For saving simpel data types, libGDX offers Preferences. However, if you want to save custom objects, in particular your whole game state – usually to save it to disk so it can be restored later – you need to serialize it first. There are a couple of different ways for doing this.
JSON serialization
libGDX’s JSON classes can automatically convert Java objects to and from JSON. Check out the corresponding wiki article to find out more.
Binary serialization
Another option for efficiently serializing Java objects is the Kryo library. Kryo can handle most POJOs and other classes, but some classes need special handling. Below are a few custom serializers for libGDX classes.
Note that classes like Texture should not be serialized in most cases. It would be better to have a String instead of a Texture object in your object graph. After serializing you would process the objects and look up the texture using the string path.
// Register a custom Array serializer
kryo.register(Array.class, new Serializer<Array>() {
{
setAcceptsNull(true);
}
private Class genericType;
public void setGenerics (Kryo kryo, Class[] generics) {
if (generics != null && kryo.isFinal(generics[0])) genericType = generics[0];
else genericType = null;
}
public void write (Kryo kryo, Output output, Array array) {
int length = array.size;
output.writeInt(length, true);
if (length == 0) {
genericType = null;
return;
}
if (genericType != null) {
Serializer serializer = kryo.getSerializer(genericType);
genericType = null;
for (Object element : array)
kryo.writeObjectOrNull(output, element, serializer);
} else {
for (Object element : array)
kryo.writeClassAndObject(output, element);
}
}
public Array read (Kryo kryo, Input input, Class<Array> type) {
Array array = new Array();
kryo.reference(array);
int length = input.readInt(true);
array.ensureCapacity(length);
if (genericType != null) {
Class elementClass = genericType;
Serializer serializer = kryo.getSerializer(genericType);
genericType = null;
for (int i = 0; i < length; i++)
array.add(kryo.readObjectOrNull(input, elementClass, serializer));
} else {
for (int i = 0; i < length; i++)
array.add(kryo.readClassAndObject(input));
}
return array;
}
});
// Register a custom IntArray serializer
kryo.register(IntArray.class, new Serializer<IntArray>() {
{
setAcceptsNull(true);
}
public void write (Kryo kryo, Output output, IntArray array) {
int length = array.size;
output.writeInt(length, true);
if (length == 0) return;
for (int i = 0, n = array.size; i < n; i++)
output.writeInt(array.get(i), true);
}
public IntArray read (Kryo kryo, Input input, Class<IntArray> type) {
IntArray array = new IntArray();
kryo.reference(array);
int length = input.readInt(true);
array.ensureCapacity(length);
for (int i = 0; i < length; i++)
array.add(input.readInt(true));
return array;
}
});
// Register a custom FloatArray serializer
kryo.register(FloatArray.class, new Serializer<FloatArray>() {
{
setAcceptsNull(true);
}
public void write (Kryo kryo, Output output, FloatArray array) {
int length = array.size;
output.writeInt(length, true);
if (length == 0) return;
for (int i = 0, n = array.size; i < n; i++)
output.writeFloat(array.get(i));
}
public FloatArray read (Kryo kryo, Input input, Class<FloatArray> type) {
FloatArray array = new FloatArray();
kryo.reference(array);
int length = input.readInt(true);
array.ensureCapacity(length);
for (int i = 0; i < length; i++)
array.add(input.readFloat());
return array;
}
});
// Register a custom Color serializer
kryo.register(Color.class, new Serializer<Color>() {
public Color read (Kryo kryo, Input input, Class<Color> type) {
Color color = new Color();
Color.rgba8888ToColor(color, input.readInt());
return color;
}
public void write (Kryo kryo, Output output, Color color) {
output.writeInt(Color.rgba8888(color));
}
});