Example adapter that recovers from JsonDataExceptions.

examples/src/main/java/com/squareup/moshi/recipes/DefaultOnDataMismatchAdapter.java

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+/*
+ * 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.recipes;
+
+import com.squareup.moshi.JsonAdapter;
+import com.squareup.moshi.JsonDataException;
+import com.squareup.moshi.JsonReader;
+import com.squareup.moshi.JsonWriter;
+import com.squareup.moshi.Moshi;
+import java.io.IOException;
+import java.lang.annotation.Annotation;
+import java.lang.reflect.Type;
+import java.util.Set;
+
+public final class DefaultOnDataMismatchAdapter<T> extends JsonAdapter<T> {
+  private final JsonAdapter<T> delegate;
+  private final T defaultValue;
+  private final JsonAdapter<Object> objectAdapter;
+
+  private DefaultOnDataMismatchAdapter(JsonAdapter<T> delegate, T defaultValue,
+      JsonAdapter<Object> objectAdapter) {
+    this.delegate = delegate;
+    this.defaultValue = defaultValue;
+    this.objectAdapter = objectAdapter;
+  }
+
+  @Override public T fromJson(JsonReader reader) throws IOException {
+    // Read the value first so that the reader will be in a known state even if there's an
+    // exception. Otherwise it may be awkward to recover: it might be between calls to
+    // beginObject() and endObject() for example.
+    Object jsonValue = objectAdapter.fromJson(reader);
+
+    // Use the delegate to convert the JSON value to the target type.
+    try {
+      return delegate.fromJsonValue(jsonValue);
+    } catch (JsonDataException e) {
+      return defaultValue;
+    }
+  }
+
+  @Override public void toJson(JsonWriter writer, T value) throws IOException {
+    delegate.toJson(writer, value);
+  }
+
+  public static <T> Factory newFactory(final Class<T> type, final T defaultValue) {
+    return new Factory() {
+      @Override public JsonAdapter<?> create(
+          Type requestedType, Set<? extends Annotation> annotations, Moshi moshi) {
+        if (type != requestedType) return null;
+        JsonAdapter<Object> objectAdapter = moshi.adapter(Object.class);
+        JsonAdapter<T> delegate = moshi.nextAdapter(this, type, annotations);
+        return new DefaultOnDataMismatchAdapter<>(delegate, defaultValue, objectAdapter);
+      }
+    };
+  }
+}

examples/src/main/java/com/squareup/moshi/recipes/RecoverFromTypeMismatch.java

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+/*
+ * 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.recipes;
+
+import com.squareup.moshi.JsonAdapter;
+import com.squareup.moshi.Moshi;
+import com.squareup.moshi.Types;
+import com.squareup.moshi.recipes.models.Suit;
+import java.util.List;
+
+public final class RecoverFromTypeMismatch {
+  public void run() throws Exception {
+    String json = "[\"DIAMONDS\", \"STARS\", \"HEARTS\"]";
+
+    Moshi moshi = new Moshi.Builder()
+        .add(DefaultOnDataMismatchAdapter.newFactory(Suit.class, Suit.CLUBS))
+        .build();
+    JsonAdapter<List<Suit>> jsonAdapter = moshi.adapter(
+        Types.newParameterizedType(List.class, Suit.class));
+
+    List<Suit> suits = jsonAdapter.fromJson(json);
+    System.out.println(suits);
+  }
+
+  public static void main(String[] args) throws Exception {
+    new RecoverFromTypeMismatch().run();
+  }
+}