ValueChangeConverter (OmniFaces 4.5 API)

java.lang.Object
- org.omnifaces.converter.ValueChangeConverter<T>

All Implemented Interfaces:

Converter<T>
```
public abstract class ValueChangeConverter<T>
extends Object
implements Converter<T>
```
By default, Faces converters run on every request, regardless of whether the submitted value has changed or not. In case of conversion against the DB on complex objects which are already stored in the model in a broader scope, such as the view scope, this may result in unnecessarily expensive service/DAO calls. In such case, you'd like to perform the expensive service/DAO call only when the submitted value is really changed as compared to the model value.
This converter offers you a template to do it transparently. To use it, just change your converters from:
```
 public class YourConverter implements Converter<YourEntity> {

     public YourEntity getAsObject(FacesContext context, UIComponent component, String submittedValue) {
         // ...
     }

     // ...
 }
 
```
to
```
 public class YourConverter extends ValueChangeConverter<YourEntity> {

     public YourEntity getAsChangedObject(FacesContext context, UIComponent component, String submittedValue) {
         // ...
     }

     // ...
 }
 
```
So, essentially, just replace implements Converter by extends ValueChangeConverter and rename the method from getAsObject to getAsChangedObject. Note: the getAsString method of your converter doesn't need to be changed.
Since:

1.6

Author:

Bauke Scholtz

Field Summary
- Fields inherited from interface jakarta.faces.convert.Converter
  DATETIMECONVERTER_DEFAULT_TIMEZONE_IS_SYSTEM_TIMEZONE_PARAM_NAME

Constructor Summary

Constructors
Constructor Description

ValueChangeConverter()

Method Summary

All Methods Instance Methods Abstract Methods Concrete Methods
Modifier and Type	Method	Description
`abstract T`	`getAsChangedObject(FacesContext context, UIComponent component, String submittedValue)`	Use this method instead of `getAsObject(FacesContext, UIComponent, String)` if you intend to perform the conversion only when the submitted value is really changed as compared to the model value.
`T`	`getAsObject(FacesContext context, UIComponent component, String submittedValue)`	If the component is an instance of `EditableValueHolder` and the string representation of its old object value is equal to the submitted value, then immediately return its old object value unchanged.

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface jakarta.faces.convert.Converter
getAsString

- Constructor Detail
  - ValueChangeConverter
```
public ValueChangeConverter()
```
- Method Detail
  - getAsObject
```
public T getAsObject(FacesContext context,
                     UIComponent component,
                     String submittedValue)
```
    If the component is an instance of EditableValueHolder and the string representation of its old object value is equal to the submitted value, then immediately return its old object value unchanged. Otherwise, invoke getAsChangedObject(FacesContext, UIComponent, String) which may in turn do the necessary possibly expensive DAO operations.
    
    Specified by:
    
    getAsObject in interface Converter<T>
    
    Throws:
    
    ClassCastException - When T is of wrong type.
  - getAsChangedObject
```
public abstract T getAsChangedObject(FacesContext context,
                                     UIComponent component,
                                     String submittedValue)
```
    Use this method instead of getAsObject(FacesContext, UIComponent, String) if you intend to perform the conversion only when the submitted value is really changed as compared to the model value.
    
    Parameters:
    
    context - The involved faces context.
    
    component - The involved UI component.
    
    submittedValue - The submitted value.
    
    Returns:
    
    The converted value, exactly like as when you use getAsObject(FacesContext, UIComponent, String) the usual way.