一、bug:Unasble to reload Maven project
我在学习Java后端框架ssm时经常会出现导入的依赖包一片片的爆红,就像下面这样,想想就气人,刚刚建个项目,还没开始写代码呢,在pom.xml下面导个包都给我报错,我在连续入坑两次(一次只下载配了maven环境变量,没有在idea中配置,还有一次maven版本不兼容)后,决定写一篇解决方案来帮助大家避坑。
可能大家在学习过程中,很多老师都不会说版本兼容问题,导致我们都是直接从官网下载的3.8.3版本,就会与idea2020版的不兼容,然后爆红之后都会按照老师说的在右上角点击maven刷新,结果就会弹出这个框框,提示你的maven版本不可用,maven版本与idea不兼容。
二、如何解决
版本不兼容的话,那肯定只有两个办法,一个是下载安装idea新版,一个安装老版本的maven
下面是maven与idea的兼容版本
三、maven3.6.3链接
这里给大家提供maven3.6.3的安装包,maven3.8.3在官网首页就有,这里就不给了
链接:https://pan.baidu.com/s/1Leai9n9iDPg3nZN21x5EUw
提取码:17hs
四、配置maven环境变量
- 下载到指定的目录下面之后,右键此电脑–>属性–>高级系统设置–>环境变量
- 新建变量MAVEN_HOME = D:\program\maven\apache-maven-3.6.3-bin\apache-maven-3.6.3(以自己的安装路径为准)
变量值是自己maven的下载路径
- 编辑变量Path,添加变量值%MAVEN_HOME%\bin
- 最后win+R运行cmd,输入mvn -version,如图所示则配置成功
五、配置本地仓库
- 在下载路径下新建maven-repository文件夹,用作maven的本地库
- 在路径D:\program\maven\apache-maven-3.6.3-bin\apache-maven-3.6.3\conf下找到settings.xml文件
- 打开settings.xml文件,找到节点localRepository,在注释外添加
<localRepository>D:\program\maven\apache-maven-3.6.3-bin\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。
六、配置镜像
- 在settings.xml配置文件中找到mirrors节点
- 添加如下配置(注意要添加在和两个标签之间,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
七、配置JDK
- 在settings.xml配置文件中找到profiles节点
- 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(D:\program\maven\apache-maven-3.6.3-bin\maven-repository)中会出现很多文件
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
八、完整配置文件
<?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>D:\program\maven\apache-maven-3.6.3-bin\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> </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>
大家可以直接复制到自己的settings.xml文件中去,但是注意在把本地仓库那里需要改一下自己的路径