／var／logmarcus chiu

Java - JaCoCo - Instrumentation

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Introduction

<properties>
   <!-- can be overridden with `mvn clean test -Djacoco.skip.instrument=false` -->
   <jacoco.skip.instrument>true</jacoco.skip.instrument>
</properties>
...
<execution>
   <id>jacoco-instrument</id>
   <phase>test</phase>
   <goals>
      <goal>instrument</goal>
   </goals>
   <configuration>
      <skip>${jacoco.skip.instrument}</skip>
   </configuration>
</execution>

Instrumentation should not be done on every build. You do not want to release instrumented code, first because this is bad practice and second code will not run unless jacocoagent.jar is in the classpath. This is why instrumentation should be disabled by default with jacoco.skip.instrument=true in pom.xml property, which can be overridden when needed with mvn clean test -Djacoco.skip.instrument=false command. Another option is separate pom-offline.xml file and build with it when needed

The maven application gets packaged to a single JAR file by mvn clean package. If instrumentation gets put in package phase then it is not working, as packaging happens before instrumentation. This is why test phase is the correct for the current example, as package includes test by default

mvn clean package -Djacoco.skip.instrument=false command. You can easily check if given class has been instrumented by opening it with some kind of decompiler. The image below shows instrumented class on the right hand side vs non-instrumented in the left hand side

Not Instrumented

Instrumented

mvn clean test

public class BookService {
    public BookService() {
    }

    public List<String> getBooks() {
        return BookDB.getAll();
    }
}

mvn clean test -Djacoco.skip.instrument=false

public class BookService {
    public BookService() {
		boolean[] var1 = $jacocoInit();
		super();
		var1[0] = true;
	}

    public java.util.List<java.lang.String> getBookNames() {
		boolean[] var1 = $jacocoInit();
		List var10000 = BookDB.getAll();
		var1[1] = true;
		return var10000;
	}
}

Instrumentation Offline vs Online

<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>org.jacoco</groupId>
    <artifactId>org.jacoco.examples.maven</artifactId>
    <version>0.8.8-SNAPSHOT</version>
    <packaging>jar</packaging>
    <name>JaCoCo Maven plug-in example with Offline Instrumentation</name>
    <url>http://www.jacoco.org/jacoco</url>
    <properties>
        <maven.compiler.source>1.5</maven.compiler.source>
        <maven.compiler.target>1.5</maven.compiler.target>
    </properties>
    <dependencies>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.10</version>
            <scope>test</scope>
        </dependency>
        <!--  must be on the classpath  -->
        <dependency>
            <groupId>org.jacoco</groupId>
            <artifactId>org.jacoco.agent</artifactId>
            <classifier>runtime</classifier>
            <version>0.8.8-SNAPSHOT</version>
            <scope>test</scope>
        </dependency>
    </dependencies>
    <build>
        <plugins>
            <plugin>
                <groupId>org.jacoco</groupId>
                <artifactId>jacoco-maven-plugin</artifactId>
                <version>0.8.8-SNAPSHOT</version>
                <executions>
                    <execution>
                        <id>default-instrument</id>
                        <goals>
                            <goal>instrument</goal>
                        </goals>
                    </execution>
                    <execution>
                        <id>default-restore-instrumented-classes</id>
                        <goals>
                            <goal>restore-instrumented-classes</goal>
                        </goals>
                    </execution>
                    <execution>
                        <id>default-report</id>
                        <goals>
                            <goal>report</goal>
                        </goals>
                    </execution>
                    <execution>
                        <id>default-check</id>
                        <goals>
                            <goal>check</goal>
                        </goals>
                        <configuration>
                            <rules>
                                <rule>
                                    <element>BUNDLE</element>
                                    <limits>
                                        <limit>
                                            <counter>COMPLEXITY</counter>
                                            <value>COVEREDRATIO</value>
                                            <minimum>0.60</minimum>
                                        </limit>
                                    </limits>
                                </rule>
                            </rules>
                        </configuration>
                    </execution>
                </executions>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-surefire-plugin</artifactId>
                <version>2.12.2</version>
                <configuration>
                    <systemPropertyVariables>
                        <jacoco-agent.destfile>target/jacoco.exec</jacoco-agent.destfile>
                    </systemPropertyVariables>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>

<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>org.jacoco</groupId>
    <artifactId>org.jacoco.examples.maven</artifactId>
    <version>0.8.8-SNAPSHOT</version>
    <packaging>jar</packaging>
    <name>JaCoCo Maven plug-in example with Online Instrumentation</name>
    <url>http://www.jacoco.org/jacoco</url>
    <properties>
        <maven.compiler.source>1.5</maven.compiler.source>
        <maven.compiler.target>1.5</maven.compiler.target>
    </properties>
    <dependencies>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.13.1</version>
            <scope>test</scope>
        </dependency>
    </dependencies>
    <build>
        <plugins>
            <plugin>
                <groupId>org.jacoco</groupId>
                <artifactId>jacoco-maven-plugin</artifactId>
                <version>0.8.8-SNAPSHOT</version>
                <executions>
                    <execution>
                        <id>default-prepare-agent</id>
                        <goals>
                            <goal>prepare-agent</goal>
                        </goals>
                    </execution>
                    <execution>
                        <id>default-report</id>
                        <goals>
                            <goal>report</goal>
                        </goals>
                    </execution>
                    <execution>
                        <id>default-check</id>
                        <goals>
                            <goal>check</goal>
                        </goals>
                        <configuration>
                            <rules>
                                <rule>
                                    <element>BUNDLE</element>
                                    <limits>
                                        <limit>
                                            <counter>COMPLEXITY</counter>
                                            <value>COVEREDRATIO</value>
                                            <minimum>0.60</minimum>
                                        </limit>
                                    </limits>
                                </rule>
                            </rules>
                        </configuration>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>
</project>