public class CombinedConfiguration extends BaseHierarchicalConfiguration implements EventListener<ConfigurationEvent>
A hierarchical composite configuration class.
This class maintains a list of configuration objects, which can be added
using the diverse addConfiguration() methods. After that the
configurations can be accessed either by name (if one was provided when the
configuration was added) or by index. For the whole set of managed
configurations a logical node structure is constructed. For this purpose a
NodeCombiner
object can be set. This makes it possible to specify different algorithms for
the combination process.
The big advantage of this class is that it creates a truly hierarchical structure of all the properties stored in the contained configurations - even if some of them are no hierarchical configurations per se. So all enhanced features provided by a hierarchical configuration (e.g. choosing an expression engine) are applicable.
The class works by registering itself as an event listener at all added
configurations. So it gets notified whenever one of these configurations is
changed and can invalidate its internal node structure. The next time a
property is accessed the node structure will be re-constructed using the
current state of the managed configurations. Note that, depending on the used
NodeCombiner, this may be a complex operation.
Because of the way a CombinedConfiguration is working it has more or
less view character: it provides a logic view on the configurations it
contains. In this constellation not all methods defined for hierarchical
configurations - especially methods that update the stored properties - can
be implemented in a consistent manner. Using such methods (like
addProperty(), or clearProperty() on a
CombinedConfiguration is not strictly forbidden, however, depending
on the current NodeCombiner and the involved properties, the results
may be different than expected. Some examples may illustrate this:
CombinedConfiguration cc containing two child
configurations with the following content:
gui.background = blue gui.position = (10, 10, 400, 200)
gui.background = black gui.foreground = white home.dir = /data
NodeCombiner a
OverrideCombiner is used. This combiner will ensure that defined user
settings take precedence over the default values. If the resulting
CombinedConfiguration is queried for the background color,
blue will be returned because this value is defined in
user.properties. Now consider what happens if the key
gui.background is removed from the CombinedConfiguration:
cc.clearProperty("gui.background");
Will a cc.containsKey("gui.background") now return false? No,
it won't! The clearProperty() operation is executed on the node set
of the combined configuration, which was constructed from the nodes of the
two child configurations. It causes the value of the background node
to be cleared, which is also part of the first child configuration. This
modification of one of its child configurations causes the
CombinedConfiguration to be re-constructed. This time the
OverrideCombiner cannot find a gui.background property in the
first child configuration, but it finds one in the second, and adds it to the
resulting combined configuration. So the property is still present (with a
different value now).addProperty() can also be problematic: Most node combiners use
special view nodes for linking parts of the original configurations' data
together. If new properties are added to such a special node, they do not
belong to any of the managed configurations and thus hang in the air. Using
the same configurations as in the last example, the statement
addProperty("database.user", "scott");
would cause such a hanging property. If now one of the child configurations
is changed and the CombinedConfiguration is re-constructed, this
property will disappear! (Add operations are not problematic if they result
in a child configuration being updated. For instance an
addProperty("home.url", "localhost"); will alter the second child
configuration - because the prefix home is here already present;
when the CombinedConfiguration is re-constructed, this change is
taken into account.)Because of such problems it is recommended to perform updates only on the managed child configurations.
Whenever the node structure of a CombinedConfiguration becomes
invalid (either because one of the contained configurations was modified or
because the invalidate() method was directly called) an event is
generated. So this can be detected by interested event listeners. This also
makes it possible to add a combined configuration into another one.
Notes about thread-safety: This configuration implementation uses a
Synchronizer object to protect instances against concurrent access.
The concrete Synchronizer implementation used determines whether an
instance of this class is thread-safe or not. In contrast to other
implementations derived from BaseHierarchicalConfiguration,
thread-safety is an issue here because the nodes structure used by this
configuration has to be constructed dynamically when a child configuration is
changed. Therefore, when multiple threads are involved which also manipulate
one of the child configurations, a proper Synchronizer object should
be set. Note that the Synchronizer objects used by the child
configurations do not really matter. Because immutable in-memory nodes
structures are used for them there is no danger that updates on child
configurations could interfere with read operations on the combined
configuration.
BaseHierarchicalConfiguration.BuilderVisitor| Modifier and Type | Field and Description |
|---|---|
static EventType<ConfigurationEvent> |
COMBINED_INVALIDATE
Constant for the event type fired when the internal node structure of a
combined configuration becomes invalid.
|
| Constructor and Description |
|---|
CombinedConfiguration()
Creates a new instance of
CombinedConfiguration that uses
a union combiner. |
CombinedConfiguration(NodeCombiner comb)
Creates a new instance of
CombinedConfiguration and
initializes the combiner to be used. |
| Modifier and Type | Method and Description |
|---|---|
void |
addConfiguration(Configuration config)
Adds a new configuration to this combined configuration.
|
void |
addConfiguration(Configuration config,
String name)
Adds a new configuration to this combined configuration with an optional
name.
|
void |
addConfiguration(Configuration config,
String name,
String at)
Adds a new configuration to this combined configuration.
|
protected void |
beginRead(boolean optimize)
Notifies this configuration's
Synchronizer that a read operation
is about to start. |
protected void |
beginWrite(boolean optimize)
Notifies this configuration's
Synchronizer that an update
operation is about to start. |
protected void |
clearInternal()
Clears this configuration.
|
Object |
clone()
Returns a copy of this object.
|
Configuration |
getConfiguration(int index)
Returns the configuration at the specified index.
|
Configuration |
getConfiguration(String name)
Returns the configuration with the given name.
|
List<String> |
getConfigurationNameList()
Returns a List of the names of all the configurations that have been
added in the order they were added.
|
Set<String> |
getConfigurationNames()
Returns a set with the names of all configurations contained in this
combined configuration.
|
List<Configuration> |
getConfigurations()
Returns a List of all the configurations that have been added.
|
ExpressionEngine |
getConversionExpressionEngine()
Returns the
ExpressionEngine for converting flat child
configurations to hierarchical ones. |
NodeCombiner |
getNodeCombiner()
Returns the node combiner that is used for creating the combined node
structure.
|
int |
getNumberOfConfigurations()
Returns the number of configurations that are contained in this combined
configuration.
|
Configuration |
getSource(String key)
Returns the configuration source, in which the specified key is defined.
|
Set<Configuration> |
getSources(String key)
Returns a set with the configuration sources, in which the specified key
is defined.
|
void |
invalidate()
Invalidates this combined configuration.
|
void |
onEvent(ConfigurationEvent event)
Event listener call back for configuration update events.
|
boolean |
removeConfiguration(Configuration config)
Removes the specified configuration from this combined configuration.
|
Configuration |
removeConfiguration(String name)
Removes the configuration with the specified name.
|
Configuration |
removeConfigurationAt(int index)
Removes the configuration at the specified index.
|
void |
setConversionExpressionEngine(ExpressionEngine conversionExpressionEngine)
Sets the
ExpressionEngine for converting flat child
configurations to hierarchical ones. |
void |
setNodeCombiner(NodeCombiner nodeCombiner)
Sets the node combiner.
|
childConfigurationsAt, childConfigurationsAt, cloneNodeModel, configurationAt, configurationAt, configurationsAt, configurationsAt, createSubConfigurationForTrackedNode, getNodeModel, getSubConfigurationNodeSelector, getSubConfigurationParentModel, immutableChildConfigurationsAt, immutableConfigurationAt, immutableConfigurationAt, immutableConfigurationsAt, initSubConfigurationForThisParent, interpolatedConfiguration, subnodeConfigurationChanged, subsetaddNodes, addNodesInternal, addPropertyDirect, addPropertyInternal, clearPropertyDirect, clearTree, clearTreeInternal, containsKeyInternal, fetchNodeList, getExpressionEngine, getKeysInternal, getKeysInternal, getMaxIndex, getMaxIndexInternal, getModel, getPropertyInternal, getRootElementName, getRootElementNameInternal, isEmptyInternal, nodeDefined, nodeKey, resolveAddKey, resolveKey, resolveNodeKey, resolveUpdateKey, setExpressionEngine, setPropertyInternal, sizeInternal, toStringaddErrorLogListener, addProperty, append, clear, clearProperty, cloneInterpolator, containsKey, copy, endRead, endWrite, get, get, getArray, getArray, getBigDecimal, getBigDecimal, getBigInteger, getBigInteger, getBoolean, getBoolean, getBoolean, getByte, getByte, getByte, getCollection, getCollection, getConfigurationDecoder, getConversionHandler, getDouble, getDouble, getDouble, getEncodedString, getEncodedString, getFloat, getFloat, getFloat, getInt, getInt, getInteger, getInterpolator, getKeys, getKeys, getList, getList, getList, getList, getListDelimiterHandler, getLogger, getLong, getLong, getLong, getProperties, getProperties, getProperty, getShort, getShort, getShort, getString, getString, getStringArray, getSynchronizer, immutableSubset, initLogger, installInterpolator, interpolate, interpolate, isEmpty, isScalarValue, isThrowExceptionOnMissing, lock, setConfigurationDecoder, setConversionHandler, setDefaultLookups, setInterpolator, setListDelimiterHandler, setLogger, setParentInterpolator, setPrefixLookups, setProperty, setSynchronizer, setThrowExceptionOnMissing, size, unlockaddEventListener, clearErrorListeners, clearEventListeners, copyEventListeners, createErrorEvent, createEvent, fireError, fireEvent, getEventListenerRegistrations, getEventListeners, isDetailEvents, removeEventListener, setDetailEventsequals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, waitaddProperty, clear, clearProperty, getInterpolator, installInterpolator, setInterpolator, setPropertygetSynchronizer, lock, setSynchronizer, unlockcontainsKey, get, get, getArray, getArray, getBigDecimal, getBigDecimal, getBigInteger, getBigInteger, getBoolean, getBoolean, getBoolean, getByte, getByte, getByte, getCollection, getCollection, getDouble, getDouble, getDouble, getEncodedString, getEncodedString, getFloat, getFloat, getFloat, getInt, getInt, getInteger, getKeys, getKeys, getList, getList, getList, getList, getLong, getLong, getLong, getProperties, getProperty, getShort, getShort, getShort, getString, getString, getStringArray, immutableSubset, isEmpty, sizepublic static final EventType<ConfigurationEvent> COMBINED_INVALIDATE
public CombinedConfiguration(NodeCombiner comb)
CombinedConfiguration and
initializes the combiner to be used.comb - the node combiner (can be null, then a union combiner
is used as default)public CombinedConfiguration()
CombinedConfiguration that uses
a union combiner.UnionCombinerpublic NodeCombiner getNodeCombiner()
public void setNodeCombiner(NodeCombiner nodeCombiner)
IllegalArgumentException exception is thrown. Changing the
node combiner causes an invalidation of this combined configuration, so
that the new combiner immediately takes effect.nodeCombiner - the node combinerpublic ExpressionEngine getConversionExpressionEngine()
ExpressionEngine for converting flat child
configurations to hierarchical ones.public void setConversionExpressionEngine(ExpressionEngine conversionExpressionEngine)
ExpressionEngine for converting flat child
configurations to hierarchical ones. When constructing the root node for
this combined configuration the properties of all child configurations
must be combined to a single hierarchical node structure. In this
process, non hierarchical configurations are converted to hierarchical
ones first. This can be problematic if a child configuration contains
keys that are no compatible with the default expression engine used by
hierarchical configurations. Therefore it is possible to specify a
specific expression engine to be used for this purpose.conversionExpressionEngine - the conversion expression engineConfigurationUtils.convertToHierarchical(Configuration, ExpressionEngine)public void addConfiguration(Configuration config, String name, String at)
ConfigurationRuntimeException will
be thrown. With the optional at argument you can specify
where in the resulting node structure the content of the added
configuration should appear. This is a string that uses dots as property
delimiters (independent on the current expression engine). For instance
if you pass in the string "database.tables",
all properties of the added configuration will occur in this branch.config - the configuration to add (must not be null)name - the name of this configuration (can be null)at - the position of this configuration in the combined tree (can be
null)public void addConfiguration(Configuration config, String name)
config - the configuration to add (must not be null)name - the name of this configuration (can be null)public void addConfiguration(Configuration config)
config - the configuration to add (must not be null)public int getNumberOfConfigurations()
public Configuration getConfiguration(int index)
index - the indexpublic Configuration getConfiguration(String name)
name - the name of the configurationpublic List<Configuration> getConfigurations()
public List<String> getConfigurationNameList()
public boolean removeConfiguration(Configuration config)
config - the configuration to be removedpublic Configuration removeConfigurationAt(int index)
index - the indexpublic Configuration removeConfiguration(String name)
name - the name of the configuration to be removedpublic Set<String> getConfigurationNames()
public void invalidate()
EVENT_COMBINED_INVALIDATE is fired. Note that while other
events most times appear twice (once before and once after an update),
this event is only fired once (after update).public void onEvent(ConfigurationEvent event)
onEvent in interface EventListener<ConfigurationEvent>event - the update eventprotected void clearInternal()
clearInternal in class AbstractHierarchicalConfiguration<ImmutableNode>public Object clone()
clone in class AbstractHierarchicalConfiguration<ImmutableNode>public Configuration getSource(String key)
IllegalArgumentException is
thrown (in this case no unique source can be determined).key - the key of a configuration propertyIllegalArgumentException - if the key maps to multiple properties
and the source cannot be determined, or if the key is nullpublic Set<Configuration> getSources(String key)
key - the key of a configuration propertyprotected void beginRead(boolean optimize)
Synchronizer that a read operation
is about to start. This method is called by all methods which access this
configuration in a read-only mode. Subclasses may override it to perform
additional actions before this read operation. The boolean
optimize argument can be evaluated by overridden methods in
derived classes. Some operations which require a lock do not need a fully
initialized configuration object. By setting this flag to
true, such operations can give a corresponding hint. An
overridden implementation of beginRead() can then decide to skip
some initialization steps. All basic operations in this class (and most
of the basic Configuration implementations) call this method with
a parameter value of false. In any case the
inherited method must be called! Otherwise, proper synchronization is not
guaranteed. This implementation checks whether a combined root node
is available. If not, it is constructed by requesting a write lock.beginRead in class AbstractConfigurationoptimize - a flag whether optimization can be performedprotected void beginWrite(boolean optimize)
Synchronizer that an update
operation is about to start. This method is called by all methods which
modify this configuration. Subclasses may override it to perform
additional operations before an update. For a description of the boolean
optimize argument refer to the documentation of
beginRead(). In any case the inherited method must be
called! Otherwise, proper synchronization is not guaranteed. This implementation checks whether a combined root node
is available. If not, it is constructed now.beginWrite in class AbstractConfigurationoptimize - a flag whether optimization can be performedAbstractConfiguration.beginRead(boolean)Copyright © 2001–2020 The Apache Software Foundation. All rights reserved.