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package javax.faces.event;
import javax.el.ELContext;
import javax.el.ELException;
import javax.el.MethodExpression;
import javax.el.MethodNotFoundException;
import javax.faces.context.FacesContext;
import javax.faces.component.StateHolder;
/**
* MethodExpressionValueChangeListener
* is a {@link ValueChangeListener} that wraps a {@link
* MethodExpression}. When it receives a {@link ValueChangeEvent}, it
* executes a method on an object identified by the {@link
* MethodExpression}.
*/
public class MethodExpressionValueChangeListener implements ValueChangeListener,
StateHolder {
// ------------------------------------------------------ Instance Variables
private MethodExpression methodExpressionOneArg = null;
private MethodExpression methodExpressionZeroArg = null;
private boolean isTransient;
private final static Class[] VALUECHANGE_LISTENER_ZEROARG_SIG = new Class[] { };
public MethodExpressionValueChangeListener() { }
/**
* Construct a {@link
* ValueChangeListener} that contains a {@link
* MethodExpression}.To accomodate method expression targets
* that take no arguments instead of taking a {@link
* ValueChangeEvent} argument, the implementation of this
* class must take the argument methodExpressionOneArg
,
* extract its expression string, and create another
* MethodExpression
whose expected param types match
* those of a zero argument method. The usage requirements for both
* of these MethodExpression
instances are described in
* {@link #processValueChange}.
*
* @param methodExpressionOneArg a MethodExpression
* that points to a method that returns void
and takes
* a single argument of type {@link ValueChangeEvent}.
*/
public MethodExpressionValueChangeListener(MethodExpression methodExpressionOneArg) {
super();
this.methodExpressionOneArg = methodExpressionOneArg;
FacesContext context = FacesContext.getCurrentInstance();
ELContext elContext = context.getELContext();
this.methodExpressionZeroArg = context.getApplication().
getExpressionFactory().createMethodExpression(elContext,
methodExpressionOneArg.getExpressionString(), Void.class,
VALUECHANGE_LISTENER_ZEROARG_SIG);
}
/**
* Construct a {@link ValueChangeListener} that contains a {@link MethodExpression}.
*/
public MethodExpressionValueChangeListener(MethodExpression methodExpressionOneArg,
MethodExpression methodExpressionZeroArg) {
super();
this.methodExpressionOneArg = methodExpressionOneArg;
this.methodExpressionZeroArg = methodExpressionZeroArg;
}
// ------------------------------------------------------- Event Method
/**
* Call through to the
* {@link MethodExpression} passed in our constructor. First, try to invoke the
* MethodExpression
passed to the constructor of this
* instance, passing the argument {@link ValueChangeEvent} as the
* argument. If a {@link MethodNotFoundException} is thrown, call
* to the zero argument MethodExpression
derived from
* the MethodExpression
passed to the constructor of
* this instance. If that fails for any reason, throw an {@link
* AbortProcessingException}, including the cause of the
* failure.
*
* @throws NullPointerException {@inheritDoc}
* @throws AbortProcessingException {@inheritDoc}
*/
public void processValueChange(ValueChangeEvent valueChangeEvent) throws AbortProcessingException {
if (valueChangeEvent == null) {
throw new NullPointerException();
}
FacesContext context = FacesContext.getCurrentInstance();
ELContext elContext = context.getELContext();
// PENDING: The corresponding code in MethodExpressionActionListener
// has an elaborate message capture, logging, and rethrowing block.
// Why not here?
try {
methodExpressionOneArg.invoke(elContext, new Object[] {valueChangeEvent});
} catch (MethodNotFoundException mnf) {
if (null != methodExpressionZeroArg) {
try {
// try to invoke a no-arg version
methodExpressionZeroArg.invoke(elContext, new Object[]{});
}
catch (ELException ee) {
throw new AbortProcessingException(ee.getMessage(), ee.getCause());
}
}
} catch (ELException ee) {
throw new AbortProcessingException(ee.getMessage(), ee.getCause());
}
}
// ------------------------------------------------ Methods from StateHolder
/**
* Both {@link MethodExpression}
* instances described in the constructor must be saved.
*/
public Object saveState(FacesContext context) {
if (context == null) {
throw new NullPointerException();
}
return new Object[] { methodExpressionOneArg, methodExpressionZeroArg };
}
/**
* Both {@link MethodExpression}
* instances described in the constructor must be restored.
*/
public void restoreState(FacesContext context, Object state) {
if (context == null) {
throw new NullPointerException();
}
if (state == null) {
return;
}
methodExpressionOneArg = (MethodExpression) ((Object[]) state)[0];
methodExpressionZeroArg = (MethodExpression) ((Object[]) state)[1];
}
public boolean isTransient() {
return isTransient;
}
public void setTransient(boolean newTransientValue) {
isTransient = newTransientValue;
}
}