Complex Event Processing

EventSchema can be used to define events on API client.

public class EventSchema {
  private String eventType;                         
  private List<String> fieldNames;                  
  private List<Entity.DATA_TYPE> fieldTypes;           
  private List<Entity.DATA_FORM> fieldForms;            
  private List<Integer> fieldExtraParams;              
}

Parameters

• eventType: A String indicating the event.
• fieldNames: A String indicating the field names.
• fieldTypes: Data types of fields.
• fieldForms: Data forms of fields.
• fieldExtraParams: A non-negative int used to specify the scale when the field type is DECIMAL.

EventSender can be used to write serialized event data into heterogeneous stream tables, which are subscribed by CEP engines in DolphinDB to capture and process the events.

public EventSender(DBConnection conn, String tableName, List<EventSchema> eventSchemas, List<String> eventTimeKeys, List<String> commonKeys)

public void sendEvent(String eventType, List<Entity> attributes)

The API provides the EventClient tool for subscribing to events in heterogeneous stream tables. These tables typically receive event data processed and serialized by the DolphinDB CEP engine.

public EventClient(List<EventSchema> eventSchemas, List<String> eventTimeKeys, List<String> commonKeys)

public void subscribe(String host, int port, String tableName, String actionName, MessageHandler handler, long offset, boolean reconnect, String userName, String password)

EventMessageHandler handler = new EventMessageHandler() {
    @Override
    public void doEvent(String eventType, List<Entity> attribute) {
        // Handling logic
    }
};

public void unsubscribe(String host, int port, String tableName, String actionName)

Parameters

• host: IP address of the publisher node.
• port: Port number of the publisher node.
• tableName: Name of the publisher stream table.
• actionName: The subscription task.

This example introduces how to create events on the server, interfaces for serializing events, heterogeneous stream tables for writing and outputting events, and the CEP engine for processing events. Then use EventSender on the API to send events to the heterogeneous stream table. After the CEP engine processes and outputs messages to another heterogeneous stream table through subscription, use EventClient on the API side to subscribe to the output events.

The following script will create two heterogeneous stream tables input and output, two streamEventSerializer (serialization interfaces), a CEP engine, and a MarketData event on the DolphinDB server.

login("admin","123456");

class MarketData{
  market :: STRING
  code :: SYMBOL
  price :: DOUBLE
  qty :: INT
  eventTime :: TIMESTAMP
  def MarketData(m,c,p,q){
    market = m
    code = c
    price = p
    qty = q
    eventTime = now()   
  }
}   

class MainMonitor{
  
  def MainMonitor(){
  }
  def updateMarketData(event)

  def onload(){
    addEventListener(updateMarketData,'MarketData',,'all')
      }

  def updateMarketData(event){
    emitEvent(event)
  }
}

dummy = table(array(TIMESTAMP, 0) as eventTime, array(STRING, 0) as eventType, array(BLOB, 0) as blobs)
share streamTable(array(TIMESTAMP, 0) as eventTime, array(STRING, 0) as eventType, array(BLOB, 0) as blobs) as intput
share streamTable(array(TIMESTAMP, 0) as eventTime, array(STRING, 0) as eventType, array(BLOB, 0) as blobs) as output
schema = table(1:0, `eventType`eventKeys`eventValuesTypeString`eventValueTypeID`eventValuesFormID, [STRING, STRING, STRING, INT[], INT[]])
insert into schema values("MarketData", "market,code,price,qty,eventTime", "STRING,STRING,DOUBLE,INT,TIMESTAMP", [18 18 16 4 12], [0 0 0 0 0])
inputSerializer = streamEventSerializer(name=`serInput, eventSchemes=schema, outputTable=intput, eventTimeKey = "eventTime")
outputSerializer = streamEventSerializer(name=`serOutput, eventSchemes=schema, outputTable=output, eventTimeKey = "eventTime")

engine = createCEPEngine('cep1', <MainMonitor()>, dummy, [MarketData], 1, 'eventTime', 10000, outputSerializer)
subscribeTable(,`intput, `subopt, 0, getStreamEngine('cep1'),true)

marketData1 = MarketData('sz', 's001', 9.8, 100)
marketData2 = MarketData('sz', 's002', 6.9, 100)
marketData3 = MarketData('sz', 's003', 4.8, 100)
marketData4 = MarketData('sz', 's004', 9.8, 100)
marketData5 = MarketData('sz', 's005', 9.8, 100)
appendEvent(inputSerializer, [marketData1,marketData2,marketData3,marketData4,marketData5])

Then write data to input via EventSender on API.

// Define schema
EventSchema schema = new EventSchema();
schema.setEventType("MarketData");
schema.setFieldNames(Arrays.asList("market", "code", "price", "qty", "eventTime"));
schema.setFieldTypes(Arrays.asList(DT_STRING, DT_STRING, DT_DOUBLE, DT_INT, DT_TIMESTAMP));
schema.setFieldForms(Arrays.asList(DF_SCALAR, DF_SCALAR, DF_SCALAR, DF_SCALAR, DF_SCALAR));
List<EventSchema> eventSchemas = Collections.singletonList(scheme);
List<String> eventTimeKeys = Collections.singletonList("eventTime");
List<String> commonKeys = new ArrayList<>();

// Create EventSender
DBConnection conn = new DBConnection(true);
conn.connect(HOST, PORT, "admin", "123456");
EventSender sender = new EventSender(conn, "input", eventSchemas, eventTimeKeys, commonKeys);

// Prepare data
List<Entity> attributes = new ArrayList<>();
attributes.add(new BasicString("sz"));
attributes.add(new BasicString("s001"));
attributes.add(new BasicDouble(9.8));
attributes.add(new BasicInt(100));
attributes.add(new BasicTimestamp(LocalDateTime.of(2024,3,13,15,11,10,630)));

sender.sendEvent("MarketData", attributes);

The stream table input is subscribed by a CEP engine, which generates events to the output table.

Then use EventClient to subscribe to the output table.

EventSchema scheme = new EventSchema();
scheme.setEventType("MarketData");
scheme.setFieldNames(Arrays.asList("market", "code", "price", "qty", "eventTime"));
scheme.setFieldTypes(Arrays.asList(DT_STRING, DT_STRING, DT_DOUBLE, DT_INT, DT_TIMESTAMP));
scheme.setFieldForms(Arrays.asList(DF_SCALAR, DF_SCALAR, DF_SCALAR, DF_SCALAR, DF_SCALAR));
List<EventSchema> eventSchemas = Collections.singletonList(scheme);
List<String> eventTimeKeys = Collections.singletonList("eventTime");
List<String> commonKeys = new ArrayList<>();

// user-defined callback
EventMessageHandler handler = new EventMessageHandler() {
    @Override
    public void doEvent(String eventType, List<Entity> attribute) {
        // user-defined processing
        System.out.println("eventType: " + eventType);
        for (Entity entity : attribute) {
            System.out.println(entity.getString());
        }
        System.out.println("\n");
    }
};

// create EventClient
EventClient client = new EventClient(eventSchemas, eventTimeKeys, commonKeys);
// create subscription
client.subscribe(HOST, PORT, "output", "ss1", handler, 0, true, "admin", "123456");
Thread.sleep(10000);

// cancel subscription
client.unsubscribe(HOST, PORT, "output", "ss1");