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 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
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 * accompanied this code).
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package com.sun.beans.decoder;

The base class for element handlers.
Author:
Sergey A. Malenkov
See Also:
DocumentHandler
Since:
1.7/**
 * The base class for element handlers.
 *
 * @since 1.7
 *
 * @author Sergey A. Malenkov
 *
 * @see DocumentHandler
 */
public abstract class ElementHandler {
    private DocumentHandler owner;
    private ElementHandler parent;

    private String id;

    
Returns the document handler that creates this element handler.
Returns:
the owner document handler/**
     * Returns the document handler that creates this element handler.
     *
     * @return the owner document handler
     */
    public final DocumentHandler getOwner() {
        return this.owner;
    }

    
Sets the document handler that creates this element handler.
The owner document handler should be set after instantiation.
Such approach is used to simplify the extensibility.
Params:
owner –  the owner document handler
See Also:
DocumentHandler.startElement/**
     * Sets the document handler that creates this element handler.
     * The owner document handler should be set after instantiation.
     * Such approach is used to simplify the extensibility.
     *
     * @param owner  the owner document handler
     * @see DocumentHandler#startElement
     */
    final void setOwner(DocumentHandler owner) {
        if (owner == null) {
            throw new IllegalArgumentException("Every element should have owner");
        }
        this.owner = owner;
    }

    
Returns the element handler that contains this one.
Returns:
the parent element handler/**
     * Returns the element handler that contains this one.
     *
     * @return the parent element handler
     */
    public final ElementHandler getParent() {
        return this.parent;
    }

    
Sets the element handler that contains this one.
The parent element handler should be set after instantiation.
Such approach is used to simplify the extensibility.
Params:
parent –  the parent element handler
See Also:
DocumentHandler.startElement/**
     * Sets the element handler that contains this one.
     * The parent element handler should be set after instantiation.
     * Such approach is used to simplify the extensibility.
     *
     * @param parent  the parent element handler
     * @see DocumentHandler#startElement
     */
    final void setParent(ElementHandler parent) {
        this.parent = parent;
    }

    
Returns the value of the variable with specified identifier.
Params:
id –  the identifier
Returns:
the value of the variable/**
     * Returns the value of the variable with specified identifier.
     *
     * @param id  the identifier
     * @return the value of the variable
     */
    protected final Object getVariable(String id) {
        if (id.equals(this.id)) {
            ValueObject value = getValueObject();
            if (value.isVoid()) {
                throw new IllegalStateException("The element does not return value");
            }
            return value.getValue();
        }
        return (this.parent != null)
                ? this.parent.getVariable(id)
                : this.owner.getVariable(id);
    }

    
Returns the value of the parent element.
Returns:
the value of the parent element/**
     * Returns the value of the parent element.
     *
     * @return the value of the parent element
     */
    protected Object getContextBean() {
        if (this.parent != null) {
            ValueObject value = this.parent.getValueObject();
            if (!value.isVoid()) {
                return value.getValue();
            }
            throw new IllegalStateException("The outer element does not return value");
        } else {
            Object value = this.owner.getOwner();
            if (value != null) {
                return value;
            }
            throw new IllegalStateException("The topmost element does not have context");
        }
    }

    
Parses attributes of the element.
By default, the following attribute is supported:

id
the identifier of the variable that is intended to store the result

Params:
name –   the attribute name
value –  the attribute value/**
     * Parses attributes of the element.
     * By default, the following attribute is supported:
     * <dl>
     * <dt>id
     * <dd>the identifier of the variable that is intended to store the result
     * </dl>
     *
     * @param name   the attribute name
     * @param value  the attribute value
     */
    public void addAttribute(String name, String value) {
        if (name.equals("id")) { // NON-NLS: the attribute name
            this.id = value;
        } else {
            throw new IllegalArgumentException("Unsupported attribute: " + name);
        }
    }

    
This method is called before parsing of the element's body.
All attributes are parsed at this point.
By default, do nothing.
/**
     * This method is called before parsing of the element's body.
     * All attributes are parsed at this point.
     * By default, do nothing.
     */
    public void startElement() {
    }

    
This method is called after parsing of the element's body.
By default, it calculates the value of this element.
The following tasks are executing for any non-void value:

If the id attribute is set the value of the variable with the specified identifier is set to the value of this element.
This element is used as an argument of parent element if it is possible.

See Also:
isArgument/**
     * This method is called after parsing of the element's body.
     * By default, it calculates the value of this element.
     * The following tasks are executing for any non-void value:
     * <ol>
     * <li>If the {@code id} attribute is set
     * the value of the variable with the specified identifier
     * is set to the value of this element.</li>
     * <li>This element is used as an argument of parent element if it is possible.</li>
     * </ol>
     *
     * @see #isArgument
     */
    public void endElement() {
        // do nothing if no value returned
        ValueObject value = getValueObject();
        if (!value.isVoid()) {
            if (this.id != null) {
                this.owner.setVariable(this.id, value.getValue());
            }
            if (isArgument()) {
                if (this.parent != null) {
                    this.parent.addArgument(value.getValue());
                } else {
                    this.owner.addObject(value.getValue());
                }
            }
        }
    }

    
Adds the character that contained in this element.
By default, only whitespaces are acceptable.
Params:
ch –  the character/**
     * Adds the character that contained in this element.
     * By default, only whitespaces are acceptable.
     *
     * @param ch  the character
     */
    public void addCharacter(char ch) {
        if ((ch != ' ') && (ch != '\n') && (ch != '\t') && (ch != '\r')) {
            throw new IllegalStateException("Illegal character with code " + (int) ch);
        }
    }

    
Adds the argument that is used to calculate the value of this element.
By default, no arguments are acceptable.
Params:
argument –  the value of the element that contained in this one/**
     * Adds the argument that is used to calculate the value of this element.
     * By default, no arguments are acceptable.
     *
     * @param argument  the value of the element that contained in this one
     */
    protected void addArgument(Object argument) {
        throw new IllegalStateException("Could not add argument to simple element");
    }

    
Tests whether the value of this element can be used
as an argument of the element that contained in this one.
Returns:
true if the value of this element can be used as an argument of the element that contained in this one, false otherwise/**
     * Tests whether the value of this element can be used
     * as an argument of the element that contained in this one.
     *
     * @return {@code true} if the value of this element can be used
     *         as an argument of the element that contained in this one,
     *         {@code false} otherwise
     */
    protected boolean isArgument() {
        return this.id == null;
    }

    
Returns the value of this element.
Returns:
the value of this element/**
     * Returns the value of this element.
     *
     * @return the value of this element
     */
    protected abstract ValueObject getValueObject();
}