Maven的聚合和依赖

左手的ㄟ右手 2022-03-09 08:56 213阅读 0赞

### 前言 ###

前几章我们介绍了Maven的基本安装和使用.本章我们将介绍下Maven的聚合和依赖.

在一个复杂的项目内,我们经常会遇到`聚合和依赖`问题.(PS: 我们上章所说的Jar包的引用其实就是依赖的一种.)

PS: 本文所用的Maven例子可以在我的Github仓库内找到  
[https://github.com/SeanYanxml/maven-train][https_github.com_SeanYanxml_maven-train]

--------------------

### 聚合 ###

一般的大型项目都会分为多个子项目,例如如下的项目模式.

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly95YW54bWwuYmxvZy5jc2RuLm5ldA_size_16_color_FFFFFF_t_70][]

目录结构如下所示:

maven-train-parent/
    ├── maven-train-parent-son
    │   ├── pom.xml
    │   ├── src
    │   │   ├── main
    │   │   │   ├── java
    │   │   │   │   └── com
    │   │   │   │       └── yanxml
    │   │   │   │           └── parent
    │   │   │   │               └── son
    │   │   │   │                   └── HelloMain.java
    │   │   │   └── resources
    │   │   └── test
    │   │       ├── java
    │   │       └── resources
    │   └── target
    │       ├── classes
    │       │   ├── META-INF
    │       │   │   ├── MANIFEST.MF
    │       │   │   └── maven
    │       │   │       └── com.yanxml
    │       │   │           └── maven-train-parent-son
    │       │   │               ├── pom.properties
    │       │   │               └── pom.xml
    │       │   └── com
    │       │       └── yanxml
    │       │           └── parent
    │       │               └── son
    │       │                   └── HelloMain.class
    │       └── test-classes
    ├── maven-train-parent-util
    │   ├── pom.xml
    │   ├── src
    │   │   ├── main
    │   │   │   ├── java
    │   │   │   │   └── com
    │   │   │   │       └── yanxml
    │   │   │   │           └── parent
    │   │   │   │               └── util
    │   │   │   │                   └── StringUtil.java
    │   │   │   └── resources
    │   │   └── test
    │   │       ├── java
    │   │       └── resources
    │   └── target
    │       ├── classes
    │       │   ├── META-INF
    │       │   │   ├── MANIFEST.MF
    │       │   │   └── maven
    │       │   │       └── com.yanxml
    │       │   │           └── maven-train-parent-util
    │       │   │               ├── pom.properties
    │       │   │               └── pom.xml
    │       │   └── com
    │       │       └── yanxml
    │       │           └── parent
    │       │               └── util
    │       │                   └── StringUtil.class
    │       └── test-classes
    └── pom.xml

由上节,`Maven的基本使用`我们可以知道.Maven项目的管理主要是通过`pom.xml`文件进行管理的,此项目内的pom.xml文件如图所示:

*  pom.xml(maven-train-parent )

<?xml version="1.0"?>
    <project xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd" xmlns="http://maven.apache.org/POM/4.0.0"
        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
      <modelVersion>4.0.0</modelVersion>
      
      <parent>
        <groupId>com.yanxml</groupId>
        <artifactId>maven-train</artifactId>
        <version>0.0.1-SNAPSHOT</version>
      </parent>
      
      <groupId>com.yanxml</groupId>
      <artifactId>maven-train-parent</artifactId>
      <version>0.0.1-SNAPSHOT</version>
      <name>maven-train-parent</name>
      <url>http://maven.apache.org</url>
      <packaging>pom</packaging>
      
      <modules>
      	<module>maven-train-parent-util</module>
      	<module>maven-train-parent-son</module>
      </modules>
      
      <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
      </properties>
      
      <dependencyManagement>
      	<dependencies>
      	
    	<dependency>
        	<groupId>com.alibaba</groupId>
        	<artifactId>fastjson</artifactId>
        	<version>1.2.44</version>
    	</dependency>
      </dependencies>
      	
      </dependencyManagement>
      
      <dependencies>
        
    	<dependency>
        	<groupId>org.apache.commons</groupId>
        	<artifactId>commons-lang3</artifactId>
        	<version>3.7</version>
    	</dependency>
      </dependencies>
    
    </project>

其中的`<modules>`主要列出项目内的多个子项目.由上可知,此项目是一个Maven父项目,项目下有2个子项目.

*  pom.xml(maven-train-parent-util)

由上可知,此项目是一个Maven子项目,父项目为`maven-train-parent`.

*  pom.xml(maven-train-parent-son)

<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>
      <parent>
        <groupId>com.yanxml</groupId>
        <artifactId>maven-train-parent</artifactId>
        <version>0.0.1-SNAPSHOT</version>
      </parent>
      <artifactId>maven-train-parent-son</artifactId>
      
      <dependencies>
      	
      	
      	<dependency>
      		<groupId>com.yanxml</groupId>
      		<artifactId>maven-train-parent-util</artifactId>
      		<version>0.0.1-SNAPSHOT</version>
      	</dependency>
      	
      </dependencies>
    </project>

由上可知,此项目是一个Maven子项目,父项目为`maven-train-parent`.且依赖子项目`maven-train-parent-util`.

### 依赖 ###

本节.我们的目标为在`maven-train-parent-util`内编写一个工具类,让`maven-train-parent-son`对其进行使用.让其像我们引用的Jar包一样进行引用.

*  工具类(maven-train-parent-util)

package com.yanxml.parent.util;
    
    import org.apache.commons.lang3.StringUtils;
    
    public class StringUtil {
    	
    	public static boolean isEmpty(String blank){
    		boolean flag = false;
    		if(StringUtils.isEmpty(blank)){
    			flag = true;
    		}
    		return false;
    	}
    
    }

*  工具类(使用 maven-train-parent-son\`)

package com.yanxml.parent.son;
    
    import com.yanxml.parent.util.StringUtil;
    
    public class HelloMain {
    	public static void main(String[] args) {
    		String string = "hello";
    		
    		// StringUtil 自己写的工具类(maven-train-parent-util)
    		if(StringUtil.isEmpty(string)){
    			System.out.println("String is null");
    		}else{
    			System.out.println("String is not null.");
    		}
    	}
    
    }

*  项目结构  
    我们可以明显的在`maven-train-parent-son`发现其引用了`maven-train-parent-util`项目.  
    ![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly95YW54bWwuYmxvZy5jc2RuLm5ldA_size_16_color_FFFFFF_t_70 1][]

当然,我们也可以将工具包打包,随后放入Maven仓库直接使用.具体操作如下:

localhost:maven-train-parent-util Sean$ mvn package install
    Picked up JAVA_TOOL_OPTIONS: -Dfile.encoding=UTF-8
    [INFO] Scanning for projects...
    [INFO]
    [INFO] ------------------------------------------------------------------------
    [INFO] Building maven-train-parent-util 0.0.1-SNAPSHOT
    [INFO] ------------------------------------------------------------------------
    [INFO]
    [INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ maven-train-parent-util ---
    [INFO] Using 'UTF-8' encoding to copy filtered resources.
    [INFO] Copying 0 resource
    [INFO]
    [INFO] --- maven-compiler-plugin:3.1:compile (default-compile) @ maven-train-parent-util ---
    [INFO] Changes detected - recompiling the module!
    [INFO] Compiling 1 source file to /Users/Sean/Documents/Gitrep/maven-train/maven-train-parent/maven-train-parent-util/target/classes
    [INFO]
    [INFO] --- maven-resources-plugin:2.6:testResources (default-testResources) @ maven-train-parent-util ---
    [INFO] Using 'UTF-8' encoding to copy filtered resources.
    [INFO] Copying 0 resource
    [INFO]
    [INFO] --- maven-compiler-plugin:3.1:testCompile (default-testCompile) @ maven-train-parent-util ---
    [INFO] Nothing to compile - all classes are up to date
    [INFO]
    [INFO] --- maven-surefire-plugin:2.12.4:test (default-test) @ maven-train-parent-util ---
    [INFO]
    [INFO] --- maven-jar-plugin:2.4:jar (default-jar) @ maven-train-parent-util ---
    [INFO] Building jar: /Users/Sean/Documents/Gitrep/maven-train/maven-train-parent/maven-train-parent-util/target/maven-train-parent-util-0.0.1-SNAPSHOT.jar
    [INFO] META-INF/maven/com.yanxml/maven-train-parent-util/pom.xml already added, skipping
    [INFO] META-INF/maven/com.yanxml/maven-train-parent-util/pom.properties already added, skipping
    [INFO]
    [INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ maven-train-parent-util ---
    [INFO] Using 'UTF-8' encoding to copy filtered resources.
    [INFO] Copying 0 resource
    [INFO]
    [INFO] --- maven-compiler-plugin:3.1:compile (default-compile) @ maven-train-parent-util ---
    [INFO] Nothing to compile - all classes are up to date
    [INFO]
    [INFO] --- maven-resources-plugin:2.6:testResources (default-testResources) @ maven-train-parent-util ---
    [INFO] Using 'UTF-8' encoding to copy filtered resources.
    [INFO] Copying 0 resource
    [INFO]
    [INFO] --- maven-compiler-plugin:3.1:testCompile (default-testCompile) @ maven-train-parent-util ---
    [INFO] Nothing to compile - all classes are up to date
    [INFO]
    [INFO] --- maven-surefire-plugin:2.12.4:test (default-test) @ maven-train-parent-util ---
    [INFO] Skipping execution of surefire because it has already been run for this configuration
    [INFO]
    [INFO] --- maven-jar-plugin:2.4:jar (default-jar) @ maven-train-parent-util ---
    [INFO]
    [INFO] --- maven-install-plugin:2.4:install (default-install) @ maven-train-parent-util ---
    [INFO] Installing /Users/Sean/Documents/Gitrep/maven-train/maven-train-parent/maven-train-parent-util/target/maven-train-parent-util-0.0.1-SNAPSHOT.jar to /Users/Sean/.m2/repository/com/yanxml/maven-train-parent-util/0.0.1-SNAPSHOT/maven-train-parent-util-0.0.1-SNAPSHOT.jar
    [INFO] Installing /Users/Sean/Documents/Gitrep/maven-train/maven-train-parent/maven-train-parent-util/pom.xml to /Users/Sean/.m2/repository/com/yanxml/maven-train-parent-util/0.0.1-SNAPSHOT/maven-train-parent-util-0.0.1-SNAPSHOT.pom
    [INFO] ------------------------------------------------------------------------
    [INFO] BUILD SUCCESS
    [INFO] ------------------------------------------------------------------------
    [INFO] Total time: 2.427 s
    [INFO] Finished at: 2019-03-12T20:08:46+08:00
    [INFO] Final Memory: 17M/170M
    [INFO] ------------------------------------------------------------------------

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly95YW54bWwuYmxvZy5jc2RuLm5ldA_size_16_color_FFFFFF_t_70 2]  
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--------------------

### Reference ###

\[1\] [maven-train][https_github.com_SeanYanxml_maven-train]

[https_github.com_SeanYanxml_maven-train]: https://github.com/SeanYanxml/maven-train
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