I have a POJO with a String field that is already serialized JSON. Performance is key here, so I want to avoid parsing it and then re-serializing it.
public class SomeObject {
String someString = "";
String jsonString = "{\"one\":4, \"two\":\"hello\"}";
long someLong = 4;
}
Currently GSON serialises it like so:
{ "someString":"", "jsonString":"{\"one\":4, \"two\":\"hello\"}", "someLong":4 }
I wrote a JsonSerializer/Deserializer in hopes of using the #JsonAdapter annotation, but it only supports TypeAdapter or TypeAdapterFactory.
public class JsonStringTypeAdapter implements JsonSerializer<String>, JsonDeserializer<String> {
#Override
public JsonElement serialize(String t, Type type, JsonSerializationContext jsc) {
return new JsonParser().parse(t).getAsJsonObject();
}
#Override
public String deserialize(JsonElement je, Type type, JsonDeserializationContext jdc) throws JsonParseException {
return je.getAsString();
}
#Override
public void write(JsonWriter writer, String t) throws IOException {
writer.jsonValue(t);
}
}
So I wrote the following simple TypeAdapter that works perfectly for serialisation, but I can't work out how to deserialise a Json object to String in a TypeAdapter.
public class JsonStringTypeAdapter extends TypeAdapter<String> {
#Override
public void write(JsonWriter writer, String t) throws IOException {
writer.jsonValue(t);
}
#Override
public String read(JsonReader reader) throws IOException {
throw new UnsupportedOperationException("Not supported yet.");
}
}
I know Jackson has an annotation for this. Any ideas for doing it with GSON?
Solved it using TypeAdapterFactory.
public class JsonStringTypeAdapterFactory implements TypeAdapterFactory {
#Override
public <T> TypeAdapter<T> create(Gson gson, TypeToken<T> tokenType) {
if (!JsonString.class.isAssignableFrom(tokenType.getRawType())) return null;
return (TypeAdapter<T>) new JsonStringTypeAdapter(gson);
}
}
And completing the read method
/* The JsonStringTypeAdapter writes the raw string value directly to the JSON output
* this offers great performance by avoiding parsing then reserialising
* Note: Care must be taken to ensure the input JsonString is well formed JSON.
* Otherwise, when it is deserialised, errors will occur.
*
* #author adamjohnson
*/
public class JsonStringTypeAdapter extends TypeAdapter<JsonString> {
private final Gson gson;
public JsonStringTypeAdapter(Gson gson) {
this.gson = gson;
}
#Override
public void write(JsonWriter writer, JsonString t) throws IOException {
/* check for invalid json string, if so create empty object. */
if (t.value().equals("")) {
writer.jsonValue("{}");
} else /* write raw string directly to json output */ {
writer.jsonValue(t.value());
}
}
#Override
public JsonString read(JsonReader reader) throws IOException {
return new JsonString(gson.getAdapter(JsonElement.class).read(reader).getAsString());
}
}
Related
I have a JSON string and I want to alter the value while constructing the JsonNode using Jackson library.
eg:-
input: {"name":"xyz","price":"90.00"}
output:{"name":"xyz-3","price":90.90}
I created my own JsonFactory and passed my own Parser. but I can only alter the keys, not the values associated with a key.
code:
private static ObjectMapper create() {
ObjectMapper objectMapper = new ObjectMapper(new JsonFactory() {
#Override
protected JsonParser _createParser(byte[] data, int offset, int len, IOContext ctxt) throws IOException {
return new MyParser(super._createParser(data, offset, len, ctxt));
}
#Override
protected JsonParser _createParser(InputStream in, IOContext ctxt) throws IOException {
return new MyParser(super._createParser(in, ctxt));
}
#Override
protected JsonParser _createParser(Reader r, IOContext ctxt) throws IOException {
return new MyParser(super._createParser(r, ctxt));
}
#Override
protected JsonParser _createParser(char[] data, int offset, int len, IOContext ctxt, boolean recyclable)
throws IOException {
return new MyParser(super._createParser(data, offset, len, ctxt, recyclable));
}
});
private static final class MyParser extends JsonParserDelegate {
private MyParser(JsonParser d) {
super(d);
}
#Override
public String getCurrentName() throws IOException, JsonParseException {
....
}
#Override
public String getText() throws IOException, JsonParseException {
...
}
#Override
public Object getCurrentValue() {
...
}
#Override
public String getValueAsString() throws IOException {
...
}
#Override
public String getValueAsString(String defaultValue) throws IOException {
...
}
}
Below is the code to construct the JsonNode from the string.
mapper.readTree(jsonStr);
In this case when the readTree method is called the getCurrentValue or getValueAsString methods are not called, so I am not able to alter the value while creating the JsonNode itself.
Also the json strings can be different. Basically I want to construct a JsonNode from the string. so tying to a specific schema/bean is not a good choice here.
How to address this ? TIA
Adding the updated code for version 2.7.4:-
static class MyParser extends JsonParserDelegate {
MyParser(final JsonParser delegate) {
super(delegate);
}
#Override
public String getText() throws IOException {
final String text = super.getText();
if ("name".equals(getCurrentName())) {
return text + "-3";
}
return text;
}
#Override
public JsonToken nextToken() throws IOException {
if ("price".equals(getCurrentName())) {
// Advance token anyway
super.nextToken();
return JsonToken.VALUE_NUMBER_FLOAT;
}
return super.nextToken();
}
#Override
public int getCurrentTokenId() {
try {
if ("price".equals(getCurrentName())) {
return JsonTokenId.ID_NUMBER_FLOAT;
}
} catch (final IOException e) {
//
}
return super.getCurrentTokenId();
}
#Override
public NumberType getNumberType() throws IOException {
if ("price".equals(getCurrentName())) {
return NumberType.FLOAT;
}
return super.getNumberType();
}
#Override
public float getFloatValue() throws IOException {
return Float.parseFloat(getValueAsString("0")) + 0.09F;
}
#Override
public double getDoubleValue() throws IOException {
return Double.parseDouble(getValueAsString("0")) + 0.09D;
}
}
pom.xml:-
<dependency>
<groupId>com.fasterxml.jackson.dataformat</groupId>
<artifactId>jackson-dataformat-yaml</artifactId>
<version>2.8.7</version>
<!--<scope>test</scope>-->
</dependency>
<dependency>
<groupId>com.fasterxml.jackson.dataformat</groupId>
<artifactId>jackson-dataformat-xml</artifactId>
<version>2.8.7</version>
</dependency>
Edit: there is a subtle difference between 2.7.* and 2.9.*.
While 2.9.* is able to differentiate between double and float with
getDoubleValue()
getFloatValue()
instead 2.7.* only uses
getDoubleValue()
even for ID_NUMBER_FLOAT tokens.
So, you need to decide if you want to maintain retro-compatibility or not.
You can also override both, like I did here.
This is all what you need for your custom MyParser
static class MyParser extends JsonParserDelegate {
MyParser(final JsonParser delegate) {
super(delegate);
}
#Override
public String getText() throws IOException {
final String text = super.getText();
if ("name".equals(getCurrentName())) {
return text + "-3";
}
return text;
}
#Override
public JsonToken nextToken() throws IOException {
if ("price".equals(getCurrentName())) {
// Advance token anyway
super.nextToken();
return JsonToken.VALUE_NUMBER_FLOAT;
}
return super.nextToken();
}
#Override
public int getCurrentTokenId() {
try {
if ("price".equals(getCurrentName())) {
return JsonTokenId.ID_NUMBER_FLOAT;
}
} catch (final IOException e) {
//
}
return super.getCurrentTokenId();
}
#Override
public NumberType getNumberType() throws IOException {
if ("price".equals(getCurrentName())) {
return NumberType.FLOAT;
}
return super.getNumberType();
}
#Override
public float getFloatValue() throws IOException {
return Float.parseFloat(getValueAsString("0")) + 0.09F;
}
#Override
public double getDoubleValue() throws IOException {
return Double.parseDouble(getValueAsString("0")) + 0.09D;
}
}
Output: {"name":"xyz-3","price":90.09}
Your code seems fine, and it's tested and working ;)
Are you really sure that regarding the Separation of Concerns it is a good idea to mix parsing and changes within the parsed data?
If you still want to do this, you could use a Custom Deserializer and treat your wanted field names and types the way you want it, like:
class CustomDeserializer extends StdDeserializer<Entity> {
public CustomDeserializer(Class<Entity> t) {
super(t);
}
#Override
public Entity deserialize(JsonParser jp, DeserializationContext dc) throws IOException {
String name = null;
float price = 0;
JsonToken currentToken = null;
while ((currentToken = jp.nextValue()) != null) {
switch (currentToken) {
case VALUE_STRING:
switch (jp.getCurrentName()) {
case "name":
name = jp.getText() + "-3"; // change this text to whatever you want;
break;
case "price":
price = Float.parseFloat(jp.getText()); // parse
break;
default:
break;
}
break;
default:
break;
}
}
return new Entity(name, price);
}
}
And after registering your custom deserializer it works on any object mapper you want:
#Test
public void customDeserialization() throws IOException {
// given
ObjectMapper mapper = new ObjectMapper();
SimpleModule module = new SimpleModule();
module.addDeserializer(Entity.class, new CustomDeserializer(Entity.class));
mapper.registerModule(module);
// when
Entity entity = mapper.readValue("{\"name\":\"xyz\",\"price\":\"90.00\"}", Entity.class);
// then
assertThat(entity.getName()).isEqualTo("xyz-3");
assertThat(entity.getPrice()).isEqualTo(90f);
}
I'm trying to write a GSON TypeAdapterFactory to convert all the keys in String-type key/value pairs to lowercase; i.e. it would convert:
[{"Foo","Bar"}]
to
[{"foo","Bar"}]
This is what I have so far, but I'm having trouble with determining when the key is a String value. The JsonTreeWriter class has a name() Setter method, but no method for Getting the name?
TypeAdapterFactory lowercaseKeyTypeAdapterFactory = new TypeAdapterFactory() {
#Override
public <T> TypeAdapter<T> create(Gson gson, TypeToken<T> type) {
final TypeAdapter<JsonElement> elementAdapter = gson.getAdapter(JsonElement.class);
final TypeAdapter<T> delegate = gson.getDelegateAdapter(this, type); //
return new TypeAdapter<T>() {
public void write(JsonWriter out, T value) throws IOException {
if( out instanceof JsonTreeWriter )
out.name( out.getName().toLowerCase();
JsonElement tree = delegate.toJsonTree(value);
elementAdapter.write(out, tree);
}
public T read(JsonReader in) throws IOException {
JsonElement tree = elementAdapter.read(in);
return delegate.fromJsonTree(tree);
}
};
}
};
To be clear, let introduse some model:
interface A {
boolean isSomeCase();
}
class AAdapter implements JsonSerializer<A> {
public JsonElement serialize(A src, Type typeOfSrc, JsonSerializationContext context) {
if (src.isSomeCase()) {
/* some logic */
return result;
} else {
JsonObject json = new JsonObject();
JsonElement valueJson = <???>; // TODO serialize src like POJO
json.add(src.getClass().getSimpleName(), valueJson);
return json;
}
}
}
Gson gson = new GsonBuilder()
.registerTypeHierarchyAdapter(A.class. new AAdapter())
.create();
How it is possible to serealize some instance of A, which isSomeCase() = false, like any other object, that is serialized by ReflectiveTypeAdapterFactory.Adapter.
You can write a custom TypeAdapterFactory and handle incoming object's isSomeCase() result in its TypeAdapter's write() method and apply your logic there:
public class ATypeAdapterFactory implements TypeAdapterFactory {
public TypeAdapter<A> create(Gson gson, TypeToken type) {
if (!A.class.isAssignableFrom(type.getRawType())) {
// Check if incoming raw type is an instance of A interface
return null;
}
final TypeAdapter<A> delegate = gson.getDelegateAdapter(this, type);
return new TypeAdapter<A>() {
#Override
public void write(JsonWriter out, A value) throws IOException {
if(value.isSomeCase()) {
// your custom logic here
out.beginObject();
out.name("x").value(0);
out.endObject();
} else {
// default serialization here
delegate.write(out, value);
}
}
#Override
public A read(JsonReader in) throws IOException {
return delegate.read(in);
}
};
}
}
Test:
final GsonBuilder gsonBuilder = new GsonBuilder();
// Register custom type adapter factory
gsonBuilder.registerTypeAdapterFactory(new ATypeAdapterFactory());
final Gson gson = gsonBuilder.create();
A aSomeCaseTrue = new AImpl(true);
System.out.print("aSomeCaseTrue:" + gson.toJson(aSomeCaseTrue));
// writes; aSomeCaseTrue:{"x":0}
A aSomeCaseFalse = new AImpl(false);
System.out.print("aSomeCaseFalse:" + gson.toJson(aSomeCaseFalse););
// writes; aSomeCaseFalse:{"someCase":false}
Extras:
1) Your interface:
interface A {
boolean isSomeCase();
}
2) A sample class which implements your sample interface:
class AImpl implements A {
boolean someCase;
public AImpl(boolean value) {
this.someCase = value;
}
#Override
public boolean isSomeCase() {
return someCase;
}
}
I am trying to use TypeAdapterFactory to serialize and deserialize some customer objects. I would like to serialize all the objects to a particular type at runtime.
So given a String classpath and a JsonObject object I would like to deserialize the object to an instance of Class.forName(classpath).
public <T> TypeAdapter<T> create(final Gson gson, final TypeToken<T> tokenType)
{
final TypeAdapter<T> delegate = gson.getDelegateAdapter(this, tokenType);
final TypeAdapter<JsonElement> elementAdapter = gson.getAdapter(JsonElement.class);
return new TypeAdapter<T>()
{
#Override
public T read(JsonReader reader) throws IOException
{
Class<?> clazz = Class.forName(classpath);
JsonObject jsonObject = elementAdapter.read(reader).getAsJsonObject();
// Here I want to return an instance of clazz
}
#Override
public void write(JsonWriter writer, T value) throws IOException
{
}
};
}
How would I go about this?
You can try something like this (code wont compile, you need to catch exceptions). Maybe there is a better syntax for THIS too.
final class MyClass implements TypeAdapterFactory {
#Override
public <T> TypeAdapter<T> create(final Gson gson, final TypeToken<T> tokenType) {
final MyClass THIS = this;
return new TypeAdapter<T>() {
#Override
public T read(JsonReader reader) throws IOException {
Class<?> clazz = Class.forName(classpath);
TypeToken<T> token = (TypeToken<T>) TypeToken.get(clazz);
TypeAdapter<T> adapter = gson.getDelegateAdapter(THIS, token);
JsonElement tree = gson.getAdapter(JsonElement.class).read(reader);
T out = adapter.fromJsonTree(tree);
return out;
}
#Override
public void write(JsonWriter writer, T value) throws IOException {
}
};
}
}
I've this enum:
enum RequestStatus {
OK(200), NOT_FOUND(400);
private final int code;
RequestStatus(int code) {
this.code = code;
}
public int getCode() {
return this.code;
}
};
and in my Request-class, I have this field: private RequestStatus status.
When using Gson to convert the Java object to JSON the result is like:
"status": "OK"
How can I change my GsonBuilder or my Enum object to give me an output like:
"status": {
"value" : "OK",
"code" : 200
}
You can use something like this:
GsonBuilder builder = new GsonBuilder();
builder.registerTypeAdapterFactory(new MyEnumAdapterFactory());
or more simply (as Jesse Wilson indicated):
GsonBuilder builder = new GsonBuilder();
builder.registerTypeAdapter(RequestStatus.class, new MyEnumTypeAdapter());
and
public class MyEnumAdapterFactory implements TypeAdapterFactory {
#Override
public <T> TypeAdapter<T> create(final Gson gson, final TypeToken<T> type) {
Class<? super T> rawType = type.getRawType();
if (rawType == RequestStatus.class) {
return new MyEnumTypeAdapter<T>();
}
return null;
}
public class MyEnumTypeAdapter<T> extends TypeAdapter<T> {
public void write(JsonWriter out, T value) throws IOException {
if (value == null) {
out.nullValue();
return;
}
RequestStatus status = (RequestStatus) value;
// Here write what you want to the JsonWriter.
out.beginObject();
out.name("value");
out.value(status.name());
out.name("code");
out.value(status.getCode());
out.endObject();
}
public T read(JsonReader in) throws IOException {
// Properly deserialize the input (if you use deserialization)
return null;
}
}
}
In addition to Polet's answer, if you need a generic Enum serializer, you can achieve it via reflection:
public class EnumAdapterFactory implements TypeAdapterFactory
{
#Override
public <T> TypeAdapter<T> create(final Gson gson, final TypeToken<T> type)
{
Class<? super T> rawType = type.getRawType();
if (rawType.isEnum())
{
return new EnumTypeAdapter<T>();
}
return null;
}
public class EnumTypeAdapter<T> extends TypeAdapter<T>
{
#Override
public void write(JsonWriter out, T value) throws IOException
{
if (value == null || !value.getClass().isEnum())
{
out.nullValue();
return;
}
try
{
out.beginObject();
out.name("value");
out.value(value.toString());
Arrays.stream(Introspector.getBeanInfo(value.getClass()).getPropertyDescriptors())
.filter(pd -> pd.getReadMethod() != null && !"class".equals(pd.getName()) && !"declaringClass".equals(pd.getName()))
.forEach(pd -> {
try
{
out.name(pd.getName());
out.value(String.valueOf(pd.getReadMethod().invoke(value)));
} catch (IllegalAccessException | InvocationTargetException | IOException e)
{
e.printStackTrace();
}
});
out.endObject();
} catch (IntrospectionException e)
{
e.printStackTrace();
}
}
public T read(JsonReader in) throws IOException
{
// Properly deserialize the input (if you use deserialization)
return null;
}
}
}
Usage:
#Test
public void testEnumGsonSerialization()
{
List<ReportTypes> testEnums = Arrays.asList(YourEnum.VALUE1, YourEnum.VALUE2);
GsonBuilder builder = new GsonBuilder();
builder.registerTypeAdapterFactory(new EnumAdapterFactory());
Gson gson = builder.create();
System.out.println(gson.toJson(reportTypes));
}