Sometimes when the required libraries / dependencies is not available in the Maven Central Repository we need to manually install it to our local repository. This library must be placed in the correct directory in our local repository to enable Maven to find it. The default location is under the ${user.home}/.m2/repository.
To make this job easier Maven provides a maven-install-plugin that will help us to install the third-party library in the correct place. The following command shows how to do it.
-DpomFile = the location to the library pom.xml file
Starting with the Maven version 2.5 you can use even a simpler command. When the library is build by Maven, a pom.xml file will be placed under the META-INF directory. This pom.xml file will be used by default when we install the library. To install a library all you need is the following command:
The following configuration will use Google’s mirror of the Maven Central repository. Alter your ${M2_HOME}/conf/settings.xml or ${user.home}/.m2/settings.xml to add the mirror as seen in the following configuration file.
When we work behind a proxy server, we need to configure Maven to be able to connect to the internet. To enable proxy we can configure Maven settings.xml file, either in ${M2_HOME}/conf/settings.xml or ${user.home}/.m2/settings.xml file.
The <proxy> element in the configuration above contains the information about the proxy server. These include information about the host, port, username and password. Set these elements to match your proxy server configuration.
When you need to compile a project for a specific Java version you can configure maven compiler plugin to set the source and the target version. The following pom.xml file configuration show you how to do it.
Invalid value for the source and the target version in our project will make our project compilation process failed. For example when we try to use the diamond operator (<>) which available in Java 7, while the maven compiler plugin is set to version 1.5, can produce compiler error like this:
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.1:compile (default-compile) on project servlet-example: Compilation failure
[ERROR] /Users/wsaryada/Studio/kodejava.org/webapp-example/servlet-example/src/main/java/org/kodejava/example/servlet/SessionCounter.java:[10,51] diamond operator is not supported in -source 1.5
[ERROR] (use -source 7 or higher to enable diamond operator)
In this post you will learn how to create a simple project, a Hello World project using Maven. If you haven’t installed Maven in your machine you can read Introduction to Apache Maven posted earlier in this blog. In this post you will see what the basic configuration for creating a maven project. Such as the basic of pom.xml file and how maven structure the directory of our project files.
At this time we won’t use any special IDE such as Eclipse, Netbeans or IntelliJ to create our project. We’ll just work using a simple text editor and the command prompt. Let us begin.
Step 1 – Create a project directory and the pom.xml file.
Create a directory where you will place the project files. As an example I’ll create my project in D:\Projects\HelloWorld.
Create a file called pom.xml in the HelloWorld directory. POM stands for Project Object Model, and it represents a Maven project.
Type the following information in the pom.xml file.
At this point we have our pom.xml file created. What you’ve seen above is the simplest example of a pom file. And here is a brief description of the pom file above:
groupId: the unique id of a Maven project. Typically, it uses your company name domain in reverse order just like how you would create a package for your Java project. For example here I use org.kodejava.
artifactId: is the name of the project, we’ll be using HelloWorld.
version: is the version number of our project.
packaging: the project artifact type. In this case we will ask Maven to package our example as a jar file.
modelVersion: is the version of the POM file we are using for this project.
Maven works by applying a concept called convention over configuration. This will apply for example on how the directory of a project is structured. All Maven project will use the same directory for organising the files in the project. There is a directory for Java source codes, unit testing codes, configuration files, etc. This will make easier for developer to jump from one Maven project to the other projects. Now let us continue to the next step.
Step 2 – Create the HelloWorld class.
Create a directory for Java source code in the project root directory. Actually you’ll create three directories. These directories are src\main\java.
Create a file HellWorld.java under the java directory you’ve created above.
Type the following code for the HelloWorld class.
public class HelloWorld {
public static void main(String[] args) {
System.out.println("Hello World!");
}
}
Now we have our class created we can start to use maven to build our project. But before we do let see what you should have after finishing these steps. You should see that you have a project structure that similar the screen capture below:
Steps 3 – Compiling the Project.
At this time we have our first Maven project created, and we are ready to build it. To build this basic project we don’t have to add anything to Maven. It already comes with a predefined sets of build related task such as clean, compile, test, package, etc.
Open a Command Prompt and go to your project directory. You should be in the HelloWorld directory where you can see the pom.xml file.
To compile your project type mvn compile in the command prompt.
D:\Projects\HelloWorld>mvn compile
[INFO] Scanning for projects...
[INFO]
[INFO] ------------------------------------------------------------------------
[INFO] Building HelloWorld 1.0-SNAPSHOT
[INFO] ------------------------------------------------------------------------
[INFO] Compiling 1 source file to D:\Projects\HelloWorld\target\classes
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 2.405s
[INFO] Finished at: Tue Sep 24 10:18:10 CST 2013
[INFO] Final Memory: 7M/23M
[INFO] ------------------------------------------------------------------------
D:\Projects\HelloWorld>
What you see above is the typical result of a success build. You might see longer message such as information about the artifact downloaded by Maven during the compile process.
If you list the project directory you’ll see a new directory called targetclasses is created. And inside the classes directory you’ll find your HelloWorld.class file.
To run the class cd to targetclasses and type java HelloWorld.
Steps 4 – Clean and Package the Project.
Now if you want to clean your previous built project you can use mvn clean. Make sure you are executing this command from the project root directory where the pom.xml file is located.
Executing this command will give you the similar output like this.
As you can see it deleted the previously created target directory.
In the pom.xml file we have defined the packaging of our project as jar file. So let’s create it now.
To package a Maven project type mvn package command.
D:\Projects\HelloWorld>mvn package
[INFO] Scanning for projects...
[INFO] ------------------------------------------------------------------------
[INFO] Building HelloWorld 1.0-SNAPSHOT
[INFO] ------------------------------------------------------------------------
[INFO] Compiling 1 source file to D:\Projects\HelloWorld\target\classes
[INFO] skip non existing resourceDirectory D:\Projects\HelloWorld\src\test\resources
[INFO] --- maven-compiler-plugin:2.3.2:testCompile (default-testCompile) @ HelloWorld ---
[INFO] No sources to compile
[INFO] --- maven-surefire-plugin:2.7.2:test (default-test) @ HelloWorld ---
[INFO] No tests to run.
[INFO] Surefire report directory: D:\Projects\HelloWorld\target\surefire-reports
[INFO] -------------------------------------------------------
[INFO] T E S T S
[INFO] -------------------------------------------------------
There are no tests to run.
Results :
Tests run: 0, Failures: 0, Errors: 0, Skipped: 0
[INFO] --- maven-jar-plugin:2.3.1:jar (default-jar) @ HelloWorld ---
[INFO] Building jar: D:\Projects\HelloWorld\target\HelloWorld-1.0-SNAPSHOT.jar
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 3.040s
[INFO] Finished at: Tue Sep 24 10:32:41 CST 2013
[INFO] Final Memory: 8M/20M
[INFO] ------------------------------------------------------------------------
D:\Projects\HelloWorld>
The mvn package gives you a longer console output. From the output above you can see that executing the package command made Maven to compile the Java source code, unit test source code (we don’t have it at this time). It also runs the unit test and finally build the jar file.
The jar file is created under the target directory and named HelloWorld-1.0-SNAPSHOT.jar. The name comes from the artifactId, version and packaging information defined in the pom.xml file.
That are all the steps that you need to create and manage a simple project using Maven. We start by creating a pom.xml file and then create a directory structure for storing our classes file. And then we learn how to compile, clean and package our Maven project. In the next Maven post we’ll learn more on Maven dependency management and starting to use an IDE to set up our Maven project.
Thank your for reading and see you on the next Maven post.
In this post you will learn about Apache Maven. What is Maven? In simple words, Maven is a tool that we can use to build and manage a Java based project. Compare to the older type of build tool such as Ant, which is also an Apache project, Maven gives developers a standard way to build projects, a clear definition of the projects consisted of, an easy way to publish project information and an easy management of the project libraries dependency.
In Maven, the project libraries (Jars) will be maintained in the Maven repository and can be shared among projects. We don’t need to include the Jars in the project’s source code, as what we usually do when using tool like Ant. And here are the main objectives of the Apache Maven project:
Making the build process easy.
Providing a uniform build system.
Providing quality project information.
Providing guidelines for best practices development.
Allowing transparent migration to a new features.
After you know a little about Maven, let’s continue to the next step, installing the Apache Maven.
Step 1. Downloading Apache Maven
Go to Apache Maven and from the Get Maven section on the left sidebar click Download link.
Download the appropriate installer for your platform. For example, I am downloading the .zip file. The latest version when this post is written is Maven 3.1.0 (apache-maven-3.1.0-bin.zip).
Extract the downloaded zip file. For example, I am extracting it into D:\Toolbox\apache-maven-3.1.0 directory.
Step 2. Configuring Environment Variables
After extracting Maven distribution you have to define M2_HOME environment variable. The value of this variable is the path to your Maven installation.
You can create environment variable using the following steps:
Right click on My Computer.
Select Properties menu.
Select Advanced system settings.
In the System Properties window select the Advanced tab and click the Environment Variables button.
Add the variable in the System variables section.
Click OK to proceed.
Add the %M2_HOME%\bin; into your PATH environment variable so that you can execute Maven command from any path inside your command prompt. This PATH variable can also be updated in the System variables section.
Open your command prompt and type echo %M2_HOME%. Pressing Enter and you should see the value of the variable printed on the console. For example:
D:\>echo %M2_HOME%
D:\Toolbox\apache-maven-3.1.0
To check if Maven also in your Path variable you can execute echo %PATH% in your command prompt. You should see the path to Maven binary in the Path variable.
Congratulations! You’ve installed Apache Maven successfully on your development machine. On the next post I will show you how to create a new project using Maven.
