カスタムタイプのアダプタを使用する必要があります。さらに、あなたの代わりに再帰のループを使用してstackoverflowsを防ぐことができます。
public class TreeItemTypeAdapter<T> extends TypeAdapter<TreeItem<T>> {
private Gson gson;
public void setGson(Gson gson) {
this.gson = gson;
}
private final Class<T> valueClass;
public TreeItemTypeAdapter(Class<T> valueClass) {
if (valueClass == null) {
throw new IllegalArgumentException();
}
this.valueClass = valueClass;
}
public static TreeItemTypeAdapter<String> createStringTreeItemAdapter() {
return new TreeItemTypeAdapter<>(String.class);
}
private void writeValue(JsonWriter writer, T t) throws IOException {
if (gson == null) {
writer.value(Objects.toString(t, null));
} else {
gson.toJson(t, valueClass, writer);
}
}
private T readValue(JsonReader reader) throws IOException {
if (gson == null) {
Object value = reader.nextString();
return (T) value;
} else {
return gson.fromJson(reader, valueClass);
}
}
@Override
public void write(JsonWriter writer, TreeItem<T> t) throws IOException {
writer.beginObject().name("value");
writeValue(writer, t.getValue());
writer.name("children").beginArray();
LinkedList<Iterator<TreeItem<T>>> iterators = new LinkedList<>();
iterators.add(t.getChildren().iterator());
while (!iterators.isEmpty()) {
Iterator<TreeItem<T>> last = iterators.peekLast();
if (last.hasNext()) {
TreeItem<T> ti = last.next();
writer.beginObject().name("value");
writeValue(writer, ti.getValue());
writer.name("children").beginArray();
iterators.add(ti.getChildren().iterator());
} else {
writer.endArray().endObject();
iterators.pollLast();
}
}
}
@Override
public TreeItem<T> read(JsonReader reader) throws IOException {
if (gson == null && !valueClass.getName().equals("java.lang.String")) {
throw new IllegalStateException("cannot parse classes other than String without gson provided");
}
reader.beginObject();
if (!"value".equals(reader.nextName())) {
throw new IOException("value expected");
}
TreeItem<T> root = new TreeItem<>(readValue(reader));
TreeItem<T> item = root;
if (!"children".equals(reader.nextName())) {
throw new IOException("children expected");
}
reader.beginArray();
int depth = 1;
while (depth > 0) {
if (reader.hasNext()) {
reader.beginObject();
if (!"value".equals(reader.nextName())) {
throw new IOException("value expected");
}
TreeItem<T> newItem = new TreeItem<>(readValue(reader));
item.getChildren().add(newItem);
item = newItem;
if (!"children".equals(reader.nextName())) {
throw new IOException("children expected");
}
reader.beginArray();
depth++;
} else {
depth--;
reader.endArray();
reader.endObject();
item = item.getParent();
}
}
return root;
}
}
public static void main(String[] args) {
TreeItem<String> ti = new TreeItem<>("Hello world");
TreeItem<String> ti2 = new TreeItem<>("42");
TreeItem<String> ti3 = new TreeItem<>("Foo");
TreeItem<String> ti4 = new TreeItem<>("Bar");
ti.getChildren().addAll(ti2, ti3);
ti2.getChildren().add(ti4);
TreeItemTypeAdapter<String> adapter = new TreeItemTypeAdapter<>(String.class);
Gson gson = new GsonBuilder().registerTypeAdapter(TreeItem.class, adapter).create();
adapter.setGson(gson);
System.out.println(gson.toJson(ti));
System.out.println(toString(gson.fromJson("{\"value\":\"Hello world\",\"children\":[{\"value\":\"42\",\"children\":[{\"value\":\"Bar\",\"children\":[]}]},{\"value\":\"Foo\",\"children\":[]}]}",
TreeItem.class)));
}
private static String toString(TreeItem ti) {
StringBuilder sb = new StringBuilder("TreeItem [ value: \"").append(ti.getValue()).append("\" children [");
boolean notFirst = false;
for (TreeItem i : (List<TreeItem>) ti.getChildren()) {
if (notFirst) {
sb.append(",");
} else {
notFirst = true;
}
sb.append(toString(i));
}
return sb.append("]]").toString();
}
も参照してください:http://stackoverflow.com/q/40196602/59087 –