Class SetNestedPropertiesRule
- java.lang.Object
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- org.apache.commons.digester.Rule
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- org.apache.commons.digester.SetNestedPropertiesRule
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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]
For each child element of [widget], a corresponding setter method is located on the object on the top of the digester stack, the body text of the child element is converted to the type specified for the (sole) parameter to the setter method, then the setter method is invoked.
This rule supports custom mapping of xml element names to property names. The default mapping for particular elements 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 theExtendedBaseRules
rules manager; thisRule
, however, works fine with the defaultRulesBase
rules manager.Note that this rule is designed to be used to set only "primitive" bean properties, eg String, int, boolean. If some of the child xml elements match ObjectCreateRule rules (ie cause objects to be created) then you must use one of the more complex constructors to this rule to explicitly skip processing of that xml element, and define a SetNextRule (or equivalent) to handle assigning the child object to the appropriate property instead.
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.
TODO: Optimise this class. Currently, each time begin is called, new AnyChildRules and AnyChildRule objects are created. It should be possible to cache these in normal use (though watch out for when a rule instance is invoked re-entrantly!).
- Since:
- 1.6
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Nested Class Summary
Nested Classes Modifier and Type Class Description private class
SetNestedPropertiesRule.AnyChildRule
private class
SetNestedPropertiesRule.AnyChildRules
Private Rules implementation
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Field Summary
Fields Modifier and Type Field Description private boolean
allowUnknownChildElements
private java.util.HashMap
elementNames
private org.apache.commons.logging.Log
log
private boolean
trimData
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Fields inherited from class org.apache.commons.digester.Rule
digester, namespaceURI
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Constructor Summary
Constructors Constructor Description SetNestedPropertiesRule()
Base constructor, which maps every child element into a bean property with the same name as the xml element.SetNestedPropertiesRule(java.lang.String[] elementNames, java.lang.String[] propertyNames)
Constructor which allows element->property mapping to be overridden.SetNestedPropertiesRule(java.lang.String elementName, java.lang.String propertyName)
Convenience constructor which overrides the default mappings for just one property.
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description void
addAlias(java.lang.String elementName, java.lang.String propertyName)
Add an additional custom xml-element -> property 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()
boolean
getTrimData()
SeesetTrimData(boolean)
.void
setAllowUnknownChildElements(boolean allowUnknownChildElements)
Determines whether an error is reported when a nested element is encountered for which there is no corresponding property-setter method.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
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Constructor Detail
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SetNestedPropertiesRule
public SetNestedPropertiesRule()
Base constructor, which maps every child element into a bean property with the same name as the xml element.It is an error if a child xml element exists but the target java bean has no such property (unless setAllowUnknownChildElements has been set to true).
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SetNestedPropertiesRule
public SetNestedPropertiesRule(java.lang.String elementName, java.lang.String propertyName)
Convenience constructor which overrides the default mappings for just one property.
For details about how this works, see
SetNestedPropertiesRule(String[] elementNames, String[] propertyNames)
.- Parameters:
elementName
- is the child xml element to matchpropertyName
- is the java bean property to be assigned the value of the specified xml element. This may be null, in which case the specified xml element will be ignored.
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SetNestedPropertiesRule
public SetNestedPropertiesRule(java.lang.String[] elementNames, java.lang.String[] propertyNames)
Constructor which allows element->property mapping to be overridden.
Two arrays are passed in. One contains xml element names and the other java bean property names. The element name / property name pairs are matched by position; in order words, the first string in the element name array corresponds to the first string in the property name array and so on.
If a property name is null or the xml element name has no matching property name due to the arrays being of different lengths then this indicates that the xml element should be ignored.
Example One
The following constructs a rule that maps the
alt-city
element to thecity
property and thealt-state
to thestate
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
xml element to theclassName
property. The xml elementignore-me
is not mapped, ie is ignored. 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 mappropertyNames
- names of properties mapped to
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Method Detail
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setDigester
public void setDigester(Digester digester)
Invoked when rule is added to digester.- Overrides:
setDigester
in classRule
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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.
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getTrimData
public boolean getTrimData()
SeesetTrimData(boolean)
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setAllowUnknownChildElements
public void setAllowUnknownChildElements(boolean allowUnknownChildElements)
Determines whether an error is reported when a nested element is encountered for which there is no corresponding property-setter method.When set to false, any child element for which there is no corresponding object property will cause an error to be reported.
When set to true, any child element for which there is no corresponding object property will simply be ignored.
The default value of this attribute is false (unknown child elements are not allowed).
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getAllowUnknownChildElements
public boolean getAllowUnknownChildElements()
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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.
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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.
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addAlias
public void addAlias(java.lang.String elementName, java.lang.String propertyName)
Add an additional custom xml-element -> property mapping.This is primarily intended to be used from the xml rules module (as it is not possible there to pass the necessary parameters to the constructor for this class). However it is valid to use this method directly if desired.
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toString
public java.lang.String toString()
Render a printable version of this Rule.- Overrides:
toString
in classjava.lang.Object
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