Maven的安装配置-项目管理工具

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今天我们来学习：Maven的安装配置-项目管理工具

1.什么是Maven？Maven用来干什么的？

2.我们如何创建一个Maven项目呢？

3.Maven有两个大功能：

3.1.项目构建

3.2.管理依赖

3.2.1原来如何引入依赖

3.2.2现在如何引入依赖

3.2.3.但是我们发现我们明明只引入了一个mysql的依赖却出现了两个

3.3.4.也可以：安装Maven Helper插件

4.Maven仓库：

4.1.如何查找Jar的坐标

4.2配置国内源

大家也可以直接复制我的XML文件

4.3.刚才阿里云提到的私有服务器（私服）

1.什么是Maven？Maven用来干什么的？

Maven是一个项目管理工具, 通过配置pom.xml文件，然后自动从“仓库”中获取jar包。

官方对于Maven的描述：

Welcome to Apache Maven – Maven

Apache Maven is a software project management and comprehension tool. Based on the

concept of a project object model (POM), Maven can manage a project's build, reporting and documentation from a central piece of information.

Maven是⼀个项项目理工具。基于POM(Project Object Model,项⽬对象模型)的概念，Maven可以通过一小段描述信息来管理项目的构建、报告和文档。

我们不需要单独下载Maven了，IDEA里面已经集成了Maven

2.我们如何创建一个Maven项目呢？

我以2023.2的IDEA专业版为例子

点击create就创建好了，创建好的项目大概长这个样子（我们点击pom.xml）会出现一些标签

我解释一些其他标签的含义：（这里不过多的解释，后面我们遇到了再进行解释）

<packaging>：

指定项目的打包方式，如 jar、war、pom 等。

示例：<packaging>jar</packaging>。

<dependencies>：

定义项目所依赖的外部库。

<properties>：定义一些属性值，可以在 POM 中重复使用。

<build>：配置项目的构建过程，包括插件和资源文件。

3.Maven有两个大功能：

3.1.项目构建

Maven 提供了标准的,跨平台(Linux, Windows, MacOS等)的自动化项目构建方式。

当我们开发了⼀个项目之后，代码需要经过编译, 测试, 打包, 发布等流程, 每次代码的修改，都需要经过这些流程, 如果代码反复调试修改，这个流程就需要反复进行, 就显得特别麻烦，而Maven 给我们提供了⼀套简单的命令来完成项目的构建

clean：删除 target 目录（清理旧构建文件（.class文件））。
validate：检查项目配置是否正确（如 pom.xml 是否有效）。
compile：编译源代码（.java → .class）。
test：运行单元测试（检查代码逻辑）。
package：打包代码（生成 JAR/WAR 文件）。
verify：验证测试和代码质量（如集成测试）。
install：将包安装到本地仓库（供其他项目使用）。
deploy：发布到远程仓库（团队共享依赖）。
site：生成项目文档网站（如报告、API 文档）。

3.2.管理依赖

Maven是一个项目管理工具, 通过配置pom.xml文件，然后自动从“仓库”中获取jar包

这个jar包就是依赖

Maven 的“依赖管理”可以通俗地理解为：我们的项目需要用到别人的“工具包”（譬如库），而 Maven 就像是一个“自动管家”，帮我们一键下载、整理这些工具包，并确保它们之间不会“打架”。

举个生活化的例子 🌰

假设你想做一道菜（开发项目），需要用到：

刀（库A）
砧板（库B）
酱油（库C）

但问题来了：

刀（库A）本身需要搭配一个磨刀石（库D）才能用。
酱油（库C）必须用某个特定品牌（版本1.2），否则会太咸。

没有 Maven 时：

你得自己跑超市买齐所有东西，还得记住每个工具的版本和兼容性。
一旦买错版本（比如酱油版本1.3），整道菜可能就毁了。

有了 Maven 时：

Maven 会：
1. 自动下载：刀、砧板、酱油，甚至磨刀石（传递性依赖）。
2. 检查版本：确保酱油是1.2，避免冲突。
3. 整理工具包：所有工具按分类放好（本地仓库），随用随取。

3.2.1原来如何引入依赖

3.2.2现在如何引入依赖

我们只需要在pom.xml中引⼊mysql-connector-java的依赖就可以了

我们的需要的依赖一般都在中央仓库中

中央仓库

然后在这个网站中去找https://mvnrepository.com/

然后在pom.xml中引入依赖

3.2.3.但是我们发现我们明明只引入了一个mysql的依赖却出现了两个

多的这个就是依赖的依赖，如果我们不需要怎么排除这些依赖呢？

通过标签<exclusions></exlusions>排除也可以安装Maven Helper插件

3.3.4.也可以：安装Maven Helper插件

Installa安装就好了

4.Maven仓库：

中央仓库: maven 软件中内置⼀个远程仓库地址，就是中央仓库，服务于整个互联网. 由 Maven 团队维护，全球唯⼀.

仓库地址： https://repo1.maven.org/maven2/

可以通过 https://mvnrepository.com 这个网站来查询并下载

我们也可以把自己写好的Jar包上传到中央仓库(具备⼀定的要求), 也可以从中央仓库下载Jar包

4.1.如何查找Jar的坐标

1.访问 https://mvnrepository.com/

2.查找比如mysql

4.2配置国内源

由于中央仓库是在国外维护的，所以我们第一次导入jar包从中央仓库中是很慢的

国内有没有呢？

有的我们可以更换阿里云的仓库（也可以称之为私服）

首先：打开settings.xml（Maven的配置文件）, 在 mirrors 节点上，添加内容如下：

 <mirror>
     <id>aliyunmaven</id>
     <mirrorOf>central</mirrorOf>
     <name>阿⾥云公共仓库</name>
     <url>http://maven.aliyun.com/nexus/content/groups/public/</url>
 </mirror>

这个配置文件的地址是

如果我们修改可settings的地址，需要在这里也进行修改，还有防止以后新建项目也要修改。

我们这个时候还要对这个地方进行修改（还是和刚才一样的操作）

大家也可以直接复制我的XML文件

This XML file does not appear to have any style information associated with it. The document tree is shown below.
<!-- 
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 https://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>
   -->
<!--  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>
      -->
<mirror>
<id>aliyunmaven</id>
<mirrorOf>*</mirrorOf>
<name>阿里云公共仓库</name>
<url>https://maven.aliyun.com/repository/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.
   |
   | -->
<profiles>
<!--  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>

4.3.刚才阿里云提到的私有服务器（私服）

私服: 一般由公司团队搭建的私有仓库.

私服属于某个公司,或者某个部门, 往往需要⼀定权限.

有了私服之后, Maven依赖下载的顺序又发生了变化

当Maven需要下载资源的时候

1. 先从本地仓库获取, 本地仓库存在, 则直接返回

2. 如果本地仓库没有, 就从私服请求, 私服存在该资源, 就直接返回

3. 如果私服上不存在该资源，则从中央仓库下载, 中央仓库不存在, 就报错了...

4. 如果中央仓库中存在, 就先缓存在私服上之后，再缓存到本地仓库里, 再为Maven的下载请求提供服务