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Spring Framework example source code file (SelectTag.java)

This example Spring Framework source code file (SelectTag.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Spring Framework tags/keywords

abstracthtmlinputelementtag, empty, empty, eval_body_include, eval_page, http, jspexception, jspexception, list_value_page_attribute, object, object, optionwriter, selecttag, servlet, string, string, util

The Spring Framework SelectTag.java source code

/*
 * Copyright 2002-2007 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.servlet.tags.form;

import java.util.Collection;
import java.util.Map;

import javax.servlet.jsp.JspException;

import org.springframework.util.ObjectUtils;
import org.springframework.web.bind.WebDataBinder;
import org.springframework.web.servlet.support.BindStatus;

/**
 * Databinding-aware JSP tag that renders an HTML '<code>select'
 * element.
 *
 * <p>Inner 'option' tags can be rendered using one of the
 * approaches supported by the OptionWriter class.
 *
 * <p>Also supports the use of nested {@link OptionTag OptionTags} or
 * (typically one) nested {@link OptionsTag}.
 *
 * @author Rob Harrop
 * @author Juergen Hoeller
 * @since 2.0
 * @see OptionTag
 */
public class SelectTag extends AbstractHtmlInputElementTag {

	/**
	 * The {@link javax.servlet.jsp.PageContext} attribute under
	 * which the bound value is exposed to inner {@link OptionTag OptionTags}.
	 */
	public static final String LIST_VALUE_PAGE_ATTRIBUTE =
			"org.springframework.web.servlet.tags.form.SelectTag.listValue";

	/**
	 * Marker object for items that have been specified but resolve to null.
	 * Allows to differentiate between 'set but null' and 'not set at all'.
	 */
	private static final Object EMPTY = new Object();


	/**
	 * The {@link Collection}, {@link Map} or array of objects used to generate the inner
	 * '<code>option' tags.
	 */
	private Object items;

	/**
	 * The name of the property mapped to the '<code>value' attribute
	 * of the '<code>option' tag.
	 */
	private String itemValue;

	/**
	 * The name of the property mapped to the inner text of the
	 * '<code>option' tag.
	 */
	private String itemLabel;

	/**
	 * The value of the HTML '<code>size' attribute rendered
	 * on the final '<code>select' element.
	 */
	private String size;

	/**
	 * Indicates whether or not the '<code>select' tag allows
	 * multiple-selections.
	 */
	private Object multiple = Boolean.FALSE;

	/**
	 * The {@link TagWriter} instance that the output is being written.
	 * <p>Only used in conjunction with nested {@link OptionTag OptionTags}.
	 */
	private TagWriter tagWriter;


	/**
	 * Set the {@link Collection}, {@link Map} or array of objects used to
	 * generate the inner '<code>option' tags.
	 * <p>Required when wishing to render 'option' tags from
	 * an array, {@link Collection} or {@link Map}.
	 * <p>Typically a runtime expression.
	 * @param items the items that comprise the options of this selection
	 */
	public void setItems(Object items) {
		this.items = (items != null ? items : EMPTY);
	}

	/**
	 * Get the value of the '<code>items' attribute.
	 * <p>May be a runtime expression.
	 */
	protected Object getItems() {
		return this.items;
	}

	/**
	 * Set the name of the property mapped to the '<code>value'
	 * attribute of the '<code>option' tag.
	 * <p>Required when wishing to render 'option' tags from
	 * an array or {@link Collection}.
	 * <p>May be a runtime expression.
	 */
	public void setItemValue(String itemValue) {
		this.itemValue = itemValue;
	}

	/**
	 * Get the value of the '<code>itemValue' attribute.
	 * <p>May be a runtime expression.
	 */
	protected String getItemValue() {
		return this.itemValue;
	}

	/**
	 * Set the name of the property mapped to the label (inner text) of the
	 * '<code>option' tag.
	 * <p>May be a runtime expression.
	 */
	public void setItemLabel(String itemLabel) {
		this.itemLabel = itemLabel;
	}

	/**
	 * Get the value of the '<code>itemLabel' attribute.
	 * <p>May be a runtime expression.
	 */
	protected String getItemLabel() {
		return this.itemLabel;
	}

	/**
	 * Set the value of the HTML '<code>size' attribute rendered
	 * on the final '<code>select' element.
	 * <p>May be a runtime expression.
	 * @param size the desired value of the '<code>size' attribute
	 */
	public void setSize(String size) {
		this.size = size;
	}

	/**
	 * Get the value of the '<code>size' attribute.
	 * <p>May be a runtime expression.
	 */
	protected String getSize() {
		return this.size;
	}

	/**
	 * Set the value of the HTML '<code>multiple' attribute rendered
	 * on the final '<code>select' element.
	 * <p>May be a runtime expression.
	 */
	public void setMultiple(Object multiple) {
		this.multiple = multiple;
	}

	/**
	 * Get the value of the HTML '<code>multiple' attribute rendered
	 * on the final '<code>select' element.
	 * <p>May be a runtime expression.
	 */
	protected Object getMultiple() {
		return this.multiple;
	}


	/**
	 * Renders the HTML '<code>select' tag to the supplied
	 * {@link TagWriter}.
	 * <p>Renders nested 'option' tags if the
	 * {@link #setItems items} property is set, otherwise exposes the
	 * bound value for the nested {@link OptionTag OptionTags}.
	 */
	protected int writeTagContent(TagWriter tagWriter) throws JspException {
		tagWriter.startTag("select");
		writeDefaultAttributes(tagWriter);
		if (isMultiple()) {
			tagWriter.writeAttribute("multiple", "multiple");
		}
		tagWriter.writeOptionalAttributeValue("size", getDisplayString(evaluate("size", getSize())));

		Object items = getItems();
		if (items != null) {
			// Items specified, but might still be empty...
			if (items != EMPTY) {
				Object itemsObject = (items instanceof String ? evaluate("items", (String) items) : items);
				if (itemsObject != null) {
					String valueProperty = (getItemValue() != null ?
							ObjectUtils.getDisplayString(evaluate("itemValue", getItemValue())) : null);
					String labelProperty = (getItemLabel() != null ?
							ObjectUtils.getDisplayString(evaluate("itemLabel", getItemLabel())) : null);
					OptionWriter optionWriter =
							new OptionWriter(itemsObject, getBindStatus(), valueProperty, labelProperty, isHtmlEscape());
					optionWriter.writeOptions(tagWriter);
				}
			}
			tagWriter.endTag(true);
			writeHiddenTagIfNecessary(tagWriter);
			return EVAL_PAGE;
		}
		else {
			// Using nested <form:option/> tags, so just expose the value in the PageContext...
			tagWriter.forceBlock();
			this.tagWriter = tagWriter;
			this.pageContext.setAttribute(LIST_VALUE_PAGE_ATTRIBUTE, getBindStatus());
			return EVAL_BODY_INCLUDE;
		}
	}

	/**
	 * If using a multi-select, a hidden element is needed to make sure all
	 * items are correctly unselected on the server-side in response to a
	 * <code>null post.
	 */
	private void writeHiddenTagIfNecessary(TagWriter tagWriter) throws JspException {
		if (isMultiple()) {
			tagWriter.startTag("input");
			tagWriter.writeAttribute("type", "hidden");
			tagWriter.writeAttribute("name", WebDataBinder.DEFAULT_FIELD_MARKER_PREFIX + getName());
			tagWriter.writeAttribute("value", "1");
			tagWriter.endTag();
		}
	}

	private boolean isMultiple() throws JspException {
		Object multiple = getMultiple();
		if (Boolean.TRUE.equals(multiple) || "true".equals(multiple) || "multiple".equals(multiple)) {
			return true;
		}
		else if (this.multiple instanceof String) {
			Object evaluatedValue = evaluate("multiple", multiple);
			return Boolean.TRUE.equals(evaluatedValue);
		}
		return forceMultiple();
	}

	/**
	 * Returns '<code>true' if the bound value requires the
	 * resultant '<code>select' tag to be multi-select.
	 */
	private boolean forceMultiple() throws JspException {
		BindStatus bindStatus = getBindStatus();
		Class valueType = bindStatus.getValueType();
		if (valueType != null && typeRequiresMultiple(valueType)) {
			return true;
		}
		else if (bindStatus.getEditor() != null) {
			Object editorValue = bindStatus.getEditor().getValue();
			if (editorValue != null && typeRequiresMultiple(editorValue.getClass())) {
				return true;
			}
		}
		return false;
	}

	/**
	 * Returns '<code>true' for arrays, {@link Collection Collections}
	 * and {@link Map Maps}.
	 */
	private static boolean typeRequiresMultiple(Class type) {
		return (type.isArray() || Collection.class.isAssignableFrom(type) || Map.class.isAssignableFrom(type));
	}

	/**
	 * Closes any block tag that might have been opened when using
	 * nested {@link OptionTag options}.
	 */
	public int doEndTag() throws JspException {
		if (this.tagWriter != null) {
			this.tagWriter.endTag();
			writeHiddenTagIfNecessary(tagWriter);
		}
		return EVAL_PAGE;
	}

	/**
	 * Clears the {@link TagWriter} that might have been left over when using
	 * nested {@link OptionTag options}.
	 */
	public void doFinally() {
		super.doFinally();
		this.tagWriter = null;
		this.pageContext.removeAttribute(LIST_VALUE_PAGE_ATTRIBUTE);
	}

}

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