Kdb Java API

Examples of querying, subscribing and a java feedhandler are available to download and are detailed below:

Useful Code KX Information
Querying
Subscribing to tickerplant data
Feedhandler - sending data to tickerplant

Example of kdb Java API

Commands to run

# query a table example 
# assumes kdb server on localhost port 5001
wget -q http://www.timestored.com/kdb-guides/kdb-java-api-examples.jar
java -cp kdb-java-api-examples.jar com.timestored.kdb.examples.TableQueryExample
java -cp kdb-java-api-examples.jar com.timestored.kdb.examples.TableQueryExample "([] a:til 10; b:10?100)"

# subscrbe to tickerplant 
# assumes tickerplant on machine FXtick01port 5010
java -cp kdb-java-api-examples.jar com.timestored.kdb.examples.SubscriberExample FXtick01 5010

# Feedhandler sending data to tickerplant
# in kdb on localhost port 5001
# trade:([]time:();sym:();price:();size:();stop:();cond:();ex:())
# .u.upd:insert
java -cp kdb-java-api-examples.jar com.timestored.kdb.examples.feedhandler.FeedDemo

Useful Code KX Information

The Interfacing kdb with Java page on the code KX website documents the API. Useful snippets include:

Connecting

Signature	Notes
public c(String host, int port, String usernameAndPassword) throws KException, IOException	Throws a KException if access is denied by the kdb+ server. The username and password should be of the format "username:password"
public c(String host, int port) throws KException, IOException	Uses the user.name property as the login name and password. It throws a KException if access is denied by the kdb server

Method Calls

Comm Type	Method	Description
Asynchronous	public void ks(String s) throws IOException	Send string query.
Asynchronous	public void ks(Object x) throws IOException	Send K object.
Synchronous	public Object k(String s) throws KException, IOException	Send string query, wait and return response.
Synchronous	public Object k(Object x) throws KException, IOException	Send K object, wait and return response
	public Object k() throws KException, IOException	Retrieve waiting messages without sending a query.

Querying

See the TableQueryExample.java in the java example code. This is an almost a direct copy from code.kx.com. The steps are:

Connect
Send query - either string or K object
Cast the returned result then parse

c.Flip tableResult = null;
c c = null;
try {
    c = new c("localhost", 5001,"username:password");
    String query="([]date:.z.D;time:.z.T;sym:n?`8;price:`float$n?500.0;size:n?100;r:til (n:100))";
    tableResult = (c.Flip) c.k(query);
} catch (Exception ex) {
    Logger.getLogger(TableQueryExample.class.getName()).log(Level.SEVERE, null, ex);
} finally {
    if (c != null) {try{c.close();} catch (IOException ex) {}
    }
}

Subscribing to Kdb tickerplant

See the SubscriberExample.java in the java example code. This demonstrates connecting a tickerplant and subscribing to the trade table. The steps are:

Connect
Subscribe to all syms on the trade table
loop forever, calling k() to receive incoming data.
Parse and print the first line of each table update.

c con = new c(host, port);
con.k(".u.sub[`trade;`]"); 

while (true) {
    try {
        Object r = con.k();
        if (r != null) {
            Object[] data = (Object[]) r;

            String tblname = (data[1]).toString();
            c.Flip tbl = (c.Flip) data[2];
            String[] colNames = tbl.x;
            Object[] colData = tbl.y;

            String s = tblname + " update. row 1/" + colData.length + " ->";
            for (int i = 0; i < colData.length; i++) {
                s += " " + colNames[i] + ":" + c.at(colData[i], 0).toString();
            }
            System.out.println(s);
        }
    } catch (Exception e) {
            System.err.println(e.toString());
    }
}

Feedhandler - sending data to tickerplant

Demonstrate creating feedhandler, making it listen to incoming data and forwarding to the kdb server. Before running start a fresh kdb server on port 5000 and enter the below:

trade:([]time:`time$();sym:`symbol$();price:`float$();size:`int$();stop:`boolean$();cond:`char$();ex:`char$())
.u.upd:insert; / Allows using the same commands as a kdb tickerplant.

Create our feed handler that forwards data to a q process on localhost port 5000 and attach to a fake feed.

FeedDemo.java

public class FeedDemo {
    public static void main(String... args) throws KException, IOException {
            FeedHandler feedHandler = new FeedHandler("localhost", 5001);
            FakeFeed.INSTANCE.addListener(feedHandler);
    }
}

FeedHandler.java

/**
 * Implements {@link FeedListener} so can listen to feeds which it will then
 * parse to a K object and forward to a kdb server.
 */
public class FeedHandler implements FeedListener {

	private static final String[] COL_NAMES 
		= new String[] { "time", "sym", "price", "size", "stop", "cond", "ex" };
	
	private c conn;
	
	public FeedHandler(String host, int port) throws KException, IOException {
		conn = new c(host, port);
	}

	@Override
	public void tradeEvent(List<TradeEvent> trades) {

		int numRecords = trades.size();
		System.out.print("Recieved " + numRecords + " records from fakefeed. ");
		
		// create the vectors for each column
		Time[] t = new Time[numRecords];
		String[] sym = new String[numRecords];
		double[] price = new double[numRecords];
		int[] size = new int[numRecords];
		boolean[] stop = new boolean[numRecords];
		char[] cond = new char[numRecords];
		char[] ex = new char[numRecords];
		
		// loop through filling the columns with data
		for(int i=0; i<trades.size(); i++) {
			TradeEvent te = trades.get(i);
			t[i] = te.time;
			sym[i] = te.sym;
			price[i] = te.price;
			size[i] = te.size;
			stop[i] = te.stop;
			cond[i] = te.cond;
			ex[i] = te.ex;
		}
		
		// create the table itself from the separate columns
		Object[] data = new Object[] { t, sym, price, size, stop, cond, ex };
		c.Flip tab = new c.Flip(new c.Dict(COL_NAMES, data));
		// create the command to insert the table of data into the named table.
		Object[] updStatement = new Object[] { ".u.upd", "trade", tab };
		try {
			conn.ks(updStatement); // send asynchronously
			System.out.println("Sent " + numRecords + " records to kdb server");
		} catch (IOException e) {
			System.err.println("error sending feed to server.");
		}
	}
	
}

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