org.apache.commons.digester
Class SetNestedPropertiesRule

java.lang.Object
  |
  +--org.apache.commons.digester.Rule
        |
        +--org.apache.commons.digester.SetNestedPropertiesRule

public class SetNestedPropertiesRule

extends Rule

Rule implementation that sets properties on the object at the top of the stack, based on child elements with names matching properties on that object.

Example input that can be processed by this rule:

   [widget]
    [height]7[/height]
    [width]8[/width]
    [label]Hello, world[/label]
   [/widget]
 

This rule supports custom mapping of attribute names to property names. The default mapping for particular attributes can be overridden by using SetNestedPropertiesRule(String[] elementNames, String[] propertyNames). This allows child elements to be mapped to properties with different names. Certain elements can also be marked to be ignored.

A very similar effect can be achieved using a combination of the BeanPropertySetterRule and the ExtendedBaseRules rules manager; this Rule, however, works fine with the default RulesBase rules manager.

Implementation Notes

This class works by creating its own simple Rules implementation. When begin is invoked on this rule, the digester's current rules object is replaced by a custom one. When end is invoked for this rule, the original rules object is restored. The digester rules objects therefore behave in a stack-like manner.

For each child element encountered, the custom Rules implementation ensures that a special AnyChildRule instance is included in the matches returned to the digester, and it is this rule instance that is responsible for setting the appropriate property on the target object (if such a property exists). The effect is therefore like a "trailing wildcard pattern". The custom Rules implementation also returns the matches provided by the underlying Rules implementation for the same pattern, so other rules are not "disabled" during processing of a SetNestedPropertiesRule.

Since:

1.6

Nested Class Summary

private class	SetNestedPropertiesRule.AnyChildRule
private class	SetNestedPropertiesRule.AnyChildRules Private Rules implementation

Field Summary

private boolean	allowUnknownChildElements
private SetNestedPropertiesRule.AnyChildRule	anyChildRule
private java.util.HashMap	elementNames
private org.apache.commons.logging.Log	log
private SetNestedPropertiesRule.AnyChildRules	newRules
private Rules	oldRules
private static java.lang.String	PROP_IGNORE Dummy object that can be placed in collections to indicate an ignored property when null cannot be used for that purpose.
private boolean	trimData

Fields inherited from class org.apache.commons.digester.Rule

digester, namespaceURI

Constructor Summary

SetNestedPropertiesRule()
Base constructor.

SetNestedPropertiesRule(java.lang.String[] elementNames, java.lang.String[] propertyNames)
Constructor allows element->property mapping to be overriden.

SetNestedPropertiesRule(java.lang.String elementName, java.lang.String propertyName)
Convenience constructor overrides the mapping for just one property.

Method Summary

void	addAlias(java.lang.String elementName, java.lang.String propertyName) Add an additional element name to property name mapping.
void	begin(java.lang.String namespace, java.lang.String name, org.xml.sax.Attributes attributes) Process the beginning of this element.
void	body(java.lang.String bodyText) This is only invoked after all child elements have been processed, so we can remove the custom Rules object that does the child-element-matching.
boolean	getAllowUnknownChildElements() See setAllowUnknownChildElements(boolean).
boolean	getTrimData() See setTrimData(boolean).
void	setAllowUnknownChildElements(boolean allowUnknownChildElements) When set to true, any child element for which there is no corresponding object property will cause an error to be reported.
void	setDigester(Digester digester) Invoked when rule is added to digester.
void	setTrimData(boolean trimData) When set to true, any text within child elements will have leading and trailing whitespace removed before assignment to the target object.
java.lang.String	toString() Render a printable version of this Rule.

Methods inherited from class org.apache.commons.digester.Rule

begin, body, end, end, finish, getDigester, getNamespaceURI, setNamespaceURI

Methods inherited from class java.lang.Object

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

Field Detail

PROP_IGNORE

private static final java.lang.String PROP_IGNORE

Dummy object that can be placed in collections to indicate an ignored property when null cannot be used for that purpose.

See Also:

Constant Field Values

log

private org.apache.commons.logging.Log log

anyChildRule

private SetNestedPropertiesRule.AnyChildRule anyChildRule

newRules

private SetNestedPropertiesRule.AnyChildRules newRules

oldRules

private Rules oldRules

trimData

private boolean trimData

allowUnknownChildElements

private boolean allowUnknownChildElements

elementNames

private java.util.HashMap elementNames

Constructor Detail

SetNestedPropertiesRule

public SetNestedPropertiesRule()

Base constructor.

SetNestedPropertiesRule

public SetNestedPropertiesRule(java.lang.String elementName,
                               java.lang.String propertyName)

Convenience constructor overrides the mapping for just one property.

For details about how this works, see SetNestedPropertiesRule(String[] elementNames, String[] propertyNames).

Parameters:

elementName - map the child element to match

propertyName - to a property with this name

SetNestedPropertiesRule

public SetNestedPropertiesRule(java.lang.String[] elementNames,
                               java.lang.String[] propertyNames)

Constructor allows element->property mapping to be overriden.

Two arrays are passed in. One contains the element names and the other the property names. The element name / property name pairs are match by position In order words, the first string in the element name list matches to the first string in the property name list and so on.

If a property name is null or the element name has no matching property name, then this indicates that the element should be ignored.

Example One

The following constructs a rule that maps the alt-city element to the city property and the alt-state to the state property. All other child elements are mapped as usual using exact name matching.

      SetNestedPropertiesRule(
                new String[] {"alt-city", "alt-state"}, 
                new String[] {"city", "state"});
 

Example Two

The following constructs a rule that maps the class element to the className property. The element ignore-me is not mapped. All other elements are mapped as usual using exact name matching.

      SetPropertiesRule(
                new String[] {"class", "ignore-me"}, 
                new String[] {"className"});
 

Parameters:

elementNames - names of elements to map

propertyNames - names of properties mapped to

Method Detail

setDigester

public void setDigester(Digester digester)

Invoked when rule is added to digester.

Overrides:

setDigester in class Rule

setTrimData

public void setTrimData(boolean trimData)

When set to true, any text within child elements will have leading and trailing whitespace removed before assignment to the target object. The default value for this attribute is true.

getTrimData

public boolean getTrimData()

See setTrimData(boolean).

setAllowUnknownChildElements

public void setAllowUnknownChildElements(boolean allowUnknownChildElements)

When set to true, any child element for which there is no corresponding object property will cause an error to be reported. The default value of this attribute is false (not allowed).

getAllowUnknownChildElements

public boolean getAllowUnknownChildElements()

See setAllowUnknownChildElements(boolean).

begin

public void begin(java.lang.String namespace,
                  java.lang.String name,
                  org.xml.sax.Attributes attributes)
           throws java.lang.Exception

Process the beginning of this element.

Overrides:

begin in class Rule

Parameters:

namespace - is the namespace this attribute is in, or null

name - is the name of the current xml element

attributes - is the attribute list of this element

java.lang.Exception

body

public void body(java.lang.String bodyText)
          throws java.lang.Exception

This is only invoked after all child elements have been processed, so we can remove the custom Rules object that does the child-element-matching.

Overrides:

body in class Rule

Parameters:

bodyText - The text of the body of this element

java.lang.Exception

addAlias

public void addAlias(java.lang.String elementName,
                     java.lang.String propertyName)

Add an additional element name to property name mapping. This is intended to be used from the xml rules.

toString

public java.lang.String toString()

Render a printable version of this Rule.

Overrides:

toString in class java.lang.Object