plugins/tasks/tasks-core/src/com/intellij/tasks/impl/gson/NullCheckingFactory.java

package com.intellij.tasks.impl.gson;

import com.google.gson.Gson;
import com.google.gson.TypeAdapter;
import com.google.gson.TypeAdapterFactory;
import com.google.gson.reflect.TypeToken;
import com.google.gson.stream.JsonReader;
import com.google.gson.stream.JsonWriter;
import com.intellij.util.ReflectionUtil;

import java.io.IOException;
import java.lang.reflect.Field;

/**
* @author Mikhail Golubev
*/
class NullCheckingFactory implements TypeAdapterFactory {
  public static final NullCheckingFactory INSTANCE = new NullCheckingFactory();

  @Override
  public <T> TypeAdapter<T> create(Gson gson, final TypeToken<T> type) {
    if (type.getRawType().getAnnotation(RestModel.class) == null) {
      return null;
    }
    final TypeAdapter<T> defaultAdapter = gson.getDelegateAdapter(this, type);
    return new TypeAdapter<T>() {
      @Override
      public void write(JsonWriter out, T value) throws IOException {
        defaultAdapter.write(out, value);
      }

      @Override
      public T read(JsonReader in) throws IOException {
        T stub = defaultAdapter.read(in);
        for (Field field : ReflectionUtil.collectFields(type.getRawType())) {
          if (field.getAnnotation(Mandatory.class) != null) {
            try {
              field.setAccessible(true);
              if (field.get(stub) == null) {
                throw new IllegalArgumentException(String.format("Field '%s' is mandatory, but missing in response", field.getName()));
              }
            }
            catch (IllegalAccessException e) {
              throw new RuntimeException(e);
            }
          }
        }
        return stub;
      }
    };
  }
}