在使用Maven以及Eclipse的Maven插件时，我和同事遇到了一下几个问题，本着知其然知其所以然的学习精神，总结如下：
- Unrecognised tag
问题
由于我使用本地代理仓库，所以settings.xml设置如下：<profiles>
<profile>
<id>nexus</id>
<repositories>
<repository>
<id>nexus</id>
<name>Nexus</name>
<url>http://localhost:8081/nexus/content/groups/public</url>
<releases><enabled>true</enabled></releases>
<snapshots><enabled>true</enabled></snapshots>
</repository>
</repositories>
<pluginRepositories>
<pluginRepository>
<id>nexus</id>
<name>Nexus</name>
<url>http://localhost:8081/nexus/content/groups/public</url>
<releases><enabled>true</enabled></releases>
<snapshots><enabled>true</enabled></snapshots>
</pluginRepository>
</pluginRepositories>
</profile>
<!--激活配置-->
<activeProfiles>
<activeProfile>nexus</activeProfile>
</activeProfiles>
</profiles>但在Maven编译时报了如下异常：
[WARNING] Some problems were encountered while building the effective settings
[WARNING] Unrecognised tag: ‘activeProfiles’ (position: START_TAG seen …\n\t… @269:18) @ C:\Documents and Settings\Administrator.ZQFGROUP.000\.m2\settings.xml, line 269, column 18
[WARNING]解决
这是因为错把activeProfiles配置到了profiles节点里了，应该把activeProfiles移到profiles之外，更多settings.xml配置信息请参考这里。 - No goals
问题
Eclipse安装了Maven插件后，在项目的pom.xml上右键能看到如下：
而我自作聪明地认为:Maven build 与 mvn compile 是等价的，于是我再点击”Maven build…”之后，“Goals”是空的，如：
于是就报了这样的错误：[ERROR] No goals have been specified for this build. You must specify a valid lifecycle phase or a goal in the format:or:[:]:. Available lifecycle phases are: validate, initialize, generate-sources, process-sources, generate-resources, process-resources, compile, process-classes, generate-test-sources, process-test-sources, generate-test-resources, process-test-resources, test-compile, process-test-classes, test, prepare-package, package, pre-integration-test, integration-test, post-integration-test, verify, install, deploy, pre-site, site, post-site, site-deploy, pre-clean, clean, post-clean. -> [Help 1]
解决
解决方法至少有两种：- 再点击”Maven build…”之后，输入你要执行的“Goals”，如compile,clean,test等等;
- 在pom.xml中配置默认的Goal，如：
<build>
<defaultGoal>clean</defaultGoal>
</build>作为project的子节点。
- not a JRE
问题
在使用pom.xml配置默认Goal的时，如果默认的Goal为clean就没问题，但如果是如:<build>
<defaultGoal>clean compile</defaultGoal>
</build>就会报错误：
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:2.3.2:compile (default-compile) on project Demo: Compilation failure
[ERROR] Unable to locate the Javac Compiler in:
[ERROR] C:\Program Files\Java\jre7\..\lib\tools.jar
[ERROR] Please ensure you are using JDK 1.4 or above and
[ERROR] not a JRE (the com.sun.tools.javac.Main class is required).
[ERROR] In most cases you can change the location of your Java
[ERROR] installation by setting the JAVA_HOME environment variable.经过几番尝试，才发现并不是多个Goal的问题，而是compile Goal的问题。但使用命令的”mvn compile”又是OK的。
几经折腾才发现错误里说的很清楚：Please ensure you are using JDK 1.4 or above and not a JRE”，它需要的是JDK而不是JRE。我给的项目中使用的是公共JRE：
解决
修改Eclipse的配置，使用JDK：Eclipse->Window->Preferences->Java->Installed JREs
Finish后，项目如：
OK，知之为知之，不知创造条件必须知
！！
