1.Maven

https://maven.apache.org/download.cgi

为什么要学习Maven

1. 在javaweb开发中需要使用大量的jar包
2. 如何能够让一个东西自动帮我们生成jar包

1.1Maver项目架构管理工具

Maven的核心思想：约定大于配置

• 有约束，不要去违反

Maven会规定好你该如何去编写我们的代码

1.2 下载安装Maven

1.3 配置环境变量

1. M2_HOME

​ D:\JavaMaven\apache-maven-3.8.5\bin

2. MAVEN_HOME

​ D:\JavaMaven\apache-maven-3.8.5

3. path

   %MAVEN_HOME%\bin

测试Maven是否安装成功

1.4 阿里云镜像

• 镜像 mirrors

  • 作用：加速我们的下载

• 国内建议使用阿里云镜像

<mirror>
      <id>alimaven</id>
      <name>aliyun maven</name>
      <url>http://maven.aliyun.com/nexus/content/groups/public/</url>
      <mirrorOf>central</mirrorOf>        
    </mirror>

1.5 本地仓库

建立一个本地仓库: localRepository

  <localRepository>D:\JavaMaven\apache-maven-3.8.5\maven-repo</localRepository>

1.6 在IDEA中使用Maven

4. 观察Maven仓库在多了什么东西

5. idea中的Maven设置

   idea项目创建成功后看一眼Maven的配置

1.7 创建一个普通的Maven项目

5.8在IDEA中标记文件夹功能

1.8 标记文件夹功能

1.9 在IDEA中配置Tomcat

1.10 pom文件

maven由于它的约定大于配置

一、安装本地Maven

tips: 官网为外网，下载速度较慢，这里提供3.6.3版本的三方链接下载Maven下载

1. 无视下载速度以及需要其他版本的伙伴点此进入Maven官网下载

2. 选择左侧Download
   

3. 点击箭头所指的链接进行下载
   

4. 下载完成后，选择一个路径进行解压

5. 然后配置path环境变量,如图

• 系统变量:MAVEN_HOME = F:\dev\apache-maven-3.6.1
• 系统变量:path = %MAVEN_HOME%\bin
  MAVEN_HOME:
  

path:

6. 然后win+R 运行cmd 输入 mvn -version，如图所示则配置成功

二、配置settings文件

1. 在F:\dev\apache-maven-3.6.1\conf下可以找到settings文件，打开(嫌麻烦的直接看最后一步)

2. 找到第52行，这里是maven默认的仓库
   

3. 我们复制第53行

<localRepository>/path/to/local/repo</localRepository>

将它拿到注释外并将中间的内容改成你需要的路径，如图

<localRepository>F:/repository</localRepository>

这里的路径随便设置，注意这里是正斜杠

4. 因为国外的服务器下载jar包很慢所以我们改为阿里云服务器（大约在150行左右），这两个仓库只用选一个(根据大家反馈建议使用第一个，第二个在有的版本可能会出现warning)

 <!-- 阿里云仓库 -->
        <mirror>
            <id>alimaven</id>
            <mirrorOf>central</mirrorOf>
            <name>aliyun maven</name>
            <url>http://maven.aliyun.com/nexus/content/repositories/central/</url>
        </mirror>
     或者
      <mirror>
		<id>nexus-aliyun</id>
		<mirrorOf>*</mirrorOf>
        <name>Nexus aliyun</name>
        <url>http://maven.aliyun.com/nexus/content/groups/public</url>
	 </mirror>

5. 如图，要夹在两个mirrors标签之间
   

6. 在最后配置jdk，也要夹在两个profiles标签之间(我这里使用的为jdk8)

<!-- java版本 --> 
<profile>
      <id>jdk-1.8</id>
      <activation>
	    <activeByDefault>true</activeByDefault>
        <jdk>1.8</jdk>
      </activation>

      <properties>
        <maven.compiler.source>1.8</maven.compiler.source>
		<maven.compiler.target>1.8</maven.compiler.target>
		<maven.compiler.compilerVersion>1.8</maven.compiler.compilerVersion>
      </properties>
</profile>

7. 配置完成，在命令行输入mvn help:system测试，看到下载链接里面是ailiyun的链接表示配置成功

8. 嫌麻烦的直接复制配置文件的内容即可,不过路径还是要改(参考第3步)

<?xml version="1.0" encoding="UTF-8"?>

<!--
Licensed to the Apache Software Foundation (ASF) under one
or more contributor license agreements.  See the NOTICE file
distributed with this work for additional information
regarding copyright ownership.  The ASF licenses this file
to you under the Apache License, Version 2.0 (the
"License"); you may not use this file except in compliance
with the License.  You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing,
software distributed under the License is distributed on an
"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
KIND, either express or implied.  See the License for the
specific language governing permissions and limitations
under the License.
-->

<!--
 | This is the configuration file for Maven. It can be specified at two levels:
 |
 |  1. User Level. This settings.xml file provides configuration for a single user,
 |                 and is normally provided in ${user.home}/.m2/settings.xml.
 |
 |                 NOTE: This location can be overridden with the CLI option:
 |
 |                 -s /path/to/user/settings.xml
 |
 |  2. Global Level. This settings.xml file provides configuration for all Maven
 |                 users on a machine (assuming they're all using the same Maven
 |                 installation). It's normally provided in
 |                 ${maven.conf}/settings.xml.
 |
 |                 NOTE: This location can be overridden with the CLI option:
 |
 |                 -gs /path/to/global/settings.xml
 |
 | The sections in this sample file are intended to give you a running start at
 | getting the most out of your Maven installation. Where appropriate, the default
 | values (values used when the setting is not specified) are provided.
 |
 |-->
<settings xmlns="http://maven.apache.org/SETTINGS/1.0.0"
          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
          xsi:schemaLocation="http://maven.apache.org/SETTINGS/1.0.0 http://maven.apache.org/xsd/settings-1.0.0.xsd">
  <!-- localRepository
   | The path to the local repository maven will use to store artifacts.
   |
   | Default: ${user.home}/.m2/repository
  <localRepository>/path/to/local/repo</localRepository>
  -->
<localRepository>F:/repository</localRepository>
  <!-- interactiveMode
   | This will determine whether maven prompts you when it needs input. If set to false,
   | maven will use a sensible default value, perhaps based on some other setting, for
   | the parameter in question.
   |
   | Default: true
  <interactiveMode>true</interactiveMode>
  -->

  <!-- offline
   | Determines whether maven should attempt to connect to the network when executing a build.
   | This will have an effect on artifact downloads, artifact deployment, and others.
   |
   | Default: false
  <offline>false</offline>
  -->

  <!-- pluginGroups
   | This is a list of additional group identifiers that will be searched when resolving plugins by their prefix, i.e.
   | when invoking a command line like "mvn prefix:goal". Maven will automatically add the group identifiers
   | "org.apache.maven.plugins" and "org.codehaus.mojo" if these are not already contained in the list.
   |-->
  <pluginGroups>
    <!-- pluginGroup
     | Specifies a further group identifier to use for plugin lookup.
    <pluginGroup>com.your.plugins</pluginGroup>
    -->
  </pluginGroups>

  <!-- proxies
   | This is a list of proxies which can be used on this machine to connect to the network.
   | Unless otherwise specified (by system property or command-line switch), the first proxy
   | specification in this list marked as active will be used.
   |-->
  <proxies>
    <!-- proxy
     | Specification for one proxy, to be used in connecting to the network.
     |
    <proxy>
      <id>optional</id>
      <active>true</active>
      <protocol>http</protocol>
      <username>proxyuser</username>
      <password>proxypass</password>
      <host>proxy.host.net</host>
      <port>80</port>
      <nonProxyHosts>local.net|some.host.com</nonProxyHosts>
    </proxy>
    -->
  </proxies>

  <!-- servers
   | This is a list of authentication profiles, keyed by the server-id used within the system.
   | Authentication profiles can be used whenever maven must make a connection to a remote server.
   |-->
  <servers>
    <!-- server
     | Specifies the authentication information to use when connecting to a particular server, identified by
     | a unique name within the system (referred to by the 'id' attribute below).
     |
     | NOTE: You should either specify username/password OR privateKey/passphrase, since these pairings are
     |       used together.
     |
    <server>
      <id>deploymentRepo</id>
      <username>repouser</username>
      <password>repopwd</password>
    </server>
    -->

    <!-- Another sample, using keys to authenticate.
    <server>
      <id>siteServer</id>
      <privateKey>/path/to/private/key</privateKey>
      <passphrase>optional; leave empty if not used.</passphrase>
    </server>
    -->
  </servers>

  <!-- mirrors
   | This is a list of mirrors to be used in downloading artifacts from remote repositories.
   |
   | It works like this: a POM may declare a repository to use in resolving certain artifacts.
   | However, this repository may have problems with heavy traffic at times, so people have mirrored
   | it to several places.
   |
   | That repository definition will have a unique id, so we can create a mirror reference for that
   | repository, to be used as an alternate download site. The mirror site will be the preferred
   | server for that repository.
   |-->
  
    <!-- mirror
	<mirrors>
     | Specifies a repository mirror site to use instead of a given repository. The repository that
     | this mirror serves has an ID that matches the mirrorOf element of this mirror. IDs are used
     | for inheritance and direct lookup purposes, and must be unique across the set of mirrors.
     |
    <mirror>
      <id>mirrorId</id>
      <mirrorOf>repositoryId</mirrorOf>
      <name>Human Readable Name for this Mirror.</name>
      <url>http://my.repository.com/repo/path</url>
    </mirror>
	 </mirrors>
     -->
     <!-- 阿里云仓库 -->
 <mirrors>
	 <mirror>
			<id>nexus-aliyun</id>
			<mirrorOf>*</mirrorOf>
			<name>Nexus aliyun</name>
			<url>http://maven.aliyun.com/nexus/content/groups/public</url>
	</mirror>
</mirrors>
  <!-- profiles
   | This is a list of profiles which can be activated in a variety of ways, and which can modify
   | the build process. Profiles provided in the settings.xml are intended to provide local machine-
   | specific paths and repository locations which allow the build to work in the local environment.
   |
   | For example, if you have an integration testing plugin - like cactus - that needs to know where
   | your Tomcat instance is installed, you can provide a variable here such that the variable is
   | dereferenced during the build process to configure the cactus plugin.
   |
   | As noted above, profiles can be activated in a variety of ways. One way - the activeProfiles
   | section of this document (settings.xml) - will be discussed later. Another way essentially
   | relies on the detection of a system property, either matching a particular value for the property,
   | or merely testing its existence. Profiles can also be activated by JDK version prefix, where a
   | value of '1.4' might activate a profile when the build is executed on a JDK version of '1.4.2_07'.
   | Finally, the list of active profiles can be specified directly from the command line.
   |
   | NOTE: For profiles defined in the settings.xml, you are restricted to specifying only artifact
   |       repositories, plugin repositories, and free-form properties to be used as configuration
   |       variables for plugins in the POM.
   |
   |-->
    <!-- profile
	<profiles>
     | Specifies a set of introductions to the build process, to be activated using one or more of the
     | mechanisms described above. For inheritance purposes, and to activate profiles via <activatedProfiles/>
     | or the command line, profiles have to have an ID that is unique.
     |
     | An encouraged best practice for profile identification is to use a consistent naming convention
     | for profiles, such as 'env-dev', 'env-test', 'env-production', 'user-jdcasey', 'user-brett', etc.
     | This will make it more intuitive to understand what the set of introduced profiles is attempting
     | to accomplish, particularly when you only have a list of profile id's for debug.
     |
     | This profile example uses the JDK version to trigger activation, and provides a JDK-specific repo.
    <profile>
      <id>jdk-1.4</id>

      <activation>
        <jdk>1.4</jdk>
      </activation>

      <repositories>
        <repository>
          <id>jdk14</id>
          <name>Repository for JDK 1.4 builds</name>
          <url>http://www.myhost.com/maven/jdk14</url>
          <layout>default</layout>
          <snapshotPolicy>always</snapshotPolicy>
        </repository>
      </repositories>
    </profile>
    -->

    <!--
     | Here is another profile, activated by the system property 'target-env' with a value of 'dev',
     | which provides a specific path to the Tomcat instance. To use this, your plugin configuration
     | might hypothetically look like:
     |
     | ...
     | <plugin>
     |   <groupId>org.myco.myplugins</groupId>
     |   <artifactId>myplugin</artifactId>
     |
     |   <configuration>
     |     <tomcatLocation>${tomcatPath}</tomcatLocation>
     |   </configuration>
     | </plugin>
     | ...
     |
     | NOTE: If you just wanted to inject this configuration whenever someone set 'target-env' to
     |       anything, you could just leave off the <value/> inside the activation-property.
     |
    <profile>
      <id>env-dev</id>

      <activation>
        <property>
          <name>target-env</name>
          <value>dev</value>
        </property>
      </activation>

      <properties>
        <tomcatPath>/path/to/tomcat/instance</tomcatPath>
      </properties>
    </profile>
	  
    -->
<profiles>
<profile>
      <id>jdk-1.8</id>
      <activation>
	    <activeByDefault>true</activeByDefault>
        <jdk>1.8</jdk>
      </activation>

      <properties>
        <maven.compiler.source>1.8</maven.compiler.source>
		<maven.compiler.target>1.8</maven.compiler.target>
		<maven.compiler.compilerVersion>1.8</maven.compiler.compilerVersion>
      </properties>
</profile>
</profiles>



  <!-- activeProfiles
   | List of profiles that are active for all builds.
   |
  <activeProfiles>
    <activeProfile>alwaysActiveProfile</activeProfile>
    <activeProfile>anotherAlwaysActiveProfile</activeProfile>
  </activeProfiles>
  -->
</settings>

一、安装Maven

1. 官网下载maven
   

Binary是可执行版本，已经编译好可以直接使用。
Source是源代码版本，需要自己编译成可执行软件才可使用。

tar.gz和zip两种压缩格式,其实这两个压缩文件里面包含的内容是同样的,只是压缩格式不同
tar.gz格式的文件比zip文件小很多,用于unix操作系统。
zip格式用于Windows操作系统,但在Windows系统使用WinRar工具一样能够解压缩tar.gz格式

2. 下载完成后，解压到某一路径下。本文以E:\Tools\Maven\apache-maven-3.8.1为例，实际配置环境变量时以自己安装的路径为准。
   

二、配置环境变量

1. 右键此电脑–>属性–>高级系统设置–>环境变量
   
2. 新建变量MAVEN_HOME = E:\Tools\Maven\apache-maven-3.8.1（以自己的安装路径为准）
   
3. 编辑变量Path，添加变量值%MAVEN_HOME%\bin
   
4. 然后win+R运行cmd，输入mvn -version，如图所示则配置成功
   

三、配置本地仓库

1. 在E:\Tools\Maven\路径下新建maven-repository文件夹，用作maven的本地库。
   

2. 在路径E:\Tools\Maven\apache-maven-3.8.1\conf下找到settings.xml文件
   

3. 找到节点localRepository，在注释外添加

<localRepository>E:\Tools\Maven\maven-repository</localRepository>

localRepository节点用于配置本地仓库，本地仓库其实起到了一个缓存的作用，它的默认地址是 C:\Users\用户名.m2。
当我们从maven中获取jar包的时候，maven首先会在本地仓库中查找，如果本地仓库有则返回；如果没有则从远程仓库中获取包，并在本地库中保存。
此外，我们在maven项目中运行mvn install，项目将会自动打包并安装到本地仓库中。

四、配置镜像

1. 在settings.xml配置文件中找到mirrors节点
2. 添加如下配置（注意要添加在<mirrors>和</mirrors>两个标签之间，其它配置同理）

<!-- 阿里云仓库 -->
<mirror>
	<id>alimaven</id>
	<mirrorOf>central</mirrorOf>
	<name>aliyun maven</name>
	<url>http://maven.aliyun.com/nexus/content/repositories/central/</url>
</mirror>

因为国外的服务器下载jar包很慢所以我们改为阿里云服务器

虽然mirrors可以配置多个子节点，但是它只会使用其中的一个节点，即默认情况下配置多个mirror的情况下，只有第一个生效，只有当前一个mirror无法连接的时候，才会去找后一个；而我们想要的效果是：当a.jar在第一个mirror中不存在的时候，maven会去第二个mirror中查询下载，但是maven不会这样做！

五、配置JDK

1. 在settings.xml配置文件中找到profiles节点
2. 添加如下配置

<!-- java版本 --> 
<profile>
	  <id>jdk-1.8</id>
	  <activation>
		<activeByDefault>true</activeByDefault>
		<jdk>1.8</jdk>
	  </activation>

	  <properties>
		<maven.compiler.source>1.8</maven.compiler.source>
		<maven.compiler.target>1.8</maven.compiler.target>
		<maven.compiler.compilerVersion>1.8</maven.compiler.compilerVersion>
	  </properties>
</profile>

配置完成，win+R运行cmd，输入mvn help:system测试，配置成功则本地仓库（E:\Tools\Maven\maven-repository）中会出现一些文件

首次执行 mvn help:system 命令，Maven相关工具自动帮我们到Maven中央仓库下载缺省的或者Maven中央仓库更新的各种配置文件和类库（jar包)到Maven本地仓库中。
下载完各种文件后， mvn help:system 命令会打印出所有的Java系统属性和环境变量，这些信息对我们日常的编程工作很有帮助。

若需要IDEA配置Maven，请参考 https://blog.csdn.net/qq_38190185/article/details/115943152?spm=1001.2014.3001.5501

附录

完整的settings.xml配置文件，可以直接复制使用，只需要修改相应的路径即可

<?xml version="1.0" encoding="UTF-8"?>

<!--
Licensed to the Apache Software Foundation (ASF) under one
or more contributor license agreements.  See the NOTICE file
distributed with this work for additional information
regarding copyright ownership.  The ASF licenses this file
to you under the Apache License, Version 2.0 (the
"License"); you may not use this file except in compliance
with the License.  You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing,
software distributed under the License is distributed on an
"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
KIND, either express or implied.  See the License for the
specific language governing permissions and limitations
under the License.
-->

<!--
 | This is the configuration file for Maven. It can be specified at two levels:
 |
 |  1. User Level. This settings.xml file provides configuration for a single user,
 |                 and is normally provided in ${user.home}/.m2/settings.xml.
 |
 |                 NOTE: This location can be overridden with the CLI option:
 |
 |                 -s /path/to/user/settings.xml
 |
 |  2. Global Level. This settings.xml file provides configuration for all Maven
 |                 users on a machine (assuming they're all using the same Maven
 |                 installation). It's normally provided in
 |                 ${maven.conf}/settings.xml.
 |
 |                 NOTE: This location can be overridden with the CLI option:
 |
 |                 -gs /path/to/global/settings.xml
 |
 | The sections in this sample file are intended to give you a running start at
 | getting the most out of your Maven installation. Where appropriate, the default
 | values (values used when the setting is not specified) are provided.
 |
 |-->
<settings xmlns="http://maven.apache.org/SETTINGS/1.2.0"
          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
          xsi:schemaLocation="http://maven.apache.org/SETTINGS/1.2.0 http://maven.apache.org/xsd/settings-1.2.0.xsd">
  <!-- localRepository
   | The path to the local repository maven will use to store artifacts.
   |
   | Default: ${user.home}/.m2/repository
  <localRepository>/path/to/local/repo</localRepository>
  -->
  <localRepository>E:\Tools\Maven\maven-repository</localRepository>
  <!-- interactiveMode
   | This will determine whether maven prompts you when it needs input. If set to false,
   | maven will use a sensible default value, perhaps based on some other setting, for
   | the parameter in question.
   |
   | Default: true
  <interactiveMode>true</interactiveMode>
  -->

  <!-- offline
   | Determines whether maven should attempt to connect to the network when executing a build.
   | This will have an effect on artifact downloads, artifact deployment, and others.
   |
   | Default: false
  <offline>false</offline>
  -->

  <!-- pluginGroups
   | This is a list of additional group identifiers that will be searched when resolving plugins by their prefix, i.e.
   | when invoking a command line like "mvn prefix:goal". Maven will automatically add the group identifiers
   | "org.apache.maven.plugins" and "org.codehaus.mojo" if these are not already contained in the list.
   |-->
  <pluginGroups>
    <!-- pluginGroup
     | Specifies a further group identifier to use for plugin lookup.
    <pluginGroup>com.your.plugins</pluginGroup>
    -->
  </pluginGroups>

  <!-- proxies
   | This is a list of proxies which can be used on this machine to connect to the network.
   | Unless otherwise specified (by system property or command-line switch), the first proxy
   | specification in this list marked as active will be used.
   |-->
  <proxies>
    <!-- proxy
     | Specification for one proxy, to be used in connecting to the network.
     |
    <proxy>
      <id>optional</id>
      <active>true</active>
      <protocol>http</protocol>
      <username>proxyuser</username>
      <password>proxypass</password>
      <host>proxy.host.net</host>
      <port>80</port>
      <nonProxyHosts>local.net|some.host.com</nonProxyHosts>
    </proxy>
    -->
  </proxies>

  <!-- servers
   | This is a list of authentication profiles, keyed by the server-id used within the system.
   | Authentication profiles can be used whenever maven must make a connection to a remote server.
   |-->
  <servers>
    <!-- server
     | Specifies the authentication information to use when connecting to a particular server, identified by
     | a unique name within the system (referred to by the 'id' attribute below).
     |
     | NOTE: You should either specify username/password OR privateKey/passphrase, since these pairings are
     |       used together.
     |
    <server>
      <id>deploymentRepo</id>
      <username>repouser</username>
      <password>repopwd</password>
    </server>
    -->

    <!-- Another sample, using keys to authenticate.
    <server>
      <id>siteServer</id>
      <privateKey>/path/to/private/key</privateKey>
      <passphrase>optional; leave empty if not used.</passphrase>
    </server>
    -->
  </servers>

  <!-- mirrors
   | This is a list of mirrors to be used in downloading artifacts from remote repositories.
   |
   | It works like this: a POM may declare a repository to use in resolving certain artifacts.
   | However, this repository may have problems with heavy traffic at times, so people have mirrored
   | it to several places.
   |
   | That repository definition will have a unique id, so we can create a mirror reference for that
   | repository, to be used as an alternate download site. The mirror site will be the preferred
   | server for that repository.
   |-->
  <mirrors>
    <!-- mirror
     | Specifies a repository mirror site to use instead of a given repository. The repository that
     | this mirror serves has an ID that matches the mirrorOf element of this mirror. IDs are used
     | for inheritance and direct lookup purposes, and must be unique across the set of mirrors.
     |
    <mirror>
      <id>mirrorId</id>
      <mirrorOf>repositoryId</mirrorOf>
      <name>Human Readable Name for this Mirror.</name>
      <url>http://my.repository.com/repo/path</url>
    </mirror>
     -->
	 
	 <!-- 阿里云仓库 -->
	<mirror>
		<id>alimaven</id>
		<mirrorOf>central</mirrorOf>
		<name>aliyun maven</name>
		<url>http://maven.aliyun.com/nexus/content/repositories/central/</url>
	</mirror>
	
    <mirror>
      <id>maven-default-http-blocker</id>
      <mirrorOf>external:http:*</mirrorOf>
      <name>Pseudo repository to mirror external repositories initially using HTTP.</name>
      <url>http://0.0.0.0/</url>
      <blocked>true</blocked>
    </mirror>
  </mirrors>

  <!-- profiles
   | This is a list of profiles which can be activated in a variety of ways, and which can modify
   | the build process. Profiles provided in the settings.xml are intended to provide local machine-
   | specific paths and repository locations which allow the build to work in the local environment.
   |
   | For example, if you have an integration testing plugin - like cactus - that needs to know where
   | your Tomcat instance is installed, you can provide a variable here such that the variable is
   | dereferenced during the build process to configure the cactus plugin.
   |
   | As noted above, profiles can be activated in a variety of ways. One way - the activeProfiles
   | section of this document (settings.xml) - will be discussed later. Another way essentially
   | relies on the detection of a system property, either matching a particular value for the property,
   | or merely testing its existence. Profiles can also be activated by JDK version prefix, where a
   | value of '1.4' might activate a profile when the build is executed on a JDK version of '1.4.2_07'.
   | Finally, the list of active profiles can be specified directly from the command line.
   |
   | NOTE: For profiles defined in the settings.xml, you are restricted to specifying only artifact
   |       repositories, plugin repositories, and free-form properties to be used as configuration
   |       variables for plugins in the POM.
   |
   |-->
  <profiles>
  
	<!-- java版本 --> 
	<profile>
		  <id>jdk-1.8</id>
		  <activation>
			<activeByDefault>true</activeByDefault>
			<jdk>1.8</jdk>
		  </activation>

		  <properties>
			<maven.compiler.source>1.8</maven.compiler.source>
			<maven.compiler.target>1.8</maven.compiler.target>
			<maven.compiler.compilerVersion>1.8</maven.compiler.compilerVersion>
		  </properties>
	</profile>
	
    <!-- profile
     | Specifies a set of introductions to the build process, to be activated using one or more of the
     | mechanisms described above. For inheritance purposes, and to activate profiles via <activatedProfiles/>
     | or the command line, profiles have to have an ID that is unique.
     |
     | An encouraged best practice for profile identification is to use a consistent naming convention
     | for profiles, such as 'env-dev', 'env-test', 'env-production', 'user-jdcasey', 'user-brett', etc.
     | This will make it more intuitive to understand what the set of introduced profiles is attempting
     | to accomplish, particularly when you only have a list of profile id's for debug.
     |
     | This profile example uses the JDK version to trigger activation, and provides a JDK-specific repo.
    <profile>
      <id>jdk-1.4</id>

      <activation>
        <jdk>1.4</jdk>
      </activation>

      <repositories>
        <repository>
          <id>jdk14</id>
          <name>Repository for JDK 1.4 builds</name>
          <url>http://www.myhost.com/maven/jdk14</url>
          <layout>default</layout>
          <snapshotPolicy>always</snapshotPolicy>
        </repository>
      </repositories>
    </profile>

    -->

    <!--
     | Here is another profile, activated by the system property 'target-env' with a value of 'dev',
     | which provides a specific path to the Tomcat instance. To use this, your plugin configuration
     | might hypothetically look like:
     |
     | ...
     | <plugin>
     |   <groupId>org.myco.myplugins</groupId>
     |   <artifactId>myplugin</artifactId>
     |
     |   <configuration>
     |     <tomcatLocation>${tomcatPath}</tomcatLocation>
     |   </configuration>
     | </plugin>
     | ...
     |
     | NOTE: If you just wanted to inject this configuration whenever someone set 'target-env' to
     |       anything, you could just leave off the <value/> inside the activation-property.
     |
    <profile>
      <id>env-dev</id>

      <activation>
        <property>
          <name>target-env</name>
          <value>dev</value>
        </property>
      </activation>

      <properties>
        <tomcatPath>/path/to/tomcat/instance</tomcatPath>
      </properties>
    </profile>
    -->
  </profiles>

  <!-- activeProfiles
   | List of profiles that are active for all builds.
   |
  <activeProfiles>
    <activeProfile>alwaysActiveProfile</activeProfile>
    <activeProfile>anotherAlwaysActiveProfile</activeProfile>
  </activeProfiles>
  -->
</settings>

References

https://blog.csdn.net/a805814077/article/details/100545928
https://blog.csdn.net/github_37759996/article/details/90748461
https://www.cnblogs.com/Lints/p/11163073.html