caching JSON from webservice on android - pattern?

Here's a simply way to do this that doesn't involve a service, threads, alarms, etc. just define a wrapper around your JSON, like,

class MyJson {    JSONObject getJson() { ... };}

the implementation of getJson() does the following,

if (cached json file exists) {  if (json file last modified + 1 day > current time) {    json = get from network;    cache json in file;  } else [    json = get from file;  }} else {    json = get from network;    cache json in file;}

in other words, lazy-fetch the fresh json from the network when you need it. this is vastly simpler than periodically updating a cache file by setting alarms and running a service to update the cache ...

from your app, you do the same thing whether it's the first load or the Nth load of the data. you call getJson(),

new Thread(new Runnable() {  public void run() {    json = getJson();    // do whatever you need to do after the json is loaded  }}).start();

the only downside is that occasionally, the call to get the JSON will take longer, and consequently you must run it in a thread so as not to ANR the UI ... but you should do that anyway, because whether it's in a file or fetched from the network, you should avoid doing IO in the UI thread.