Maven Exercises

A simple collection of Maven exercises for use in a 2-hour introductory training session. You should have Maven 3 or later installed.

You can find the instructions for each exercise below. The exercises build on each other, so you need to complete them in sequence. If you get stuck on an exercise the answers are available in branches, so for example: if you fail to get exercise1 working, just git checkout answer1 and continue from there.

Exercises

Exercise 1: Build the project

Exercise: git checkout exercise1

In this exercise you simply need to build the project. Change into the project directory and then do mvn clean install.

Oh no! It failed with a compilation error:

[INFO] -------------------------------------------------------------
[ERROR] COMPILATION ERROR :
[INFO] -------------------------------------------------------------
[ERROR] /c:/dev/mattpwest/maven-exercises/src/main/java/za/co/entelect/forums/java/prac/task3/Corruption.java:[22,60] diamond operator is not supported in -source 1.5
  (use -source 7 or higher to enable diamond operator)
[ERROR] /c:/dev/mattpwest/maven-exercises/src/main/java/za/co/entelect/forums/java/example/App.java:[45,45] diamond operator is not supported in -source 1.5
  (use -source 7 or higher to enable diamond operator)
[ERROR] /c:/dev/mattpwest/maven-exercises/src/main/java/za/co/entelect/forums/java/prac/task2/BigBrother.java:[20,56] diamond operator is not supported in -source 1.5
  (use -source 7 or higher to enable diamond operator)
[ERROR] /c:/dev/mattpwest/maven-exercises/src/main/java/za/co/entelect/forums/java/prac/task1/ColorSpotter.java:[29,65] diamond operator is not supported in -source 1.5
  (use -source 7 or higher to enable diamond operator)
[INFO] 4 errors

You'll need to configure the Maven Compiler Plugin to use Java 1.7 or 1.8.

Once you have this properly configured your build should succeed:

[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 10.171 s
[INFO] Finished at: 2015-07-12T11:45:34+02:00
[INFO] Final Memory: 21M/200M
[INFO] ------------------------------------------------------------------------

You can run one of the examples with: java -cp target/maven-exercises-1.0.0-SNAPSHOT.jar za.co.entelect.forums.java.prac.task1.ColorSpotter.

Answer: git checkout answer1

Exercise 2: Repositories

Exercise: git checkout exercise2

We're not actually going to use it in the project, but let's just add a big dependency to your pom.xml to explore the benefits of the local repository and/or repository server:

<dependency>
    <groupId>com.badlogicgames.gdx</groupId>
    <artifactId>gdx</artifactId>
    <version>1.6.1</version>
</dependency>

To ensure that you don't already have the artifact in your local repository run: rm -R ~/.m2/repository/com/badlogicgames.

Now run mvn clean install and look at the output:

...
[INFO] ------------------------------------------------------------------------
[INFO] Building maven-exercises 1.0.0-SNAPSHOT
[INFO] ------------------------------------------------------------------------
Downloading: https://repo.maven.apache.org/maven2/com/badlogicgames/gdx/gdx/1.6.1/gdx-1.6.1.pom
Downloaded: https://repo.maven.apache.org/maven2/com/badlogicgames/gdx/gdx/1.6.1/gdx-1.6.1.pom (2 KB at 0.7 KB/sec)
Downloading: https://repo.maven.apache.org/maven2/com/badlogicgames/gdx/gdx-parent/1.6.1/gdx-parent-1.6.1.pom
Downloaded: https://repo.maven.apache.org/maven2/com/badlogicgames/gdx/gdx-parent/1.6.1/gdx-parent-1.6.1.pom (5 KB at 5.6 KB/sec)
Downloading: https://repo.maven.apache.org/maven2/com/badlogicgames/gdx/gdx/1.6.1/gdx-1.6.1.jar
Downloaded: https://repo.maven.apache.org/maven2/com/badlogicgames/gdx/gdx/1.6.1/gdx-1.6.1.jar (1722 KB at 323.7 KB/sec)
[INFO]
[INFO] --- maven-clean-plugin:2.5:clean (default-clean) @ maven-exercises ---
...
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 12.894 s
...

Note how Maven downloaded the gdx artifact and its transitive dependency gdx-parent for you.

Now run mvn clean install again:

...
[INFO] ------------------------------------------------------------------------
[INFO] Building maven-exercises 1.0.0-SNAPSHOT
[INFO] ------------------------------------------------------------------------
[INFO]
[INFO] --- maven-clean-plugin:2.5:clean (default-clean) @ maven-exercises ---
...
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 4.290 s
...

Note that Maven didn't need to download the dependencies this time, so the build was much faster. You can go explore the contents of your local repository by browsing to ~/.m2/repository/ - you'll see that artefacts are organised in a hierarchial structure:

~/.m2/repository
        \_ com
            \_ badlogicgames
                \_ gdx
                    \_ gdx
                        \_ 1.6.1
                    \_ gdx-parent
                        \_ 1.6.1

The rest of this exercise is optional and deals with configuring Maven to use the repository manager at your company to speed up builds and reduce bandwidth used by Maven.

First copy example.m2.settings.xml into ~/.m2 and rename it to settings.xml.

Then edit the file and:

• Delete the <servers> section (you're not going to be pushing artifacts for this exercise).
• Go through the <profiles> section and replace the servers with the settings supplied by your instructor.
• Note the <activeProfiles> section which enables this profile by default for all builds on your machine.

Now do rm -R ~/.m2/repository/com/badlogicgames followed by mvn clean install again and look at the output:

...
[INFO] ------------------------------------------------------------------------
[INFO] Building maven-exercises 1.0.0-SNAPSHOT
[INFO] ------------------------------------------------------------------------
Downloading: http://esjavatools:8080/artifactory/libs-release/com/badlogicgames/gdx/gdx/1.6.1/gdx-1.6.1.pom
Downloaded: http://esjavatools:8080/artifactory/libs-release/com/badlogicgames/gdx/gdx/1.6.1/gdx-1.6.1.pom (2 KB at 7.4 KB/sec)
Downloading: http://esjavatools:8080/artifactory/libs-release/com/badlogicgames/gdx/gdx-parent/1.6.1/gdx-parent-1.6.1.pom
Downloaded: http://esjavatools:8080/artifactory/libs-release/com/badlogicgames/gdx/gdx-parent/1.6.1/gdx-parent-1.6.1.pom (5 KB at 74.3 KB/sec)
Downloading: http://esjavatools:8080/artifactory/libs-release/com/badlogicgames/gdx/gdx/1.6.1/gdx-1.6.1.jar
Downloaded: http://esjavatools:8080/artifactory/libs-release/com/badlogicgames/gdx/gdx/1.6.1/gdx-1.6.1.jar (1722 KB at 4959.8 KB/sec)
[INFO]
[INFO] --- maven-clean-plugin:2.5:clean (default-clean) @ maven-exercises ---
...
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 5.130 s
...

Note how Maven now downloads the artefacts from your repository manager, greatly speeding up the build.

Answer: git checkout answer2

Exercise 3: Tests

Exercise: git checkout exercise3

Your example project includes some tests (OK - a test). To run it, execute mvn clean test and look at the output:

...
-------------------------------------------------------
 T E S T S
-------------------------------------------------------
Running za.co.entelect.forums.java.AppTest
Woohoo - tests!
Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.01 sec

Results :

Tests run: 1, Failures: 0, Errors: 0, Skipped: 0

[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 3.880 s
...

If you examine your project there are some important things to note:

• You are using junit:3.8.1 for tests (that's ancient).
• Your test file is named AppTest.java.

If you were to rename AppTest.java to App.java and rerun mvn clean test you'll see that tests are no longer executed - this is because the Maven Surefire plugin by default only looks for tests in files matching the following patterns:

• **/Test*.java
• **/*Test.java
• **/*TestCase.java

Junit 3 is the default included in the project dependencies when you use an archetype to generate a Maven project, but it's ancient and version 4's syntax is much more concise - let's upgrade our project to the latest version of JUnit (junit:4.12).

Make the following changes to the test file AppTest.java:

• Remove all import statements.
• Remove extends TestCase from the class definition.
• Remove the constructor.
• Remove the static method suite.
• Add the @Test annotation above the testApp() method.
• Replace assertTrue(true); with Assert.assertTrue(true);.

Then update your pom.xml to use junit:4.12 and use your IDE to add the missing imports in test App.java.

Now run mvn clean test to make sure your changes are working.

Answer: git checkout answer3

Exercise 4: Multi-module Web Project

Exercise: git checkout exercise4

Step 1: Domain module

As your final exercise, let's convert the project into a multi-module web project. The overall structure of the new version will be as follows:

 maven-exercises
   \_ domain: All the current code in the project will move into the domain.
   \_ web: Web module will contain a single controller and page that will show the output of the corruption exercise.

First edit your current project's pom.xml:

• Change <groupId> value to za.co.entelect.forums.java.maven.exercises.
• Change <packaging> value to pom.

Now you can generate your domain module using the simple project archetype:

mvn -B archetype:generate \
      -DarchetypeGroupId=org.apache.maven.archetypes \
      -DgroupId=za.co.entelect.forums.java.maven.exercises \
      -DartifactId=domain

Now make the following changes to the generated module's pom.xml:

• Remove the redundant <groupId> (inherited from parent project).
• Update the version to 1.0.0-SNAPSHOT to be consistent with the parent project.
• Add <packaging>jar</packaging>.
• Remove <version> from your JUnit dependency.

Now move the code from src/main/java/ and src/test/java in your parent project into the new module.

Now make the following changes to your parent pom.xml:

• Wrap the existing <dependencies> element in a <dependencyManagement> element.
• Delete the src folder from the parent module.

Finally run mvn clean install - if all went well your domain module should build and its test should run.

Step 2: Web module

Begin by generating your web module:

mvn archetype:generate \
    -DgroupId=za.co.entelect.forums.java.maven.exercises \
    -DartifactId=web \
    -DarchetypeArtifactId=maven-archetype-webapp \
    -DinteractiveMode=false

Now make the following changes to the generated module's pom.xml:

• Remove the redundant <groupId> (inherited from parent project).
• Update the version to 1.0.0-SNAPSHOT to be consistent with the parent project.
• Remove <version> from your JUnit dependency.

Edit your generated web.xml to upgrade to servlet 3.0:

<web-app xmlns="http://java.sun.com/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
         version="3.0">

    <display-name>Corruption Web Application</display-name>
</web-app>

Add the following properties to your web/pom.xml:

    <properties>
		<spring.version>4.1.1.RELEASE</spring.version>
		<jstl.version>1.2</jstl.version>
		<logback.version>1.0.13</logback.version>
		<jcl-over-slf4j.version>1.7.5</jcl-over-slf4j.version>
	</properties>

Add the following dependencies to your web/pom.xml:

    <dependency>
        <groupId>za.co.entelect.forums.java.maven.exercises</groupId>
        <artifactId>domain</artifactId>
        <version>1.0.0-SNAPSHOT</version>
    </dependency>
    
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-core</artifactId>
        <version>${spring.version}</version>
        <exclusions>
            <exclusion>
                <groupId>commons-logging</groupId>
                <artifactId>commons-logging</artifactId>
            </exclusion>
        </exclusions>
    </dependency>

    <dependency>
        <groupId>org.slf4j</groupId>
        <artifactId>jcl-over-slf4j</artifactId>
        <version>${jcl-over-slf4j.version}</version>
    </dependency>

    <dependency>
        <groupId>ch.qos.logback</groupId>
        <artifactId>logback-classic</artifactId>
        <version>${logback.version}</version>
    </dependency>

    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-web</artifactId>
        <version>${spring.version}</version>
    </dependency>

    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-webmvc</artifactId>
        <version>${spring.version}</version>
    </dependency>

    <!-- jstl -->
    <dependency>
        <groupId>jstl</groupId>
        <artifactId>jstl</artifactId>
        <version>${jstl.version}</version>
    </dependency>

Add the following build plugin to your web/pom.xml to use to run the web application:

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.tomcat.maven</groupId>
                <artifactId>tomcat7-maven-plugin</artifactId>
                <version>2.2</version>
                <configuration>
                    <path>/corruption</path>
                </configuration>
            </plugin>
        </plugins>
    </build>

Add a Spring controller web/src/main/java/za/co/entelect/forums/java/maven/web/BaseController.java:

package za.co.entelect.forums.java.maven.web;

import org.slf4j.LoggerFactory;
import org.springframework.stereotype.Controller;
import org.springframework.ui.ModelMap;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import za.co.entelect.forums.java.example.App;
import za.co.entelect.forums.java.example.domain.Gantry;
import za.co.entelect.forums.java.example.domain.Vehicle;

import java.math.BigDecimal;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

@Controller
public class BaseController {

    private static final String VIEW_INDEX = "index";
    private final static org.slf4j.Logger logger = LoggerFactory.getLogger(BaseController.class);

    @RequestMapping(value = "/", method = RequestMethod.GET)
    public String welcome(ModelMap model) {
        Map<Vehicle, BigDecimal> vehicleBills = getVehicleBills();

        model.addAttribute("vehicles", vehicleBills.keySet());
        model.addAttribute("bills", vehicleBills);
        logger.debug("Showing vehicle bills : " + vehicleBills.toString());

        // Spring uses InternalResourceViewResolver and return back index.jsp
        return VIEW_INDEX;
    }

    private Map<Vehicle, BigDecimal> getVehicleBills() {
        List<Gantry> gantries = App.getGantryList();
        Map<Vehicle, BigDecimal> vehicleBill = new HashMap<>();

        for (Gantry gantry : gantries) {
            for (Vehicle vehicle : gantry.getVehicles()) {
                if (!vehicleBill.containsKey(vehicle)) {
                    vehicleBill.put(vehicle, new BigDecimal(gantry.getToll()));
                } else {
                    BigDecimal value = vehicleBill.get(vehicle);
                    vehicleBill.put(vehicle, value.add(new BigDecimal(gantry.getToll())));
                }
            }
        }

        return vehicleBill;
    }
}

Add a Spring configuration file WEB-INF/mvc-dispatcher-servlet.xml:

<beans xmlns="http://www.springframework.org/schema/beans"
	xmlns:context="http://www.springframework.org/schema/context"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="
        http://www.springframework.org/schema/beans     
        http://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/context 
        http://www.springframework.org/schema/context/spring-context.xsd">
 
	<context:component-scan base-package="za.co.entelect.forums.java.maven.web" />
 
	<bean
		class="org.springframework.web.servlet.view.InternalResourceViewResolver">
		<property name="prefix">
			<value>/WEB-INF/pages/</value>
		</property>
		<property name="suffix">
			<value>.jsp</value>
		</property>
	</bean>
</beans>

Add Spring web.xml configuration:

    <servlet>
		<servlet-name>mvc-dispatcher</servlet-name>
		<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
		<load-on-startup>1</load-on-startup>
	</servlet>
 
	<servlet-mapping>
		<servlet-name>mvc-dispatcher</servlet-name>
		<url-pattern>/</url-pattern>
	</servlet-mapping>
 
	<context-param>
		<param-name>contextConfigLocation</param-name>
		<param-value>/WEB-INF/mvc-dispatcher-servlet.xml</param-value>
	</context-param>
 
	<listener>
		<listener-class>
           org.springframework.web.context.ContextLoaderListener
        </listener-class>
	</listener>

Move index.jsp to WEB-INF/pages and give it some useful content:

<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>

<html>
<body>
<h1>Corruption Bills</h1>

<c:forEach var="vehicle" items="${vehicles}">
    <h2>Vehicle : ${vehicle.registrationNumber}</h2>
    <p>Bill: R ${bills[vehicle]}</p>
</c:forEach>
</body>
</html>

Create web/src/main/resources/logback.xml:

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
    <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
        <layout class="ch.qos.logback.classic.PatternLayout">

            <Pattern>
                %d{yyyy-MM-dd HH:mm:ss} [%thread] %-5level %logger{36} - %msg%n
            </Pattern>

        </layout>
    </appender>

    <logger name="za.co.entelect.forums.java.maven.web" level="debug"
            additivity="false">
        <appender-ref ref="STDOUT"/>
    </logger>

    <root level="debug">
        <appender-ref ref="STDOUT"/>
    </root>
</configuration>

If all went well you should now be able to build and run your web application:

• mvn clean install
• mvn tomcat:run
• Then visit: http://locahost:8080/web/

Exercise: git checkout answer4