        <sdk>
          <platform>21</platform>
        </sdk>
        <dex>
          <coreLibrary>true</coreLibrary>
          <jvmArguments><jvmArgument>-Xmx2048m</jvmArgument></jvmArguments>
          <multiDex>true</multiDex>
          <mainDexList>maindex.txt</mainDexList>
        </dex>
        <extractDuplicates>true</extractDuplicates>
        <apk>
          <metaInf>
            <includes>
              <include>services/**</include>
              <include>kmodule.*</include>
              <include>HelloKB/**</include>
              <include>drools**</include>
              <include>maven/${project.groupId}/${project.artifactId}/**</include>
            </includes>
          </metaInf>
        </apk>
      </configuration>
    </plugin>
  </plugins>
</build>

14.2. Integration with Roboguice

Figure 14.2. Injects KieBase by name from pre-serialized resource

@KBase("kbase1")
private KieBase kbase;

14.2.1.2. AndroidManifest.xml configuration

The Roboguice module needs to be specified in the manifest.

Example 14.3. Roboguice manifest with pre-serialized knowledge base

<application
   android:largeHeap="true"
   android:allowBackup="true"
   android:icon="@drawable/ic_launcher"
   android:label="@string/app_name"
   android:theme="@style/AppTheme">
      <meta-data
         android:name="roboguice.modules"
         android:value="org.drools.android.roboguice.DroolsModule"/>
      <activity
         android:label="@string/app_name"
         android:name="org.drools.examples.android.SplashActivity">
      <intent-filter>
         <action android:name="android.intent.action.MAIN"/>
         <category android:name="android.intent.category.LAUNCHER"/>
      </intent-filter>
   </activity>
</application>

14.2.2. KieContainer with drools-compiler dependency and Roboguice

With Roboguice and drools-compiler almost the full CDI syntax can be used to inject KieContainers, KieBases, and KieSessions.

14.2.2.1. Annotations

@KContainer, @KBase and @KSession all support an optional 'name' attribute. CDI typically does "getOrCreate" when it injects, all injections receive the same instance for the same set of annotations. the 'name' annotation forces a unique instance for each name, although all instance for that name will be identity equals.

14.2.2.1.1. @KContainer

Figure 14.3. Injects Classpath KieContainer

@Inject
private KieContainer kContainer;

14.2.2.1.2. @KBase

The default argument, if given, maps to the value attribute and specifies the name of the KieBase from the kmodule.xml file.

Figure 14.4. Injects the Default KieBase from the Classpath KieContainer

@Inject
private KieBase kbase;

Figure 14.5. Injects KieBase by name from the Classpath KieContainer

@Inject
@KBase("kbase1")
private KieBase kbase;

14.2.2.1.3. @KSession for KieSession

@KSession is optional as it can be detected and added by the use of @Inject and variable type inference.

The default argument, if given, maps to the value attribute and specifies the name of the KieSession from the kmodule.xml file

Figure 14.6. Injects the Default KieSession from the Classpath KieContainer

@Inject
private KieSession ksession;

Figure 14.7. Injects StatelessKieSession by name from the Classpath KieContainer

@Inject
@KSession("ksession1")
private KieSession ksession;

14.2.2.1.4. @KSession for StatelessKieSession

@KSession is optional as it can be detected and added by the use of @Inject and variable type inference.

The default argument, if given, maps to the value attribute and specifies the name of the KieSession from the kmodule.xml file.

Figure 14.8. Injects the Default StatelessKieSession from the Classpath KieContainer

@Inject
private StatelessKieSession ksession;

Figure 14.9. Injects StatelessKieSession by name from the Classpath KieContainer

@Inject
@KSession("ksession1")
private StatelessKieSession ksession;

14.2.2.2. AndroidManifest.xml configuration

The Roboguice module needs to be specified in the manifest.

Example 14.4. Roboguice manifest configuration

<application
   android:largeHeap="true"
   android:allowBackup="true"
   android:icon="@drawable/ic_launcher"
   android:label="@string/app_name"
   android:theme="@style/AppTheme">
   <meta-data
      android:name="roboguice.modules"
      android:value="org.drools.android.roboguice.DroolsContainerModule"/>
   <activity
      android:label="@string/app_name"
      android:name="org.drools.examples.android.SplashActivity">
      <intent-filter>
         <action android:name="android.intent.action.MAIN"/>
         <category android:name="android.intent.category.LAUNCHER"/>
      </intent-filter>
   </activity>
</application>