在使用IDEA的时候，出现过多次因为maven环境原因，导致编译出错，找不到包或者找不到符号，或者点击run无反应的情况。以下说明一些常见的情况，以及处理方式。
1.该项目未被识别为maven项目
在pom.xml上，右键add as maven。
2.该项目的pom发生了更改，jar包未引入成功
在pom.xml上，右键maven reinport
3.jar无法下载下来
比如你设置了公司内网下的镜像，导致无法下载，建议直接设置为阿里云和maven的仓库。
jar包的查找顺序：本地仓库->公司或者团队私有库->阿里云镜像->maven镜像。
maven 配置setting文件：（file->setting->build execution deployment）
一个可供参考的setting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.home}/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>C:\Users\Administrator\.m2\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>
-->
<!--
<mirror>
<id>ibiblio</id>
<mirrorOf>central</mirrorOf>
<name>Human Readable Name for this Mirror.</name>
<url>http://mirrors.ibiblio.org/maven2/</url>
</mirror>
-->
<mirror>
<id>alimaven</id>
<name>aliyun maven</name>
<url>http://maven.aliyun.com/nexus/content/groups/public/</url>
<mirrorOf>central</mirrorOf>
</mirror>
<mirror>
<id>nexus</id>
<name>internal nexus repository</name>
<url>http://repo.maven.apache.org/maven2</url>
<mirrorOf>central</mirrorOf>
</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>-->
<!--<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>
4、jar包在本地仓库已经存在，但是在maven项目上依然显示红线，或者引用不到
删除本地库中的对应jar包，然后maven reinport
5、重新编译
（1）删除项目下所有target文件，重新编译。菜单栏Build ->Build Project。（也可以直接Rebuild Project，该操作会删除target，重新编译）。
（2）右侧maven project->lifecycle->maven clean 也会删除本地target，重新编译。
6、点击run或者debug后变灰色，无反应
（1）该问题在springcloud项目中出现的比较多。需要查看出错模块的pom是否有问题，测试方式是删除某一个或者几个jar包引用后，maven reimport，然后重新编译项目是否报错。如果依旧无任何反应，很可能是pom文件出现了问题，建议从其他正常模块中拷贝一个pom文件（空的），逐个增加jar包引入，编译，排查是哪个jar的问题。（我是这么解决的）
7、项目使用的jdk版本是否一致
项目使用jdk版本
项目编译的jdk版本
8、文件编码
9、父子项目的编译
父子项目的编译，需要在父项目上进行maven compile或者package操作，父项目会确定项目编译的先后顺序，被依赖项目将会最先运行。
或者，在运行模块前，先maven install其子模块。（maven install操作会将本模块打包注册到本地仓库）
10、invalidate and restart
群途末路了，可以试下，将会清除ide缓存
题外话：
设置默认的setting或者project structure可以通过file->other setting进入设置。
