Bye bye Groovy, you won't be missed :(

src/main/java/io/kamax/mxisd/util/GsonParser.java

@@ -0,0 +1,96 @@
+/*
+ * mxisd - Matrix Identity Server Daemon
+ * Copyright (C) 2017 Maxime Dor
+ *
+ * https://max.kamax.io/
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, either version 3 of the
+ * License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package io.kamax.mxisd.util;
+
+import com.google.gson.*;
+import io.kamax.mxisd.exception.InvalidResponseJsonException;
+import io.kamax.mxisd.exception.JsonMemberNotFoundException;
+import org.apache.commons.io.IOUtils;
+import org.apache.http.HttpResponse;
+
+import javax.servlet.http.HttpServletRequest;
+import java.io.IOException;
+import java.io.InputStream;
+import java.nio.charset.StandardCharsets;
+import java.util.Optional;
+
+public class GsonParser {
+
+    private JsonParser parser = new JsonParser();
+    private Gson gson;
+
+    public GsonParser() {
+        this(new GsonBuilder().setFieldNamingPolicy(FieldNamingPolicy.LOWER_CASE_WITH_UNDERSCORES).create());
+    }
+
+    public GsonParser(Gson gson) {
+        this.gson = gson;
+    }
+
+    public JsonObject parse(InputStream stream) throws IOException {
+        JsonElement el = parser.parse(IOUtils.toString(stream, StandardCharsets.UTF_8));
+        if (!el.isJsonObject()) {
+            throw new InvalidResponseJsonException("Response body is not a JSON object");
+        }
+
+        return el.getAsJsonObject();
+    }
+
+    public <T> T parse(HttpServletRequest req, Class<T> type) throws IOException {
+        return gson.fromJson(parse(req.getInputStream()), type);
+    }
+
+    public <T> T parse(HttpResponse res, Class<T> type) throws IOException {
+        return gson.fromJson(parse(res.getEntity().getContent()), type);
+    }
+
+    public JsonObject parse(InputStream stream, String property) throws IOException {
+        JsonObject obj = parse(stream);
+        if (!obj.has(property)) {
+            throw new JsonMemberNotFoundException("Member " + property + " does not exist");
+        }
+
+        JsonElement el = obj.get(property);
+        if (!el.isJsonObject()) {
+            throw new InvalidResponseJsonException("Member " + property + " is not a JSON object");
+        }
+
+        return el.getAsJsonObject();
+    }
+
+    public <T> T parse(InputStream stream, String memberName, Class<T> type) throws IOException {
+        JsonObject obj = parse(stream, memberName);
+        return gson.fromJson(obj, type);
+    }
+
+    public <T> T parse(HttpResponse res, String memberName, Class<T> type) throws IOException {
+        return parse(res.getEntity().getContent(), memberName, type);
+    }
+
+    public <T> Optional<T> parseOptional(HttpResponse res, String memberName, Class<T> type) throws IOException {
+        try {
+            return Optional.of(parse(res.getEntity().getContent(), memberName, type));
+        } catch (JsonMemberNotFoundException e) {
+            return Optional.empty();
+        }
+    }
+
+}