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    1   /**
    2    *
    3    * Copyright 2003-2004 The Apache Software Foundation
    4    *
    5    *  Licensed under the Apache License, Version 2.0 (the "License");
    6    *  you may not use this file except in compliance with the License.
    7    *  You may obtain a copy of the License at
    8    *
    9    *     http://www.apache.org/licenses/LICENSE-2.0
    10   *
    11   *  Unless required by applicable law or agreed to in writing, software
    12   *  distributed under the License is distributed on an "AS IS" BASIS,
    13   *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    14   *  See the License for the specific language governing permissions and
    15   *  limitations under the License.
    16   */
    17
    18  //
    19  // This source code implements specifications defined by the Java
    20  // Community Process. In order to remain compliant with the specification
    21  // DO NOT add / change / or delete method signatures!
    22  //
    23
    24  package javax.servlet.jsp.tagext;
    25
    26  import javax.servlet.jsp.JspException;
    27
    28  /**
    29   * The IterationTag interface extends Tag by defining one additional
    30   * method that controls the reevaluation of its body.
    31   *
    32   * <p> A tag handler that implements IterationTag is treated as one that
    33   * implements Tag regarding  the doStartTag() and doEndTag() methods.
    34   * IterationTag provides a new method: <code>doAfterBody()</code>.
    35   *
    36   * <p> The doAfterBody() method is invoked after every body evaluation
    37   * to control whether the body will be reevaluated or not.  If doAfterBody()
    38   * returns IterationTag.EVAL_BODY_AGAIN, then the body will be reevaluated.
    39   * If doAfterBody() returns Tag.SKIP_BODY, then the body will be skipped
    40   * and doEndTag() will be evaluated instead.
    41   *
    42   * <p><B>Properties</B>
    43   * There are no new properties in addition to those in Tag.
    44   *
    45   * <p><B>Methods</B>
    46   * There is one new methods: doAfterBody().
    47   *
    48   * <p><B>Lifecycle</B>
    49   *
    50   * <p> Lifecycle details are described by the transition diagram
    51   * below.  Exceptions that are thrown during the computation of
    52   * doStartTag(), BODY and doAfterBody() interrupt the execution
    53   * sequence and are propagated up the stack, unless the tag handler
    54   * implements the TryCatchFinally interface; see that interface for
    55   * details.
    56   *
    57   * <p>
    58   * <IMG src="doc-files/IterationTagProtocol.gif"
    59   *      alt="Lifecycle Details Transition Diagram for IterationTag"/>
    60   *
    61   * <p><B>Empty and Non-Empty Action</B>
    62   * <p> If the TagLibraryDescriptor file indicates that the action must
    63   * always have an empty element body, by a &lt;body-_content&gt; entry of
    64   * "empty", then the doStartTag() method must return SKIP_BODY.
    65   *
    66   * <p>Note that which methods are invoked after the doStartTag() depends on
    67   * both the return value and on if the custom action element is empty
    68   * or not in the JSP page, not on how it's declared in the TLD.
    69   *
    70   * <p>
    71   * If SKIP_BODY is returned the body is not evaluated, and then doEndTag()
    72   * is invoked.
    73   *
    74   * <p>
    75   * If EVAL_BODY_INCLUDE is returned, and the custom action element is not
    76   * empty, the body is evaluated and "passed through" to the current out,
    77   * then doAfterBody() is invoked and, after zero or more iterations,
    78   * doEndTag() is invoked.
    79   */
    80
    81  public interface IterationTag extends Tag {
    82
    83      /**
    84       * Request the reevaluation of some body.
    85       * Returned from doAfterBody.
    86       *
    87       * For compatibility with JSP 1.1, the value is carefully selected
    88       * to be the same as the, now deprecated, BodyTag.EVAL_BODY_TAG,
    89       *
    90       */
    91
    92      public final static int EVAL_BODY_AGAIN = 2;
    93
    94      /**
    95       * Process body (re)evaluation.  This method is invoked by the
    96       * JSP Page implementation object after every evaluation of
    97       * the body into the BodyEvaluation object. The method is
    98       * not invoked if there is no body evaluation.
    99       *
    100      * <p>
    101      * If doAfterBody returns EVAL_BODY_AGAIN, a new evaluation of the
    102      * body will happen (followed by another invocation of doAfterBody).
    103      * If doAfterBody returns SKIP_BODY, no more body evaluations will occur,
    104      * and the doEndTag method will be invoked.
    105      *
    106      * <p>
    107      * If this tag handler implements BodyTag and doAfterBody returns
    108      * SKIP_BODY, the value of out will be restored using the popBody
    109      * method in pageContext prior to invoking doEndTag.
    110      *
    111      * <p>
    112      * The method re-invocations may be lead to different actions because
    113      * there might have been some changes to shared state, or because
    114      * of external computation.
    115      *
    116      * <p>
    117      * The JSP container will resynchronize the values of any AT_BEGIN and
    118      * NESTED variables (defined by the associated TagExtraInfo or TLD) after
    119      * the invocation of doAfterBody().
    120      *
    121      * @return whether additional evaluations of the body are desired
    122      * @throws JspException if an error occurred while processing this tag
    123      */
    124
    125     int doAfterBody() throws JspException;
    126 }