Change the adapter for Object.class to delegate.

moshi/src/main/java/com/squareup/moshi/StandardJsonAdapters.java

@@ -20,6 +20,7 @@
 import java.lang.reflect.Type;
 import java.util.Arrays;
 import java.util.Collection;
+import java.util.List;
 import java.util.Map;
 import java.util.Set;
 
@@ -266,13 +267,45 @@ static final class EnumJsonAdapter<T extends Enum<T>> extends JsonAdapter<T> {
    */
   static final class ObjectJsonAdapter extends JsonAdapter<Object> {
     private final Moshi moshi;
+    private final JsonAdapter<List> listJsonAdapter;
+    private final JsonAdapter<Map> mapAdapter;
+    private final JsonAdapter<String> stringAdapter;
+    private final JsonAdapter<Double> doubleAdapter;
+    private final JsonAdapter<Boolean> booleanAdapter;
 
     ObjectJsonAdapter(Moshi moshi) {
       this.moshi = moshi;
+      this.listJsonAdapter = moshi.adapter(List.class);
+      this.mapAdapter = moshi.adapter(Map.class);
+      this.stringAdapter = moshi.adapter(String.class);
+      this.doubleAdapter = moshi.adapter(Double.class);
+      this.booleanAdapter = moshi.adapter(Boolean.class);
     }
 
     @Override public Object fromJson(JsonReader reader) throws IOException {
-      return reader.readJsonValue();
+      switch (reader.peek()) {
+        case BEGIN_ARRAY:
+          return listJsonAdapter.fromJson(reader);
+
+        case BEGIN_OBJECT:
+          return mapAdapter.fromJson(reader);
+
+        case STRING:
+          return stringAdapter.fromJson(reader);
+
+        case NUMBER:
+          return doubleAdapter.fromJson(reader);
+
+        case BOOLEAN:
+          return booleanAdapter.fromJson(reader);
+
+        case NULL:
+          return reader.nextNull();
+
+        default:
+          throw new IllegalStateException(
+              "Expected a value but was " + reader.peek() + " at path " + reader.getPath());
+      }
     }
 
     @Override public void toJson(JsonWriter writer, Object value) throws IOException {

moshi/src/test/java/com/squareup/moshi/ObjectAdapterTest.java

@@ -15,6 +15,10 @@
  */
 package com.squareup.moshi;
 
+import java.io.IOException;
+import java.lang.annotation.Annotation;
+import java.lang.reflect.Type;
+import java.math.BigDecimal;
 import java.util.AbstractCollection;
 import java.util.AbstractList;
 import java.util.AbstractMap;
@@ -26,12 +30,17 @@
 import java.util.Iterator;
 import java.util.LinkedHashMap;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import java.util.Set;
+import javax.annotation.Nullable;
 import org.junit.Ignore;
 import org.junit.Test;
 
+import static java.util.Collections.singletonList;
+import static java.util.Collections.singletonMap;
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.entry;
 
 public final class ObjectAdapterTest {
   @Test public void toJsonUsesRuntimeType() throws Exception {
@@ -170,6 +179,107 @@ public final class ObjectAdapterTest {
     assertThat(adapter.toJson(Arrays.asList(new Date(1), new Date(2)))).isEqualTo("[1,2]");
   }
 
+  /**
+   * Confirm that the built-in adapter for Object delegates to user-supplied adapters for JSON value
+   * types like strings.
+   */
+  @Test public void objectAdapterDelegatesStringNamesAndValues() throws Exception {
+    JsonAdapter<String> stringAdapter = new JsonAdapter<String>() {
+      @Nullable @Override public String fromJson(JsonReader reader) throws IOException {
+        return reader.nextString().toUpperCase(Locale.US);
+      }
+
+      @Override public void toJson(JsonWriter writer, @Nullable String value) {
+        throw new UnsupportedOperationException();
+      }
+    };
+
+    Moshi moshi = new Moshi.Builder()
+        .add(String.class, stringAdapter)
+        .build();
+    JsonAdapter<Object> objectAdapter = moshi.adapter(Object.class);
+    Map<?, ?> value = (Map<?, ?>) objectAdapter.fromJson("{\"a\":\"b\", \"c\":\"d\"}");
+    assertThat(value).containsExactly(entry("A", "B"), entry("C", "D"));
+  }
+
+  /**
+   * Confirm that the built-in adapter for Object delegates to any user-supplied adapters for
+   * Object. This is necessary to customize adapters for primitives like numbers.
+   */
+  @Test public void objectAdapterDelegatesObjects() throws Exception {
+    JsonAdapter.Factory objectFactory = new JsonAdapter.Factory() {
+      @Override public @Nullable JsonAdapter<?> create(
+          Type type, Set<? extends Annotation> annotations, Moshi moshi) {
+        if (type != Object.class) return null;
+
+        final JsonAdapter<Object> delegate = moshi.nextAdapter(this, Object.class, annotations);
+        return new JsonAdapter<Object>() {
+          @Override public @Nullable Object fromJson(JsonReader reader) throws IOException {
+            if (reader.peek() != JsonReader.Token.NUMBER) {
+              return delegate.fromJson(reader);
+            } else {
+              return new BigDecimal(reader.nextString());
+            }
+          }
+
+          @Override public void toJson(JsonWriter writer, @Nullable Object value) {
+            throw new UnsupportedOperationException();
+          }
+        };
+      }
+    };
+
+    Moshi moshi = new Moshi.Builder()
+        .add(objectFactory)
+        .build();
+    JsonAdapter<Object> objectAdapter = moshi.adapter(Object.class);
+    List<?> value = (List<?>) objectAdapter.fromJson("[0, 1, 2.0, 3.14]");
+    assertThat(value).isEqualTo(Arrays.asList(new BigDecimal("0"), new BigDecimal("1"),
+        new BigDecimal("2.0"), new BigDecimal("3.14")));
+  }
+
+  /** Confirm that the built-in adapter for Object delegates to user-supplied adapters for lists. */
+  @Test public void objectAdapterDelegatesLists() throws Exception {
+    JsonAdapter<List<?>> listAdapter = new JsonAdapter<List<?>>() {
+      @Override public @Nullable List<?> fromJson(JsonReader reader) throws IOException {
+        reader.skipValue();
+        return singletonList("z");
+      }
+
+      @Override public void toJson(JsonWriter writer, @Nullable List<?> value) {
+        throw new UnsupportedOperationException();
+      }
+    };
+
+    Moshi moshi = new Moshi.Builder()
+        .add(List.class, listAdapter)
+        .build();
+    JsonAdapter<Object> objectAdapter = moshi.adapter(Object.class);
+    Map<?, ?> mapOfList = (Map<?, ?>) objectAdapter.fromJson("{\"a\":[\"b\"]}");
+    assertThat(mapOfList).isEqualTo(singletonMap("a", singletonList("z")));
+  }
+
+  /** Confirm that the built-in adapter for Object delegates to user-supplied adapters for maps. */
+  @Test public void objectAdapterDelegatesMaps() throws Exception {
+    JsonAdapter<Map<?, ?>> mapAdapter = new JsonAdapter<Map<?, ?>>() {
+      @Override public @Nullable Map<?, ?> fromJson(JsonReader reader) throws IOException {
+        reader.skipValue();
+        return singletonMap("x", "y");
+      }
+
+      @Override public void toJson(JsonWriter writer, @Nullable Map<?, ?> value) {
+        throw new UnsupportedOperationException();
+      }
+    };
+
+    Moshi moshi = new Moshi.Builder()
+        .add(Map.class, mapAdapter)
+        .build();
+    JsonAdapter<Object> objectAdapter = moshi.adapter(Object.class);
+    List<?> listOfMap = (List<?>) objectAdapter.fromJson("[{\"b\":\"c\"}]");
+    assertThat(listOfMap).isEqualTo(singletonList(singletonMap("x", "y")));
+  }
+
   static class Delivery {
     String address;
     List<Object> items;