/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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 javax.servlet.jsp.tagext;

import javax.servlet.jsp.JspException;


/**
 * The IterationTag interface extends Tag by defining one additional method that controls the reevaluation of its body.
 * <p>
 * A tag handler that implements IterationTag is treated as one that implements Tag regarding the doStartTag() and
 * doEndTag() methods. IterationTag provides a new method: <code>doAfterBody()</code>.
 * <p>
 * The doAfterBody() method is invoked after every body evaluation to control whether the body will be reevaluated or
 * not. If doAfterBody() returns IterationTag.EVAL_BODY_AGAIN, then the body will be reevaluated. If doAfterBody()
 * returns Tag.SKIP_BODY, then the body will be skipped and doEndTag() will be evaluated instead.
 * <p>
 * <B>Properties</B> There are no new properties in addition to those in Tag.
 * <p>
 * <B>Methods</B> There is one new methods: doAfterBody().
 * <p>
 * <B>Lifecycle</B>
 * <p>
 * Lifecycle details are described by the transition diagram below. Exceptions that are thrown during the computation of
 * doStartTag(), BODY and doAfterBody() interrupt the execution sequence and are propagated up the stack, unless the tag
 * handler implements the TryCatchFinally interface; see that interface for details.
 * <p>
 * <IMG src="doc-files/IterationTagProtocol.gif" alt="Lifecycle Details Transition Diagram for IterationTag">
 * <p>
 * <B>Empty and Non-Empty Action</B>
 * <p>
 * If the TagLibraryDescriptor file indicates that the action must always have an empty element body, by a
 * &lt;body-content&gt; entry of "empty", then the doStartTag() method must return SKIP_BODY.
 * <p>
 * Note that which methods are invoked after the doStartTag() depends on both the return value and on if the custom
 * action element is empty or not in the JSP page, not on how it's declared in the TLD.
 * <p>
 * If SKIP_BODY is returned the body is not evaluated, and then doEndTag() is invoked.
 * <p>
 * If EVAL_BODY_INCLUDE is returned, and the custom action element is not empty, the body is evaluated and "passed
 * through" to the current out, then doAfterBody() is invoked and, after zero or more iterations, doEndTag() is invoked.
 */

public interface IterationTag extends Tag {

    /**
     * Request the reevaluation of some body. Returned from doAfterBody. For compatibility with JSP 1.1, the value is
     * carefully selected to be the same as the, now deprecated, BodyTag.EVAL_BODY_TAG,
     */
    int EVAL_BODY_AGAIN = 2;

    /**
     * Process body (re)evaluation. This method is invoked by the JSP Page implementation object after every evaluation
     * of the body into the BodyEvaluation object. The method is not invoked if there is no body evaluation.
     * <p>
     * If doAfterBody returns EVAL_BODY_AGAIN, a new evaluation of the body will happen (followed by another invocation
     * of doAfterBody). If doAfterBody returns SKIP_BODY, no more body evaluations will occur, and the doEndTag method
     * will be invoked.
     * <p>
     * If this tag handler implements BodyTag and doAfterBody returns SKIP_BODY, the value of out will be restored using
     * the popBody method in pageContext prior to invoking doEndTag.
     * <p>
     * The method re-invocations may be lead to different actions because there might have been some changes to shared
     * state, or because of external computation.
     * <p>
     * The JSP container will resynchronize the values of any AT_BEGIN and NESTED variables (defined by the associated
     * TagExtraInfo or TLD) after the invocation of doAfterBody().
     *
     * @return whether additional evaluations of the body are desired
     *
     * @throws JspException if an error occurred while processing this tag
     */
    int doAfterBody() throws JspException;
}
