Java Interface
The Java interface is centered around the class PrologSession,
which represents a connection (or session) to a Prolog
server. PrologSession contains static methods for looking up
named PrologSession instances using JNDI (Java Naming and
Directory Interface) as well as methods for querying the Prolog server.
Other important classes are: QueryAnswer, which contains the
answer for a query sent to the Prolog server; Term, which
represents a Prolog term; and Bindings, which supports stuffing
of variable values used in queries.
General information about Java, Servlets and JNDI is available at the
Java Technology site: http://java.sun.com/
A brief description of the methods in the provided Java classes are
presented below.
The PrologSession object is the connection to the Prolog
server. The constructor PrologSession()
creates a PrologSession with the default settings
(host = localhost, port = 8066.
PrologSession contains the following methods:
static PrologSession getPrologSession (String name)
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Method on PrologSession |
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. See Tomcat configuration in pbn-exs-tomcat.
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static PrologSession getPrologSession (String name, HTTPSession session)
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Method on PrologSession |
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).
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String getHost ()
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Method on PrologSession |
returns the host of the Prolog server (exactly as registered in
setHost).
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void setHost (String prologServerHost)
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Method on PrologSession |
sets the host of the Prolog server (default localhost). Either
IP-address or host name is allowed.
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int getPort ()
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Method on PrologSession |
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returns the port of the Prolog server.
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void setPort (int port)
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Method on PrologSession |
sets the port of the Prolog server (default 8066).
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void connect ()
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Method on PrologSession |
connects to the Prolog server. By default the executeQuery will
automatically connect to the server when called.
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void setAutoConnect (boolean autoConnect)
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Method on PrologSession |
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 true
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boolean isAutoConnecting ()
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Method on PrologSession |
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returns the state of the AutoConnect mode.
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QueryAnswer executeQuery (String query)
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Method on PrologSession |
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.
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QueryAnswer executeQuery (String query, Bindings bindings)
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Method on PrologSession |
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."));
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The QueryAnswer contains the answer (new bindings) for a query
(or the error that occurred during the query process).
QueryAnswer inherits from Bindings, and extends and
modifies it with the following methods:
Term getValue (String variableName)
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Method on QueryAnswer |
returns the value of the given variable. If there is a value a
Term (a parsed Prolog term) is returned, otherwise
null is returned. All bindings from the query are
available in the QueryAnswer.
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boolean queryFailed ()
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Method on QueryAnswer |
returns true if the query failed (e.g. the Prolog returned no).
In this case, there will be no answers (no new bindings, and
isError will return false).
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boolean isError ()
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Method on QueryAnswer |
returns true if there was an error.
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String getError ()
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Method on QueryAnswer |
returns the error message (which is only set if there was an error,
otherwise it will be null).
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The Term object is for representing parsed Prolog terms, and has
the following methods:
boolean isAtom ()
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Method on Term |
returns true if the Term is an atom.
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boolean isInteger ()
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Method on Term |
returns true if the Term is an integer.
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boolean isFloat ()
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Method on Term |
returns true if the Term is a floating-point number.
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boolean isCompound ()
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Method on Term |
returns true if the Term is a compound term.
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boolean isList ()
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Method on Term |
returns true if and only if Term is a compound term with
principal functor ./2.
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boolean isString ()
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Method on Term |
returns true if the Term an instance
of PBString (which can be used for fast string access
by a type-cast to PBString and the use of the method
getString() that returns the string).
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boolean isVariable ()
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Method on Term |
returns true if the Term is a variable.
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int intValue ()
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Method on Term |
returns the int value of the integer.
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long longValue ()
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Method on Term |
returns the long value of the integer.
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float floatValue ()
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Method on Term |
returns the float value of the floating-point number.
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double doubleValue ()
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Method on Term |
returns the double value of the floating-point number.
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String getName ()
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Method on Term |
returns the functor name of the Term (see functor/3).
If the Term represents a variable (isVariable() returns true),
the variable name is returned.
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int getArity ()
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Method on Term |
returns the number of arguments of this term
(e.g. parent(A1,A2) would return 2) (see functor/3).
If the term is not a compound term, getArity() will return 0.
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Term getArgument (int index)
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Method on Term |
returns the Term representing the argument at the position
given by index. If there are no arguments, or if an argument
with the specified index does not exist,
IndexOutOfBoundsException will be thrown. The first argument
has index one (see arg/3).
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Bindings is used for binding variables to values
in a query sent to the Prolog. The values will be automatically
stuffed before they are sent to the Prolog server.
void bind (String name, int value)
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Method on Bindings |
binds the variable with the given name to the given
value. Please note: this method is also available for values
of type long, float, double, and
Term.
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void bind (String name, String value)
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Method on Bindings |
binds the variable with the given name to the given value. The value
will be seen as a list of UNICODE character codes in Prolog.
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void bindAtom (String name, String value)
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Method on Bindings |
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binds the variable with the given name to the given
value. Please note: this method will encode the String as an
atom when querying the Prolog server.
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