Make Object and JsonElement deserialization iterative

gson/src/main/java/com/google/gson/internal/bind/ObjectTypeAdapter.java

@@ -17,18 +17,19 @@
 package com.google.gson.internal.bind;
 
 import com.google.gson.Gson;
-import com.google.gson.ToNumberStrategy;
 import com.google.gson.ToNumberPolicy;
+import com.google.gson.ToNumberStrategy;
 import com.google.gson.TypeAdapter;
 import com.google.gson.TypeAdapterFactory;
 import com.google.gson.internal.LinkedTreeMap;
 import com.google.gson.reflect.TypeToken;
 import com.google.gson.stream.JsonReader;
 import com.google.gson.stream.JsonToken;
 import com.google.gson.stream.JsonWriter;
-
 import java.io.IOException;
+import java.util.ArrayDeque;
 import java.util.ArrayList;
+import java.util.Deque;
 import java.util.List;
 import java.util.Map;
 
@@ -70,42 +71,98 @@ public static TypeAdapterFactory getFactory(ToNumberStrategy toNumberStrategy) {
     }
   }
 
+  /**
+   * Tries to begin reading a JSON array or JSON object, returning {@code null} if
+   * the next element is neither of those.
+   */
+  private Object tryBeginNesting(JsonReader in, JsonToken peeked) throws IOException {
+    switch (peeked) {
+      case BEGIN_ARRAY:
+        in.beginArray();
+        return new ArrayList<>();
+      case BEGIN_OBJECT:
+        in.beginObject();
+        return new LinkedTreeMap<>();
+      default:
+        return null;
+    }
+  }
+
+  /** Reads an {@code Object} which cannot have any nested elements */
+  private Object readTerminal(JsonReader in, JsonToken peeked) throws IOException {
+    switch (peeked) {
+      case STRING:
+        return in.nextString();
+      case NUMBER:
+        return toNumberStrategy.readNumber(in);
+      case BOOLEAN:
+        return in.nextBoolean();
+      case NULL:
+        in.nextNull();
+        return null;
+      default:
+        // When read(JsonReader) is called with JsonReader in invalid state
+        throw new IllegalStateException("Unexpected token: " + peeked);
+    }
+  }
+
   @Override public Object read(JsonReader in) throws IOException {
-    JsonToken token = in.peek();
-    switch (token) {
-    case BEGIN_ARRAY:
-      List<Object> list = new ArrayList<>();
-      in.beginArray();
-      while (in.hasNext()) {
-        list.add(read(in));
-      }
-      in.endArray();
-      return list;
+    // Either List or Map
+    Object current;
+    JsonToken peeked = in.peek();
+
+    current = tryBeginNesting(in, peeked);
+    if (current == null) {
+      return readTerminal(in, peeked);
+    }
+
+    Deque<Object> stack = new ArrayDeque<>();
 
-    case BEGIN_OBJECT:
-      Map<String, Object> map = new LinkedTreeMap<>();
-      in.beginObject();
+    while (true) {
       while (in.hasNext()) {
-        map.put(in.nextName(), read(in));
-      }
-      in.endObject();
-      return map;
+        String name = null;
+        // Name is only used for JSON object members
+        if (current instanceof Map) {
+          name = in.nextName();
+        }
 
-    case STRING:
-      return in.nextString();
+        peeked = in.peek();
+        Object value = tryBeginNesting(in, peeked);
+        boolean isNesting = value != null;
 
-    case NUMBER:
-      return toNumberStrategy.readNumber(in);
+        if (value == null) {
+          value = readTerminal(in, peeked);
+        }
 
-    case BOOLEAN:
-      return in.nextBoolean();
+        if (current instanceof List) {
+          @SuppressWarnings("unchecked")
+          List<Object> list = (List<Object>) current;
+          list.add(value);
+        } else {
+          @SuppressWarnings("unchecked")
+          Map<String, Object> map = (Map<String, Object>) current;
+          map.put(name, value);
+        }
+
+        if (isNesting) {
+          stack.addLast(current);
+          current = value;
+        }
+      }
 
-    case NULL:
-      in.nextNull();
-      return null;
+      // End current element
+      if (current instanceof List) {
+        in.endArray();
+      } else {
+        in.endObject();
+      }
 
-    default:
-      throw new IllegalStateException();
+      if (stack.isEmpty()) {
+        return current;
+      } else {
+        // Continue with enclosing element
+        current = stack.removeLast();
+      }
     }
   }
 

gson/src/main/java/com/google/gson/internal/bind/TypeAdapters.java

@@ -16,6 +16,22 @@
 
 package com.google.gson.internal.bind;
 
+import com.google.gson.Gson;
+import com.google.gson.JsonArray;
+import com.google.gson.JsonElement;
+import com.google.gson.JsonIOException;
+import com.google.gson.JsonNull;
+import com.google.gson.JsonObject;
+import com.google.gson.JsonPrimitive;
+import com.google.gson.JsonSyntaxException;
+import com.google.gson.TypeAdapter;
+import com.google.gson.TypeAdapterFactory;
+import com.google.gson.annotations.SerializedName;
+import com.google.gson.internal.LazilyParsedNumber;
+import com.google.gson.reflect.TypeToken;
+import com.google.gson.stream.JsonReader;
+import com.google.gson.stream.JsonToken;
+import com.google.gson.stream.JsonWriter;
 import java.io.IOException;
 import java.lang.reflect.AccessibleObject;
 import java.lang.reflect.Field;
@@ -27,10 +43,12 @@
 import java.net.URL;
 import java.security.AccessController;
 import java.security.PrivilegedAction;
+import java.util.ArrayDeque;
 import java.util.ArrayList;
 import java.util.BitSet;
 import java.util.Calendar;
 import java.util.Currency;
+import java.util.Deque;
 import java.util.GregorianCalendar;
 import java.util.HashMap;
 import java.util.List;
@@ -42,23 +60,6 @@
 import java.util.concurrent.atomic.AtomicInteger;
 import java.util.concurrent.atomic.AtomicIntegerArray;
 
-import com.google.gson.Gson;
-import com.google.gson.JsonArray;
-import com.google.gson.JsonElement;
-import com.google.gson.JsonIOException;
-import com.google.gson.JsonNull;
-import com.google.gson.JsonObject;
-import com.google.gson.JsonPrimitive;
-import com.google.gson.JsonSyntaxException;
-import com.google.gson.TypeAdapter;
-import com.google.gson.TypeAdapterFactory;
-import com.google.gson.annotations.SerializedName;
-import com.google.gson.internal.LazilyParsedNumber;
-import com.google.gson.reflect.TypeToken;
-import com.google.gson.stream.JsonReader;
-import com.google.gson.stream.JsonToken;
-import com.google.gson.stream.JsonWriter;
-
 /**
  * Type adapters for basic types.
  */
@@ -695,44 +696,99 @@ public void write(JsonWriter out, Locale value) throws IOException {
   public static final TypeAdapterFactory LOCALE_FACTORY = newFactory(Locale.class, LOCALE);
 
   public static final TypeAdapter<JsonElement> JSON_ELEMENT = new TypeAdapter<JsonElement>() {
+    /**
+     * Tries to begin reading a JSON array or JSON object, returning {@code null} if
+     * the next element is neither of those.
+     */
+    private JsonElement tryBeginNesting(JsonReader in, JsonToken peeked) throws IOException {
+      switch (peeked) {
+        case BEGIN_ARRAY:
+          in.beginArray();
+          return new JsonArray();
+        case BEGIN_OBJECT:
+          in.beginObject();
+          return new JsonObject();
+        default:
+          return null;
+      }
+    }
+
+    /** Reads a {@link JsonElement} which cannot have any nested elements */
+    private JsonElement readTerminal(JsonReader in, JsonToken peeked) throws IOException {
+      switch (peeked) {
+        case STRING:
+          return new JsonPrimitive(in.nextString());
+        case NUMBER:
+          String number = in.nextString();
+          return new JsonPrimitive(new LazilyParsedNumber(number));
+        case BOOLEAN:
+          return new JsonPrimitive(in.nextBoolean());
+        case NULL:
+          in.nextNull();
+          return JsonNull.INSTANCE;
+        default:
+          // When read(JsonReader) is called with JsonReader in invalid state
+          throw new IllegalStateException("Unexpected token: " + peeked);
+      }
+    }
+
     @Override public JsonElement read(JsonReader in) throws IOException {
       if (in instanceof JsonTreeReader) {
         return ((JsonTreeReader) in).nextJsonElement();
       }
 
-      switch (in.peek()) {
-      case STRING:
-        return new JsonPrimitive(in.nextString());
-      case NUMBER:
-        String number = in.nextString();
-        return new JsonPrimitive(new LazilyParsedNumber(number));
-      case BOOLEAN:
-        return new JsonPrimitive(in.nextBoolean());
-      case NULL:
-        in.nextNull();
-        return JsonNull.INSTANCE;
-      case BEGIN_ARRAY:
-        JsonArray array = new JsonArray();
-        in.beginArray();
+      // Either JsonArray or JsonObject
+      JsonElement current;
+      JsonToken peeked = in.peek();
+
+      current = tryBeginNesting(in, peeked);
+      if (current == null) {
+        return readTerminal(in, peeked);
+      }
+
+      Deque<JsonElement> stack = new ArrayDeque<>();
+
+      while (true) {
         while (in.hasNext()) {
-          array.add(read(in));
+          String name = null;
+          // Name is only used for JSON object members
+          if (current instanceof JsonObject) {
+            name = in.nextName();
+          }
+
+          peeked = in.peek();
+          JsonElement value = tryBeginNesting(in, peeked);
+          boolean isNesting = value != null;
+
+          if (value == null) {
+            value = readTerminal(in, peeked);
+          }
+
+          if (current instanceof JsonArray) {
+            ((JsonArray) current).add(value);
+          } else {
+            ((JsonObject) current).add(name, value);
+          }
+
+          if (isNesting) {
+            stack.addLast(current);
+            current = value;
+          }
         }
-        in.endArray();
-        return array;
-      case BEGIN_OBJECT:
-        JsonObject object = new JsonObject();
-        in.beginObject();
-        while (in.hasNext()) {
-          object.add(in.nextName(), read(in));
+
+        // End current element
+        if (current instanceof JsonArray) {
+          in.endArray();
+        } else {
+          in.endObject();
+        }
+
+        if (stack.isEmpty()) {
+          return current;
+        } else {
+          // Continue with enclosing element
+          current = stack.removeLast();
         }
-        in.endObject();
-        return object;
-      case END_DOCUMENT:
-      case NAME:
-      case END_OBJECT:
-      case END_ARRAY:
-      default:
-        throw new IllegalArgumentException();
       }
     }
 
@@ -803,7 +859,7 @@ public EnumTypeAdapter(final Class<T> classOfT) {
           T constant = (T)(constantField.get(null));
           String name = constant.name();
           String toStringVal = constant.toString();
-          
+
           SerializedName annotation = constantField.getAnnotation(SerializedName.class);
           if (annotation != null) {
             name = annotation.value();

gson/src/test/java/com/google/gson/JsonParserParameterizedTest.java

@@ -0,0 +1,41 @@
+package com.google.gson;
+
+import static org.junit.Assert.assertEquals;
+
+import java.io.IOException;
+import java.util.Arrays;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.Parameterized;
+import org.junit.runners.Parameterized.Parameter;
+import org.junit.runners.Parameterized.Parameters;
+
+@RunWith(Parameterized.class)
+public class JsonParserParameterizedTest {
+  @Parameters
+  public static Iterable<String> data() {
+    return Arrays.asList(
+      "[]",
+      "{}",
+      "null",
+      "1.0",
+      "true",
+      "\"string\"",
+      "[true,1.0,null,{},2.0,{\"a\":[false]},[3.0,\"test\"],4.0]",
+      "{\"\":1.0,\"a\":true,\"b\":null,\"c\":[],\"d\":{\"a1\":2.0,\"b2\":[true,{\"a3\":3.0}]},\"e\":[{\"f\":4.0},\"test\"]}"
+    );
+  }
+
+  private final TypeAdapter<JsonElement> adapter = new Gson().getAdapter(JsonElement.class);
+  @Parameter
+  public String json;
+
+  @Test
+  public void testParse() throws IOException {
+    JsonElement deserialized = JsonParser.parseString(json);
+    String actualSerialized = adapter.toJson(deserialized);
+
+    // Serialized JsonElement should be the same as original JSON
+    assertEquals(json, actualSerialized);
+  }
+}