// 把JSON写到文件中
public void saveCrimes(ArrayList<Crime> crimes) throws JSONException, IOException {
// build an array in JSON
JSONArray array = new JSONArray();
for (Crime c : crimes) array.put(c.toJSON());
// write the file to disk
Writer writer = null;
try {
OutputStream out = mContext.openFileOutput(mFilename, Context.MODE_PRIVATE);
writer = new OutputStreamWriter(out);
writer.write(array.toString());
} finally {
if (writer != null) writer.close();
}
}