Implement JarProcessor to determine jar type. (#2797)

* Implement JarProcessor to determine jar type and use Truth for tests

build.gradle

@@ -77,6 +77,7 @@ subprojects {
     MAVEN_PLUGIN_ANNOTATIONS: 'org.apache.maven.plugin-tools:maven-plugin-annotations:3.6.0',
 
     //test
+    TRUTH: 'com.google.truth:truth:1.0.1',
     JUNIT: 'junit:junit:4.13',
     MAVEN_TESTING_HARNESS: 'org.apache.maven.plugin-testing:maven-plugin-testing-harness:3.3.0',
     MAVEN_VERIFIER: 'org.apache.maven.shared:maven-verifier:1.7.2',

jib-cli/build.gradle

@@ -23,6 +23,7 @@ dependencies {
   implementation dependencyStrings.PICOCLI
 
   testImplementation dependencyStrings.JUNIT
+  testImplementation dependencyStrings.TRUTH
   testImplementation dependencyStrings.MOCKITO_CORE
   testImplementation dependencyStrings.SLF4J_API
   testImplementation dependencyStrings.SYSTEM_RULES

jib-cli/src/main/java/com/google/cloud/tools/jib/cli/jar/JarProcessor.java

@@ -0,0 +1,52 @@
+/*
+ * Copyright 2020 Google LLC.
+ *
+ * Licensed 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 com.google.cloud.tools.jib.cli.jar;
+
+import java.io.IOException;
+import java.nio.file.Path;
+import java.util.jar.JarFile;
+
+public class JarProcessor {
+
+  /**
+   * Jar Type.
+   *
+   * <ul>
+   *   <li>{@code STANDARD} a regular jar.
+   *   <li>{@code SPRING_BOOT} a spring boot fat jar.
+   * </ul>
+   */
+  public enum JarType {
+    STANDARD,
+    SPRING_BOOT;
+  }
+
+  /**
+   * Determines whether the jar is a spring boot or regular jar, given a path to the jar.
+   *
+   * @param jarPath path to the jar.
+   * @return the jar type.
+   * @throws IOException if I/O error occurs when opening the file.
+   */
+  public static JarType determineJarType(Path jarPath) throws IOException {
+    JarFile jarFile = new JarFile(jarPath.toFile());
+    if (jarFile.getEntry("BOOT-INF") != null) {
+      return JarType.SPRING_BOOT;
+    }
+    return JarType.STANDARD;
+  }
+}

jib-cli/src/test/java/com/google/cloud/tools/jib/cli/jar/JarProcessorTest.java

@@ -0,0 +1,47 @@
+/*
+ * Copyright 2020 Google LLC.
+ *
+ * Licensed 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 com.google.cloud.tools.jib.cli.jar;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import com.google.cloud.tools.jib.cli.jar.JarProcessor.JarType;
+import com.google.common.io.Resources;
+import java.io.IOException;
+import java.net.URISyntaxException;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import org.junit.Test;
+
+public class JarProcessorTest {
+
+  private static final String SPRING_BOOT_RESOURCE_DIR = "jar/springboot/springboot_sample.jar";
+  private static final String STANDARD_RESOURCE_DIR = "jar/standard/standardJar.jar";
+
+  @Test
+  public void testDetermineJarType_springBoot() throws IOException, URISyntaxException {
+    Path springBootJar = Paths.get(Resources.getResource(SPRING_BOOT_RESOURCE_DIR).toURI());
+    JarType jarType = JarProcessor.determineJarType(springBootJar);
+    assertThat(jarType).isEqualTo(JarType.SPRING_BOOT);
+  }
+
+  @Test
+  public void testDetermineJarType_standard() throws IOException, URISyntaxException {
+    Path standardJar = Paths.get(Resources.getResource(STANDARD_RESOURCE_DIR).toURI());
+    JarType jarType = JarProcessor.determineJarType(standardJar);
+    assertThat(jarType).isEqualTo(JarType.STANDARD);
+  }
+}