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    1   /*
    2    * Licensed to the Apache Software Foundation (ASF) under one or more
    3    * contributor license agreements.  See the NOTICE file distributed with
    4    * this work for additional information regarding copyright ownership.
    5    * The ASF licenses this file to You under the Apache License, Version 2.0
    6    * (the "License"); you may not use this file except in compliance with
    7    * the License.  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  package org.apache.commons.scxml.invoke;
    18
    19  import java.util.Map;
    20
    21  import org.apache.commons.scxml.SCInstance;
    22  import org.apache.commons.scxml.TriggerEvent;
    23
    24  /***
    25   * <p>The Invoker interface is used to define the possible interactions
    26   * between the parent state machine (executor) and the types of invocable
    27   * activities.</p>
    28   *
    29   * <p>Invocable activities must first register an Invoker implementation class
    30   * for the appropriate "targettype" (attribute of &lt;invoke&gt;) with the
    31   * parent <code>SCXMLExecutor</code>.</p>
    32   *
    33   * <p>The communication link between the parent state machine executor and
    34   * the invoked activity is a bi-directional events pipe.</p>
    35   *
    36   * <p>All events triggered on the parent state machine get forwarded to the
    37   * invoked activity. The processing semantics for these events depend
    38   * upon the "targettype", and thereby vary per concrete implementation of
    39   * this interface.</p>
    40   *
    41   * <p>The invoked activity in turn must fire a special "done" event
    42   * when it concludes. It may fire additional events before the "done"
    43   * event. The semantics of any additional events depend upon the
    44   * "targettype". The invoked activity must not fire any events after the
    45   * "done" event. The name of the special "done" event must be
    46   * the ID of the parent state wherein the corresponding &lt;invoke&gt;
    47   * resides, with the String ".invoke.done" appended.</p>
    48   *
    49   * <p>The Invoker "lifecycle" is outlined below:
    50   *  <ol>
    51   *   <li>Instantiation via {@link Class#newInstance()}
    52   *       (Invoker implementation requires accessible constructor).</li>
    53   *   <li>Configuration (setters for parent state ID and
    54   *       {@link SCInstance}).</li>
    55   *   <li>Initiation of invoked activity via invoke() method, passing
    56   *       the source URI and the map of params.</li>
    57   *   <li>Zero or more bi-directional event triggering.</li>
    58   *   <li>Either completion or cancellation.</li>
    59   *  </ol>
    60   * </p>
    61   *
    62   * <p><b>Note:</b> The semantics of &lt;invoke&gt; are necessarily
    63   * asynchronous, tending towards long(er) running interactions with external
    64   * processes. Implementations must not communicate with the parent state
    65   * machine executor in a synchronous manner. For synchronous
    66   * communication semantics, use &lt;event&gt; or custom actions instead.</p>
    67   */
    68  public interface Invoker {
    69
    70      /***
    71       * Set the state ID of the owning state for the &lt;invoke&gt;.
    72       * Implementations must use this ID for constructing the event name for
    73       * the special "done" event (and optionally, for other event names
    74       * as well).
    75       *
    76       * @param parentStateId The ID of the parent state.
    77       */
    78      void setParentStateId(String parentStateId);
    79
    80      /***
    81       * Set the "context" of the parent state machine, which provides the
    82       * channel.
    83       *
    84       * @param scInstance The "context" of the parent state machine.
    85       */
    86      void setSCInstance(SCInstance scInstance);
    87
    88      /***
    89       * Begin this invocation.
    90       *
    91       * @param source The source URI of the activity being invoked.
    92       * @param params The &lt;param&gt; values
    93       * @throws InvokerException In case there is a fatal problem with
    94       *                          invoking the source.
    95       */
    96      void invoke(String source, Map params)
    97      throws InvokerException;
    98
    99      /***
    100      * Forwards the events triggered on the parent state machine
    101      * on to the invoked activity.
    102      *
    103      * @param evts
    104      *            an array of external events which triggered during the last
    105      *            time quantum
    106      *
    107      * @throws InvokerException In case there is a fatal problem with
    108      *                          processing the events forwarded by the
    109      *                          parent state machine.
    110      */
    111     void parentEvents(TriggerEvent[] evts)
    112     throws InvokerException;
    113
    114     /***
    115      * Cancel this invocation.
    116      *
    117      * @throws InvokerException In case there is a fatal problem with
    118      *                          canceling this invoke.
    119      */
    120     void cancel()
    121     throws InvokerException;
    122
    123 }
    124