name.martingeisse.webeco.wicket.QueueTextFeeder.java Source code

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Here is the source code for name.martingeisse.webeco.wicket.QueueTextFeeder.java

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/**
 * Copyright (c) 2010 Martin Geisse
 *
 * This file is distributed under the terms of the MIT license.
 */

package name.martingeisse.webeco.wicket;

import java.util.Queue;

import name.martingeisse.terra.javascript.JavascriptAssemblerUtil;
import name.martingeisse.terra.wicket.util.WicketHeadUtil;

import org.apache.wicket.ajax.AbstractAjaxTimerBehavior;
import org.apache.wicket.ajax.AjaxRequestTarget;
import org.apache.wicket.markup.html.IHeaderContributor;
import org.apache.wicket.markup.html.IHeaderResponse;
import org.apache.wicket.markup.html.form.TextArea;

/**
 * This class feeds text from a queue to a text area on AJAX requests. This can be
 * conbined, for example, with an {@link AbstractAjaxTimerBehavior} to have a stream
 * of text arrive at the client without user interaction.
 */
public class QueueTextFeeder extends TextArea<String> implements IHeaderContributor {

    /**
     * the queue
     */
    private final Queue<String> queue;

    /**
     * Constructor.
     * @param id the wicket id
     * @param queue the queue from which text is fetched
     */
    public QueueTextFeeder(final String id, final Queue<String> queue) {
        super(id);
        setOutputMarkupId(true);
        this.queue = queue;
    }

    /* (non-Javadoc)
     * @see org.apache.wicket.markup.html.IHeaderContributor#renderHead(org.apache.wicket.markup.html.IHeaderResponse)
     */
    @Override
    public void renderHead(final IHeaderResponse response) {
        WicketHeadUtil.includeClassJavascript(response, QueueTextFeeder.class);
    }

    /**
     * Takes as much text from the queue as possible and feeds it to the client.
     * @param ajaxRequestTarget the AJAX request target
     */
    public void feed(final AjaxRequestTarget ajaxRequestTarget) {
        ajaxRequestTarget.appendJavaScript("updateQueueTextFeeder('" + getMarkupId() + "', "
                + JavascriptAssemblerUtil.formatStringLiteral(fetchText()) + ");");
    }

    /**
     * Fetches as much text as possible from the queue.
     * @return the fetched text
     */
    private String fetchText() {
        final StringBuilder builder = new StringBuilder();
        while (true) {
            final String part = queue.poll();
            if (part != null) {
                builder.append(part);
            } else {
                break;
            }
        }
        return builder.toString();
    }

}