Maven 變得簡單：輕鬆建立 Java 項目

使用 Maven 進行自動化建置的簡單易懂的指南

Maven 是 Java 開發人員的必備工具，可以簡化專案建置、依賴管理和版本控制。無論您是 Java 新手還是經驗豐富的開發人員，了解 Maven 都可以顯著增強您的工作流程。在本文中，我們將探討 Maven 的工作原理、其核心功能，以及為什麼它是管理複雜 Java 專案的首選解決方案。從自動化重複性任務到確保專案保持井井有條，Maven 讓開發更加順暢和有效率。最後，您將清楚地掌握如何將 Maven 整合到您的專案中，以實現更快、更可靠的建置。

Maven 不僅僅用於管理依賴項；它也用於管理依賴項。它還涉及簡化整個開發流程。它遵循簡單但功能強大的結構，使用「pom.xml」檔案來定義專案的依賴項、建置配置和插件。這種方法可確保您的專案在不同環境中保持一致，從而輕鬆與團隊合作。此外，Maven 的生命週期階段可以自動執行編譯、測試和打包等任務，因此您可以更專注於編寫程式碼。透過掌握 Maven，您不僅可以提高建置效率，還可以提高 Java 應用程式的整體品質和可擴充性。讓我們更深入地了解 Maven 的好處！

建置工具

建置工具對於自動化建置應用程式的過程至關重要。建置工具會自動處理這些任務，而不是手動編譯程式碼、下載依賴項、執行測試和打包應用程式。它們簡化了開發並確保一致性。

以下是建置工具通常執行的操作：

• 將原始碼編譯為可執行形式。
• 下載必要的依賴項，例如 Spring Boot、Hibernate、JUnit 等
• 運行單元測試以確保程式碼能如預期運作。
• 將應用程式打包成JAR（對於獨立應用程式）或WAR（對於網路應用程式）檔案。

流行的 Java 建置工具包括

• 螞蟻
• Maven
• 搖籃

「身為 Java 開發人員，我利用 Maven 進行高效的專案管理、自動化建置和處理依賴項，確保簡化的開發和交付流程。」

梅文

Maven 是一個免費的開源建置工具，可以自動化應用程式開發的建置流程。它是由 Apache 組織給予的。它是一個使用java程式語言開發的軟體。 借助maven我們可以建立專案資料夾結構，當我們開發專案時需要很多程式庫和框架，我們手動新增專案很困難對於 Java 開發人員來說，這很耗時。該程式庫和框架稱為專案依賴項，依賴項例如（例如：Spring-Boot、Hibernate、Kafaka、電子郵件等）。我們可以告訴 maven s/w 下載依賴項，而不是下載依賴項。也使用 maven 編譯原始程式碼，執行用於測試 API 功能的測試案例，並將應用程式打包為 jar(Java Archieve) / war(Web Archieve)。

要開始使用Maven，安裝過程包括從Maven 官方網站下載二進位包，為MAVEN_HOME 設定環境變量，並透過終端機或命令提示字元執行mvn -版本.

Windows 上的 Maven 安裝

第 1 步：下載 Maven 開始

從官網下載Maven：進入Maven下載頁面。下載最新版本 Maven 的二進位 zip 檔案。

第 2 步：提取 Maven

下載後：將下載的 ZIP 檔案解壓縮到資料夾中。例如，您可以使用 C:Program FilesApachemaven 或您選擇的其他位置。

第三步：設定環境變數

為了確保 Maven 可從命令列使用，您需要設定環境變數。右鍵點選此電腦並選擇屬性

點選進階系統設定→環境變數。

在系統變數中，點選新建並新增：

變數名稱：MAVEN_HOME

變數值

C:\Program Files\Apache\maven

（或您提取 Maven 的目錄）。

接下來，在系統變數中找到 Path 變量，選擇它，然後按一下編輯。

Add a new entry: %MAVEN_HOME%\bin.

第 4 步：驗證安裝

To check if Maven is installed correctly, open a command prompt and run the following command:

mvn -version

Maven Terminology

Archetype

An Archetype is a template that helps you quickly create a Maven project with a predefined structure. It defines the directory layout and initial configuration files to simplify project setup.

groupId

The groupId identifies the organization or project to which a Maven artifact belongs. It follows a reverse domain name convention (e.g., com.example.project) and ensures that dependencies are uniquely identifiable across the system.

artifactId

The artifactId is the name of the project or library. It's used along with the groupId and version to uniquely identify a specific project artifact, such as a JAR, WAR, or other packages.

packaging

The packaging type defines the build output type for your Maven project. Common options include jar, war, or pom. It determines how Maven will package the code, usually as a JAR or WAR file.

version

The version specifies the release or iteration of a Maven project. It's crucial for managing different versions of a library or artifact, allowing you to reference a specific version when adding dependencies to other projects.

SNAPSHOT : Under development
RELEASE : Development completed

Creating a Stand-Alone Application Using Maven With CMD

Maven is an excellent tool for building and managing Java projects, especially when it comes to creating stand-alone applications. Let’s walk through the steps of setting up a basic stand-alone Java application using Maven.

mvn archetype:generate -DgroupId=com.example.app -DartifactId=standalone-app -DarchetypeArtifactId=maven-archetype-quickstart -DinteractiveMode=false

• groupId: Uniquely identifies the project’s group.
• artifactId: The name of your application.
• archetypeArtifactId: Specifies the archetype for a simple Java project.

Once project created then verify project folder structure

standalone-app
│
├── src
│   ├── main
│   │   └── java               # Application source code (.java files)
│   │
│   ├── test
│   │   └── java               # Application Unit Test code (.java files)
│
└── pom.xml                    # Project Object Model (Maven configuration file)

src/main/java is containing the application source code.
src/test/java is containing the application test source code.
pom.xml file containing the maven configurations.

POM.XML

The pom.xml file, which stands for Project Object Model, is a crucial component of any Maven project. It is automatically generated when you create a Maven project and serves as the input file for Maven software. The pom.xml file defines the project’s metadata, including its name, version, and dependencies on various frameworks such as Spring, Hibernate, Kafka, and more. Instead of manually downloading these dependencies, you can specify them in the pom.xml file, and Maven will automatically fetch them for you. This makes managing project dependencies efficient and organized, allowing developers to focus on writing code without worrying about handling each library individually. Essentially, the pom.xml acts as a roadmap for Maven, guiding it on how to build and manage your Java project.

pom.xml

<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>com.example.app</groupId>
    <artifactId>standalone-app</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>jar</packaging>

    <properties>
        <maven.compiler.source>17</maven.compiler.source>  <!-- Java version -->
        <maven.compiler.target>17</maven.compiler.target>
    </properties>

    <dependencies>
        <!-- JUnit for unit testing -->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.13.2</version>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <!-- Maven Compiler Plugin -->
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.8.1</version>
                <configuration>
                    <source>${maven.compiler.source}</source>
                    <target>${maven.compiler.target}</target>
                </configuration>
            </plugin>

            <!-- Maven Shade Plugin for creating an executable JAR -->
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-shade-plugin</artifactId>
                <version>3.2.4</version>
                <executions>
                    <execution>
                        <phase>package</phase>
                        <goals>
                            <goal>shade</goal>
                        </goals>
                        <configuration>
                            <transformers>
                                <transformer implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
                                    <mainClass>com.example.app.App</mainClass>  <!-- Main class -->
                                </transformer>
                            </transformers>
                        </configuration>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>
</project>

Maven Goals

Maven goals represent specific tasks that can be executed during the build lifecycle of a Maven project. Each goal corresponds to a distinct action, such as compiling code, running tests, packaging artifacts, or deploying to a repository.

By invoking these goals, developers can automate and streamline their build processes, ensuring that projects are built consistently and efficiently. Each goal can be run individually or as part of a larger lifecycle phase, providing flexibility in project management.

clean: Deletes the target directory, which contains compiled code and packaged artifacts, ensuring a fresh build.

compile: Compiles the source code of the project, producing class files from Java source files in the src/main/java directory.

test: Runs the unit tests defined in the src/test/java directory using a testing framework like JUnit.

package: Packages the compiled code into a distributable format, such as a JAR or WAR file, based on the project configuration in pom.xml.

install: Installs the packaged JAR/WAR file into the local Maven repository, making it available for other projects on the same machine.

deploy: Copies the packaged JAR/WAR file to a remote repository, making it available for other developers and projects.

site: Generates a site for the project, including documentation, reports, and project information, typically found in the target/site directory.

validate: Validates the project’s configuration and verifies that all required information is available before the build begins.

verify: Runs any checks to ensure the package is valid and meets quality standards, executing any verification tasks defined in the project.

archetype: Creates a new Maven project based on a specified archetype, setting up a project structure and initial files.

These goals can be executed from the command line, allowing developers to manage the build lifecycle effectively. You can run a specific goal using the following command format:

mvn [Goal]

Maven Repository

Maven repositories store project artifacts like libraries an dependencies. There are three main types of Maven repositories

Local Repository
Stores artifacts on your machine for quick access. it is a oyr system specific.

Remote Repository
Hosts artifacts on a server, accessible over the network. it is a organization specific.

Central Repository
Default public repository for widely used open-source libraries. it is accessed by everyone.

When you create a project and build it using Maven, it first checks your local repository (typically located at ~/.m2/repository) for any dependencies the project needs. If it finds the required dependencies in the local repository, Maven uses them directly, without downloading them again.

If the dependencies aren't available locally, Maven fetches them from a remote repository, such as Maven Central or another configured repository. Once downloaded, the dependencies are stored in the local repository for future use, so they don't need to be re-downloaded. This process helps optimize resource use and speeds up the build by preventing unnecessary downloads.

Maven build lifecycle

The Maven build lifecycle is a series of phases that automate the process of building and managing Java projects. It consists of three main lifecycles: default, clean, and site. The default lifecycle is the most commonly used, handling tasks like validating the project structure, compiling the code, running tests, packaging the output (e.g., into a JAR or WAR), and deploying the package to a remote repository. The clean lifecycle is responsible for cleaning up the project by deleting generated files from previous builds, while the site lifecycle is used to generate project documentation and reports. Each lifecycle consists of specific phases that are executed in sequence, ensuring that Maven handles everything from code compilation to deployment in a structured, automated way.

Conclusion

Maven has revolutionized how Java projects are built and managed, offering developers an efficient and automated approach to handling essential project tasks. Its core strength lies in dependency management, where Maven checks for required libraries in the local repository and fetches them from remote repositories like Maven Central if they're not available. This saves time and eliminates the need for manual dependency tracking, ensuring that projects always have the correct versions of required libraries.

The declarative nature of Maven, governed by the pom.xml file, standardizes the build process, making it easier to maintain consistency across different development environments. Whether it’s compiling code, running tests, or packaging the project for deployment, Maven's build lifecycle manages these steps seamlessly.

Additionally, Maven’s plugin system enhances its flexibility, enabling developers to integrate a wide array of tools and functionalities. Plugins for running tests, generating documentation, deploying artifacts, and more extend Maven’s utility far beyond a basic build tool.

By automating repetitive tasks and streamlining complex project setups, Maven allows developers to focus on writing code, improving productivity, and reducing potential errors. Its widespread adoption within the Java ecosystem makes it an indispensable tool for building modern, scalable, and maintainable Java applications.

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