JSON formatting using Gson (#1125)

Author: nedtwigg

CHANGES.md

@@ -10,6 +10,8 @@ This document is intended for Spotless developers.
 We adhere to the [keepachangelog](https://keepachangelog.com/en/1.0.0/) format (starting after version `1.27.0`).
 
 ## [Unreleased]
+### Added
+* Added support for JSON formatting based on [Gson](https://github.com/google/gson) ([#1125](https://github.com/diffplug/spotless/pull/1125)).
 
 ### Changed
 

README.md

@@ -30,8 +30,8 @@ It's easy to build such a function, but there are some gotchas and lots of integ
 ## Current feature matrix
 
 <!---freshmark matrix
-function lib(className)   { return '| [`' + className + '`](lib/src/main/java/com/diffplug/spotless/' + className.replace('.', '/') + '.java) | ' }
-function extra(className) { return '| [`' + className + '`](lib-extra/src/main/java/com/diffplug/spotless/extra/' + className.replace('.', '/') + '.java) | ' }
+function lib(className)   { return '| [`' + className + '`](lib/src/main/java/com/diffplug/spotless/' + className.replaceAll('\\.', '/') + '.java) | ' }
+function extra(className) { return '| [`' + className + '`](lib-extra/src/main/java/com/diffplug/spotless/extra/' + className.replaceAll('\\.', '/') + '.java) | ' }
 
 //                                               | GRADLE        | MAVEN        | SBT          | (new)   |
 output = [
@@ -61,6 +61,8 @@ lib('java.ImportOrderStep')                      +'{{yes}}       | {{yes}}
 lib('java.PalantirJavaFormatStep')               +'{{yes}}       | {{yes}}      | {{no}}       | {{no}}  |',
 lib('java.RemoveUnusedImportsStep')              +'{{yes}}       | {{yes}}      | {{yes}}      | {{no}}  |',
 extra('java.EclipseJdtFormatterStep')            +'{{yes}}       | {{yes}}      | {{yes}}      | {{no}}  |',
+lib('json.gson.GsonStep')                        +'{{yes}}       | {{no}}       | {{no}}       | {{no}}  |',
+lib('json.JsonSimpleStep')                       +'{{yes}}       | {{no}}       | {{no}}       | {{no}}  |',
 lib('kotlin.KtLintStep')                         +'{{yes}}       | {{yes}}      | {{yes}}      | {{no}}  |',
 lib('kotlin.KtfmtStep')                          +'{{yes}}       | {{yes}}      | {{no}}       | {{no}}  |',
 lib('kotlin.DiktatStep')                         +'{{yes}}       | {{yes}}      | {{no}}       | {{no}}  |',
@@ -102,6 +104,8 @@ extra('wtp.EclipseWtpFormatterStep')             +'{{yes}}       | {{yes}}
 | [`java.PalantirJavaFormatStep`](lib/src/main/java/com/diffplug/spotless/java/PalantirJavaFormatStep.java) | :+1:       | :+1:      | :white_large_square:       | :white_large_square:  |
 | [`java.RemoveUnusedImportsStep`](lib/src/main/java/com/diffplug/spotless/java/RemoveUnusedImportsStep.java) | :+1:       | :+1:      | :+1:      | :white_large_square:  |
 | [`java.EclipseJdtFormatterStep`](lib-extra/src/main/java/com/diffplug/spotless/extra/java/EclipseJdtFormatterStep.java) | :+1:       | :+1:      | :+1:      | :white_large_square:  |
+| [`json.gson.GsonStep`](lib/src/main/java/com/diffplug/spotless/json/gson/GsonStep.java) | :+1:       | :white_large_square:       | :white_large_square:       | :white_large_square:  |
+| [`json.JsonSimpleStep`](lib/src/main/java/com/diffplug/spotless/json/JsonSimpleStep.java) | :+1:       | :white_large_square:       | :white_large_square:       | :white_large_square:  |
 | [`kotlin.KtLintStep`](lib/src/main/java/com/diffplug/spotless/kotlin/KtLintStep.java) | :+1:       | :+1:      | :+1:      | :white_large_square:  |
 | [`kotlin.KtfmtStep`](lib/src/main/java/com/diffplug/spotless/kotlin/KtfmtStep.java) | :+1:       | :+1:      | :white_large_square:       | :white_large_square:  |
 | [`kotlin.DiktatStep`](lib/src/main/java/com/diffplug/spotless/kotlin/DiktatStep.java) | :+1:       | :+1:      | :white_large_square:       | :white_large_square:  |

lib/src/main/java/com/diffplug/spotless/json/gson/GsonBuilderWrapper.java

@@ -0,0 +1,54 @@
+/*
+ * Copyright 2022 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.spotless.json.gson;
+
+import java.lang.reflect.Constructor;
+import java.lang.reflect.Method;
+
+import com.diffplug.spotless.JarState;
+
+class GsonBuilderWrapper extends GsonWrapperBase {
+
+	private final Constructor<?> constructor;
+	private final Method serializeNullsMethod;
+	private final Method disableHtmlEscapingMethod;
+	private final Method createMethod;
+
+	GsonBuilderWrapper(JarState jarState) {
+		Class<?> clazz = loadClass(jarState.getClassLoader(), "com.google.gson.GsonBuilder");
+		this.constructor = getConstructor(clazz);
+		this.serializeNullsMethod = getMethod(clazz, "serializeNulls");
+		this.disableHtmlEscapingMethod = getMethod(clazz, "disableHtmlEscaping");
+		this.createMethod = getMethod(clazz, "create");
+	}
+
+	Object createGsonBuilder() {
+		return newInstance(constructor);
+	}
+
+	Object serializeNulls(Object gsonBuilder) {
+		return invoke(serializeNullsMethod, gsonBuilder);
+	}
+
+	Object disableHtmlEscaping(Object gsonBuilder) {
+		return invoke(disableHtmlEscapingMethod, gsonBuilder);
+	}
+
+	Object create(Object gsonBuilder) {
+		return invoke(createMethod, gsonBuilder);
+	}
+
+}

lib/src/main/java/com/diffplug/spotless/json/gson/GsonStep.java

@@ -0,0 +1,106 @@
+/*
+ * Copyright 2022 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.spotless.json.gson;
+
+import java.io.IOException;
+import java.io.Serializable;
+import java.io.StringWriter;
+import java.util.Collections;
+import java.util.Objects;
+
+import com.diffplug.spotless.FormatterFunc;
+import com.diffplug.spotless.FormatterStep;
+import com.diffplug.spotless.JarState;
+import com.diffplug.spotless.Provisioner;
+
+public class GsonStep {
+	private static final String MAVEN_COORDINATES = "com.google.code.gson:gson";
+
+	public static FormatterStep create(int indentSpaces, boolean sortByKeys, boolean escapeHtml, String version, Provisioner provisioner) {
+		Objects.requireNonNull(provisioner, "provisioner cannot be null");
+		return FormatterStep.createLazy("gson", () -> new State(indentSpaces, sortByKeys, escapeHtml, version, provisioner), State::toFormatter);
+	}
+
+	private static final class State implements Serializable {
+		private static final long serialVersionUID = -1493479043249379485L;
+
+		private final int indentSpaces;
+		private final boolean sortByKeys;
+		private final boolean escapeHtml;
+		private final JarState jarState;
+
+		private State(int indentSpaces, boolean sortByKeys, boolean escapeHtml, String version, Provisioner provisioner) throws IOException {
+			this.indentSpaces = indentSpaces;
+			this.sortByKeys = sortByKeys;
+			this.escapeHtml = escapeHtml;
+			this.jarState = JarState.from(MAVEN_COORDINATES + ":" + version, provisioner);
+		}
+
+		FormatterFunc toFormatter() {
+			JsonWriterWrapper jsonWriterWrapper = new JsonWriterWrapper(jarState);
+			JsonElementWrapper jsonElementWrapper = new JsonElementWrapper(jarState);
+			JsonObjectWrapper jsonObjectWrapper = new JsonObjectWrapper(jarState, jsonElementWrapper);
+			GsonBuilderWrapper gsonBuilderWrapper = new GsonBuilderWrapper(jarState);
+			GsonWrapper gsonWrapper = new GsonWrapper(jarState, jsonElementWrapper, jsonWriterWrapper);
+
+			Object gsonBuilder = gsonBuilderWrapper.serializeNulls(gsonBuilderWrapper.createGsonBuilder());
+			if (!escapeHtml) {
+				gsonBuilder = gsonBuilderWrapper.disableHtmlEscaping(gsonBuilder);
+			}
+			Object gson = gsonBuilderWrapper.create(gsonBuilder);
+
+			return inputString -> {
+				String result;
+				if (inputString.isEmpty()) {
+					result = "";
+				} else {
+					Object jsonElement = gsonWrapper.fromJson(gson, inputString, jsonElementWrapper.getWrappedClass());
+					if (jsonElement == null) {
+						throw new AssertionError(GsonWrapperBase.FAILED_TO_PARSE_ERROR_MESSAGE);
+					}
+					if (sortByKeys && jsonElementWrapper.isJsonObject(jsonElement)) {
+						jsonElement = sortByKeys(jsonObjectWrapper, jsonElementWrapper, jsonElement);
+					}
+					try (StringWriter stringWriter = new StringWriter()) {
+						Object jsonWriter = jsonWriterWrapper.createJsonWriter(stringWriter);
+						jsonWriterWrapper.setIndent(jsonWriter, generateIndent(indentSpaces));
+						gsonWrapper.toJson(gson, jsonElement, jsonWriter);
+						result = stringWriter + "\n";
+					}
+				}
+				return result;
+			};
+		}
+
+		private Object sortByKeys(JsonObjectWrapper jsonObjectWrapper, JsonElementWrapper jsonElementWrapper, Object jsonObject) {
+			Object result = jsonObjectWrapper.createJsonObject();
+			jsonObjectWrapper.keySet(jsonObject).stream().sorted()
+					.forEach(key -> {
+						Object element = jsonObjectWrapper.get(jsonObject, key);
+						if (jsonElementWrapper.isJsonObject(element)) {
+							element = sortByKeys(jsonObjectWrapper, jsonElementWrapper, element);
+						}
+						jsonObjectWrapper.add(result, key, element);
+					});
+			return result;
+		}
+
+		private String generateIndent(int indentSpaces) {
+			return String.join("", Collections.nCopies(indentSpaces, " "));
+		}
+	}
+
+}

lib/src/main/java/com/diffplug/spotless/json/gson/GsonWrapper.java

@@ -0,0 +1,41 @@
+/*
+ * Copyright 2022 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.spotless.json.gson;
+
+import java.lang.reflect.Method;
+
+import com.diffplug.spotless.JarState;
+
+class GsonWrapper extends GsonWrapperBase {
+
+	private final Method fromJsonMethod;
+	private final Method toJsonMethod;
+
+	GsonWrapper(JarState jarState, JsonElementWrapper jsonElementWrapper, JsonWriterWrapper jsonWriterWrapper) {
+		Class<?> clazz = loadClass(jarState.getClassLoader(), "com.google.gson.Gson");
+		this.fromJsonMethod = getMethod(clazz, "fromJson", String.class, Class.class);
+		this.toJsonMethod = getMethod(clazz, "toJson", jsonElementWrapper.getWrappedClass(), jsonWriterWrapper.getWrappedClass());
+	}
+
+	Object fromJson(Object gson, String json, Class<?> type) {
+		return invoke(fromJsonMethod, gson, json, type);
+	}
+
+	void toJson(Object gson, Object jsonElement, Object jsonWriter) {
+		invoke(toJsonMethod, gson, jsonElement, jsonWriter);
+	}
+
+}

lib/src/main/java/com/diffplug/spotless/json/gson/GsonWrapperBase.java

@@ -0,0 +1,71 @@
+/*
+ * Copyright 2022 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.spotless.json.gson;
+
+import java.lang.reflect.Constructor;
+import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.Method;
+
+abstract class GsonWrapperBase {
+
+	static final String INCOMPATIBLE_ERROR_MESSAGE = "There was a problem interacting with Gson; maybe you set an incompatible version?";
+	static final String FAILED_TO_PARSE_ERROR_MESSAGE = "Unable to format JSON";
+
+	protected final Class<?> loadClass(ClassLoader classLoader, String className) {
+		try {
+			return classLoader.loadClass(className);
+		} catch (ClassNotFoundException cause) {
+			throw new IllegalStateException(INCOMPATIBLE_ERROR_MESSAGE, cause);
+		}
+	}
+
+	protected final Constructor<?> getConstructor(Class<?> clazz, Class<?>... argumentTypes) {
+		try {
+			return clazz.getConstructor(argumentTypes);
+		} catch (NoSuchMethodException cause) {
+			throw new IllegalStateException(INCOMPATIBLE_ERROR_MESSAGE, cause);
+		}
+	}
+
+	protected final Method getMethod(Class<?> clazz, String name, Class<?>... argumentTypes) {
+		try {
+			return clazz.getMethod(name, argumentTypes);
+		} catch (NoSuchMethodException cause) {
+			throw new IllegalStateException(INCOMPATIBLE_ERROR_MESSAGE, cause);
+		}
+	}
+
+	protected final <T> T newInstance(Constructor<T> constructor, Object... args) {
+		try {
+			return constructor.newInstance(args);
+		} catch (InstantiationException | IllegalAccessException cause) {
+			throw new IllegalStateException(INCOMPATIBLE_ERROR_MESSAGE, cause);
+		} catch (InvocationTargetException cause) {
+			throw new AssertionError(FAILED_TO_PARSE_ERROR_MESSAGE, cause.getCause());
+		}
+	}
+
+	protected Object invoke(Method method, Object targetObject, Object... args) {
+		try {
+			return method.invoke(targetObject, args);
+		} catch (IllegalAccessException cause) {
+			throw new IllegalStateException(INCOMPATIBLE_ERROR_MESSAGE, cause);
+		} catch (InvocationTargetException cause) {
+			throw new AssertionError(FAILED_TO_PARSE_ERROR_MESSAGE, cause.getCause());
+		}
+	}
+
+}

lib/src/main/java/com/diffplug/spotless/json/gson/JsonElementWrapper.java

@@ -0,0 +1,40 @@
+/*
+ * Copyright 2022 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.spotless.json.gson;
+
+import java.lang.reflect.Method;
+
+import com.diffplug.spotless.JarState;
+
+class JsonElementWrapper extends GsonWrapperBase {
+
+	private final Class<?> clazz;
+	private final Method isJsonObjectMethod;
+
+	JsonElementWrapper(JarState jarState) {
+		this.clazz = loadClass(jarState.getClassLoader(), "com.google.gson.JsonElement");
+		this.isJsonObjectMethod = getMethod(clazz, "isJsonObject");
+	}
+
+	boolean isJsonObject(Object jsonElement) {
+		return (boolean) invoke(isJsonObjectMethod, jsonElement);
+	}
+
+	Class<?> getWrappedClass() {
+		return clazz;
+	}
+
+}