You can use a JsonQualifier to generalize this.
From your example, you might use it like
final class Foo {
@SingleToArray final List users;
}
Here's the code with a test to demonstrate more thouroughly.
@Retention(RUNTIME)
@JsonQualifier public @interface SingleToArray {
final class Adapter extends JsonAdapter> {
final JsonAdapter> delegateAdapter;
final JsonAdapter elementAdapter;
public static final Factory FACTORY = new Factory() {
@Nullable @Override
public JsonAdapter create(Type type, Set annotations,
Moshi moshi) {
Set delegateAnnotations =
Types.nextAnnotations(annotations, SingleToArray.class);
if (delegateAnnotations == null) {
return null;
}
if (Types.getRawType(type) != List.class) {
throw new IllegalArgumentException(
"Only lists may be annotated with @SingleToArray. Found: " + type);
}
Type elementType = Types.collectionElementType(type, List.class);
JsonAdapter> delegateAdapter = moshi.adapter(type, delegateAnnotations);
JsonAdapter elementAdapter = moshi.adapter(elementType);
return new Adapter(delegateAdapter, elementAdapter);
}
};
Adapter(JsonAdapter> delegateAdapter, JsonAdapter elementAdapter) {
this.delegateAdapter = delegateAdapter;
this.elementAdapter = elementAdapter;
}
@Nullable @Override public List fromJson(JsonReader reader) throws IOException {
if (reader.peek() != JsonReader.Token.BEGIN_ARRAY) {
return Collections.singletonList(elementAdapter.fromJson(reader));
}
return delegateAdapter.fromJson(reader);
}
@Override public void toJson(JsonWriter writer, @Nullable List value)
throws IOException {
if (value.size() == 1) {
elementAdapter.toJson(writer, value.get(0));
} else {
delegateAdapter.toJson(writer, value);
}
}
}
}
@Test public void singleToArray() throws Exception {
Moshi moshi = new Moshi.Builder().add(SingleToArray.Adapter.FACTORY).build();
JsonAdapter> adapter =
moshi.adapter(Types.newParameterizedType(List.class, String.class), SingleToArray.class);
assertThat(adapter.fromJson("[\"Tom\",\"Huck\"]")).isEqualTo(Arrays.asList("Tom", "Huck"));
assertThat(adapter.toJson(Arrays.asList("Tom", "Huck"))).isEqualTo("[\"Tom\",\"Huck\"]");
assertThat(adapter.fromJson("\"Jim\"")).isEqualTo(Collections.singletonList("Jim"));
assertThat(adapter.toJson(Collections.singletonList("Jim"))).isEqualTo("\"Jim\"");
assertThat(adapter.fromJson("[]")).isEqualTo(Collections.emptyList());
assertThat(adapter.toJson(Collections.emptyList())).isEqualTo("[]");
}
加载中...