Do not include optional dependencies

Closes gh-66

Author: rwinch

spring-boot-testjars-maven/src/main/java/org/springframework/experimental/boot/server/exec/MavenClasspathEntry.java

@@ -47,6 +47,7 @@
 import org.eclipse.aether.transport.file.FileTransporterFactory;
 import org.eclipse.aether.transport.http.HttpTransporterFactory;
 import org.eclipse.aether.util.artifact.JavaScopes;
+import org.eclipse.aether.util.filter.AndDependencyFilter;
 import org.eclipse.aether.util.filter.DependencyFilterUtils;
 import org.eclipse.aether.util.repository.SimpleArtifactDescriptorPolicy;
 
@@ -128,13 +129,15 @@ public List<String> resolve() {
 
 		Artifact artifact = new DefaultArtifact(this.coords);
 
-		DependencyFilter classpathFlter = DependencyFilterUtils.classpathFilter(JavaScopes.RUNTIME, JavaScopes.COMPILE);
+		DependencyFilter scopeFilter = DependencyFilterUtils.classpathFilter(JavaScopes.RUNTIME, JavaScopes.COMPILE);
+		DependencyFilter optionalFilter = (node, parents) -> !node.getDependency().isOptional();
+		DependencyFilter dependencyFilter = new AndDependencyFilter(scopeFilter, optionalFilter);
 
 		CollectRequest collectRequest = new CollectRequest();
 		collectRequest.setRoot(new Dependency(artifact, JavaScopes.RUNTIME));
 		collectRequest.setRepositories(this.repositories);
 
-		DependencyRequest dependencyRequest = new DependencyRequest(collectRequest, classpathFlter);
+		DependencyRequest dependencyRequest = new DependencyRequest(collectRequest, dependencyFilter);
 
 		List<String> result = new ArrayList<>();
 		try {

spring-boot-testjars-maven/src/test/java/org/springframework/experimental/boot/server/exec/MavenClasspathEntryTests.java

@@ -57,6 +57,15 @@ void runtimeDependencyResolved() {
 		assertThat(entries).anyMatch(entry -> entry.contains(runtimeDependency));
 	}
 
+	@Test
+	void optionalDependencyNotResolved() {
+		MavenClasspathEntry classpath = new MavenClasspathEntry(
+				"org.springframework.data:spring-data-commons:3.2.9");
+		List<String> entries = classpath.resolve();
+		String optionalDependency = "spring-expression";
+		assertThat(entries).noneMatch(entry -> entry.contains(optionalDependency));
+	}
+
 	@Test
 	void jdk() {
 		String cloudVersion = "4.2.0";