org.springframework.web.servlet.tags.form.AbstractFormTag Maven / Gradle / Ivy
/*
* 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.beans.PropertyEditor;
import javax.servlet.jsp.JspException;
import org.springframework.util.ObjectUtils;
import org.springframework.web.servlet.tags.HtmlEscapingAwareTag;
import org.springframework.web.util.ExpressionEvaluationUtils;
/**
* Base class for all JSP form tags. Provides utility methods for
* null-safe EL evaluation and for accessing and working with a {@link TagWriter}.
*
* Subclasses should implement the {@link #writeTagContent(TagWriter)} to perform
* actual tag rendering.
*
*
Subclasses (or test classes) can override the {@link #createTagWriter()} method to
* redirect output to a {@link java.io.Writer} other than the {@link javax.servlet.jsp.JspWriter}
* associated with the current {@link javax.servlet.jsp.PageContext}.
*
* @author Rob Harrop
* @since 2.0
*/
public abstract class AbstractFormTag extends HtmlEscapingAwareTag {
/** Helper for rendering values into HTML */
private final ValueFormatter valueFormatter = new ValueFormatter();
/**
* Evaluates the supplied value for the supplied attribute name. If the supplied value
* is null then null is returned, otherwise evaluation is
* handled using {@link ExpressionEvaluationUtils#evaluate(String, String, javax.servlet.jsp.PageContext)}.
*/
protected Object evaluate(String attributeName, Object value) throws JspException {
if (value instanceof String) {
return ExpressionEvaluationUtils.evaluate(attributeName, (String) value, this.pageContext);
}
else {
return value;
}
}
/**
* Optionally writes the supplied value under the supplied attribute name into the supplied
* {@link TagWriter}. In this case, the supplied value is {@link #evaluate evaluated} first
* and then the {@link ObjectUtils#getDisplayString String representation} is written as the
* attribute value. If the resultant String representation is null
* or empty, no attribute is written.
* @see TagWriter#writeOptionalAttributeValue(String, String)
*/
protected final void writeOptionalAttribute(TagWriter tagWriter, String attributeName, String value)
throws JspException {
if (value != null) {
tagWriter.writeOptionalAttributeValue(attributeName, getDisplayString(evaluate(attributeName, value)));
}
}
/**
* Creates the {@link TagWriter} which all output will be written to. By default,
* the {@link TagWriter} writes its output to the {@link javax.servlet.jsp.JspWriter}
* for the current {@link javax.servlet.jsp.PageContext}. Subclasses may choose to
* change the {@link java.io.Writer} to which output is actually written.
*/
protected TagWriter createTagWriter() {
return new TagWriter(this.pageContext.getOut());
}
/**
* Provides a simple template method that calls {@link #createTagWriter()} and passes
* the created {@link TagWriter} to the {@link #writeTagContent(TagWriter)} method.
* @return the value returned by {@link #writeTagContent(TagWriter)}
*/
protected final int doStartTagInternal() throws Exception {
return writeTagContent(createTagWriter());
}
/**
* Gets the display value of the supplied Object, HTML escaped
* as required. This version is not {@link PropertyEditor}-aware.
*/
protected String getDisplayString(Object value) {
return this.valueFormatter.getDisplayString(value, isHtmlEscape());
}
/**
* Gets the display value of the supplied Object, HTML escaped
* as required. If the supplied value is not a {@link String} and the supplied
* {@link PropertyEditor} is not null then the {@link PropertyEditor} is used
* to obtain the display value.
*/
protected String getDisplayString(Object value, PropertyEditor propertyEditor) {
return this.valueFormatter.getDisplayString(value, propertyEditor, isHtmlEscape());
}
/**
* Subclasses should implement this method to perform tag content rendering.
* @return valid tag render instruction as per {@link javax.servlet.jsp.tagext.Tag#doStartTag()}.
*/
protected abstract int writeTagContent(TagWriter tagWriter) throws JspException;
}