se.sics.prologbeans

Class PrologSession

java.lang.Object

se.sics.prologbeans.PrologSession

public class PrologSession
extends java.lang.Object

PrologSession handles the connection with the Prolog Server. Currently only synchronous connections with the server are supported.

Field Summary

Fields

Modifier and Type	Field and Description
static java.lang.String	SESSION_ATTRIBUTE_NAME The HttpSession session attribute name.

Constructor Summary

Constructors

Constructor and Description
PrologSession() Creates a new PrologSession instance with default Prolog server settings.

Method Summary

Modifier and Type	Method and Description
protected void	cancelQuery() Called by the timeout monitor when a query takes too long.
void	connect() Connects to the Prolog server.
static boolean	debugging()
void	disconnect() Closes the connection with the Prolog server.
QueryAnswer	executeQuery(java.lang.String query) Sends a query to the Prolog server and waits for the answer before returning the QueryAnswer.
QueryAnswer	executeQuery(java.lang.String query, Bindings bindings) Sends a query to the Prolog server and waits for the answer before returning the QueryAnswer.
QueryAnswer	executeQuery(java.lang.String query, Bindings bindings, java.lang.String sessionID) Sends a query to the Prolog server and waits for the answer before returning the QueryAnswer.
java.lang.String	getHost() Returns the host of the Prolog server (exactly as registered in setHost()).
int	getPort() Returns the port of the Prolog server.
static PrologSession	getPrologSession(java.lang.String name) Returns the PrologSession registered in JNDI with the given name.
static PrologSession	getPrologSession(java.lang.String name, javax.servlet.http.HttpSession httpSession) Returns the PrologSession registered in JNDI with the given name.
int	getTimeout() Returns the timeout in milliseconds before the connection to the Prolog server is reset (when a query is not answered).
boolean	isAlwaysClosing()
boolean	isAutoConnecting() Returns the state of the auto connect mode.
boolean	isConnected() Returns true if a connection with the Prolog server is open and false otherwise.
void	setAlwaysClose(boolean close) Set whether to close connections after each send.
void	setAutoConnect(boolean autoConnect) Sets the connection mode of this PrologSession.
void	setHost(java.lang.String prologServerHost) Sets the host of the Prolog server (default is localhost).
void	setPort(int prologServerPort) Sets the port of the Prolog server (default 8066).
void	setTimeout(int timeout) Sets the timeout in milliseconds before the connection to the Prolog server is reset (when a query is not answered).

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

SESSION_ATTRIBUTE_NAME

public static final java.lang.String SESSION_ATTRIBUTE_NAME

The HttpSession session attribute name.

See Also:

Constant Field Values

Constructor Detail

PrologSession

public PrologSession()

Creates a new PrologSession instance with default Prolog server settings.

Method Detail

debugging

public static boolean debugging()

Returns:

whether debugging of this package is in effect

getTimeout

public int getTimeout()

Returns the timeout in milliseconds before the connection to the Prolog server is reset (when a query is not answered).

Returns:

the timeout

setTimeout

public void setTimeout(int timeout)

Sets the timeout in milliseconds before the connection to the Prolog server is reset (when a query is not answered). Setting the timeout to 0 will disable timeouts for this prolog session. Default is 2000 milliseconds. When a connection times out it will be closed silently.

Parameters:

timeout - int timeout in milliseconds or 0 to disable timeouts

getPrologSession

public static PrologSession getPrologSession(java.lang.String name)

Returns the PrologSession registered in JNDI with the given name. Use this method in application servers where services are registered using JNDI. Please note: the application server must be configured to register the PrologSession with the given name for this method to work.

Parameters:

name - the name of the prolog session

Returns:

the named prolog session or null if no such session could be found

getPrologSession

public static PrologSession getPrologSession(java.lang.String name,
                                             javax.servlet.http.HttpSession httpSession)

Returns the PrologSession registered in JNDI with the given name. The PrologSession will make use of sessions and the session id will be the same as in the HTTPSession. Use this method in web application servers with support for servlets and HTTPSession (and when support for sessions is desired). Note: This will cause the PrologSession to include the session id in its queries.

Parameters:

name - the name of the prolog session

httpSession - the http session

Returns:

the named prolog session

getPort

public int getPort()

Returns the port of the Prolog server.

Returns:

the port number

setPort

public void setPort(int prologServerPort)

Sets the port of the Prolog server (default 8066).

Parameters:

prologServerPort - the port of the Prolog server

getHost

public java.lang.String getHost()

Returns the host of the Prolog server (exactly as registered in setHost()).

Returns:

the host name

setHost

public void setHost(java.lang.String prologServerHost)

Sets the host of the Prolog server (default is localhost). The host can be specified as either IP-address or host name.

Parameters:

prologServerHost - the host as an IP-address or host name

isAlwaysClosing

public boolean isAlwaysClosing()

Returns:

whether

setAlwaysClose

public void setAlwaysClose(boolean close)

Set whether to close connections after each send. Default false.

Parameters:

close - whether to close after each send

setAutoConnect

public void setAutoConnect(boolean autoConnect)

Sets the connection mode of this PrologSession. If set to true it will ensure that it is connected to the Prolog server as soon as a call to executeQuery() or anything else causing a need for communication happens. This is by default set to false.

Parameters:

autoConnect - whether to auto-connect

isAutoConnecting

public boolean isAutoConnecting()

Returns the state of the auto connect mode.

Returns:

whether auto-connect is in effect

See Also:

setAutoConnect(boolean)

executeQuery

public QueryAnswer executeQuery(java.lang.String query)
                         throws java.io.IOException,
                                IllegalCharacterSetException

Sends a query to the Prolog server and waits for the answer before returning the QueryAnswer. Anonymous variables (underscore, _), will be ignored, and thus not accessible in the QueryAnswer. executeQuery throws IOException if communication problems with the server occurs. Please note: executeQuery will only return one answer.

Parameters:

query - the query to send to the prolog server. The characters in the query are restricted to ISO-8859-1.

Returns:

the answer from the prolog server

Throws:

java.io.IOException - if an error occurs. A possible cause is a timeout.

IllegalCharacterSetException - if the query contains non-ISO-8859-1 characters

See Also:

setTimeout(int)

executeQuery

public QueryAnswer executeQuery(java.lang.String query,
                                Bindings bindings)
                         throws java.io.IOException,
                                IllegalCharacterSetException

Sends a query to the Prolog server and waits for the answer before returning the QueryAnswer. bindings are variable bindings for the given query and will ensure that the values are stuffed correctly.

An example:

 QueryAnswer answer = executeQuery("evaluate(In,Out)", new Bindings().bind("In", "4*9."));
 

Parameters:

query - the query to send to the prolog server The characters in the query are restricted to ISO-8859-1.

bindings - the variable bindings to use in the query

Returns:

the answer from the prolog server

Throws:

java.io.IOException - if an error occurs. A possible cause is a timeout.

IllegalCharacterSetException - if the query contains non-ISO-8859-1 characters

See Also:

setTimeout(int)

executeQuery

public QueryAnswer executeQuery(java.lang.String query,
                                Bindings bindings,
                                java.lang.String sessionID)
                         throws java.io.IOException,
                                IllegalCharacterSetException

Sends a query to the Prolog server and waits for the answer before returning the QueryAnswer. bindings are variable bindings for the given query and will ensure that the values are stuffed correctly.

Parameters:

query - the query to send to the prolog server The characters in the query are restricted to ISO-8859-1.

bindings - the variable bindings to use in the query

sessionID - the session id to give to the prolog server

Returns:

the answer from the prolog server

Throws:

java.io.IOException - if an error occurs. A possible cause is a timeout.

IllegalCharacterSetException - if the query contains non-ISO-8859-1 characters

See Also:

setTimeout(int)

connect

public void connect()
             throws java.io.IOException

Connects to the Prolog server. By default executeQuery() will automatically connect to the server when called.

Throws:

java.io.IOException - if there is an error connecting

isConnected

public boolean isConnected()

Returns true if a connection with the Prolog server is open and false otherwise.

Returns:

whether there is a connection to a Prolog server

disconnect

public void disconnect()

Closes the connection with the Prolog server. The connection can be opened again with connect().

cancelQuery

protected void cancelQuery()

Called by the timeout monitor when a query takes too long. Override this method to handle the timeout in some way other than silently closing the connection.