Okay this might be a crazy idea but as Coherence is a data source it was worth writing a JDBC driver for it. Of course spending time to write a complete SQL engine would be too much without any real motivation. But a simple proof of concept was on the cards. So here you go:
First thing is the client:
public static void main (String [] args) {
// -- Create a URL: hostname and port being of the proxy
String url = "jdbc:coh:@localhost:9099";
String sql = "SELECT * FROM Positions";
try {
// -- Load the Coherence Database Driver
Class.forName("com.ezduck.driver.GridDriver");
Connection conn = DriverManager.getConnection(url);
Statement stmt = conn.createStatement();
stmt.executeQuery(sql);
} catch (ClassNotFoundException e) {
e.printStackTrace();
} catch (SQLException e) {
e.printStackTrace();
}
}
Now the Driver:
public class GridDriver implements Driver {
static {
try {
DriverManager.registerDriver(new GridDriver ());
} catch (SQLException e) {
// TODO
}
}
// -- "jdbc:coh:@localhost:9099"
public GridDriver() {
}
public Connection connect(String url, Properties info) {
int hostIndex = url.indexOf("@") + 1;
int portIndex = url.lastIndexOf(":");
if (hostIndex < 0 || portIndex < 0) {
throw new IllegalStateException ("Driver URL incorrect");
}
String hostName = url.substring(hostIndex, portIndex);
String port = url.substring(portIndex + 1);
return new GridConnection (hostName, port);
}
...
}
Hmm Now the Connection:
public class GridConnection implements Connection {
public GridConnection(String hostName, String port) {
ConfigurableCacheFactory factory = CacheFactory.getConfigurableCacheFactory();
XmlElement cc = new SimpleElement("cache-config");
XmlElement sMap = cc.addElement("caching-scheme-mapping");
XmlElement cMap = sMap.addElement ("cache-mapping");
cMap.addElement("cache-name").setString("*");
cMap.addElement("scheme-name").setString("extend-dist");
XmlElement rcs =
cc.addElement("caching-schemes").addElement("remote-cache-scheme");
rcs.addElement("scheme-name").setString ("extend-dist");
rcs.addElement("service-name").setString("ExtendTcpCacheService");
XmlElement xE =
rcs.addElement("initiator-config").addElement("tcp-initiator")
.addElement("remote-addresses");
XmlElement rAs = xE.addElement("socket-address");
XmlElement add = rAs.addElement("address");
add.setString(hostName);
XmlElement portId = rAs.addElement("port");
portId.setString(port);
// -- Now set the new XmlElement
factory.setConfig(cc);
// -- And of course you need to restart the Cache Service thread
factory.ensureService("ExtendTcpCacheService").stop();
factory.ensureService("ExtendTcpCacheService").start();
}
public Statement createStatement() {
return new GridStatement();
}
.......
}
Then the Statement:
public class GridStatement implements Statement {
public GridStatement() {
}
public ResultSet executeQuery(String sql) {
String command = sql.substring(0, sql.indexOf (" "));
try {
// -- There must be a way to recognize the SQL Command
ICommand cObject = (ICommand) Beans.instantiate(
this.getClass().getClassLoader(),
this.getClass().getPackage().getName() + "." +
command.toUpperCase().trim());
Set set = (Set) cObject.execute (cObject, sql);
// -- A utility to parse the SQL
Map map = SQLUtil.parseSelect(sql);
String cacheName = (String) map.get ("tables");
// -- And last the ResultSet
ResultSet rS = new GridResultSet (set, cacheName);
} catch (ClassNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
return null;
}
.......
}
And before the ResultSet, lets see a half cooked SQL SELECT:
public class SELECT implements ICommand {
String token[];
// -- Select * From Dist-A where name = 'A';
public SELECT() {
}
public Object execute(Object obj, String command) {
Map map = SQLUtil.parseSelect(command);
NamedCache nCache = CacheFactory.getCache((String)map.get("tables"));
String clauses = (String)map.get("clauses");
// -- Lets demonstrate the Select * before going crazy
if (clauses == null) {
return nCache.entrySet(AlwaysFilter.INSTANCE);
}
return null;
}
}
Last but not least - The ResultSet:
public class GridResultSet implements ResultSet {
private Iterator iter;
private Set set;
private String cacheName;
private InvocableMap.Entry entry;
public GridResultSet(Set set, String cacheName) {
this.set = set;
this.cacheName = cacheName;
iter = set.iterator();
}
public boolean next() {
entry = (InvocableMap.Entry) iter.next();
return iter.hasNext();
}
......
}
So here you go - another weekend project for Coherence!
