Eclipse Issue: source folder is not a java project－Jemmy Walker

　　在Eclipse Create一個maven-archetype-webapp專案時，丟出警告訊息，之後還是產出Project目錄。maven-archtype-webapp站台可能怪怪的，重點不在此。之前Create struts2-archetype-starter成功後，Project的圖示有M和J的字母，代表同時為Maven Project和Java Project。而maven-archtype-webapp產出的Project圖示只有M，因此我想去Create一個Package或Class或Source Folder都失敗，失敗訊息如標題所示：Source folder is not a java project。

　　每個Project目錄下至少有個.project檔，而maven-archtype-webapp的.project檔目錄內容很少，節錄如下：

<buildSpec>
    <buildCommand>
        <name>org.maven.ide.eclipse.maven2Builder</name>
        <arguments>
        </arguments>
    </buildCommand>
</buildSpec>
<natures>
    <nature>org.maven.ide.eclipse.maven2Nature</nature>
</natures>

　　相形之下，struts2-archetype-starter的.project檔，其buildCommmand和natures內容就不少：

<buildSpec>
    <buildCommand>
        <name>org.eclipse.wst.jsdt.core.javascriptValidator</name>
        <arguments>
        </arguments>
    </buildCommand>
    <buildCommand>
        <name>org.eclipse.wst.common.project.facet.core.builder</name>
        <arguments>
        </arguments>
    </buildCommand>
    <buildCommand>
        <name>org.eclipse.jdt.core.javabuilder</name>
        <arguments>
        </arguments>
    </buildCommand>
    <buildCommand>
        <name>org.eclipse.wst.validation.validationbuilder</name>
        <arguments>
        </arguments>
    </buildCommand>
    <buildCommand>
        <name>org.maven.ide.eclipse.maven2Builder</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.maven.ide.eclipse.maven2Nature</nature>
    <nature>org.eclipse.wst.common.project.facet.core.nature</nature>
    <nature>org.eclipse.wst.jsdt.core.jsNature</nature>
</natures>

標粗黑體字應該就是Java Project的設定了，不止如此，同目錄下還有個.classpath檔，標出哪些folder是source folder，內容如下：

<?xml version="1.0" encoding="UTF-8"?>
<classpath>
    <classpathentry kind="src" output="target/classes" path="src/main/java"/>
    <classpathentry excluding="**" kind="src" output="target/classes" path="src/main/resources"/>
    <classpathentry kind="src" output="target/test-classes" path="src/test/java"/>
    <classpathentry excluding="**" kind="src" output="target/test-classes" path="src/test/resources"/>
    <classpathentry kind="con" path="org.eclipse.jdt.launching.JRE_CONTAINER/org.eclipse.jdt.internal.debug.ui.launcher.StandardVMType/J2SE-1.5"/>
    <classpathentry kind="con" path="org.maven.ide.eclipse.MAVEN2_CLASSPATH_CONTAINER">
        <attributes>
            <attribute name="org.eclipse.jst.component.dependency" value="/WEB-INF/lib"/>
        </attributes>
    </classpathentry>
    <classpathentry kind="con" path="org.eclipse.jst.j2ee.internal.web.container"/>
    <classpathentry kind="con" path="org.eclipse.jst.j2ee.internal.module.container"/>
    <classpathentry kind="output" path="target/classes"/>
</classpath>

　　所以後來解決方式，就是把struts2-archetype-starter的Project目錄下.project和.classpath檔蓋到maven-archtype-webapp的Project目錄下，再Refresh，就變成兼具Maven和Java的Project。