opendap.servers

Class FunctionLibrary

java.lang.Object

opendap.servers.FunctionLibrary

public class FunctionLibrary
extends Object

Represents a library of available server-side functions for use in evaluating constraint expressions.

When created, a FunctionLibrary is empty. There are two ways to populate it, described below. Once the FunctionLibrary has been created and populated, it should be used to create a ClauseFactory, which can then be given to the CEEvaluator for use in parsing.

The most straightforward is to pass an instance of each ServerSideFunction class to the add() method. If you have a large number of ServerSideFunctions, or if you want to have choose class names for your functions independent of the actual function name, this is the approach to use.

A second, more complex method resolves server-side function names at runtime. The function library automatically looks for a class whose name matches the name requested (if a prefix is set, it will look for a class whose name is prefix + name requested). If such a class exists, and it implements the ServerSideFunction interface, a new instance of the class is created using the default constructor, added to the list of available functions, and returned to the caller.

This is not quite as complicated as it sounds. For instance, say the FunctionLibrary's prefix is set to "opendap.servers.test.SSF". Then the first time the server gets a constraint expression containing the function "dummy()", the FunctionLibrary will automatically load the class "opendap.servers.test.SSFdummy", and return a new instance using the class's default constructor.

This avoids the need to hardcode a list of server-side functions, and allows you to create new functions at any time. For instance to create a function "newfn()" you can simply create the class "opendap.servers.test.SSFnewfn" and put it somewhere in the server's classpath . Then the first CE containing this function will cause that class to be automatically loaded, just the like the dummy() function was.

Author:

joew

Field Summary

Fields

Modifier and Type	Field and Description
protected Map	boolFunctions
protected Map	btFunctions
protected String	prefix

Constructor Summary

Constructors

Constructor and Description
FunctionLibrary() Creates a new FunctionLibrary with no prefix set.
FunctionLibrary(String prefix) Creates a new FunctionLibrary.

Method Summary

Methods

Modifier and Type	Method and Description
void	add(ServerSideFunction function) Adds a function to the library.
BoolFunction	getBoolFunction(String name) Retrieves a boolean function from the library.
BTFunction	getBTFunction(String name) Retrieves a BaseType function from the library.
String	getPrefix() Returns the prefix being used for classname lookup.
protected void	loadNewFunction(String name) Tries to load a function with the given name.
void	setPrefix(String prefix) Sets the prefix to use for classname lookup.

Methods inherited from class java.lang.Object

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

Field Detail

boolFunctions

protected Map boolFunctions

btFunctions

protected Map btFunctions

prefix

protected String prefix

Constructor Detail

FunctionLibrary

public FunctionLibrary()

Creates a new FunctionLibrary with no prefix set.

FunctionLibrary

public FunctionLibrary(String prefix)

Creates a new FunctionLibrary.

Parameters:

prefix - A string that will be prepended to function names in order to create a classname for that function. For example,

Method Detail

setPrefix

public void setPrefix(String prefix)

Sets the prefix to use for classname lookup. For instance, if the prefix is "myserver.SSF", then when the library doesn't have an entry for function "xyz" it will look for a class "myserver.SSFxyz".

getPrefix

public String getPrefix()

Returns the prefix being used for classname lookup.

add

public void add(ServerSideFunction function)

Adds a function to the library. The function will be inspected to determine whether it is a boolean or BaseType function.

getBoolFunction

public BoolFunction getBoolFunction(String name)
                             throws NoSuchFunctionException

Retrieves a boolean function from the library. If the function is not found the library will attempt to load it using the mechanism described in the class documentation.

Parameters:

name - The name of the function being requested.

Returns:

Null if the function is not in the library, and the attempt to load it fails.

Throws:

NoSuchFunctionException

getBTFunction

public BTFunction getBTFunction(String name)
                         throws NoSuchFunctionException

Retrieves a BaseType function from the library. If the function is not found the library will attempt to load it using the mechanism described in the class documentation.

Parameters:

name - The name of the function being requested.

Returns:

Null if the function is not in the library, and the attempt to load it fails.

Throws:

NoSuchFunctionException

loadNewFunction

protected void loadNewFunction(String name)

Tries to load a function with the given name.