Added support for google-java-format (#33).

Author: nedtwigg

src/main/java/com/diffplug/gradle/spotless/java/GoogleJavaFormat.java

@@ -0,0 +1,67 @@
+/*
+ * Copyright 2016 DiffPlug
+ *
+ * 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.diffplug.gradle.spotless.java;
+
+import java.io.File;
+import java.lang.reflect.Method;
+import java.net.URL;
+import java.net.URLClassLoader;
+import java.util.Set;
+
+import org.gradle.api.Project;
+import org.gradle.api.artifacts.Configuration;
+import org.gradle.api.artifacts.Dependency;
+
+import com.diffplug.common.base.Errors;
+import com.diffplug.common.base.Throwing;
+
+/** Wraps up [google-java-format](https://github.com/google/google-java-format) as a FormatterStep. */
+class GoogleJavaFormat {
+	static final String NAME = "google-java-format";
+	static final String DEFAULT_VERSION = "1.1";
+	static final String MAVEN_COORDINATE = "com.google.googlejavaformat:google-java-format:";
+	static final String FORMATTER_CLASS = "com.google.googlejavaformat.java.Formatter";
+	static final String FORMATTER_METHOD = "formatSource";
+
+	/** Returns a function which will call the google-java-format tool. */
+	static Throwing.Function<String, String> createRule(String version, Project project) throws Exception {
+		// get the googleJavaFormat configuration
+		Dependency googleJavaFormatJar = project.getDependencies().create(MAVEN_COORDINATE + version);
+		Configuration configuration = project.getConfigurations().detachedConfiguration(googleJavaFormatJar);
+		configuration.setDescription("google-java-format");
+
+		// get a classloader which contains only the jars in this configuration
+		Set<File> jars;
+		try {
+			jars = configuration.resolve();
+		} catch (Exception e) {
+			System.err.println("You probably need to add a repository containing the `google-java-format` artifact to your buildscript,");
+			System.err.println("e.g.: repositories { mavenCentral() }");
+			throw e;
+		}
+		URL[] jarUrls = jars.stream().map(Errors.rethrow().wrapFunction(
+				file -> file.toURI().toURL())).toArray(size -> new URL[size]);
+		URLClassLoader classLoader = new URLClassLoader(jarUrls);
+		// TODO: dispose the classloader when the function
+		// that we return gets garbage-collected
+
+		// instantiate the formatter and get its format method
+		Class<?> formatterClazz = classLoader.loadClass(FORMATTER_CLASS);
+		Object formatter = formatterClazz.getConstructor().newInstance();
+		Method method = formatterClazz.getMethod(FORMATTER_METHOD, String.class);
+		return input -> (String) method.invoke(formatter, input);
+	}
+}

src/main/java/com/diffplug/gradle/spotless/java/JavaExtension.java

@@ -56,6 +56,21 @@ public void eclipseFormatFile(Object eclipseFormatFile) {
 		customLazy(EclipseFormatterStep.NAME, () -> EclipseFormatterStep.load(getProject().file(eclipseFormatFile))::format);
 	}
 
+	/** Uses the [google-java-format](https://github.com/google/google-java-format) jar to format source code. */
+	public void googleJavaFormat() {
+		googleJavaFormat(GoogleJavaFormat.DEFAULT_VERSION);
+	}
+
+	/**
+	 * Uses the given version of [google-java-format](https://github.com/google/google-java-format) to format source code.
+	 *
+	 * Limited to published versions.  See [issue #33](https://github.com/diffplug/spotless/issues/33#issuecomment-252315095)
+	 * for an workaround for using snapshot versions.
+	 */
+	public void googleJavaFormat(String version) {
+		customLazy(GoogleJavaFormat.NAME, () -> GoogleJavaFormat.createRule(version, getProject()));
+	}
+
 	/** If the user hasn't specified the files yet, we'll assume he/she means all of the java files. */
 	@Override
 	protected void setupTask(FormatTask task) throws Exception {

src/test/java/com/diffplug/gradle/spotless/java/GoogleJavaFormatTest.java

@@ -0,0 +1,48 @@
+/*
+ * Copyright 2016 DiffPlug
+ *
+ * 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.diffplug.gradle.spotless.java;
+
+import java.io.IOException;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+import com.diffplug.gradle.spotless.GradleIntegrationTest;
+
+public class GoogleJavaFormatTest extends GradleIntegrationTest {
+	@Test
+	public void integration() throws IOException {
+		write("build.gradle",
+				"plugins {",
+				"    id 'com.diffplug.gradle.spotless'",
+				"}",
+				"repositories { mavenCentral() }",
+				"",
+				"spotless {",
+				"    java {",
+				"        target file('test.java')",
+				"        googleJavaFormat()",
+				"    }",
+				"}");
+		String input = getTestResource("java/googlejavaformat/JavaCodeUnformatted.test");
+		write("test.java", input);
+		gradleRunner().withArguments("spotlessApply").forwardOutput().build();
+
+		String result = read("test.java");
+		String output = getTestResource("java/googlejavaformat/JavaCodeFormatted.test");
+		Assert.assertEquals(output, result);
+	}
+}

src/test/resources/java/googlejavaformat/JavaCodeFormatted.test

@@ -0,0 +1,5 @@
+public class Java {
+  public static void main(String[] args) {
+    System.out.println("hello");
+  }
+}

src/test/resources/java/googlejavaformat/JavaCodeUnformatted.test

@@ -0,0 +1,5 @@
+public class Java {
+public static void main(String[] args) {
+System.out.println("hello");
+}
+}