thredds.server.opendap.servers

Class CEEvaluator

java.lang.Object

thredds.server.opendap.servers.CEEvaluator

public class CEEvaluator
extends Object

This class is used to parse and evaluate a constraint expression. When constructed it must be passed a valid DDS along with the expression. This DDS will be used as the environment (collection of variables and functions) during the parse and evaluation of the constraint expression.

A server (servlet, CGI, ...) must first instantiate the DDS (possibly reading it from a cache) and then create and instance of this class. Once created, the constraint may be parsed and then evaluated. The class supports sending data based on the results of CE evaluation. That is, the send() method of the class combines both the evaluation of the constraint and the output of data values so that the server can return data using a single method call.

Custom parsing The CEEvaluator parses constraint expressions into Clause objects using a ClauseFactory. Customized behavior during parsing can be achieved by passing a customized ClauseFactory into the CEEvaluator.

Support for server side functions Server side functions are supported via the FunctionLibrary class. Custom server side function support is achieved by using a customized ClauseFactory which in turn contains a customized FunctionLibrary.

More details are found in the documentation for the respective classes.

See Also:

ServerDDS, ServerMethods, ClauseFactory, FunctionLibrary, Clause

Constructor Summary

Constructors

Constructor and Description
CEEvaluator(ServerDDS dds) Construct a new CEEvaluator with dds as the DDS object with which to resolve all variable and function names.
CEEvaluator(ServerDDS dds, ClauseFactory clauseFactory) Construct a new CEEvaluator with dds as the DDS object with which to resolve all variable and function names, and clauseFactory as a source of Clause objects .

Method Summary

Modifier and Type	Method and Description
void	appendClause(Clause c) Add a clause to the constraint expression.
boolean	evalClauses(Object specialO) Evaluate all of the Clauses in the Clause vector.
com.google.common.collect.ImmutableList<Clause>	getClauses() Get access to the list of clauses built by parsing the selection part of the constraint expression.
ServerDDS	getDDS() Return a reference to the CEEvaluator's DDS object.
void	markAll(boolean state) Mark all the variables in the DDS either as part of the current projection (when state is true) or not (state is false).
void	parseConstraint(String constraint, String urlencoded) Parse a constraint expression.
void	printConstraint(PrintWriter pw) Print all of the Clauses in the Clause vector.
boolean	removeClause(Clause c) Remove a clause from the constraint expression.
void	send(String dataset, OutputStream sink, Object specialO) This function sends the variables described in the constrained DDS to the output described by sink.

Methods inherited from class java.lang.Object

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

Constructor Detail

CEEvaluator

public CEEvaluator(ServerDDS dds)

Construct a new CEEvaluator with dds as the DDS object with which to resolve all variable and function names.

Parameters:

dds - DDS object describing the dataset targeted by this constraint.

CEEvaluator

public CEEvaluator(ServerDDS dds,
                   ClauseFactory clauseFactory)

Construct a new CEEvaluator with dds as the DDS object with which to resolve all variable and function names, and clauseFactory as a source of Clause objects .

Parameters:

clauseFactory - The factory which will be used by the parser to construct the clause tree. This allows servers to pass in a factory which creates custom clause objects.

dds - DDS object describing the dataset targeted by this constraint.

Method Detail

getDDS

public ServerDDS getDDS()

Return a reference to the CEEvaluator's DDS object.

parseConstraint

public void parseConstraint(String constraint,
                            String urlencoded)
                     throws opendap.dap.parsers.ParseException,
                            opendap.dap.DAP2Exception

Parse a constraint expression. Variables in the projection are marked as such in the CEEvaluator's ServerDDS instance. The selection subexpression is then parsed and a list of Clause objects is built.

The parser is located in opendap.servers.parsers.CeParser.

Parameters:

constraint - The constraint expression to parse.

Throws:

opendap.dap.parsers.ParseException

opendap.dap.DAP2Exception

appendClause

public void appendClause(Clause c)

Add a clause to the constraint expression.

Parameters:

c - The Clause to append.

removeClause

public boolean removeClause(Clause c)

Remove a clause from the constraint expression. This will will remove the first occurence of the passed clause from the constraint expression. This is done be reference, so if the passed Clause object is NOT already in the constraint expression then nothing happens. And, if it should appear more than once (which I don't think is possible) only the first occurence will be removed.

Parameters:

c - The Clause to append.

Returns:

True if constraint expression contained the passed Clause object and it was successfully removed.

getClauses

public final com.google.common.collect.ImmutableList<Clause> getClauses()

Get access to the list of clauses built by parsing the selection part of the constraint expression.

NB: This is not valid until the CE has been parsed!

send

public void send(String dataset,
                 OutputStream sink,
                 Object specialO)
          throws opendap.dap.NoSuchVariableException,
                 DAP2ServerSideException,
                 IOException

This function sends the variables described in the constrained DDS to the output described by sink. This function calls parse_constraint(), BaseType::read(), and ServerIO::serialize().

Parameters:

dataset - The name of the dataset to send.

sink - A pointer to the output buffer for the data.

specialO - An Object passed by the server. This is typically used by server implementations to deliver needed functionaliy or information to the read methods of each BaseType.

Throws:

opendap.dap.NoSuchVariableException

DAP2ServerSideException

IOException

See Also:

ServerMethods.serialize()

evalClauses

public boolean evalClauses(Object specialO)
                    throws opendap.dap.NoSuchVariableException,
                           DAP2ServerSideException,
                           IOException

Evaluate all of the Clauses in the Clause vector.

Parameters:

specialO - That special Object that can be passed down through the DDS.send() method.

Returns:

True if all the Clauses evaluate to true, false otherwise.

Throws:

opendap.dap.NoSuchVariableException

DAP2ServerSideException

IOException

markAll

public void markAll(boolean state)
             throws opendap.dap.DAP2Exception,
                    opendap.dap.NoSuchVariableException,
                    SBHException

Mark all the variables in the DDS either as part of the current projection (when state is true) or not (state is false). This is a convenience function that provides a way to clear or set an entire dataset described by a DDS with respect to its projection.

Parameters:

state - true if the variables should all be projected, false is no variable should be projected.

Throws:

opendap.dap.DAP2Exception

opendap.dap.NoSuchVariableException

SBHException

printConstraint

public void printConstraint(PrintWriter pw)

Print all of the Clauses in the Clause vector.