Spring-Maven
目录
一.什么是Maven
二.为什么要使用Maven
三.使用Maven
1.创建Maven项目
2.Maven中的命令
3.导入依赖
4.依赖的坐标
Maven中的仓库一般分为:
a.中央仓库
b.本地仓库
当我们需要引入一个依赖时:
c.私服
当我们在写入坐标后, 刷新Maven但是多次尝试都下载不下来:
四.通过Maven Helper插件解决依赖冲突的问题
一.什么是Maven
Maven是⼀个项目管理工具。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,报告和⽂档的项目管理⼯具软件。
大白话: Maven是⼀个项目管理⼯具, 通过pom.xml⽂件的配置获取jar包,而不用手动去添加jar包
二.为什么要使用Maven
一句话: 简单, 方便, 提⾼我们的开发效率, 减少我们的开发Bug。
1.创建项目
2.依赖管理
三.使用Maven
1.创建Maven项目
2.Maven中的命令
3.导入依赖
4.依赖的坐标
依赖的坐标其实就指的是,依赖的路径、依赖的包的名称、依赖的包的版本号。这个路径通常指的是Maven中央仓库中的路径。
Maven中央仓库https://repo1.maven.org/maven2/ Maven中央仓库查询网站
https://mvnrepository.com/
Maven中央仓库查询网站相比中央仓库更新较慢,有点时候Maven中央仓库中已经有了,但是Maven中央仓库查询网站中查不出来。
Maven中的仓库一般分为:
a.中央仓库
所有依赖都保存在中央仓库中,这个服务器是全球唯一的
b.本地仓库
在自己的电脑中保存的依赖的路径。
这个路径Maven配置路径和本地仓库的路径最好修改一下,否则随着时间的积累,对于IDEA默认配置的C盘,会占用其大量的空间。
在新版IDEA中默认的保存路径中是找不到settings.xml这个文件的,这就对于我们配置Maven的国内源带来了很大的困扰,此时只需要在目标路径中创建settings.xml文件,然后将下面的配置粘贴进去,然后将这个文件配置到IDEA中就可以了。
<?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 athttp://www.apache.org/licenses/LICENSE-2.0Unless 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>
当我们需要引入一个依赖时:
项目首先会去本地仓库中寻找这个依赖,如果本地仓库中没有,就会从中央仓库中寻找,如果中央仓库中有就会下载到本地仓库中,然后本地仓库中在从本地仓库中导入到项目中,如果以后再次需要用到这个依赖直接从本地仓库中获取就可以了。
c.私服
当我们在写入坐标后, 刷新Maven但是多次尝试都下载不下来:
①.在中央仓库中查询这个包是否真的存在。
②.如果存在,尝试多下载几次
③如果下载多次,都下载不下来:
可以查看Maven是否配置了国内源,本地仓库的路径中是否使用了中文,也可以到本地仓库中找到这个包然后将其删除掉重新下载,因为如果网络有问题可能会导致依赖下载了一半,但是此时项目在导入依赖是时候并不知道这个依赖是不完整的。
四.通过Maven Helper插件解决依赖冲突的问题
如上图所示在一个大的项目中包含多个项目的时候,会需要引入多个依赖,而依赖又需要引入依赖所需要的依赖,在这种情况下就很容易发送依赖冲突的问题,因为虽然都是一个依赖,但是依赖的版本可能不同。
Maven Helper可以通过这个插件来解决依赖冲突的问题。
在IDEA中安装插件: