Routine type conversion in the framework is transparent. Generally, all you need to do is ensure that HTML inputs have names that can be used in OGNL expressions. (HTML inputs are form elements and other GET/POST parameters.)

A Simple Example

{snippet:id=javadoc|javadoc=true|url=com.opensymphony.xwork2.conversion.impl.XWorkConverter}

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{snippet:id=javadoc|javadoc=true|url=org.apache.struts2.util.StrutsTypeConverter}

Built in Type Conversion Support

{snippet:id=javadoc|javadoc=true|url=com.opensymphony.xwork2.conversion.impl.XWorkBasicConverter}

Relationship to Parameter Names

The best way to take advantage of the framework's type conversion is to utilize complete objects (ideally your domain objects directly). There is no need to capture form values using intermediate Strings and primitives and then convert those values to full objects in an Action method.

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• Use complex OGNL expressions - the framework will automatically take care of creating the actual objects for you.
• Use JavaBeans! The framework can only create objects if the objects obey the JavaBean specification and provide no-arg constructions, as well as getters and setters where appropriate.
• Remember that person.name will call getPerson().setName(), but if in order for the framework to create the Person object for you, a setPerson must also exist.

• Wiki Markup
  For lists and maps, use index notation, such as _people\[0\].name_ or _friends\['patrick'\].name_. Often these HTML form elements are being rendered inside a loop. For [JSP Tags], use the iterator tag's status attribute. For [FreeMarker Tags], use the special property $\{foo_index\}\[\].

• For multiple select boxes, it isn't possible to use index notation to name each individual item. Instead, name your element people.name and the framework will understand that it should create a new Person object for each selected item and set its name accordingly.

Creating a Type Converter

To create a type converter one would need to extends StrutsTypeConverter.

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Advanced Type Conversion

The framework also handles advanced type conversion cases, like null property handling and converting values in Maps and Collections, and type conversion error handling.

Null Property Handling

Null property handling will automatically create objects where null references are found.

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{snippet:id=example|javadoc=true|url=com.opensymphony.xwork2.conversion.impl.InstantiatingNullHandler}

Collection and Map Support

Collection and Map support provides intelligent null handling and type conversion for Java Collections.

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Additionally, you can create your own custom ObjectTypeDeterminer by implementing the ObjectTypeDeterminer interface. There is also an optional ObjectTypeDeterminer that utilizes Java 5 generics. See the Annotations page for more information.

Indexing a collection by a property of that collection

It is also possible to obtain a unique element of a collection by passing the value of a given property of that element. By default, the property of the element of the collection is determined in Class-conversion.properties using KeyProperty_xxx=yyy, where xxx is the property of the bean Class that returns the collection and yyy is the property of the collection element that we want to index on.

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Unlike Map and List element properties, if {{fooCollection(22)}} does not exist, it will not be created. If you would like it created, use the notation {{fooCollection.makeNew\[index\]}} where _index_ is an integer 0, 1, and so on. Thus, parameter value pairs {{fooCollection.makeNew\[0\]=Phil}} and {{fooCollection.makeNew\[1\]=John}} would add two new Foo Objects to {{fooCollection \-\-}} one with name property value {{Phil}} and the other with name property value {{BarJohn}}. However, in the case of a Set, the {{equals}} and {{hashCode}} methods should be defined such that they don't only include the {{id}} property. Otherwise, one element of the null {{id}} properties Foos to be removed from the Set.

An advanced example for indexed Lists and Maps

Here is the model bean used within the list. The KeyProperty for this bean is the id attribute.

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<s:iterator value="beanList" id="bean">
  <stextfield name="beanList(%{bean.id}).name" />
</s:iterator>

Type Conversion Error Handling

Type conversion error handling provides a simple way to distinguish between an input validation problem and an input type conversion problem.

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By default, the conversion interceptor is included in struts-default.xml in the default stack. To keep conversion errors from reporting globally, change the interceptor stack, and add additional validation rules.

Next: Interceptors