In PlayN, how do I use the Storage interface to persist data? - playn

Question

I'm looking for a code example that demonstrates practical real-world usage of the Storage interface. I'm especially interested in HTML5 implementation. I've just started working on my own proof-of-concept, so I'll post that if no better answers arrive before then.
The Storage interface is introduced in this Google presentation here:
http://playn-2011.appspot.com/

Answer 1

Here's some code that demonstrates the use of the storage interface together with PlayN's JSON interface:
private void loadStoredData() {
// storage parameters
String storageKey = "jsonData";
Json.Object jsonData = PlayN.json().createObject();
// to reset storage, uncomment this line
//PlayN.storage().removeItem(storageKey);
// attempt to load stored data
String jsonString = PlayN.storage().getItem(storageKey);
// if not loaded, create stored data
if ( jsonString == null ) {
DemoApi.log("stored data not found");
jsonData.put("firstWrite", new Date().toString());
// else display data
} else {
jsonData = PlayN.json().parse(jsonString);
DemoApi.log("stored data loaded");
DemoApi.log("data first written at " + jsonData.getString("firstWrite"));
DemoApi.log("data last read at " + jsonData.getString("lastRead"));
DemoApi.log("data last written at " + jsonData.getString("lastWrite"));
}
// update last read
jsonData.put("lastRead", new Date().toString());
// write data (this works in Java -- not in HTML)
// see https://stackoverflow.com/q/10425877/1093087
/*
Json.Writer jsonWriter = PlayN.json().newWriter();
jsonWriter.object(jsonData).done();
jsonString = jsonWriter.write();
*/
// alternative write routine
Json.Writer jsonWriter = PlayN.json().newWriter();
jsonWriter.object();
for ( String key : jsonData.keys() ) {
jsonWriter.value(key, jsonData.getString(key));
}
jsonWriter.end();
jsonString = jsonWriter.write();
// store data as json
PlayN.storage().setItem(storageKey, jsonString);
// confirm
if ( PlayN.storage().isPersisted() ) {
DemoApi.log("data successfully persisted");
} else {
DemoApi.log("failed to persist data");
}
}
There's one little hitch with the Json.Writer that seems a bit buggy that I document in this question here: In the HTML version of PlayN, why does the following JSON-handling code throw an exception?