使用GSON和TypeAdapter将BSON（mongoDB）读入POJO

使用GSON和TypeAdapter将BSON（mongoDB）读入POJO

我使用CustomizedTypeAdapterFactory解决了它。

基本上首先写一个定制的适配器：

public abstract class CustomizedTypeAdapterFactory<C>        implements TypeAdapterFactory{    private final Class<C> customizedClass;    public CustomizedTypeAdapterFactory(Class<C> customizedClass) {        this.customizedClass = customizedClass;    }    @SuppressWarnings("unchecked") // we use a runtime check to guarantee that 'C' and 'T' are equal    public final <T> TypeAdapter<T> create(Gson gson, TypeToken<T> type) {        return type.getRawType() == customizedClass     ? (TypeAdapter<T>) customizeMyClassAdapter(gson, (TypeToken<C>) type)     : null;    }    private TypeAdapter<C> customizeMyClassAdapter(Gson gson, TypeToken<C> type) {        final TypeAdapter<C> delegate = gson.getDelegateAdapter(this, type);        final TypeAdapter<JsonElement> elementAdapter = gson.getAdapter(JsonElement.class);        return new TypeAdapter<C>() { @Override public void write(JsonWriter out, C value) throws IOException {     JsonElement tree = delegate.toJsonTree(value);     beforeWrite(value, tree);     elementAdapter.write(out, tree); } @Override public C read(JsonReader in) throws IOException {     JsonElement tree = elementAdapter.read(in);     afterRead(tree);     return delegate.fromJsonTree(tree); }        };    }        protected void beforeWrite(C source, JsonElement toSerialize) {    }        protected void afterRead(JsonElement deserialized) {    }}

然后为所有需要考虑的类创建一个子类。您必须为每个包含long的类创建一个（在这种情况下）。但是除了long值（以及任何其他bson特定值）之外，您无需序列化任何内容

public class MyTestObjectTypeAdapterFactory extends CustomizedTypeAdapterFactory<MyTestObject>{    public MyTestObjectTypeAdapterFactory()    {        super(MyTestObject.class);    }    @Override    protected void beforeWrite(MyTestObject source, JsonElement toSerialize)    {        //you could convert back the other way here, I let mongo's document parser take care of that.    }    @Override    protected void afterRead(JsonElement deserialized)    {        JsonObject timestamp = deserialized.getAsJsonObject().get("timestamp").getAsJsonObject();        deserialized.getAsJsonObject().remove("timestamp");        deserialized.getAsJsonObject().add("timestamp",timestamp.get("$numberLong"));    }}

然后生成具有以下内容的Gson：

Gson gson = new GsonBuilder().registerTypeAdapterFactory(new MyTestObjectTypeAdapterFactory()).create();