fixedzoomaction.java

esri的ArcGIS Server超级学习模板程序（for java）

package com.esri.solutions.jitk.commands;

import org.apache.log4j.LogManager;
import org.apache.log4j.Logger;
import com.esri.adf.web.data.WebContext;
import com.esri.adf.web.data.geometry.WebExtent;
import com.esri.adf.web.data.geometry.WebPoint;

/**
 * The core fixed-zoom capability, with enforced business logic for min and max
 * zoom factors. Business rule applied is:<p/>
 * <code>ZOOM_FACTOR_MIN <= zoomFactor <= ZOOM_FACTOR_MAX</code>
 */
public class FixedZoomAction {
	private static final Logger _logger = LogManager.getLogger(FixedZoomAction.class);
	private WebContext webContext = null;
	private double zoomFactor;

	/**
	 * The minimum amount one is able to zoom in, expressed as a ratio. Its
	 * inverse is the minimum amount by which one may zoom out.
	 */
	protected static final double ZOOM_FACTOR_MAX = 0.99d;

	/**
	 * The maximum amount one is able to zoom in, expressed as a ratio. Its
	 * inverse is the maximum amount by which one may zoom out.
	 */
	protected static final double ZOOM_FACTOR_MIN = 0.05d;

	public FixedZoomAction() {
		super();
	}

	/**
	 * Getter for the web context.
	 * 
	 * @return the associated WebContext
	 * @todo who needs to be able to call this? can it be protected?
	 */
	public final WebContext getWebContext() {
		return webContext;
	}

	/**
	 * Setter for the web context, called by the ADF during initialization.
	 * 
	 * @param webContext
	 *            presumably called by JSF
	 * @todo who needs to be able to call this? can it be protected?
	 */
	public final void setWebContext(WebContext webContext) {
		_logger.debug("webContext being set");
		this.webContext = webContext;
	}

	/**
	 * Computes a new scaled extent on the same center given an arbitrary
	 * (though validated!) scale factor
	 * 
	 * @param currentExtent
	 *            the extent reference with which all extent work is done: it
	 *            gets modified
	 * @param scaleFactor
	 *            the assumed-valid scale factor.
	 * @return the new extent resulting from applying the passed scalar zoom
	 *         factor to the passed extent.
	 */
	protected final WebExtent getScaledExtent(WebExtent currentExtent,
			double scaleFactor) {
		currentExtent.expand(scaleFactor);
		return currentExtent;
	}

	/**
	 * Computes a new scaled extent with the passed centerpoint given an
	 * arbitrary (though validated!) scale factor
	 * 
	 * @param currentExtent
	 *            the initial extent (before scaling)
	 * @param scaleFactor
	 *            the assumed-valid scale factor.
	 * @param webExtentCenterPoint
	 *            the new center point of the new extent
	 * @return the rescaled, recentered-at-webExtentCenterPoint new extent
	 */
	protected final WebExtent getScaledExtent(WebExtent currentExtent,
			double scaleFactor, WebPoint webExtentCenterPoint) {

		// compute the recentered, unscaled new extent
		double deltaX = currentExtent.getWidth() / 2d;
		double deltaY = currentExtent.getHeight() / 2d;
		WebPoint upperLeft = new WebPoint(webExtentCenterPoint.getX() - deltaX,
				webExtentCenterPoint.getY() - deltaY);
		WebPoint lowerRight = new WebPoint(
				webExtentCenterPoint.getX() + deltaX, webExtentCenterPoint
						.getY()
						+ deltaY);

		// and now scale the recentered extent per the zoom factor
		WebExtent newExtent = getScaledExtent(new WebExtent(upperLeft,
				lowerRight), scaleFactor);
		return newExtent;
	}

	/**
	 * Validates the zoom ratio such that the invariant is
	 * <code>ZOOM_FACTOR_MIN <= zoomFactor <= ZOOM_FACTOR_MAX</code>.
	 * 
	 * @param zoomFactor
	 *            an unvalidated scale factor
	 * @throws Exception
	 *             if the passed scale factor violates the business rule.
	 */
	public final double validateZoomFactor(double zoomFactor) throws Exception {

		if (zoomFactor > ZOOM_FACTOR_MAX) {
			throw new Exception("Zoom factor is too big");
		} 
		else if (zoomFactor < ZOOM_FACTOR_MIN) {
			throw new Exception("Zoom factor is too small");
		}
		return zoomFactor;
	}

	/**
	 * The proportion that any zoomed-in extent will be of the prior extent. Its
	 * inverse corresponds to the proportion used for zooming out.
	 * 
	 * @return the validated zoom factor
	 */
	public final double getZoomFactor() {
		return zoomFactor;
	}

	/**
	 * Setter for the zoom ratio that ensures that only valid scale factors get
	 * set; probably called by the ADF.
	 * 
	 * @param factor
	 *            the new zoom factor
	 * @throws Exception
	 *             if the scale factor value is invalid
	 */
	public final void setZoomFactor(double factor) throws Exception {
		zoomFactor = validateZoomFactor(factor);
	}

}