Google Spreadsheets for Game Configuration ~ September 2, 2013
Dynamic game configuration is always useful, and doing it cheaply and easily is especially important for small indy studios. Setting up a Google Spreadsheet with your runtime configuration data enables easy collaborative editing, and having a process that can read that data and export JSON makes it easy to use that data at runtime in whatever client language you find suitable. In this article I’m using Gson for JSON serialization, but it wouldn’t be difficult to use Jackson instead, if that’s how you roll.
When my wife and I started working on our own hidden object game for mobile, we needed a game data editor that wouldn’t take me a long time to write and would be easily extensible. We settled on using a specially formatted spreadsheet in Google Drive that would be read by a process on our dashboard server to generate JSON that the client would load either from the game server or from a static file in Amazon S3.
As shown in the example above, the conversion is pretty straightforward:
- Keys in the left column, values in the column(s) to the right.
- Keys get camel-cased automatically.
- Cells that start with an asterisk are comments.
- If a row has multiple values, it is automatically converted to an array.
- A key may be opening/closing brackets or braces to wrap arrays and objects.
- A key cell may have a compound value to open/close objects and arrays inline with a name.
- Empty rows are ignored (not shown in the example).
Code time
The public entry point to this utility takes a cell feed URL and an instance of GoogleCredential. Retreiving these values is outside the scope of this article. I recommend reading through the Google Spreadsheets API documentation for guidance in setting up your access to spreadsheets in general.
26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 | public class SpreadsheetReader {
/**
* Converts the worksheet at the given URL to JSON.
*/
public JsonObject readJson (String url, GoogleCredential cred) {
SpreadsheetService service = new SpreadsheetService("TestServiceCall");
service.setOAuth2Credentials(cred);
try {
CellFeed feed = service.getFeed(new URL(url), CellFeed.class);
return readJson(feed);
} catch (ServiceException se) {
log.warning("ServiceException reading spreadsheet", se);
} catch (IOException ioe) {
log.warning("IOException reading spreadsheet", ioe);
}
return null;
}
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Rather than go through this whole class line by line, I’m just going to talk about a couple of meaty bits. The full class may be downloaded from the link at the head of any of these inline code sections.
The static inner class SpreadsheetRow is reponsible for the bulk of the parsing work. It filters out comments:
213 214 215 216 217 218 219 220 | if (key.startsWith("*")) {
Cell cell;
// consume any more cells on this row
while ((cell = iter.hasNext() ? iter.next().getCell() : null) != null &&
cell.getRow() == row);
if (cell != null && cell.getRow() != row) iter.previous();
return rows;
}
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Finds all the values in a given row:
230 231 232 233 234 235 236 237 238 | // get any valid value cells into the values list.
Cell valueCell;
while ((valueCell = iter.hasNext() ? iter.next().getCell() : null) != null &&
valueCell.getRow() == row) {
String value = valueCell.getValue().trim();
if (!value.startsWith("*")) values.add(value);
}
// roll back the iterator if we've bumped into the next row.
if (valueCell != null && valueCell.getRow() != row) iter.previous();
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And breaks up compound keys into multiple logical rows for easier processing:
243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 | // break up any compound keys into separate key parts. Things like "} Foo Bar {"
// get broken into "}", "Foo Bar" and "{"
List<String> keyParts = new ArrayList<String>();
Matcher m = COMPLEX_CELL.matcher(key);
boolean found = false;
int end = 0;
while (m.find()) {
if (found && end != m.start())
keyParts.add(key.substring(end, m.start()).trim());
end = m.end();
if (!found && m.start() > 0) keyParts.add(key.substring(0, m.start()).trim());
found = true;
keyParts.add(key.substring(m.start(), m.end()).trim());
}
if (found) {
if (end < key.length() - 1) keyParts.add(key.substring(end).trim());
} else {
keyParts.add(key);
}
// Break compound keys into separate rows to make JSON construction much simpler.
// The values associated with this row in the spreadsheet are attached to the last
// string key or array opening bracket found in this compound key
SpreadsheetRow lastRow = null;
for (String keyPart : keyParts) {
if (keyPart.length() == 0) continue;
if (keyPart.equals("{")) rows.add(empty(keyPart));
else if (keyPart.equals("[")) rows.add(lastRow = empty(keyPart));
else if (keyPart.equals("}")) rows.add(empty(keyPart));
else if (keyPart.equals("]")) rows.add(empty(keyPart));
else rows.add(lastRow = empty(keyPart));
}
// if we found a valid key for storing a value, attach this row's value to it
if (lastRow != null) lastRow.value.addAll(values);
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Once the values of the spreadsheet cells have been read and parsed into this format, building up the JSON Object and Array representation is relatively straightforward.
60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 | /**
* Returns a JsonElement built out of the rows at the current position of rowIter. The first
* element is expected to have "{" as the key, and processing continues until a corresponding
* "}" key is found.
*/
protected JsonObject createObject (ListIterator<SpreadsheetRow> rowIter) {
if (!rowIter.hasNext()) {
return null;
}
SpreadsheetRow row = rowIter.next();
if (row.key == null || !row.key.equals("{")) {
log.warning("Object not started with {", "key", row.key);
return null;
}
JsonObject obj = new JsonObject();
while (rowIter.hasNext()) {
row = rowIter.next();
// Objects require that a key be associated with each value found. Null keys and objects
// starting without a corresponding key are an error.
if (row.key == null) {
log.warning("Null key in object");
} else if (row.key.equals("}")) {
// we've found our matching close brace, return results
return obj;
} else if (row.key.equals("{") || row.key.equals("[") || row.key.equals("]")) {
log.warning("Non key in object", "key", row.key);
} else {
if (!row.value.isEmpty()) {
JsonElement value = getValue(row.value);
if (value != null) obj.add(cellKey(row.key), value);
} else if (!rowIter.hasNext()) {
// this row had no value, and there is no next row to contain a value either.
log.warning("Obj has no value", "key", row.key);
} else {
// peek at the next row to see if it's a start of an object or array for this
// row's key.
String key = row.key;
row = rowIter.next(); rowIter.previous(); // peek
if (row.key.equals("{")) {
obj.add(cellKey(key), createObject(rowIter));
} else if (row.key.equals("[")) {
obj.add(cellKey(key), createArray(rowIter));
} else {
log.warning("Invalid row after empty obj key", "key", key, "next", row.key);
}
}
}
}
return obj;
}
/**
* Returns a JsonArray corresponding to the rows starting at the current position of the
* iterator. The rows are expected to start with a "[" key, and processing continues until a
* corresponding "]" key is found.
*/
protected JsonArray createArray (ListIterator<SpreadsheetRow> rowIter) {
SpreadsheetRow row = rowIter.next();
if (row.key == null || !row.key.equals("[")) {
log.warning("create array not started with [", row.key);
return null;
}
JsonArray arr = new JsonArray();
if (!row.value.isEmpty()) {
// the opening array row can have a value.
arr.add(getValue(row.value));
}
while (rowIter.hasNext()) {
row = rowIter.next();
if (row.key == null) {
arr.add(getValue(row.value));
} else if (row.key.equals("[")) {
rowIter.previous();
arr.add(createArray(rowIter));
} else if (row.key.equals("{")) {
rowIter.previous();
arr.add(createObject(rowIter));
} else if (row.key.equals("]")) {
// we found our corresponding array closure, bounce back the result.
return arr;
} else {
log.warning("Bad key while in array", "key", row.key);
}
}
return arr;
}
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That’s about it! Using this tool, we can quickly release tuning updates to our clients in the wild, without requiring a new client build (especially important for games in any kind of app store that has a vetting process that takes a long time). In a future article, I’ll talk about the tools we’re using to generate code for reading our configuration data format from the generated JSON files.
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