Apache Maven Tutorial – Apache Maven教程

• simple project setup that follows best practices: Maven tries to avoid as much configuration as possible, by supplying project templates (named archetypes)
• dependency management: it includes automatic updating, downloading and validating the compatibility, as well as reporting the dependency closures (known also as transitive dependencies)
• isolation between project dependencies and plugins: with Maven, project dependencies are retrieved from the dependency repositories while any plugin’s dependencies are retrieved from the plugin repositories, resulting in fewer conflicts when plugins start to download additional dependencies
• central repository system: project dependencies can be loaded from the local file system or public repositories, such as Maven Central

3. Project Object Model

3.项目对象模型

<project>
    <modelVersion>4.0.0</modelVersion>
    <groupId>com.baeldung</groupId>
    <artifactId>baeldung</artifactId>
    <packaging>jar</packaging>
    <version>1.0-SNAPSHOT</version>
    <name>com.baeldung</name>
    <url>http://maven.apache.org</url>
    <dependencies>
        <dependency>
            <groupId>org.junit.jupiter</groupId>
            <artifactId>junit-jupiter-api</artifactId>
            <version>5.8.2</version>
            <scope>test</scope>
        </dependency>
    </dependencies>
    <build>
        <plugins>
            <plugin>
            //...
            </plugin>
        </plugins>
    </build>
</project>

<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-core</artifactId>
    <version>5.3.16</version>
</dependency>

A repository in Maven is used to hold build artifacts and dependencies of varying types. The default local repository is located in the .m2/repository folder under the home directory of the user.

Maven的资源库用于存放不同类型的构建工件和依赖。默认的本地资源库位于用户主目录下的.m2/repository文件夹中。

If an artifact or a plugin is available in the local repository, Maven uses it. Otherwise, it is downloaded from a central repository and stored in the local repository. The default central repository is Maven Central.

如果本地资源库中有工件或插件，Maven就会使用它。否则，它会从中央仓库下载并存储在本地仓库中。默认的中央仓库是Maven Central。

Some libraries, such as the JBoss server, are not available at the central repository but are available at an alternate repository. For those libraries, you need to provide the URL to the alternate repository inside the pom.xml file:

有些库，如JBoss服务器，在中央仓库中是不可用的，但在另一个仓库中可用。对于这些库，你需要在pom.xml文件中提供备用库的URL。

<repositories>
    <repository>
        <id>JBoss repository</id>
        <url>http://repository.jboss.org/nexus/content/groups/public/</url>
    </repository>
</repositories>

Please note that you can use multiple repositories in your projects.

请注意，你可以在你的项目中使用多个存储库。。

3.4. Properties

3.4.属性

Custom properties can help to make your pom.xml file easier to read and maintain. In the classic use case, you would use custom properties to define versions for your project’s dependencies.

自定义属性可以帮助使你的pom.xml文件更容易阅读和维护。在经典的使用案例中，你会使用自定义属性来为你的项目的依赖性定义版本。

Maven properties are value-placeholders and are accessible anywhere within a pom.xml by using the notation ${name}, where name is the property.

Maven属性是值占位符，可以在pom.xml中的任何地方使用${name}，其中name是属性。

Let’s see an example:

让我们看一个例子。

<properties>
    <spring.version>5.3.16</spring.version>
</properties>

<dependencies>
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-core</artifactId>
        <version>${spring.version}</version>
    </dependency>
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-context</artifactId>
        <version>${spring.version}</version>
    </dependency>
</dependencies>

Now if you want to upgrade Spring to a newer version, you only have to change the value inside the<spring.version> property tag and all the dependencies using that property in their <version> tags will be updated.

现在，如果你想把Spring升级到一个较新的版本，你只需要改变<spring.version>属性标签内的值，所有在<version>标签中使用该属性的依赖关系都会被更新。

Properties are also often used to define build path variables:

属性也经常被用来定义构建路径变量。

<properties>
    <project.build.folder>${project.build.directory}/tmp/</project.build.folder>
</properties>

<plugin>
    //...
    <outputDirectory>${project.resources.build.folder}</outputDirectory>
    //...
</plugin>

3.5. Build

3.5.构建

The build section is also a very important section of the Maven POM. It provides information about the default Maven goal, the directory for the compiled project, and the final name of the application. The default build section looks like this:

build部分也是Maven POM中非常重要的部分。它提供了有关Maven默认目标、编译项目的目录和应用程序的最终名称的信息。默认的build部分看起来像这样。

<build>
    <defaultGoal>install</defaultGoal>
    <directory>${basedir}/target</directory>
    <finalName>${artifactId}-${version}</finalName>
    <filters>
      <filter>filters/filter1.properties</filter>
    </filters>
    //...
</build>

The default output folder for compiled artifacts is named target, and the final name of the packaged artifact consists of the artifactId and version, but you can change it at any time.

编译工件的默认输出文件夹被命名为target，打包工件的最终名称由artifactId和version组成，但是你可以随时改变它。。

3.6. Using Profiles

3.6.使用Profiles

Another important feature of Maven is its support for profiles. A profile is basically a set of configuration values. By using profiles, you can customize the build for different environments such as Production/Test/Development:

Maven的另一个重要特点是支持profiles。profile基本上是一组配置值。通过使用profiles，你可以为不同环境（如生产/测试/开发）定制构建。

<profiles>
    <profile>
        <id>production</id>
        <build>
            <plugins>
                <plugin>
                //...
                </plugin>
            </plugins>
        </build>
    </profile>
    <profile>
        <id>development</id>
        <activation>
            <activeByDefault>true</activeByDefault>
        </activation>
        <build>
            <plugins>
                <plugin>
                //...
                </plugin>
            </plugins>
        </build>
     </profile>
 </profiles>

As you can see in the example above, the default profile is set to development. If you want to run the production profile, you can use the following Maven command:

正如你在上面的例子中看到的，默认配置文件被设置为development。如果你想运行productionprofile，你可以使用以下Maven命令。

mvn clean install -Pproduction

4. Maven Build Lifecycles

4.Maven的构建生命周期

mvn <phase>

For example, mvn clean install will remove the previously created jar/war/zip files and compiled classes (clean) and execute all the phases necessary to install the new archive (install).

例如，mvn clean install将删除先前创建的jar/war/zip文件和编译的类（clean），并执行所有必要的阶段来安装新的存档（install）。

Please note that goals provided by plugins can be associated with different phases of the lifecycle.

请注意，由插件提供的目标可以与生命周期的不同阶段相关。

5. Your First Maven Project

5.你的第一个Maven项目

In this section, we will use the command line functionality of Maven to create a Java project.

本节中，我们将使用Maven的命令行功能来创建一个Java项目。

5.1. Generating a Simple Java Project

5.1.生成一个简单的Java项目

In order to build a simple Java project, let’s run the following command:

为了建立一个简单的Java项目，让我们运行以下命令。

As you can see, the JUnit dependency is provided by default.

正如你所看到的，JUnit的依赖性是默认提供的。

5.2. Compiling and Packaging a Project

5.2.编译和打包项目

The next step is to compile the project:

下一步是编译该项目。

mvn compile

Maven will run through all lifecycle phases needed by the compile phase to build the project’s sources. If you want to run only the test phase, you can use:

Maven将运行生命周期阶段所需的所有编译阶段，以构建项目的源代码。如果你只想运行test阶段，你可以使用。

mvn test

Now let’s invoke the package phase, which will produce the compiled archive jar file:

现在让我们调用package阶段，它将产生编译后的存档jar文件。

mvn package

5.3. Executing an Application

5.3.执行一个应用程序

Finally, we are going to execute our Java project with the exec-maven-plugin. Let’s configure the necessary plugins in the pom.xml:

最后，我们要用exec-maven-plugin来执行我们的Java项目。让我们在pom.xml中配置必要的插件。