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Maven项目中突然找不到Build Path或maven dependencies library
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这两天发现有个maven项目抽风了，一个是右击项目找不到Build Path了，一个是依赖的lib库没了，maven引入的依赖包导不了。后来发现是eclipse搞的鬼，出问题的是项目下的.classpath文件变动了。第一个问题是.classpath没了，而.project文件被改动了；第二个问题这个文件.classpath被改动了。
先看这两个文件被改动后的样子：
.project
<?xml version="1.0" encoding="UTF-8"?>
<projectDescription>
<name>ms-navigation-api</name>
<comment></comment>
<projects>
</projects>
<buildSpec>
<buildCommand>
<name>org.eclipse.m2e.core.maven2Builder</name>
<arguments>
</arguments>
</buildCommand>
</buildSpec>
<natures>
<nature>org.eclipse.m2e.core.maven2Nature</nature>
</natures>
</projectDescription>
.classpath
<?xml version="1.0" encoding="UTF-8"?>
<classpath>
<classpathentry kind="src" output="target/classes" path="src/main/resources"/>
<classpathentry kind="src" output="target/classes" path="src/test/java"/>
<classpathentry kind="src" output="target/classes" path="src/main/java"/>
<classpathentry kind="con" path="org.eclipse.jdt.launching.JRE_CONTAINER/org.eclipse.jdt.internal.debug.ui.launcher.StandardVMType/jdk1.8.0_131"/>
<classpathentry kind="output" path="target/classes"/>
</classpath>
改动前的样子
.project
<?xml version="1.0" encoding="UTF-8"?>
<projectDescription>
<name>ms-navigation-api</name>
<comment></comment>
<projects>
</projects>
<buildSpec>
<buildCommand>
<name>org.eclipse.jdt.core.javabuilder</name>
<arguments>
</arguments>
</buildCommand>
<buildCommand>
<name>org.eclipse.wst.common.project.facet.core.builder</name>
<arguments>
</arguments>
</buildCommand>
<buildCommand>
<name>org.eclipse.m2e.core.maven2Builder</name>
<arguments>
</arguments>
</buildCommand>
<buildCommand>
<name>org.eclipse.wst.validation.validationbuilder</name>
<arguments>
</arguments>
</buildCommand>
</buildSpec>
<natures>
<nature>org.eclipse.jem.workbench.JavaEMFNature</nature>
<nature>org.eclipse.wst.common.modulecore.ModuleCoreNature</nature>
<nature>org.eclipse.jdt.core.javanature</nature>
<nature>org.eclipse.m2e.core.maven2Nature</nature>
<nature>org.eclipse.wst.common.project.facet.core.nature</nature>
<nature>org.eclipse.wst.jsdt.core.jsNature</nature>
</natures>
</projectDescription>
.classpath
<?xml version="1.0" encoding="UTF-8"?>
<classpath>
<classpathentry kind="src" output="target/classes" path="src/main/java">
<attributes>
<attribute name="optional" value="true"/>
<attribute name="maven.pomderived" value="true"/>
</attributes>
</classpathentry>
<classpathentry excluding="**" kind="src" output="target/classes" path="src/main/resources">
<attributes>
<attribute name="maven.pomderived" value="true"/>
</attributes>
</classpathentry>
<classpathentry kind="src" output="target/test-classes" path="src/test/java">
<attributes>
<attribute name="optional" value="true"/>
<attribute name="maven.pomderived" value="true"/>
</attributes>
</classpathentry>
<classpathentry kind="src" path="src/test/resources"/>
<classpathentry kind="con" path="org.eclipse.jdt.launching.JRE_CONTAINER/org.eclipse.jdt.internal.debug.ui.launcher.StandardVMType/JavaSE-1.8">
<attributes>
<attribute name="maven.pomderived" value="true"/>
</attributes>
</classpathentry>
<classpathentry kind="con" path="org.eclipse.m2e.MAVEN2_CLASSPATH_CONTAINER">
<attributes>
<attribute name="maven.pomderived" value="true"/>
<attribute name="org.eclipse.jst.component.dependency" value="/WEB-INF/lib"/>
</attributes>
</classpathentry>
<classpathentry kind="output" path="target/classes"/>
</classpath>
各个maven项目.classpath文件都是一样的，所以这两个问题都需要找到另一个.classpath文件，复制到有问题的项目，而第二个问题还要做一件事：参考另一个.project文件，把缺失的内容补上（内容都是一样的，除了项目名）。改好后重启Eclipse，Build Path和Maven Dependecies终于又回来了。
