Moshi.Builder.addLast() (#1233)

This is mostly useful for KotlinJsonAdapterFactory.

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

@@ -0,0 +1,81 @@
+/*
+ * Copyright (C) 2020 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 static java.lang.annotation.ElementType.TYPE;
+import static java.lang.annotation.RetentionPolicy.RUNTIME;
+
+import com.squareup.moshi.JsonAdapter;
+import com.squareup.moshi.Moshi;
+import com.squareup.moshi.Types;
+import java.lang.annotation.Annotation;
+import java.lang.annotation.Retention;
+import java.lang.annotation.Target;
+import java.lang.reflect.Type;
+import java.util.Set;
+
+public final class IncludeNullsForAnnotatedTypes {
+  public void run() throws Exception {
+    Moshi moshi = new Moshi.Builder().add(new AlwaysSerializeNullsFactory()).build();
+
+    JsonAdapter<Driver> driverAdapter = moshi.adapter(Driver.class);
+
+    Car car = new Car();
+    car.make = "Ford";
+    car.model = "Mach-E";
+    car.color = null; // This null will show up in the JSON because Car has @AlwaysSerializeNulls.
+
+    Driver driver = new Driver();
+    driver.name = "Jesse";
+    driver.emailAddress = null; // This null will be omitted.
+    driver.favoriteCar = car;
+
+    System.out.println(driverAdapter.toJson(driver));
+  }
+
+  @Target(TYPE)
+  @Retention(RUNTIME)
+  public @interface AlwaysSerializeNulls {}
+
+  @AlwaysSerializeNulls
+  static class Car {
+    String make;
+    String model;
+    String color;
+  }
+
+  static class Driver {
+    String name;
+    String emailAddress;
+    Car favoriteCar;
+  }
+
+  static class AlwaysSerializeNullsFactory implements JsonAdapter.Factory {
+    @Override
+    public JsonAdapter<?> create(Type type, Set<? extends Annotation> annotations, Moshi moshi) {
+      Class<?> rawType = Types.getRawType(type);
+      if (!rawType.isAnnotationPresent(AlwaysSerializeNulls.class)) {
+        return null;
+      }
+      JsonAdapter<Object> delegate = moshi.nextAdapter(this, type, annotations);
+      return delegate.serializeNulls();
+    }
+  }
+
+  public static void main(String[] args) throws Exception {
+    new IncludeNullsForAnnotatedTypes().run();
+  }
+}

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

@@ -0,0 +1,60 @@
+/*
+ * Copyright (C) 2020 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.JsonWriter;
+import com.squareup.moshi.Moshi;
+import com.squareup.moshi.ToJson;
+import com.squareup.moshi.adapters.Rfc3339DateJsonAdapter;
+import com.squareup.moshi.recipes.models.Tournament;
+import java.io.IOException;
+import java.util.Date;
+
+public final class IncludeNullsForOneType {
+  public void run() throws Exception {
+    Moshi moshi =
+        new Moshi.Builder()
+            .add(Date.class, new Rfc3339DateJsonAdapter())
+            .add(new TournamentWithNullsAdapter())
+            .build();
+
+    JsonAdapter<Tournament> tournamentAdapter = moshi.adapter(Tournament.class);
+
+    // Moshi normally skips nulls, but with our adapter registered they are emitted.
+    Tournament withNulls = new Tournament("Waterloo Classic", null, null);
+    System.out.println(tournamentAdapter.toJson(withNulls));
+  }
+
+  public static final class TournamentWithNullsAdapter {
+    @ToJson
+    void toJson(JsonWriter writer, Tournament tournament, JsonAdapter<Tournament> delegate)
+        throws IOException {
+      boolean wasSerializeNulls = writer.getSerializeNulls();
+      writer.setSerializeNulls(true);
+      try {
+        // Once we've customized the JSON writer, we let the default JSON adapter do its job.
+        delegate.toJson(writer, tournament);
+      } finally {
+        writer.setLenient(wasSerializeNulls);
+      }
+    }
+  }
+
+  public static void main(String[] args) throws Exception {
+    new IncludeNullsForOneType().run();
+  }
+}