org.geotools.parameter

Class Parameters

Object

Parameters

public final class Parameters
extends Object

Utility class for methods helping implementing, and working with the parameter API from org.opengis.parameter package.

Design note

This class contains some methods working on a specific parameter in a group (e.g. searching, setting a value, etc.). Parameters are identified by their name instead of their full descriptor object, because:

• The parameter descriptor may not be always available. For example a user may looks for the "semi_major" axis length (because it is documented in OGC specification under that name) but doesn't know and doesn't care about who is providing the implementation. In such case, he doesn't have the parameter's descriptor. He only have the parameter's name, and creating a descriptor from that name (a descriptor independent of any implementation) is tedious..
• Parameter descriptors are implementation-dependent. For example if a user searchs for the above-cited "semi_major" axis length using the Geotools's descriptor for this parameter, we will fail to find this parameter in any alternative ParameterValueGroup implementations. This is against GeoAPI's inter-operability goal.

The above doesn't mean that parameter's descriptor should not be used. They are used for inspecting meta-data about parameters, not as a key for searching parameters in a group. Since each parameter's name should be unique in a given parameter group (because maximum occurs is always 1 for single parameter), the parameter name is a suffisient key.

Since:

2.1

Author:

Jody Garnett (Refractions Research), Martin Desruisseaux

Field Summary

Fields

Modifier and Type	Field and Description
static ParameterDescriptorGroup	EMPTY_GROUP An empty parameter group.

Method Summary

Modifier and Type	Method and Description
static <T> ParameterDescriptor<T>	cast(ParameterDescriptor<?> descriptor, Class<T> type) Casts the given parameter descriptor to the given type.
static <T> ParameterValue<T>	cast(ParameterValue<?> value, Class<T> type) Casts the given parameter value to the given type.
static void	copy(ParameterValueGroup source, ParameterValueGroup target) Copies all parameter values from source to target.
static boolean	ensureSet(ParameterValueGroup parameters, String name, double value, Unit<?> unit, boolean force) Ensures that the specified parameter is set.
static boolean	isValid(ParameterValue<?> parameter) Checks a parameter value against its parameter descriptor.
static List<Object>	search(GeneralParameterValue param, String name, int maxDepth) Searchs all parameters with the specified name.
static Map<String,Object>	toNameValueMap(GeneralParameterValue parameters, Map<String,Object> destination) Gets a flat view of name-value pairs.

Methods inherited from class Object

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

Field Detail

EMPTY_GROUP

public static ParameterDescriptorGroup EMPTY_GROUP

An empty parameter group. This group contains no parameters.

Method Detail

cast

public static <T> ParameterDescriptor<T> cast(ParameterDescriptor<?> descriptor,
                                              Class<T> type)
                                       throws ClassCastException

Casts the given parameter descriptor to the given type. An exception is thrown immediately if the parameter does not have the expected value class. This is a helper method for type safety when using Java 5 parameterized types.

Type Parameters:

T - The expected value class.

Parameters:

descriptor - The descriptor to cast.

type - The expected value class.

Returns:

The descriptor casted to the given type.

Throws:

ClassCastException - if the given descriptor doesn't have the expected value class.

Since:

2.5

cast

public static <T> ParameterValue<T> cast(ParameterValue<?> value,
                                         Class<T> type)
                                  throws ClassCastException

Casts the given parameter value to the given type. An exception is thrown immediately if the parameter does not have the expected value class. This is a helper method for type safety when using Java 5 parameterized types.

Type Parameters:

T - The expected value class.

Parameters:

value - The value to cast.

type - The expected value class.

Returns:

The value casted to the given type.

Throws:

ClassCastException - if the given value doesn't have the expected value class.

Since:

2.5

isValid

public static boolean isValid(ParameterValue<?> parameter)

Checks a parameter value against its parameter descriptor. This method takes care of handling checking arrays and collections against parameter descriptor.

When the value class is an array (like double[].class) or a collection (like List.class), the descriptor minimum value, maximum value and valid values will be used to check the elements.

Parameters:

parameter - The parameter to test.

Returns:

true if parameter is valid.

See Also:

Parameter.ensureValidValue(org.opengis.parameter.ParameterDescriptor<T>, java.lang.Object)

search

public static List<Object> search(GeneralParameterValue param,
                                  String name,
                                  int maxDepth)

Searchs all parameters with the specified name. The given name is compared against parameter name and alias. This method search recursively in subgroups up to the specified depth:

• If maxDepth is equals to 0, then this method returns param if and only if it matches the specified name.
• If maxDepth is equals to 1 and param is an instance of ParameterDescriptorGroup, then this method checks all elements in this group but not in subgroups.
• ...
• If maxDepth is a high number (e.g. 100), then this method checks all elements in all subgroups up to the specified depth, which is likely to be never reached. In this case, maxDepth can be seen as a safeguard against never ending loops, for example if parameters graph contains cyclic entries.

Parameters:

param - The parameter to inspect.

name - The name of the parameter to search for. See the class javadoc for a rational about the usage of name as a key instead of descriptor.

maxDepth - The maximal depth while descending down the parameter tree.

Returns:

The set (possibly empty) of parameters with the given name.

copy

public static void copy(ParameterValueGroup source,
                        ParameterValueGroup target)

Copies all parameter values from source to target. A typical usage of this method is for transfering values from an arbitrary implementation to some specific implementation (e.g. a parameter group implementation backed by a ParameterBlock for image processing operations).

Parameters:

source - The parameters to copy.

target - Where to copy the source parameters.

Since:

2.2

toNameValueMap

public static Map<String,Object> toNameValueMap(GeneralParameterValue parameters,
                                                Map<String,Object> destination)

Gets a flat view of name-value pairs. This method copies all parameter values into the supplied destination map. Keys are parameter names as String objects, and values are parameter values as arbitrary objects. All subgroups (if any) are extracted recursively.

Parameters:

parameters - The parameters to extract values from.

destination - The destination map, or null for a default one.

Returns:

destination, or a new map if destination was null.

ensureSet

public static boolean ensureSet(ParameterValueGroup parameters,
                                String name,
                                double value,
                                Unit<?> unit,
                                boolean force)

Ensures that the specified parameter is set. The value is set if and only if no value were already set by the user for the given name.

The force argument said what to do if the named parameter is already set. If the value matches, nothing is done in all case. If there is a mismatch and force is true, then the parameter is overridden with the specified value. Otherwise, the parameter is left unchanged but a warning is logged with the FINE level.

Parameters:

parameters - The set of projection parameters.

name - The parameter name to set.

value - The value to set, or to expect if the parameter is already set.

unit - The value unit.

force - true for forcing the parameter to the specified value is case of mismatch.

Returns:

true if the were a mismatch, or false if the parameters can be used with no change.