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package data;
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.JsonArray;
import com.google.gson.JsonDeserializationContext;
import com.google.gson.JsonDeserializer;
import com.google.gson.JsonElement;
import com.google.gson.JsonObject;
import com.google.gson.JsonParseException;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import java.lang.reflect.Field;
import java.lang.reflect.Type;
/**
* JSON deserializer which validates that all fields are present.
*
* @author Peter Wu.
*/
public class ValidatingJsonDeserializer<T> implements JsonDeserializer<T> {
@Override
public T deserialize(JsonElement je, Type type,
JsonDeserializationContext jdc) throws JsonParseException {
T obj = new Gson().fromJson(je, type);
checkObject(je, obj.getClass());
return obj;
}
private void checkObject(JsonElement je, Class type) {
if (!je.isJsonObject()) {
throw new JsonParseException("Expected object: " + type.getName());
}
JsonObject jsonObj = je.getAsJsonObject();
for (Field f : type.getDeclaredFields()) {
if (!jsonObj.has(f.getName())) {
if (f.getAnnotation(Nullable.class) != null) {
// null allowed, skip
continue;
}
throw new JsonParseException("Missing field: " + f.getName());
}
tryValidateProperty(jsonObj.get(f.getName()), f);
// TODO: validate type?
}
}
private void tryValidateProperty(JsonElement je, Field f) {
// assume that this annotation is only applied to objects
Validator v = f.getAnnotation(Validator.class);
if (v != null) {
Class<?> type = f.getType();
if (type.isArray()) {
// the class expects an array, so the value must have one too.
if (!je.isJsonArray()) {
throw new JsonParseException("Not an array: " + f.getName());
}
JsonArray ja = je.getAsJsonArray();
type = type.getComponentType();
// for each array element, check if the object is valid.
for (JsonElement arr_je : ja) {
checkObject(arr_je, type);
}
} else {
// not an array, assume a verifiable object
checkObject(je, type);
}
}
}
/**
* Marks a member as object that should be validated too.
*/
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.FIELD)
public @interface Validator {
Class deserializer() default ValidatingJsonDeserializer.class;
}
/**
* Marks a member as nullable, that is, it can be missing from the JSON
* object.
*/
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.FIELD)
public @interface Nullable {
}
}
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