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AspectJ: How to weave an aspect library into a Java project

I build small library (Java and Maven) – using AspectJ. Library must be independent. Library deliver Aspects and Annotations. Function of library is – “call advice when executed a method with specific annotation”. All is ok when I use everything in one module, but problem appers when i separate library and project with classes which advice must be applied. I create simple schema. Schema Library B – my library (aspects and annotations) Project A – project with buisness methods which adivce must be applied Is any posibility to do this?

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Answer

According to the AspectJ Maven documentation, chapter “using aspect libraries”, you need to

  • add the aspect library as a regular <dependency>,
  • also add the same dependency (without <version> because it is already assigned in step 1) in the plugin <configuration><aspectLibraries> section as an <aspectLibrary>.

Here is a concrete example:

Aspect library POM, marker annotation and sample aspect:

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>de.scrum-master.stackoverflow</groupId>
    <artifactId>aspectj-lib</artifactId>
    <version>0.0.1-SNAPSHOT</version>

    <name>AspectJ Library</name>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <java.source-target.version>1.8</java.source-target.version>
        <aspectj.version>1.8.7</aspectj.version>
    </properties>

    <build>
        <pluginManagement>
            <plugins>
                <plugin>
                    <groupId>org.apache.maven.plugins</groupId>
                    <artifactId>maven-compiler-plugin</artifactId>
                    <version>3.3</version>
                    <configuration>
                        <source>${java.source-target.version}</source>
                        <target>${java.source-target.version}</target>
                        <!-- IMPORTANT -->
                        <useIncrementalCompilation>false</useIncrementalCompilation>
                    </configuration>
                </plugin>
                <plugin>
                    <groupId>org.codehaus.mojo</groupId>
                    <artifactId>aspectj-maven-plugin</artifactId>
                    <version>1.7</version>
                    <configuration>
                        <!--<showWeaveInfo>true</showWeaveInfo> -->
                        <source>${java.source-target.version}</source>
                        <target>${java.source-target.version}</target>
                        <Xlint>ignore</Xlint>
                        <complianceLevel>${java.source-target.version}</complianceLevel>
                        <encoding>${project.build.sourceEncoding}</encoding>
                        <!--<verbose>true</verbose> -->
                        <!--<warn>constructorName,packageDefaultMethod,deprecation,maskedCatchBlocks,unusedLocals,unusedArguments,unusedImport</warn> -->
                    </configuration>
                    <executions>
                        <execution>
                            <!-- IMPORTANT -->
                            <phase>process-sources</phase>
                            <goals>
                                <goal>compile</goal>
                                <goal>test-compile</goal>
                            </goals>
                        </execution>
                    </executions>
                    <dependencies>
                        <dependency>
                            <groupId>org.aspectj</groupId>
                            <artifactId>aspectjtools</artifactId>
                            <version>${aspectj.version}</version>
                        </dependency>
                    </dependencies>
                </plugin>
            </plugins>
        </pluginManagement>
        <plugins>
            <plugin>
                <groupId>org.codehaus.mojo</groupId>
                <artifactId>aspectj-maven-plugin</artifactId>
            </plugin>
            <!--
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
            </plugin>
            -->
        </plugins>
    </build>

    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.aspectj</groupId>
                <artifactId>aspectjrt</artifactId>
                <version>${aspectj.version}</version>
                <scope>runtime</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>

    <dependencies>
        <dependency>
            <groupId>org.aspectj</groupId>
            <artifactId>aspectjrt</artifactId>
        </dependency>
    </dependencies>

    <organization>
        <name>Scrum-Master.de - Agile Project Management</name>
        <url>http://scrum-master.de</url>
    </organization>

</project>

package de.scrum_master.aspect;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface Marker {}

package de.scrum_master.aspect;

public aspect MyAspect {
    before() : execution(* *(..)) && @annotation(Marker) {
        System.out.println(thisJoinPoint);
    }
}

Now run mvn clean install on the aspect library project so as to install the dependency into your local Maven repo.

Java application POM and sample application:

By the way, in the POM I have also added two optional plugins:

  • One-JAR plugin packages your application with all dependencies (e.g. aspect library and AspectJ runtime) into one artifact, here target/java-app-0.0.1-SNAPSHOT.one-jar.jar. You can just run your application via java -jar target/java-app-0.0.1-SNAPSHOT.one-jar.jar.
  • Exec Maven plugin is useful if you easily want to test your application from the command line via mvn clean install exec:java.

These two are only for convenience, you do not need them if you dislike them.

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>de.scrum-master.stackoverflow</groupId>
    <artifactId>java-app</artifactId>
    <version>0.0.1-SNAPSHOT</version>

    <name>Java Application</name>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <java.source-target.version>1.8</java.source-target.version>
        <aspectj.version>1.8.7</aspectj.version>
        <main-class>de.scrum_master.app.Application</main-class>
    </properties>

    <build>
        <pluginManagement>
            <plugins>
                <plugin>
                    <groupId>org.apache.maven.plugins</groupId>
                    <artifactId>maven-compiler-plugin</artifactId>
                    <version>3.3</version>
                    <configuration>
                        <source>${java.source-target.version}</source>
                        <target>${java.source-target.version}</target>
                        <!-- IMPORTANT -->
                        <useIncrementalCompilation>false</useIncrementalCompilation>
                    </configuration>
                </plugin>
                <plugin>
                    <groupId>org.codehaus.mojo</groupId>
                    <artifactId>aspectj-maven-plugin</artifactId>
                    <version>1.7</version>
                    <configuration>
                        <!--<showWeaveInfo>true</showWeaveInfo> -->
                        <source>${java.source-target.version}</source>
                        <target>${java.source-target.version}</target>
                        <Xlint>ignore</Xlint>
                        <complianceLevel>${java.source-target.version}</complianceLevel>
                        <encoding>${project.build.sourceEncoding}</encoding>
                        <!--<verbose>true</verbose> -->
                        <!--<warn>constructorName,packageDefaultMethod,deprecation,maskedCatchBlocks,unusedLocals,unusedArguments,unusedImport</warn> -->
                        <aspectLibraries>
                            <aspectLibrary>
                                <groupId>de.scrum-master.stackoverflow</groupId>
                                <artifactId>aspectj-lib</artifactId>
                            </aspectLibrary>
                        </aspectLibraries>
                    </configuration>
                    <executions>
                        <execution>
                            <!-- IMPORTANT -->
                            <phase>process-sources</phase>
                            <goals>
                                <goal>compile</goal>
                                <goal>test-compile</goal>
                            </goals>
                        </execution>
                    </executions>
                    <dependencies>
                        <dependency>
                            <groupId>org.aspectj</groupId>
                            <artifactId>aspectjtools</artifactId>
                            <version>${aspectj.version}</version>
                        </dependency>
                    </dependencies>
                </plugin>
                <plugin>
                    <groupId>org.codehaus.mojo</groupId>
                    <artifactId>exec-maven-plugin</artifactId>
                    <version>1.4.0</version>
                    <configuration>
                        <mainClass>${main-class}</mainClass>
                    </configuration>
                </plugin>
                <plugin>
                    <groupId>org.dstovall</groupId>
                    <artifactId>onejar-maven-plugin</artifactId>
                    <version>1.4.4</version>
                    <executions>
                        <execution>
                            <goals>
                                <goal>one-jar</goal>
                            </goals>
                        </execution>
                    </executions>
                    <configuration>
                        <onejarVersion>0.96</onejarVersion>
                        <mainClass>${main-class}</mainClass>
                        <attachToBuild>true</attachToBuild>
                    </configuration>
                </plugin>
            </plugins>
        </pluginManagement>
        <plugins>
            <plugin>
                <groupId>org.codehaus.mojo</groupId>
                <artifactId>aspectj-maven-plugin</artifactId>
            </plugin>
            <!--
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
            </plugin>
            -->
            <plugin>
                <groupId>org.codehaus.mojo</groupId>
                <artifactId>exec-maven-plugin</artifactId>
                <configuration>
                    <mainClass>${main-class}</mainClass>
                </configuration>
            </plugin>
            <plugin>
                <groupId>org.dstovall</groupId>
                <artifactId>onejar-maven-plugin</artifactId>
                <configuration>
                    <mainClass>${main-class}</mainClass>
                </configuration>
            </plugin>
        </plugins>
    </build>

    <pluginRepositories>
        <pluginRepository>
            <id>OneJAR googlecode.com</id>
            <url>http://onejar-maven-plugin.googlecode.com/svn/mavenrepo</url>
        </pluginRepository>
    </pluginRepositories>

    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.aspectj</groupId>
                <artifactId>aspectjrt</artifactId>
                <version>${aspectj.version}</version>
                <scope>runtime</scope>
            </dependency>
            <dependency>
                <groupId>de.scrum-master.stackoverflow</groupId>
                <artifactId>aspectj-lib</artifactId>
                <version>0.0.1-SNAPSHOT</version>
            </dependency>
        </dependencies>
    </dependencyManagement>

    <dependencies>
        <dependency>
            <groupId>org.aspectj</groupId>
            <artifactId>aspectjrt</artifactId>
        </dependency>
            <dependency>
                <groupId>de.scrum-master.stackoverflow</groupId>
                <artifactId>aspectj-lib</artifactId>
            </dependency>
    </dependencies>

    <organization>
        <name>Scrum-Master.de - Agile Project Management</name>
        <url>http://scrum-master.de</url>
    </organization>

</project>

This little driver application demonstrates that you can now annotate methods with @Marker, in this case only foo and zot, but not bar:

package de.scrum_master.app;

import de.scrum_master.aspect.Marker;

public class Application {
    @Marker
    public static void foo() {}

    public static void bar() {}

    @Marker
    public static void zot() {}

    public static void main(String[] args) {
        foo();
        bar();
        zot();
    }
}

Console log:

java -jar target/java-app-0.0.1-SNAPSHOT.one-jar.jar

execution(void de.scrum_master.app.Application.foo())
execution(void de.scrum_master.app.Application.zot())
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