Why is Eclipse not attaching 3rd party libs source

The sources are downloaded in the Gradle cache and the classpath-entries for the source files looks ok, but Eclipse does not show the source files for 3rd party libs.

<?xml version="1.0" encoding="UTF-8"?>
<classpath>
    <classpathentry kind="output" path="bin/main"/>
    <classpathentry kind="src" path="src/main/java"/>
    <classpathentry kind="src" path="src/main/resources"/>
    <classpathentry output="bin/test" kind="src" path="src/test/java"/>
    <classpathentry output="bin/test" kind="src" path="src/test/resources"/>
    <classpathentry kind="con" path="org.eclipse.jdt.launching.JRE_CONTAINER" exported="true"/>
    <classpathentry kind="con" path="org.eclipse.jst.j2ee.internal.web.container" exported="true"/>
    <classpathentry sourcepath="D:/Users/SSchneider/.gradle/caches/artifacts-14/filestore/org.springframework/spring-webmvc/3.1.2.RELEASE/source/bc9c347358c5d59998b27e8a13c75106c3d0696/spring-webmvc-3.1.2.RELEASE-sources.jar" kind="lib" path="D:/Users/SSchneider/.gradle/caches/artifacts-14/filestore/org.springframework/spring-webmvc/3.1.2.RELEASE/jar/e02f3e5aa91c8caa37b2e9b780229d27e76c0f2e/spring-webmvc-3.1.2.RELEASE.jar" exported="true">
        <attributes>
            <attribute name="org.eclipse.jst.component.nondependency" value=""/>
        </attributes>
    </classpathentry>
    <classpathentry sourcepath="D:/Users/SSchneider/.gradle/caches/artifacts-14/filestore/org.springframework.data/spring-data-jpa/1.2.0.BUILD-SNAPSHOT/source/19e4dedbb956cdc3bb1d34d61a351229b653029a/spring-data-jpa-1.2.0.BUILD-SNAPSHOT-sources.jar" kind="lib" path="D:/Users/SSchneider/.gradle/caches/artifacts-14/filestore/org.springframework.data/spring-data-jpa/1.2.0.BUILD-SNAPSHOT/jar/2a3cfc2ea0b2c8d87f32166e16bb56e1f092568b/spring-data-jpa-1.2.0.BUILD-SNAPSHOT.jar" exported="true">
        <attributes>
            <attribute name="org.eclipse.jst.component.nondependency" value=""/>
        </attributes>
    </classpathentry>
    <classpathentry sourcepath="D:/Users/SSchneider/.gradle/caches/artifacts-14/filestore/org.springframework.security/spring-security-web/3.1.2.RELEASE/source/49e8d929d835d4ba4556ba9d138488ecc083a794/spring-security-web-3.1.2.RELEASE-sources.jar" kind="lib" path="D:/Users/SSchneider/.gradle/caches/artifacts-14/filestore/org.springframework.security/spring-security-web/3.1.2.RELEASE/jar/e43e7683289f08c1e073564a94e6f26298ec4f59/spring-security-web-3.1.2.RELEASE.jar" exported="true">
        <attributes>
            <attribute name="org.eclipse.jst.component.nondependency" value=""/>
        </attributes>
    </classpathentry>
    <classpathentry sourcepath="D:/Users/SSchneider/.gradle/caches/artifacts-14/filestore/javax.validation/validation-api/1.0.0.GA/source/7a561191db2203550fbfa40d534d4997624cd369/validation-api-1.0.0.GA-sources.jar" kind="lib" path="D:/Users/SSchneider/.gradle/caches/artifacts-14/filestore/javax.validation/validation-api/1.0.0.GA/jar/b6bd7f9d78f6fdaa3c37dae18a4bd298915f328e/validation-api-1.0.0.GA.jar" exported="true">
        <attributes>
            <attribute name="org.eclipse.jst.component.nondependency" value=""/>
        </attributes>
    </classpathentry>

</classpath>

That's a weird behavior in Eclipse with the generated .classpath-file. Just put the 'Web App Libraries' entry at the bottom of your classpath file (-> Java Build Path -> Order and Export).

The best solution is to enhance your gradle.build file (then you don't need to reorder your build path each time you generate the classpath file via gradle):

...
eclipse.classpath.file {
    // Classpath entry for Eclipse which changes the order of classpathentries; otherwise no sources for 3rd party jars are shown
    withXml { xml ->
        def node = xml.asNode()
        node.remove( node.find { it.@path == 'org.eclipse.jst.j2ee.internal.web.container' } )
        node.appendNode( 'classpathentry', [ kind: 'con', path: 'org.eclipse.jst.j2ee.internal.web.container', exported: 'true'])
    }
}