Allow configuring base docker image in DockerfileMojo (#2785)

manual/src/main/asciidoc/developer-guide/karaf-maven-plugin.adoc

@@ -991,6 +991,14 @@ The `karaf:dockerfile` goal creates a ready to use Dockerfile for a given Karaf
 |`assembly`
 |`File`
 |The directory containing the Karaf assembly (as generated by `karaf:assembly`). Default value: ${project.build.directory}/assembly
+
+|`command`
+|`String`
+|The CMD command instruction to include in the generated Dockerfile. Default value: `["karaf", "run"]`
+
+|`image`
+|`String`
+|The base Docker image (FROM instruction) to use. Default value: `eclipse-temurin:11-jre`
 |===
 
 ===== Docker
@@ -1008,7 +1016,7 @@ This goal requires a local Docker daemon and runs only on Unix. The `docker` com
 <execution>
     <id>docker</id>
     <goals>
-        <goal>docker</docker>
+        <goal>docker</goal>
     </goals>
 </execution>
 ----

tooling/karaf-maven-plugin/src/it/test-dockerfile/verify.bsh

@@ -22,4 +22,10 @@ import java.lang.*;
 import java.util.*;
 
 File generated = new File(basedir, "target/Dockerfile");
-return generated.exists();
+if (!generated.exists()) {
+    return false;
+}
+BufferedReader reader = new BufferedReader(new FileReader(generated));
+String line = reader.readLine();
+reader.close();
+return line != null && line.startsWith("FROM eclipse-temurin:11-jre");

tooling/karaf-maven-plugin/src/main/java/org/apache/karaf/tooling/DockerfileMojo.java

@@ -40,13 +40,16 @@ public class DockerfileMojo extends MojoSupport {
     @Parameter(defaultValue = "[\"karaf\", \"run\"]")
     private String command;
 
+    @Parameter(defaultValue = "eclipse-temurin:11-jre", property = "image")
+    private String image;
+
     @Override
     public void execute() throws MojoExecutionException, MojoFailureException {
         getLog().info("Creating Dockerfile");
         File dockerFile = new File(destDir, "Dockerfile");
         try {
             StringBuilder buffer = new StringBuilder();
-            buffer.append("FROM eclipse-temurin:11-jre").append("\n");
+            buffer.append("FROM ").append(image).append("\n");
             buffer.append("ENV KARAF_INSTALL_PATH /opt").append("\n");
             buffer.append("ENV KARAF_HOME $KARAF_INSTALL_PATH/apache-karaf").append("\n");
             buffer.append("ENV KARAF_EXEC exec").append("\n");

tooling/karaf-maven-plugin/src/test/java/org/apache/karaf/tooling/DockerfileMojoTest.java

@@ -0,0 +1,100 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.karaf.tooling;
+
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.TemporaryFolder;
+
+import java.io.File;
+import java.lang.reflect.Field;
+import java.nio.file.Files;
+import java.util.List;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.fail;
+
+public class DockerfileMojoTest {
+
+    @Rule
+    public final TemporaryFolder temporaryFolder = new TemporaryFolder();
+
+    @Test
+    public void testDefaultDockerfileGeneration() throws Exception {
+        DockerfileMojo mojo = new DockerfileMojo();
+        File destDir = temporaryFolder.newFolder("target");
+        File assembly = new File(destDir, "assembly");
+
+        setPrivateField(mojo, "destDir", destDir);
+        setPrivateField(mojo, "assembly", assembly);
+        setPrivateField(mojo, "command", "[\"karaf\", \"run\"]");
+        setPrivateField(mojo, "image", "eclipse-temurin:11-jre");
+
+        mojo.execute();
+
+        File dockerfile = new File(destDir, "Dockerfile");
+        assertTrue("Dockerfile should be created", dockerfile.exists());
+
+        List<String> lines = Files.readAllLines(dockerfile.toPath());
+        assertEquals("FROM eclipse-temurin:11-jre", lines.get(0));
+        assertEquals("ENV KARAF_INSTALL_PATH /opt", lines.get(1));
+        assertEquals("ENV KARAF_HOME $KARAF_INSTALL_PATH/apache-karaf", lines.get(2));
+        assertEquals("ENV KARAF_EXEC exec", lines.get(3));
+        assertEquals("ENV PATH $PATH:$KARAF_HOME/bin", lines.get(4));
+        assertEquals("COPY assembly $KARAF_HOME", lines.get(5));
+        assertEquals("EXPOSE 8101 1099 44444 8181", lines.get(6));
+        assertEquals("CMD [\"karaf\", \"run\"]", lines.get(7));
+    }
+
+    @Test
+    public void testCustomImageAndCommand() throws Exception {
+        DockerfileMojo mojo = new DockerfileMojo();
+        File destDir = temporaryFolder.newFolder("target-custom");
+        File assembly = new File(destDir, "custom-dist");
+
+        setPrivateField(mojo, "destDir", destDir);
+        setPrivateField(mojo, "assembly", assembly);
+        setPrivateField(mojo, "command", "[\"karaf\", \"server\"]");
+        setPrivateField(mojo, "image", "eclipse-temurin:17-jre");
+
+        mojo.execute();
+
+        File dockerfile = new File(destDir, "Dockerfile");
+        assertTrue("Dockerfile should be created", dockerfile.exists());
+
+        List<String> lines = Files.readAllLines(dockerfile.toPath());
+        assertEquals("FROM eclipse-temurin:17-jre", lines.get(0));
+        assertEquals("COPY custom-dist $KARAF_HOME", lines.get(5));
+        assertEquals("CMD [\"karaf\", \"server\"]", lines.get(7));
+    }
+
+    private void setPrivateField(Object obj, String fieldName, Object value) throws Exception {
+        Class<?> aClass = obj.getClass();
+        while (aClass != null) {
+            try {
+                Field field = aClass.getDeclaredField(fieldName);
+                field.setAccessible(true);
+                field.set(obj, value);
+                return;
+            } catch (final NoSuchFieldException nsfe) {
+                aClass = aClass.getSuperclass();
+            }
+        }
+        fail("cant set " + fieldName);
+    }
+}