public static void main(String[] args) {
AmazonDynamoDBClient client = new AmazonDynamoDBClient(new ProfileCredentialsProvider());
client.setRegion(Region.getRegion(Regions.US_WEST_2));
DynamoDBMapper mapper = new DynamoDBMapper(client);
// retrieve an object using a "normal" (non-composite) id
Movie m = new Movie();
m.setTitle("foxy brown");
Movie m2 = mapper.load(m);
if (m2.getExtra() != null) {
System.out.println("title:" + m2.getTitle() + " extra:" + m2.getExtra());
}
// retrieve an object using a composite key
Artist a = new Artist();
a.setId(5);
a.setName("Van Gogh");
Artist a2 = mapper.load(a);
// scan through a bunch of entries in a table and print them out
ScanRequest scanRequest = new ScanRequest().withTableName("Artists");
ScanResult result = client.scan(scanRequest);
for (Map<String, AttributeValue> item : result.getItems()) {
String o1 = item.get("id").getN();
String o2 = item.get("name").getS();
Artist artist = mapper.load(Artist.class, new Integer(o1), o2);
artist.dump();
}
}
/**
* This class relies heavily on the behavior of segmented scans with respect to which hash keys
* are scanned by each segment. Here's a rough ASCII example to help illustrate:
* ___________________________ |hk:A |hk:B | ---------------------------- ^segment 1 ^segment 2
*
* <p>Because we are scanning in segments across the entire hash key space, it is possible for the
* same hash key to appear in two different segments. We are also running all of the scan segments
* in parallel, so we have no control over which segment returns first.
*
* <p>In the example, if segment 2 was the first segment to post a result, we would store hk:B as
* a "boundary" key. That way when segment 1 eventually reaches hk:B in its scan, we know that
* another segment has already returned this hash key and we can safely skip returning it.
*
* <p>By doing this, we avoid returning a RecordIterator for the same hash key twice and we only
* need to store at most 2 hash keys per segment.
*/
@Override
public List<SingleKeyRecordIterator> buildRecordIterators(ScanContext scanContext) {
final ScanResult dynamoDbResult = scanContext.getScanResult();
final int segment = scanContext.getScanRequest().getSegment();
final List<Map<String, AttributeValue>> items = dynamoDbResult.getItems();
// If the scan returned no results, we need to shortcut and just throw back an empty result set
if (items.isEmpty()) {
return Collections.emptyList();
}
List<SingleKeyRecordIterator> recordIterators = Lists.newLinkedList();
final Iterator<Map<String, AttributeValue>> itemIterator = items.iterator();
final Map<String, AttributeValue> firstItem = itemIterator.next();
final StaticBuffer firstKey = new KeyBuilder(firstItem).build(Constants.TITAN_HASH_KEY);
// Computes the full set of boundary keys up to this point. This includes the previous end key
// for this segment.
final ImmutableSet<StaticBuffer> boundaryKeys = aggregateBoundaryKeys();
// The first key in this scan segment might already have been returned by a previous scan
// segment
if (!boundaryKeys.contains(firstKey)) {
recordIterators.add(buildRecordIteratorForHashKey(firstKey));
}
StaticBuffer hashKey = firstKey;
while (itemIterator.hasNext()) {
final Optional<StaticBuffer> nextKey = findNextHashKey(itemIterator, hashKey);
if (nextKey.isPresent()) {
// Found a new hash key. Make a record iterator and look for the next unique hash key
hashKey = nextKey.get();
recordIterators.add(buildRecordIteratorForHashKey(hashKey));
}
}
// If we've already seen the final hashKey in a previous scan segment result, we want to avoid
// returning it again.
if (!hashKey.equals(firstKey) && boundaryKeys.contains(hashKey)) {
recordIterators.remove(recordIterators.size() - 1);
}
// Update the boundary keys for this segment
if (scanContext.isFirstResult()) {
setInitialBoundaryKeys(segment, firstKey, hashKey);
} else {
updateLastKey(segment, hashKey);
}
return recordIterators;
}
/** @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response) */
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
String category = request.getParameter("category");
HashMap<String, Condition> scanFilter = new HashMap<String, Condition>();
Condition condition =
new Condition()
.withComparisonOperator(ComparisonOperator.NE.toString())
.withAttributeValueList(new AttributeValue().withN("0"));
Condition condition2 =
new Condition()
.withComparisonOperator(ComparisonOperator.NE.toString())
.withAttributeValueList(new AttributeValue().withN("0"));
Condition condition3 = new Condition().withComparisonOperator(ComparisonOperator.CONTAINS);
scanFilter.put("geoLat", condition);
scanFilter.put("geoLng", condition2);
if (category != null && !category.isEmpty()) {
condition3.withAttributeValueList(new AttributeValue().withS(category));
scanFilter.put("category", condition3);
}
// String queueUrl = SQS.getQueueUrl(new GetQueueUrlRequest(SQS_QUEUE_NAME)).getQueueUrl();
String tableName = DYNAMODB_TABLE_NAME;
ScanRequest scanRequest = new ScanRequest(tableName).withScanFilter(scanFilter);
ScanResult scanResult = DYNAMODB.scan(scanRequest);
int size = scanResult.getItems().size();
ArrayList<HashMap<String, String>> tweets = new ArrayList<HashMap<String, String>>();
for (int i = 0; i < size; i++) {
// Get latitude, longitude, content, username, created (long), category, sentiment
String categorydb = "no category";
String sentiment = "no sentiment";
if (scanResult.getItems().get(i).get("category") != null) {
categorydb = scanResult.getItems().get(i).get("category").getS();
sentiment = scanResult.getItems().get(i).get("sentiment").getS();
String lat = scanResult.getItems().get(i).get("geoLat").getN();
String lng = scanResult.getItems().get(i).get("geoLng").getN();
String content = scanResult.getItems().get(i).get("content").getS();
String username = scanResult.getItems().get(i).get("username").getS();
String created = scanResult.getItems().get(i).get("createdLong").getN();
String createdDate = scanResult.getItems().get(i).get("createdDate").getS();
// Format date.
DateFormat fromFormat = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSS'Z'");
DateFormat toFormat = new SimpleDateFormat("MMM dd ยท k:mm z");
Date date;
String createdstr;
try {
date = fromFormat.parse(createdDate);
createdstr = toFormat.format(date);
} catch (ParseException e) {
createdstr = createdDate;
}
// Create tweet hash.
HashMap<String, String> tweet = new HashMap<String, String>();
tweet.put("lat", lat);
tweet.put("lng", lng);
tweet.put("content", content);
tweet.put("username", username);
tweet.put("category", categorydb);
tweet.put("sentiment", sentiment);
tweet.put("created", created);
tweet.put("createdstr", createdstr);
// Order tweet by time created. Most recent at the top of the list.
int position = 0;
while (position < tweets.size()
&& Long.parseLong(tweets.get(position).get("created")) > Long.parseLong(created)) {
position++;
}
tweets.add(position, tweet);
}
// else {
// Send tweet with blank category for sentimental processing
// String id = scanResult.getItems().get(i).get("id").getS();
// SQS.sendMessage(new SendMessageRequest(queueUrl, id));
// }
}
// Log result.
System.out.println("Successfully handled GET request.");
if (category != null) {
System.out.println("category:" + category);
}
System.out.println("size: " + tweets.size());
// Convert object to JSON format.
String json = new Gson().toJson(tweets);
response.setContentType("application/json");
response.setCharacterEncoding("UTF-8");
response.getWriter().write(json);
}