Database Feed

[Alessandro]

Hi Gerard,

We haven't had time to work on this example yet, even if it would be pretty simple to implement.

Basically, in the case of Java, it would be enough to take the Hello-World Data Adapter and add some JDBC code to poll a DB instead of generating pseudo-random data.

Again, my call to anybody who has this example done to share it with the community.

Thanks

[amarin]

What are the pros and cons between

1)reading directly from a DB source
and
2)reading from a file like xml

I write a program to dynamically creates an XML file when a transaction takes place. Then feeds it to the LS. One file for each item with 6 fields.
I have about 30 items in all.

[Alessandro]

Amarin,

The best approach would be to have an asynchronous data feed (based on some message-oriented middleware), which does not require polling. Both a DB and an XML data source are usually based on polling. That said, choosing between a DB and an XML file depends on many aspects, such as the polling frequency, the amount of data being polled, general architecture considerations, including transactions and fail-over. So it's impossible to provide a general answer.

[amarin]

Thanks for your reply Alessandro

What would the setup look like with MOM?
Do I use it alongside lightstreamer?

Would this be ok

http://www.jboss.com/products/platforms/dataservices

or

http://www.jboss.org/projects/

Do you recommend anything else?

Thanks again

[Alessandro]

Sure, any JMS implementation would be a perfect solution.
By the way, you can find a JBoss-based example in the "Lightstreamer\DOCS-SDKs\sdk_adapter_java\examples\StockListDemo_JMS_D ataAdapter" folder of your Lightstreamer distribution.

[gerard]

Hi there,

I have to make a decision as to whether we can use Lightstreamer for a new project. Is there prospect of sample code for database integration being provided to developers in the near future.

Regards

Gerard

[Alessandro]

I modified the HelloWorldDataAdapter to poll a database, instead of generating the data internally.

Please consider this is just a five-minute effort and I've not tried to compile the code. Please let me know if you find any errors.

This Data Adapter uses JDBC to query an Access file ("C:/Data.mdb"). Every second, it reads the first record, extracts the "message" and "timestamp" fields and injects them into the Lightstreamer Kernel.

import java.util.*;<br /> import java.io.File;<br /> import java.sql.*;<br /> import com.lightstreamer.interfaces.data.*;<br /> <br /> public class HelloWorldDataAdapter implements SmartDataProvider {<br /> <br /> private ItemEventListener listener;<br /> private volatile GreetingsThread gt;<br /> private Statement command;<br /> <br /> public void init(Map params, File configDir) throws DataProviderException {<br /> try {<br /> Class.forName("sun.jdbc.odbc.JdbcOdbcDriver").newI nstance();<br /> String dbFile = "C:/Data.mdb";<br /> String database = "jdbc:odbc:Driver={Microsoft Access Driver (*.mdb)};DBQ="<br /> + dbFile.trim()+ ";DriverID=22;READONLY=true}";<br /> Connection conn = DriverManager.getConnection(database, "", "");<br /> command = conn.createStatement();<br /> } catch (Exception ex) {<br /> System.out.println(ex);<br /> throw new DataProviderException(ex.getMessage());<br /> }<br /> }<br /> <br /> public boolean isSnapshotAvailable(String itemName) throws SubscriptionException {<br /> return false;<br /> }<br /> <br /> public void setListener(ItemEventListener listener) {<br /> this.listener = listener;<br /> }<br /> <br /> public void subscribe(String itemName, Object itemHandle, boolean needsIterator)<br /> throws SubscriptionException, FailureException {<br /> if (itemName.equals("greetings")) {<br /> gt = new GreetingsThread(itemHandle);<br /> gt.start();<br /> }<br /> }<br /> <br /> public void subscribe(String itemName, boolean needsIterator)<br /> throws SubscriptionException, FailureException {<br /> } <br /> <br /> public void unsubscribe(String itemName) throws SubscriptionException,<br /> FailureException {<br /> if (itemName.equals("greetings") && gt != null) {<br /> gt.go = false;<br /> }<br /> }<br /> <br /> class GreetingsThread extends Thread {<br /> <br /> private final Object itemHandle;<br /> public volatile boolean go = true;<br /> <br /> public GreetingsThread(Object itemHandle) {<br /> this.itemHandle = itemHandle;<br /> }<br /> <br /> public void run() {<br /> int c = 0;<br /> Random rand = new Random();<br /> while(go) {<br /> try {<br /> ResultSet rs = command.executeQuery("select * from Data");<br /> if (rs.next()) {<br /> Map<String, String> data = new HashMap<String, String>();<br /> data.put("message", rs.getString("message"));<br /> data.put("timestamp", rs.getString("timestamp"));<br /> listener.smartUpdate(itemHandle, data, false);<br /> }<br /> } catch (Exception ex) {<br /> System.out.println(ex);<br /> } <br /> <br /> try {<br /> Thread.sleep(1000);<br /> } catch (InterruptedException e) {<br /> }<br /> }<br /> }<br /> }<br /> <br /> }