在 Maven 中，当下载依赖项时，存在多个仓库时会按照以下优先级顺序进行搜索：

本地仓库：Maven 会首先在本地的 Maven 仓库中查找依赖项。

私有仓库（私服）：如果在本地仓库中未找到依赖项，Maven 会按照项目的 pom.xml 文件中配置的 元素指定的顺序依次搜索私有仓库。私有仓库是你在项目中添加的自定义仓库，通常是用于存放项目内部开发的依赖项或者第三方库，它可以是一个本地服务器或者其他网络位置。

中央仓库（Maven Central Repository）：Maven 中央仓库是 Maven 官方维护的集中存储库，包含了大量常用的开源 Java 项目的构件和元数据。如果项目的 pom.xml 文件没有指定其他远程仓库，并且本地仓库中也没有所需的依赖项，Maven 会自动搜索中央仓库来下载依赖项。

其他远程仓库：如果在项目的 pom.xml 文件中配置了其他远程仓库地址，并且中央仓库、私有仓库和本地仓库都没有所需的依赖项，Maven 会按照 中指定的顺序依次搜索这些自定义远程仓库。

综上所述，Maven 下载依赖项的优先级顺序为：本地仓库 > 远程仓库（包括中央仓库） > 自定义远程仓库。Maven 会按照这个顺序查找依赖项，直到找到所需的依赖或者搜索完所有配置的仓库。如果依赖项在某个仓库中找到了，Maven 会将其下载到本地仓库，并在后续构建过程中直接使用本地仓库中的依赖，以加快构建速度和确保依赖项的一致性。

Maven的配置文件说明

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--><!--| 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本地仓库地址--><localRepository>D:\Program Files\localMavenRepoistory</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).| 在 Maven 中，<server> 元素用于配置认证信息，主要是用于在构建过程中访问需要认证的远程仓库或资源当使用 Maven 构建项目时，有些远程仓库可能需要进行身份验证（例如私有仓库），这时候就需要提供访问该仓库的用户名和密码。为了不将用户名和密码明文写在 pom.xml 文件中，可以将认证信息放在 Maven的 settings.xml 文件中的 <servers> 元素中| 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>在上述示例中，配置了一个 <server> 元素，它的 <id> 是 "deploymentRepo"，表示该认证信息用于访问 ID 为 "deploymentRepo" 的远程仓库。然后，通过 <username> 和 <password> 元素分别提供用户名和密码，这些信息将用于在访问远程仓库时进行身份验证。
当 Maven 需要访问远程仓库或资源时，会检查 settings.xml 文件中的 <servers> 元素，如果有匹配的 <server> 元素（根据 <id> 属性匹配），
就会使用该认证信息进行访问。这样，就可以安全地在 settings.xml 文件中管理认证信息，而不需要在 pom.xml 文件中明文暴露用户名和密码。--><!-- 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>--><server><id>releases</id><username>zs</username><password>pp</password></server><server><id>snapshots</id><username>zs</username><password>pp</password></server><server><id>docker.r.io</id><username>zs</username><password>pp</password></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<mirror><id>public</id><name>Nexus Public Mirror</name><url>http://repo.thunisoft.com/maven2/content/groups/public-repo/</url><mirrorOf>central</mirrorOf></mirror><mirror><id>nexus</id><mirrorOf>public-snapshots</mirrorOf><url>http://repo.thunisoft.com/maven2/content/groups/public-snapshots/</url></mirror>--><!--镜像仓库（Mirror Repository）是一种用于加速依赖项下载的机制。在 Maven 中，当你构建项目时，通常需要从远程仓库下载各种依赖项（JAR 文件、插件等）。这些远程仓库可能分布在全球各地，下载速度可能受到网络延迟和带宽限制的影响，导致构建过程较慢。
为了解决这个问题，Maven 允许配置一个镜像仓库，它是一个位于本地网络或高速服务器上的代理仓库。当你配置了镜像仓库后，Maven 将优先尝试从镜像仓库下载依赖项，而不是直接从远程仓库下载。
如果镜像仓库中已经存在所需的依赖项，下载速度将大大加快，因为镜像仓库通常位于本地网络或高速服务器上，与开发者的构建环境更近，网络延迟较小。
镜像仓库不保存所有的依赖项，它只会缓存从远程仓库下载的依赖项。当 Maven 需要下载依赖项时，首先尝试从镜像仓库获取。
如果在镜像仓库中找不到所需的依赖项，Maven 会继续从配置的其他远程仓库下载。--><mirror><id>rep</id><!-- 用于指定该镜像仓库代理的目标仓库。它的作用是告诉 Maven 该镜像仓库要替代哪个远程仓库的下载请求。 当前配置表示这个镜像仓库将代理所有远程仓库的请求，但会排除掉 ID 分别为 "private1"、"private2" 和 "private3" 的远程仓库，这些仓库的请求将不会由这个镜像仓库来处理。这样的配置是有用的，例如，当你有多个私有仓库，并且想要一个镜像仓库来加速下载公共仓库的依赖项，同时不影响私有仓库的下载请求。通过排除私有仓库的 ID，确保私有仓库的请求不会被这个镜像仓库所代理，避免了可能出现的下载问题--><mirrorOf>*,!private1,!private2,!private3</mirrorOf><url>http://maven.r.io/</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是一种用于在不同环境或需求下为项目定义不同配置选项的机制。通过使用 Profile，你可以根据不同的情况激活或禁用特定配置，从而实现项目的定制化构建|--><profiles><profile><id>env1</id><!-- 在 Maven 的 Profile 中，你可以通过 <repositories> 元素来定义特定的仓库配置。这允许你在不同的环境或需求下为项目指定不同的远程仓库，从而实现定制化的依赖管理 --><repositories><repository><id>releases</id><url>http://xxxxxx</url><releases><enabled>true</enabled></releases><snapshots><enabled>true</enabled></snapshots></repository></repositories><pluginRepositories><pluginRepository><id>rep-plugin</id><url>http://xxxxxxxx</url><releases><enabled>true</enabled></releases><snapshots><enabled>true</enabled></snapshots></pluginRepository></pluginRepositories></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.|激活指定的环境<activeProfiles><activeProfile>alwaysActiveProfile</activeProfile><activeProfile>anotherAlwaysActiveProfile</activeProfile></activeProfiles>--><activeProfiles><activeProfile>env1</activeProfile></activeProfiles>
</settings>