ValueChangeListenerHandler.java

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package com.sun.faces.facelets.tag.jsf.core;

import com.sun.faces.facelets.tag.TagHandlerImpl;
import com.sun.faces.facelets.tag.jsf.CompositeComponentTagHandler;
import com.sun.faces.facelets.util.ReflectionUtil;

import javax.el.ValueExpression;
import javax.faces.application.Resource;
import javax.faces.component.EditableValueHolder;
import javax.faces.component.UIComponent;
import javax.faces.context.FacesContext;
import javax.faces.event.AbortProcessingException;
import javax.faces.event.ValueChangeEvent;
import javax.faces.event.ValueChangeListener;
import javax.faces.view.EditableValueHolderAttachedObjectHandler;
import javax.faces.view.facelets.*;
import java.io.IOException;
import java.io.Serializable;

/**
 * Register an ValueChangeListener instance on the UIComponent associated with
 * the closest parent UIComponent custom action.<p/> See <a target="_new"
 * href="http://java.sun.com/j2ee/javaserverfaces/1.1_01/docs/tlddocs/f/valueChangeListener.html">tag
 * documentation</a>.
 * 
 * @author Jacob Hookom
 */
public final class ValueChangeListenerHandler extends TagHandlerImpl implements EditableValueHolderAttachedObjectHandler {

    private static class LazyValueChangeListener implements
                                                 ValueChangeListener,
                                                 Serializable {

        private static final long serialVersionUID = 7613811124326963180L;

        private final String type;

        private final ValueExpression binding;

        public LazyValueChangeListener(String type, ValueExpression binding) {
            this.type = type;
            this.binding = binding;
        }

        @Override
        public void processValueChange(ValueChangeEvent event)
              throws AbortProcessingException {
            ValueChangeListener instance = null;
            FacesContext faces = FacesContext.getCurrentInstance();
            if (faces == null) {
                return;
            }
            if (this.binding != null) {
                instance = (ValueChangeListener) binding
                      .getValue(faces.getELContext());
            }
            if (instance == null && this.type != null) {
                try {
                    instance = (ValueChangeListener) ReflectionUtil
                          .forName(this.type).newInstance();
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException e) {
                    throw new AbortProcessingException(
                          "Couldn't Lazily instantiate ValueChangeListener",
                          e);
                }
                if (this.binding != null) {
                    binding.setValue(faces.getELContext(), instance);
                }
            }
            if (instance != null) {
                instance.processValueChange(event);
            }
        }
    }

    private final TagAttribute binding;

    private final String listenerType;

    private final TagAttribute typeAttribute;

    public ValueChangeListenerHandler(TagConfig config) {
        super(config);
        this.binding = this.getAttribute("binding");
        this.typeAttribute = this.getAttribute("type");
        if (null != this.typeAttribute) {
            String stringType = null;
            if (!this.typeAttribute.isLiteral()) {
                FacesContext context = FacesContext.getCurrentInstance();
                FaceletContext ctx = (FaceletContext) context.getAttributes().get(FaceletContext.FACELET_CONTEXT_KEY);
                stringType = (String) this.typeAttribute.getValueExpression(ctx, String.class).getValue(ctx);
            } else {
                stringType = this.typeAttribute.getValue();
            }
            checkType(stringType);
            this.listenerType = stringType;
        } else {
            this.listenerType = null;
        }
    }

    /**
     * See taglib documentation.
     */
    @Override
    public void apply(FaceletContext ctx, UIComponent parent)
            throws IOException {
        // only process if it's been created
        if (parent == null || !(ComponentHandler.isNew(parent))) {
            return;
        }

        if (parent instanceof EditableValueHolder) {
            applyAttachedObject(ctx.getFacesContext(), parent);
        } else if (parent.getAttributes().containsKey(Resource.COMPONENT_RESOURCE_KEY)) {
            // Allow the composite component to know about the target
            // component.
            CompositeComponentTagHandler.getAttachedObjectHandlers(parent).add(this);
        } else {
            throw new TagException(this.tag,
                    "Parent is not of type EditableValueHolder, type is: " + parent);
        }
    }
        
    @Override
    public void applyAttachedObject(FacesContext context, UIComponent parent) {
        FaceletContext ctx = (FaceletContext) context.getAttributes().get(FaceletContext.FACELET_CONTEXT_KEY);
        EditableValueHolder evh = (EditableValueHolder) parent;
        ValueExpression b = null;
        if (this.binding != null) {
            b = this.binding.getValueExpression(ctx, ValueChangeListener.class);
        }
        ValueChangeListener listener = new LazyValueChangeListener(
                this.listenerType, b);
        evh.addValueChangeListener(listener);
    }
        
    @Override
    public String getFor() {
        String result = null;
        TagAttribute attr = this.getAttribute("for");

        if (null != attr) {
            if (attr.isLiteral()) {
                result = attr.getValue();
            } else {
                FacesContext context = FacesContext.getCurrentInstance();
                FaceletContext ctx = (FaceletContext) context.getAttributes().get(FaceletContext.FACELET_CONTEXT_KEY);
                result = (String)attr.getValueExpression(ctx, String.class).getValue(ctx);
            }
        }
        return result;

    }

    private void checkType(String type) {
        try {
            ReflectionUtil.forName(type);
        } catch (ClassNotFoundException e) {
            throw new TagAttributeException(typeAttribute,
                "Couldn't qualify ActionListener", e);
        }
    }


        

}