Merge pull request #222 from square/jwilson.0117.object_json_reader

First step of a JsonReader that reads a DOM.

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

@@ -0,0 +1,290 @@
+/*
+ * Copyright (C) 2017 Square, Inc.
+ *
+ * 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.squareup.moshi;
+
+import java.io.IOException;
+import java.util.Arrays;
+import java.util.Iterator;
+import java.util.List;
+import java.util.ListIterator;
+import java.util.Map;
+
+/**
+ * This class reads a JSON document by traversing a Java object comprising maps, lists, and JSON
+ * primitives. It does depth-first traversal keeping a stack starting with the root object. During
+ * traversal a stack tracks the current position in the document:
+ *
+ * <ul>
+ *   <li>The next element to act upon is on the top of the stack.
+ *   <li>When the top of the stack is a {@link List}, calling {@link #beginArray()} replaces the
+ *       list with a {@link ListIterator}. The first element of the iterator is pushed on top of the
+ *       iterator.
+ *   <li>Similarly, when the top of the stack is a {@link Map}, calling {@link #beginObject()}
+ *       replaces the map with an {@link Iterator} of its entries. The first element of the iterator
+ *       is pushed on top of the iterator.
+ *   <li>When the top of the stack is a {@link Map.Entry}, calling {@link #nextName()} returns the
+ *       entry's key and replaces the entry with its value on the stack.
+ *   <li>When an element is consumed it is popped. If the new top of the stack has a non-exhausted
+ *       iterator, the next element of that iterator is pushed.
+ *   <li>If the top of the stack is an exhausted iterator, calling {@link #endArray} or {@link
+ *       #endObject} will pop it.
+ * </ul>
+ */
+final class ObjectJsonReader extends JsonReader {
+  /** Sentinel object pushed on {@link #stack} when the reader is closed. */
+  private static final Object JSON_READER_CLOSED = new Object();
+
+  private int stackSize = 0;
+  private final Object[] stack = new Object[32];
+  private final int[] scopes = new int[32];
+  private final String[] pathNames = new String[32];
+  private final int[] pathIndices = new int[32];
+  private boolean lenient;
+  private boolean failOnUnknown;
+
+  public ObjectJsonReader(Object root) {
+    scopes[stackSize] = JsonScope.NONEMPTY_DOCUMENT;
+    stack[stackSize++] = root;
+  }
+
+  @Override public void setLenient(boolean lenient) {
+    this.lenient = lenient;
+  }
+
+  @Override public boolean isLenient() {
+    return lenient;
+  }
+
+  @Override public void setFailOnUnknown(boolean failOnUnknown) {
+    this.failOnUnknown = failOnUnknown;
+  }
+
+  @Override public boolean failOnUnknown() {
+    return failOnUnknown;
+  }
+
+  @Override public void beginArray() throws IOException {
+    List<?> peeked = require(List.class, Token.BEGIN_ARRAY);
+
+    ListIterator<?> iterator = peeked.listIterator();
+    stack[stackSize - 1] = iterator;
+    scopes[stackSize - 1] = JsonScope.EMPTY_ARRAY;
+    pathIndices[stackSize - 1] = 0;
+
+    // If the iterator isn't empty push its first value onto the stack.
+    if (iterator.hasNext()) {
+      stack[stackSize] = iterator.next();
+      stackSize++;
+    }
+  }
+
+  @Override public void endArray() throws IOException {
+    ListIterator<?> peeked = require(ListIterator.class, Token.END_ARRAY);
+    if (peeked.hasNext()) {
+      throw new JsonDataException(
+          "Expected " + Token.END_ARRAY + " but was " + peek() + " at path " + getPath());
+    }
+    remove();
+  }
+
+  @Override public void beginObject() throws IOException {
+    Map<?, ?> peeked = require(Map.class, Token.BEGIN_OBJECT);
+
+    Iterator<?> iterator = peeked.entrySet().iterator();
+    stack[stackSize - 1] = iterator;
+    scopes[stackSize - 1] = JsonScope.EMPTY_OBJECT;
+
+    // If the iterator isn't empty push its first value onto the stack.
+    if (iterator.hasNext()) {
+      stack[stackSize] = iterator.next();
+      stackSize++;
+    }
+  }
+
+  @Override public void endObject() throws IOException {
+    Iterator<?> peeked = require(Iterator.class, Token.END_OBJECT);
+    if (peeked instanceof ListIterator || peeked.hasNext()) {
+      throw new JsonDataException(
+          "Expected " + Token.END_OBJECT + " but was " + peek() + " at path " + getPath());
+    }
+    pathNames[stackSize - 1] = null;
+    remove();
+  }
+
+  @Override public boolean hasNext() throws IOException {
+    // TODO(jwilson): this is consistent with BufferedSourceJsonReader but it doesn't make sense.
+    if (stackSize == 0) return true;
+
+    Object peeked = stack[stackSize - 1];
+    return !(peeked instanceof Iterator) || ((Iterator) peeked).hasNext();
+  }
+
+  @Override public Token peek() throws IOException {
+    if (stackSize == 0) return Token.END_DOCUMENT;
+
+    // If the top of the stack is an iterator, take its first element and push it on the stack.
+    Object peeked = stack[stackSize - 1];
+    if (peeked instanceof ListIterator) return Token.END_ARRAY;
+    if (peeked instanceof Iterator) return Token.END_OBJECT;
+    if (peeked instanceof List) return Token.BEGIN_ARRAY;
+    if (peeked instanceof Map) return Token.BEGIN_OBJECT;
+    if (peeked instanceof Map.Entry) return Token.NAME;
+    if (peeked instanceof String) return Token.STRING;
+    if (peeked instanceof Boolean) return Token.BOOLEAN;
+    if (peeked instanceof Number) return Token.NUMBER;
+    if (peeked == null) return Token.NULL;
+    if (peeked == JSON_READER_CLOSED) throw new IllegalStateException("JsonReader is closed");
+
+    throw new JsonDataException("Expected a JSON value but was a " + peeked.getClass().getName()
+        + " at path " + getPath());
+  }
+
+  @Override public String nextName() throws IOException {
+    Object peeked = require(Map.Entry.class, Token.NAME);
+
+    // Swap the Map.Entry for its value on the stack and return its key.
+    String result = (String) ((Map.Entry<?, ?>) peeked).getKey();
+    stack[stackSize - 1] = ((Map.Entry<?, ?>) peeked).getValue();
+    pathNames[stackSize - 2] = result;
+    return result;
+  }
+
+  @Override int selectName(Options options) throws IOException {
+    throw new UnsupportedOperationException();
+  }
+
+  @Override public String nextString() throws IOException {
+    String peeked = require(String.class, Token.STRING);
+    remove();
+    return peeked;
+  }
+
+  @Override int selectString(Options options) throws IOException {
+    throw new UnsupportedOperationException();
+  }
+
+  @Override public boolean nextBoolean() throws IOException {
+    Boolean peeked = require(Boolean.class, Token.BOOLEAN);
+    remove();
+    return peeked;
+  }
+
+  @Override public <T> T nextNull() throws IOException {
+    require(Void.class, Token.NULL);
+    remove();
+    return null;
+  }
+
+  @Override public double nextDouble() throws IOException {
+    Number peeked = require(Number.class, Token.NUMBER);
+    remove();
+    return peeked.doubleValue(); // TODO(jwilson): precision check?
+  }
+
+  @Override public long nextLong() throws IOException {
+    Number peeked = require(Number.class, Token.NUMBER);
+    remove();
+    return peeked.longValue(); // TODO(jwilson): precision check?
+  }
+
+  @Override public int nextInt() throws IOException {
+    Number peeked = require(Number.class, Token.NUMBER);
+    remove();
+    return peeked.intValue(); // TODO(jwilson): precision check?
+  }
+
+  @Override public void skipValue() throws IOException {
+    if (failOnUnknown) {
+      throw new JsonDataException("Cannot skip unexpected " + peek() + " at " + getPath());
+    }
+
+    // If this element is in an object clear out the key.
+    if (stackSize > 1) {
+      pathNames[stackSize - 2] = "null";
+    }
+
+    Object skipped = stackSize != 0 ? stack[stackSize - 1] : null;
+
+    if (skipped instanceof Map.Entry) {
+      // We're skipping a name. Promote the map entry's value.
+      Map.Entry<?, ?> entry = (Map.Entry<?, ?>) stack[stackSize - 1];
+      stack[stackSize - 1] = entry.getValue();
+    } else if (stackSize > 0) {
+      // We're skipping a value.
+      remove();
+    }
+  }
+
+  @Override public String getPath() {
+    return JsonScope.getPath(stackSize, scopes, pathNames, pathIndices);
+  }
+
+  @Override void promoteNameToValue() throws IOException {
+    Object peeked = require(Map.Entry.class, Token.NAME);
+
+    stackSize++;
+    stack[stackSize - 2] = ((Map.Entry<?, ?>) peeked).getValue();
+    stack[stackSize - 1] = ((Map.Entry<?, ?>) peeked).getKey();
+  }
+
+  @Override public void close() throws IOException {
+    Arrays.fill(stack, 0, stackSize, null);
+    stack[0] = JSON_READER_CLOSED;
+    scopes[0] = JsonScope.CLOSED;
+    stackSize = 1;
+  }
+
+  /**
+   * Returns the top of the stack which is required to be a {@code type}. Throws if this reader is
+   * closed, or if the type isn't what was expected.
+   */
+  private <T> T require(Class<T> type, Token expected) throws IOException {
+    Object peeked = (stackSize != 0 ? stack[stackSize - 1] : null);
+
+    if (type.isInstance(peeked)) {
+      return type.cast(peeked);
+    }
+    if (peeked == null && expected == Token.NULL) {
+      return null;
+    }
+    if (peeked == JSON_READER_CLOSED) {
+      throw new IllegalStateException("JsonReader is closed");
+    }
+    throw new JsonDataException(
+        "Expected " + expected + " but was " + peek() + " at path " + getPath());
+  }
+
+  /**
+   * Removes a value and prepares for the next. If we're iterating a map or list this advances the
+   * iterator.
+   */
+  private void remove() {
+    stackSize--;
+    stack[stackSize] = null;
+    scopes[stackSize] = 0;
+
+    // If we're iterating an array or an object push its next element on to the stack.
+    if (stackSize > 0) {
+      pathIndices[stackSize - 1]++;
+
+      Object parent = stack[stackSize - 1];
+      if (parent instanceof Iterator && ((Iterator<?>) parent).hasNext()) {
+        stack[stackSize] = ((Iterator<?>) parent).next();
+        stackSize++;
+      }
+    }
+  }
+}

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

@@ -16,14 +16,50 @@
 package com.squareup.moshi;
 
 import java.io.IOException;
+import java.util.Arrays;
+import java.util.List;
+import okio.Buffer;
 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;
 
-import static com.squareup.moshi.TestUtil.newReader;
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.junit.Assume.assumeTrue;
 
+@RunWith(Parameterized.class)
 public final class JsonReaderPathTest {
+  interface Factory {
+    Factory BUFFERED_SOURCE = new Factory() {
+      @Override public JsonReader newReader(String json) {
+        Buffer buffer = new Buffer().writeUtf8(json);
+        return JsonReader.of(buffer);
+      }
+    };
+
+    Factory JSON_OBJECT = new Factory() {
+      @Override public JsonReader newReader(String json) throws IOException {
+        Moshi moshi = new Moshi.Builder().build();
+        Object object = moshi.adapter(Object.class).fromJson(json);
+        return new ObjectJsonReader(object);
+      }
+    };
+
+    JsonReader newReader(String json) throws IOException;
+  }
+
+  @Parameters(name = "{0}")
+  public static List<Object[]> parameters() {
+    return Arrays.asList(
+        new Object[] { Factory.BUFFERED_SOURCE},
+        new Object[] { Factory.JSON_OBJECT});
+  }
+
+  @Parameter public Factory factory;
+
   @Test public void path() throws IOException {
-    JsonReader reader = newReader("{\"a\":[2,true,false,null,\"b\",{\"c\":\"d\"},[3]]}");
+    JsonReader reader = factory.newReader("{\"a\":[2,true,false,null,\"b\",{\"c\":\"d\"},[3]]}");
     assertThat(reader.getPath()).isEqualTo("$");
     reader.beginObject();
     assertThat(reader.getPath()).isEqualTo("$.");
@@ -62,7 +98,7 @@ public final class JsonReaderPathTest {
   }
 
   @Test public void arrayOfObjects() throws IOException {
-    JsonReader reader = newReader("[{},{},{}]");
+    JsonReader reader = factory.newReader("[{},{},{}]");
     reader.beginArray();
     assertThat(reader.getPath()).isEqualTo("$[0]");
     reader.beginObject();
@@ -82,7 +118,7 @@ public final class JsonReaderPathTest {
   }
 
   @Test public void arrayOfArrays() throws IOException {
-    JsonReader reader = newReader("[[],[],[]]");
+    JsonReader reader = factory.newReader("[[],[],[]]");
     reader.beginArray();
     assertThat(reader.getPath()).isEqualTo("$[0]");
     reader.beginArray();
@@ -102,7 +138,7 @@ public final class JsonReaderPathTest {
   }
 
   @Test public void objectPath() throws IOException {
-    JsonReader reader = newReader("{\"a\":1,\"b\":2}");
+    JsonReader reader = factory.newReader("{\"a\":1,\"b\":2}");
     assertThat(reader.getPath()).isEqualTo("$");
 
     reader.peek();
@@ -142,7 +178,7 @@ public final class JsonReaderPathTest {
   }
 
   @Test public void arrayPath() throws IOException {
-    JsonReader reader = newReader("[1,2]");
+    JsonReader reader = factory.newReader("[1,2]");
     assertThat(reader.getPath()).isEqualTo("$");
 
     reader.peek();
@@ -172,7 +208,9 @@ public final class JsonReaderPathTest {
   }
 
   @Test public void multipleTopLevelValuesInOneDocument() throws IOException {
-    JsonReader reader = newReader("[][]");
+    assumeTrue(factory != Factory.JSON_OBJECT);
+
+    JsonReader reader = factory.newReader("[][]");
     reader.setLenient(true);
     reader.beginArray();
     reader.endArray();
@@ -183,7 +221,7 @@ public final class JsonReaderPathTest {
   }
 
   @Test public void skipArrayElements() throws IOException {
-    JsonReader reader = newReader("[1,2,3]");
+    JsonReader reader = factory.newReader("[1,2,3]");
     reader.beginArray();
     reader.skipValue();
     reader.skipValue();
@@ -191,14 +229,14 @@ public final class JsonReaderPathTest {
   }
 
   @Test public void skipObjectNames() throws IOException {
-    JsonReader reader = newReader("{\"a\":1}");
+    JsonReader reader = factory.newReader("{\"a\":1}");
     reader.beginObject();
     reader.skipValue();
     assertThat(reader.getPath()).isEqualTo("$.null");
   }
 
   @Test public void skipObjectValues() throws IOException {
-    JsonReader reader = newReader("{\"a\":1,\"b\":2}");
+    JsonReader reader = factory.newReader("{\"a\":1,\"b\":2}");
     reader.beginObject();
     reader.nextName();
     reader.skipValue();
@@ -208,7 +246,7 @@ public final class JsonReaderPathTest {
   }
 
   @Test public void skipNestedStructures() throws IOException {
-    JsonReader reader = newReader("[[1,2,3],4]");
+    JsonReader reader = factory.newReader("[[1,2,3],4]");
     reader.beginArray();
     reader.skipValue();
     assertThat(reader.getPath()).isEqualTo("$[1]");

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

@@ -0,0 +1,325 @@
+/*
+ * Copyright (C) 2017 Square, Inc.
+ *
+ * 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.squareup.moshi;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Map;
+import org.junit.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.junit.Assert.fail;
+
+public final class ObjectJsonReaderTest {
+  @Test public void array() throws Exception {
+    List<Object> root = new ArrayList<>();
+    root.add("s");
+    root.add(1.5d);
+    root.add(true);
+    root.add(null);
+    JsonReader reader = new ObjectJsonReader(root);
+
+    assertThat(reader.hasNext()).isTrue();
+    assertThat(reader.peek()).isEqualTo(JsonReader.Token.BEGIN_ARRAY);
+    reader.beginArray();
+
+    assertThat(reader.hasNext()).isTrue();
+    assertThat(reader.peek()).isEqualTo(JsonReader.Token.STRING);
+    assertThat(reader.nextString()).isEqualTo("s");
+
+    assertThat(reader.hasNext()).isTrue();
+    assertThat(reader.peek()).isEqualTo(JsonReader.Token.NUMBER);
+    assertThat(reader.nextDouble()).isEqualTo(1.5d);
+
+    assertThat(reader.hasNext()).isTrue();
+    assertThat(reader.peek()).isEqualTo(JsonReader.Token.BOOLEAN);
+    assertThat(reader.nextBoolean()).isEqualTo(true);
+
+    assertThat(reader.hasNext()).isTrue();
+    assertThat(reader.peek()).isEqualTo(JsonReader.Token.NULL);
+    assertThat(reader.nextNull()).isNull();
+
+    assertThat(reader.hasNext()).isFalse();
+    assertThat(reader.peek()).isEqualTo(JsonReader.Token.END_ARRAY);
+    reader.endArray();
+
+    assertThat(reader.peek()).isEqualTo(JsonReader.Token.END_DOCUMENT);
+  }
+
+  @Test public void object() throws Exception {
+    Map<String, Object> root = new LinkedHashMap<>();
+    root.put("a", "s");
+    root.put("b", 1.5d);
+    root.put("c", true);
+    root.put("d", null);
+    JsonReader reader = new ObjectJsonReader(root);
+
+    assertThat(reader.hasNext()).isTrue();
+    assertThat(reader.peek()).isEqualTo(JsonReader.Token.BEGIN_OBJECT);
+    reader.beginObject();
+
+    assertThat(reader.hasNext()).isTrue();
+    assertThat(reader.peek()).isEqualTo(JsonReader.Token.NAME);
+    assertThat(reader.nextName()).isEqualTo("a");
+    assertThat(reader.peek()).isEqualTo(JsonReader.Token.STRING);
+    assertThat(reader.nextString()).isEqualTo("s");
+
+    assertThat(reader.hasNext()).isTrue();
+    assertThat(reader.peek()).isEqualTo(JsonReader.Token.NAME);
+    assertThat(reader.nextName()).isEqualTo("b");
+    assertThat(reader.peek()).isEqualTo(JsonReader.Token.NUMBER);
+    assertThat(reader.nextDouble()).isEqualTo(1.5d);
+
+    assertThat(reader.hasNext()).isTrue();
+    assertThat(reader.peek()).isEqualTo(JsonReader.Token.NAME);
+    assertThat(reader.nextName()).isEqualTo("c");
+    assertThat(reader.peek()).isEqualTo(JsonReader.Token.BOOLEAN);
+    assertThat(reader.nextBoolean()).isEqualTo(true);
+
+    assertThat(reader.hasNext()).isTrue();
+    assertThat(reader.peek()).isEqualTo(JsonReader.Token.NAME);
+    assertThat(reader.nextName()).isEqualTo("d");
+    assertThat(reader.peek()).isEqualTo(JsonReader.Token.NULL);
+    assertThat(reader.nextNull()).isNull();
+
+    assertThat(reader.hasNext()).isFalse();
+    assertThat(reader.peek()).isEqualTo(JsonReader.Token.END_OBJECT);
+    reader.endObject();
+
+    assertThat(reader.peek()).isEqualTo(JsonReader.Token.END_DOCUMENT);
+  }
+
+  @Test public void nesting() throws Exception {
+    List<Map<String, List<Map<String, Double>>>> root
+        = Collections.singletonList(Collections.singletonMap(
+            "a", Collections.singletonList(Collections.singletonMap("b", 1.5d))));
+    JsonReader reader = new ObjectJsonReader(root);
+
+    assertThat(reader.hasNext()).isTrue();
+    assertThat(reader.peek()).isEqualTo(JsonReader.Token.BEGIN_ARRAY);
+    reader.beginArray();
+
+    assertThat(reader.hasNext()).isTrue();
+    assertThat(reader.peek()).isEqualTo(JsonReader.Token.BEGIN_OBJECT);
+    reader.beginObject();
+
+    assertThat(reader.hasNext()).isTrue();
+    assertThat(reader.peek()).isEqualTo(JsonReader.Token.NAME);
+    assertThat(reader.nextName()).isEqualTo("a");
+
+    assertThat(reader.hasNext()).isTrue();
+    assertThat(reader.peek()).isEqualTo(JsonReader.Token.BEGIN_ARRAY);
+    reader.beginArray();
+
+    assertThat(reader.hasNext()).isTrue();
+    assertThat(reader.peek()).isEqualTo(JsonReader.Token.BEGIN_OBJECT);
+    reader.beginObject();
+
+    assertThat(reader.hasNext()).isTrue();
+    assertThat(reader.peek()).isEqualTo(JsonReader.Token.NAME);
+    assertThat(reader.nextName()).isEqualTo("b");
+
+    assertThat(reader.hasNext()).isTrue();
+    assertThat(reader.peek()).isEqualTo(JsonReader.Token.NUMBER);
+    assertThat(reader.nextDouble()).isEqualTo(1.5d);
+
+    assertThat(reader.hasNext()).isFalse();
+    assertThat(reader.peek()).isEqualTo(JsonReader.Token.END_OBJECT);
+    reader.endObject();
+
+    assertThat(reader.hasNext()).isFalse();
+    assertThat(reader.peek()).isEqualTo(JsonReader.Token.END_ARRAY);
+    reader.endArray();
+
+    assertThat(reader.hasNext()).isFalse();
+    assertThat(reader.peek()).isEqualTo(JsonReader.Token.END_OBJECT);
+    reader.endObject();
+
+    assertThat(reader.hasNext()).isFalse();
+    assertThat(reader.peek()).isEqualTo(JsonReader.Token.END_ARRAY);
+    reader.endArray();
+
+    assertThat(reader.peek()).isEqualTo(JsonReader.Token.END_DOCUMENT);
+  }
+
+  @Test public void promoteNameToValue() throws Exception {
+    Map<String, String> root = Collections.singletonMap("a", "b");
+
+    JsonReader reader = new ObjectJsonReader(root);
+    reader.beginObject();
+    reader.promoteNameToValue();
+    assertThat(reader.peek()).isEqualTo(JsonReader.Token.STRING);
+    assertThat(reader.nextString()).isEqualTo("a");
+
+    assertThat(reader.peek()).isEqualTo(JsonReader.Token.STRING);
+    assertThat(reader.nextString()).isEqualTo("b");
+    reader.endObject();
+
+    assertThat(reader.peek()).isEqualTo(JsonReader.Token.END_DOCUMENT);
+  }
+
+  @Test public void endArrayTooEarly() throws Exception {
+    JsonReader reader = new ObjectJsonReader(Collections.singletonList("s"));
+
+    reader.beginArray();
+    try {
+      reader.endArray();
+      fail();
+    } catch (JsonDataException expected) {
+      assertThat(expected).hasMessage("Expected END_ARRAY but was STRING at path $[0]");
+    }
+  }
+
+  @Test public void endObjectTooEarly() throws Exception {
+    JsonReader reader = new ObjectJsonReader(Collections.singletonMap("a", "b"));
+
+    reader.beginObject();
+    try {
+      reader.endObject();
+      fail();
+    } catch (JsonDataException expected) {
+      assertThat(expected).hasMessage("Expected END_OBJECT but was NAME at path $.");
+    }
+  }
+
+  @Test public void unsupportedType() throws Exception {
+    JsonReader reader = new ObjectJsonReader(Collections.singletonList(new StringBuilder("x")));
+
+    reader.beginArray();
+    try {
+      reader.peek();
+      fail();
+    } catch (JsonDataException expected) {
+      assertThat(expected).hasMessage(
+          "Expected a JSON value but was a java.lang.StringBuilder at path $[0]");
+    }
+  }
+
+  @Test public void skipRoot() throws Exception {
+    JsonReader reader = new ObjectJsonReader(Collections.singletonList(new StringBuilder("x")));
+    reader.skipValue();
+    assertThat(reader.peek()).isEqualTo(JsonReader.Token.END_DOCUMENT);
+  }
+
+  @Test public void skipListValue() throws Exception {
+    List<Object> root = new ArrayList<>();
+    root.add("a");
+    root.add("b");
+    root.add("c");
+    JsonReader reader = new ObjectJsonReader(root);
+
+    reader.beginArray();
+
+    assertThat(reader.getPath()).isEqualTo("$[0]");
+    assertThat(reader.nextString()).isEqualTo("a");
+
+    assertThat(reader.getPath()).isEqualTo("$[1]");
+    reader.skipValue();
+
+    assertThat(reader.getPath()).isEqualTo("$[2]");
+    assertThat(reader.nextString()).isEqualTo("c");
+
+    reader.endArray();
+  }
+
+  @Test public void skipObjectName() throws Exception {
+    Map<String, Object> root = new LinkedHashMap<>();
+    root.put("a", "s");
+    root.put("b", 1.5d);
+    root.put("c", true);
+    JsonReader reader = new ObjectJsonReader(root);
+
+    reader.beginObject();
+
+    assertThat(reader.nextName()).isEqualTo("a");
+    assertThat(reader.getPath()).isEqualTo("$.a");
+    assertThat(reader.nextString()).isEqualTo("s");
+    assertThat(reader.getPath()).isEqualTo("$.a");
+
+    reader.skipValue();
+    assertThat(reader.getPath()).isEqualTo("$.null");
+    assertThat(reader.nextDouble()).isEqualTo(1.5d);
+    assertThat(reader.getPath()).isEqualTo("$.null");
+
+    assertThat(reader.nextName()).isEqualTo("c");
+    assertThat(reader.getPath()).isEqualTo("$.c");
+    assertThat(reader.nextBoolean()).isEqualTo(true);
+    assertThat(reader.getPath()).isEqualTo("$.c");
+
+    reader.endObject();
+  }
+
+  @Test public void skipObjectValue() throws Exception {
+    Map<String, Object> root = new LinkedHashMap<>();
+    root.put("a", "s");
+    root.put("b", 1.5d);
+    root.put("c", true);
+    JsonReader reader = new ObjectJsonReader(root);
+
+    reader.beginObject();
+
+    assertThat(reader.nextName()).isEqualTo("a");
+    assertThat(reader.getPath()).isEqualTo("$.a");
+    assertThat(reader.nextString()).isEqualTo("s");
+    assertThat(reader.getPath()).isEqualTo("$.a");
+
+    assertThat(reader.nextName()).isEqualTo("b");
+    assertThat(reader.getPath()).isEqualTo("$.b");
+    reader.skipValue();
+    assertThat(reader.getPath()).isEqualTo("$.null");
+
+    assertThat(reader.nextName()).isEqualTo("c");
+    assertThat(reader.getPath()).isEqualTo("$.c");
+    assertThat(reader.nextBoolean()).isEqualTo(true);
+    assertThat(reader.getPath()).isEqualTo("$.c");
+
+    reader.endObject();
+  }
+
+  @Test public void failOnUnknown() throws Exception {
+    JsonReader reader = new ObjectJsonReader(Collections.singletonList("a"));
+    reader.setFailOnUnknown(true);
+
+    reader.beginArray();
+    try {
+      reader.skipValue();
+      fail();
+    } catch (JsonDataException expected) {
+      assertThat(expected).hasMessage("Cannot skip unexpected STRING at $[0]");
+    }
+  }
+
+  @Test public void close() throws Exception {
+    try {
+      JsonReader reader = new ObjectJsonReader(Collections.singletonList("a"));
+      reader.beginArray();
+      reader.close();
+      reader.nextString();
+      fail();
+    } catch (IllegalStateException expected) {
+    }
+
+    try {
+      JsonReader reader = new ObjectJsonReader(Collections.singletonList("a"));
+      reader.close();
+      reader.beginArray();
+      fail();
+    } catch (IllegalStateException expected) {
+    }
+  }
+}