【java】什么是maven?|Eclipse自带Maven增加setting.xml
目录
Maven 错误 Failure to transfer ...was cached in the local repository...
什么是maven
作者：Martin Wang
链接：https://www.zhihu.com/question/32240102/answer/340029398
我先不说maven，也不说java开发，先说做菜，你可能像做个红烧小排(HongshaoxiaopaiApp)，你需要的材料是：
- 小排(xiaopai.jar)，要小猪的（version=little pig）。
- 酱油(jiangyou.jar)，要82年的酱油（version=1982）
- 盐(yan.jar)
- 糖(tang.jar)，糖要广东产的（version=guangdong）
- 生姜(shengjiang.jar)
- 茴香(huixiang.jar)
于是，你要去菜场买小排，去门口杂货店买酱油，买盐……可能你家门口的杂货店还没有1982年的酱油，你要去3公里外的农贸市场买……你买原材料的过程估计会很痛苦，可能买到的材料不是1982年的，会影响口感。
在你正式开始做小排前，你会为食材的事情，忙得半死。
现在有个超市出了个盒装版的半成品红烧小排，把生的小排，1982年的酱油，盐，广东产的糖等材料打包成一个盒子里，你回家只要按照说明，就能把红烧小排做出来，不用考虑材料的来源问题。
Maven就是那个超市，红烧小排就是你要开发的软件，酱油、盐什么的就是你开发软件要用到的jar包——我们知道，开发java系统，下载一堆jar包依赖是很正常的事情。有了maven，你不用去各个网站下载各种版本的jar包，也不用考虑这些jar包的依赖关系。Maven会给你搞定，就是超市的配菜师傅会帮你把红烧小排的配料配齐一样。
现在你应该明白Maven是做什么的了吧。
Maven 错误
Maven 错误 Failure to transfer ...was cached in the local repository...
问题描述
在使用公司内部的maven仓库编译项目时，由于新加入了几个依赖包，第一次编译失败了，此后在修复了公司内部maven仓库后编译项目出现错误:
Failure to transfer org.apache.maven:maven-archiver:pom:2.5 from http://repo.maven.apache.org/
maven2 was cached in the local repository, resolution will not be reattempted until the update
interval of central has elapsed or updates are forced. Original error: Could not transfer artifact
org.apache.maven:maven-archiver:pom:2.5 from/to central (http://repo.maven.apache.org/
maven2): No response received after 60000
问题原因
Maven默认会使用本地缓存的库来编译工程，对于上次下载失败的库，maven会在~/.m2/repository/ / / /目录下创建xxx.lastUpdated文件，一旦这个文件存在，那么在直到下一次nexus更新之前都不会更新这个依赖库。
解决办法
删除~/.m2/repository/ / / /目录下的*.lastUpdated文件（用报错的包的名称在repository 文件夹搜索，就能看到*.lastUpdated文件），然后再次运行mvn compile编译工程。
另外也有说可以修改~/.m2/settings.xml文件，将其中的仓库添加
<updatePolicy>always</updatePolicy>
来强制每次都更新依赖库，但这个方法我还没有试过，这里先记下，下次再碰到这个问题的时候再试试。
原文链接：https://blog.csdn.net/changqing5818/article/details/53558510
Eclipse自带Maven增加setting.xml
2020-03-11 15:35:29
Eclipse版本：Mars.1 Release (4.5.1)
该版本是自带Maven的，在创建Maven项目后，会存在 C:\Users\Administrator\.m2\repository ；
Eclipse->Windows->首选项->Maven->User Settings，可以看到User Settings路径下 \.m2\settings.xml，但是进入.m2目录是没有settings.xml文件，不能配置本地厂库；
所以要手动在.m2路径下新增一个settings.xml文件；添加文件的内容后保存；
然后 windows--》perferences--》maven --》Update Setting；因为在settings.xml中指定了本地厂库的路径，所以对应的Local Repository会对应改变；
备注：因为是初学Maven，对于配置还不是很了解。
对应settings.xml的内容，在百度上找了一篇，完全copy保存后，update时提示：Could not read settings.xml；
百度说什么 localrepositor 的路径用反斜杠的都试了也不行；
后来有找了一份就可以了，多了些配置项（但是配置项都为空的），不知道是否因为这个；若是在正式使用时，建议直接安装一个Maven，使用系统生成的settings.xml是最正确的。
另外用了阿里的库：
<url>http://maven.aliyun.com/nexus/content/groups/public</url>
注意这个配置项按实际地址填写:<localRepository>C:/Users/Administrator/.m2/repository</localRepository>
<?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: ~/.m2/repository
<localRepository>/path/to/local/repo</localRepository>
-->
<localRepository>C:/Users/Administrator/.m2/repository</localRepository>
<!--<localRepository>F:/eclipse_workspace20170314/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>nexus-aliyun</id>
<mirrorOf>central</mirrorOf>
<name>Nexus aliyun</name>
<url>http://maven.aliyun.com/nexus/content/groups/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>原文：Eclipse自带Maven增加setting.xml_猎虫师的博客-CSDN博客_eclipse maven setting.xml
