Add an example that decodes multiple formats

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

@@ -0,0 +1,94 @@
+/*
+ * Copyright (C) 2018 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.FromJson;
+import com.squareup.moshi.JsonAdapter;
+import com.squareup.moshi.JsonDataException;
+import com.squareup.moshi.JsonQualifier;
+import com.squareup.moshi.JsonReader;
+import com.squareup.moshi.JsonWriter;
+import com.squareup.moshi.Moshi;
+import com.squareup.moshi.ToJson;
+import com.squareup.moshi.recipes.models.Card;
+import com.squareup.moshi.recipes.models.Suit;
+import java.io.IOException;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+
+public final class MultipleFormats {
+  public void run() throws Exception {
+    Moshi moshi = new Moshi.Builder()
+        .add(new MultipleFormatsCardAdapter())
+        .add(new CardStringAdapter())
+        .build();
+
+    JsonAdapter<Card> cardAdapter = moshi.adapter(Card.class);
+
+    // Decode cards from one format or the other.
+    System.out.println(cardAdapter.fromJson("\"5D\""));
+    System.out.println(cardAdapter.fromJson("{\"suit\": \"SPADES\", \"rank\": 5}"));
+
+    // Cards are always encoded as strings.
+    System.out.println(cardAdapter.toJson(new Card('5', Suit.CLUBS)));
+  }
+
+  /** Handles cards either as strings "5D" or as objects {"suit": "SPADES", "rank": 5}. */
+  public final class MultipleFormatsCardAdapter {
+    @ToJson void toJson(JsonWriter writer, Card value,
+        @CardString JsonAdapter<Card> stringAdapter) throws IOException {
+      stringAdapter.toJson(writer, value);
+    }
+
+    @FromJson Card fromJson(JsonReader reader, @CardString JsonAdapter<Card> stringAdapter,
+        JsonAdapter<Card> defaultAdapter) throws IOException {
+      if (reader.peek() == JsonReader.Token.STRING) {
+        return stringAdapter.fromJson(reader);
+      } else {
+        return defaultAdapter.fromJson(reader);
+      }
+    }
+  }
+
+  /** Handles cards as strings only. */
+  public final class CardStringAdapter {
+    @ToJson String toJson(@CardString Card card) {
+      return card.rank + card.suit.name().substring(0, 1);
+    }
+
+    @FromJson @CardString Card fromJson(String card) {
+      if (card.length() != 2) throw new JsonDataException("Unknown card: " + card);
+
+      char rank = card.charAt(0);
+      switch (card.charAt(1)) {
+        case 'C': return new Card(rank, Suit.CLUBS);
+        case 'D': return new Card(rank, Suit.DIAMONDS);
+        case 'H': return new Card(rank, Suit.HEARTS);
+        case 'S': return new Card(rank, Suit.SPADES);
+        default: throw new JsonDataException("unknown suit: " + card);
+      }
+    }
+  }
+
+  @Retention(RetentionPolicy.RUNTIME)
+  @JsonQualifier
+  @interface CardString {
+  }
+
+  public static void main(String[] args) throws Exception {
+    new MultipleFormats().run();
+  }
+}