Fix WAR entrypoint when custom base image (#3185)

Author: chanseokoh

jib-plugins-common/src/main/java/com/google/cloud/tools/jib/plugins/common/PluginConfigurationProcessor.java

@@ -543,7 +543,8 @@ static JavaContainerBuilder getJavaContainerBuilderWithBaseImage(
    * <ol>
    *   <li>null (inheriting from the base image), if the user specified value is {@code INHERIT}
    *   <li>the user specified one, if set
-   *   <li>for a WAR project, {@code ["java", "-jar", "/usr/local/jetty/start.jar"]}
+   *   <li>for a WAR project, null (inheriting) if a custom base image is specified, and {@code
+   *       ["java", "-jar", "/usr/local/jetty/start.jar"]} otherwise (default Jetty base image)
    *   <li>for a non-WAR project, by resolving the main class
    * </ol>
    *
@@ -589,7 +590,9 @@ static List<String> computeEntrypoint(
                 "mainClass, extraClasspath, jvmFlags, and expandClasspathDependencies "
                     + "are ignored for WAR projects"));
       }
-      return Arrays.asList("java", "-jar", "/usr/local/jetty/start.jar");
+      return rawConfiguration.getFromImage().isPresent()
+          ? null
+          : Arrays.asList("java", "-jar", "/usr/local/jetty/start.jar");
     }
 
     List<String> classpath = new ArrayList<>(rawExtraClasspath);

jib-plugins-common/src/test/java/com/google/cloud/tools/jib/plugins/common/PluginConfigurationProcessorTest.java

@@ -568,6 +568,22 @@ public void testEntrypointClasspath_nonDefaultAppRoot()
         .inOrder();
   }
 
+  @Test
+  public void testWebAppEntrypoint_inheritedFromCustomBaseImage()
+      throws InvalidImageReferenceException, IOException, CacheDirectoryCreationException,
+          MainClassInferenceException, InvalidAppRootException, InvalidWorkingDirectoryException,
+          InvalidPlatformException, InvalidContainerVolumeException,
+          IncompatibleBaseImageJavaVersionException, NumberFormatException,
+          InvalidContainerizingModeException, InvalidFilesModificationTimeException,
+          InvalidCreationTimeException {
+    when(projectProperties.isWarProject()).thenReturn(true);
+    when(rawConfiguration.getFromImage()).thenReturn(Optional.of("custom-base-image"));
+
+    BuildContext buildContext = getBuildContext(processCommonConfiguration());
+
+    assertThat(buildContext.getContainerConfiguration().getEntrypoint()).isNull();
+  }
+
   @Test
   public void testGetAppRootChecked() throws InvalidAppRootException {
     when(rawConfiguration.getAppRoot()).thenReturn("/some/root");