Apache Maven入门与依赖管理实战指南

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"Apache Maven Cookbook 是一本针对初学者的 Maven 入门开发指南，全面讲解了如何使用 Maven 这个强大的依赖管理工具。书中详细介绍了 Maven 的安装、项目创建、配置文件POM.xml的使用，以及如何在 Eclipse 中导入项目。此外，还深入探讨了 Maven 如何处理依赖管理，包括直接依赖、传递性依赖、依赖范围和依赖管理等概念。对比了 Maven 与 Ant 的差异，突显 Maven 在生命周期管理和依赖管理上的优势。同时，提供了 Maven 项目结构的示例，解析了目录布局和源代码组织方式。" 在 Maven 教程中，首先对 Maven 做了简要介绍，强调其作为自动化构建工具在Java项目中的重要性。预备知识包括了解基本的Java开发环境。接着，教程指导用户如何安装 Maven，并创建一个简单的示例项目，演示了如何将生成的项目导入 Eclipse 开发环境。Maven 的核心配置文件是 POM.xml，它定义了项目的属性、依赖关系和其他构建指令。在依赖管理部分，Maven 允许开发者声明项目所需的外部库，通过`dependency`标签指定。传递性依赖是指当项目依赖A库，A库又依赖B库时，Maven会自动管理B库的引入。依赖范围（dependency scope）如compile、test、runtime等，用于控制依赖在不同阶段的可用性。`dependencyManagement`则用来集中管理多个模块间的共享依赖版本。对比 Ant 和 Maven，两者都是构建工具，但 Maven 提供了预定义的生命周期和插件，简化了构建过程。Maven 的生命周期管理包括编译、测试、打包、部署等阶段，而 Ant 需要手动编写任务脚本。在依赖管理方面，Maven 自动处理依赖关系，而 Ant 需要手动添加和管理依赖库。 Maven 项目结构通常遵循标准的目录结构，例如 `src/main/java` 存放源代码，`src/main/resources` 存放资源文件，`src/test/java` 用于放置测试代码。这样的结构有利于项目的可维护性和一致性。 "Apache Maven Cookbook" 是一份全面的 Maven 学习资料，涵盖了从基础到进阶的各个知识点，适合希望掌握 Maven 的 Java 开发者阅读。

Apache Maven Cookbook 7 / 90

Figure 1.4: Building project, step 1

Type clean install as maven goals, the click on run.

Apache Maven Cookbook 9 / 90

[INFO]

[INFO] --- maven-resources-plugin:2.6:testResources (default-testResources) @ jcg-example ←-

---

[WARNING] Using platform encoding (Cp1252 actually) to copy filtered resources, i.e. build ←-

is platform dependent!

[INFO] skip non existing resourceDirectory C:\workspace\iPlusd\jcg-example\src\test\ ←-

resources

[INFO]

[INFO] --- maven-compiler-plugin:2.5.1:testCompile (default-testCompile) @ jcg-example ---

[WARNING] File encoding has not been set, using platform encoding Cp1252, i.e. build is ←-

platform dependent!

[INFO] Compiling 1 source file to C:\workspace\iPlusd\jcg-example\target\test-classes

[INFO]

[INFO] --- maven-surefire-plugin:2.12.4:test (default-test) @ jcg-example ---

[INFO] Surefire report directory: C:\workspace\iPlusd\jcg-example\target\surefire-reports

T E S T S

Running com.javacodegeeks.example.AppTest

Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.051 sec

Results :

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

[INFO]

[INFO] --- maven-jar-plugin:2.4:jar (default-jar) @ jcg-example ---

[INFO] Building jar: C:\workspace\iPlusd\jcg-example\target\jcg-example-1.0-SNAPSHOT.jar

[INFO]

[INFO] --- maven-install-plugin:2.4:install (default-install) @ jcg-example ---

[INFO] Installing C:\workspace\iPlusd\jcg-example\target\jcg-example-1.0-SNAPSHOT.jar to C ←-

:\Users\fhernans\.m2\repository\com\javacodegeeks\example\jcg-example\1.0-SNAPSHOT\jcg- ←-

example-1.0-SNAPSHOT.jar

[INFO] Installing C:\workspace\iPlusd\jcg-example\pom.xml to C:\Users\fhernans\.m2\ ←-

repository\com\javacodegeeks\example\jcg-example\1.0-SNAPSHOT\jcg-example-1.0-SNAPSHOT. ←-

pom

[INFO] BUILD SUCCESS

[INFO] Total time: 3.718s

[INFO] Finished at: Mon Apr 04 20:35:58 CEST 2016

[INFO] Final Memory: 13M/210M

You can run it from command line, you have to navigate to the project parent directory and type mvn clean install. You

will see an output like the previous one.

1.8 Conclusions

In this tutorial you have seen the basic stuff to create, manage and build a simple jar project with maven. As you have seen,

you can quickly create and build a java jar project with maven, delegating some things (like dependency management, life-cycle

management, test execution, etc. . . ) to maven so you can focus your efforts in create a very good code in your project.

Apache Maven Cookbook 10 / 90

Chapter 2

How to Use Maven For Dependency Management

In this example, we will see how to use Maven for dependency management. Maven is a build manager tool and mostly used in

java projects. Maven was built on a central concept of project object model (POM). Maven addresses two steps for any project -

ﬁrst how a project is built and second how the dependencies are described.

2.1 Environment

• Windows 7 SP 1

• Eclipse Kepler 4.3

• Maven 3.0.4

• Java version 7

2.2 Maven for Dependency Management

Maven is used in large projects for one of its major feature and that is dependency management. Maven just not supports

dependencies for a single project, but it easily manages multi-module projects. In such projects, maven helps in maintaining a

high degree of control and stability.

2.3 Transitive Dependency

This feature of Transitive Dependency allows to avoid needing to discover and specify libraries that your own dependencies

require, and what that means is that if your project is dependent on some libraries and those libraries are dependent on other

libraries, you only specify your project’s dependencies and this feature takes care of other dependencies. There is no limit to

levels that dependencies can be gathered from, and will only cause a problem if cyclic dependency is discovered. If your project

depends on A and A depends on C and C depends on B and B depends on A.

Following features help to limit the graph of included libraries using transitive dependencies’ feature:

• Dependency Mediation- This feature determines what version of a dependency will be used when multiple versions of an

artifact are encountered. You can always guarantee a version by declaring it explicitly in project’s POM. If two dependency

versions are at the same depth in the dependency tree, the order in the declaration that counts, the ﬁrst declaration wins.

• Dependency Management- With this feature, you can specify versions of artifacts to be used when they are encountered in

transitive dependencies.

• Dependency Score- This allows you to only include dependencies appropriate for the current stage of the build.

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• Excluded Dependencies- If project X depends on project Y, and project Y depends on project Z, the project X can explicitly

exclude project Z as a dependency using the exclusion element.

• Optional Dependencies- If project Y depends on project Z, and the owner of Project Y can mark project Z as optional

dependency, using the optional element. When project X depends on project Y, X will depend only on Y and not on Y’s

optional dependency Z.

2.4 Dependency Scope

Dependency scope is used to restrict the transitivity of a dependency, and also to affect the classpath used for various build.

There are 6 scopes available:

• Compile - This is the default scope if any is indicated. The dependencies are available in all classpaths of a project.

• provided - This is used when JDK or a web container is going to provide a dependency at runtime.

• runtime - This scope indicates that the dependency is not required for compilation, but for runtime.

• test - This scope indicates the dependency is required during test compilation and execution phases.

• system - This scope is similar to provided except that you have to provide JAR which contains in explicitly.

• import - This is used inside a dependencymanagement tag. It indicates that the speciﬁed POM should be replaced with

the dependencies in that POM’s dependencymanagement section.

2.5 Dependency Management

Dependency management is a mechanism to centralize the dependency information. In a multi-module project, you can specify

in a parent project all the artifact version and it will be inherited by the child projects.

Below we will see an example where there are two POMs which extend the same parent.

project A

<project xmlns="https://maven.apache.org/POM/4.0.0" xmlns:xsi="https://www.w3.org/2001/ ←-

XMLSchema-instance"

xsi:schemaLocation="https://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd ←-

/maven-4.0.0.xsd">

<groupId>com.javacodegeeks.example</groupId>

<artifactId>java-code-geeks-parent-A</artifactId>

<groupId>group-a</groupId>

<artifactId>artifact-a</artifactId>

<groupId> group-c </groupId>

<artifactId>excluded-artifact</artifactId>

</exclusion>

</exclusions>

</dependency>

<groupId>group-a</groupId>

<artifactId>artifact-b</artifactId>

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Apache Maven入门与依赖管理实战指南

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包含apache-maven-3.9.1-bin.tar.gz和apache-maven-3.9.1-bin.zip

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