CommandBase


1   /*
2    * $Id: CommandBase.java,v 1.11 2004/06/07 20:38:42 eelco12 Exp $
3    * $Source: /cvsroot/mav/maverick/src/java/org/infohazard/maverick/flow/CommandBase.java,v $
4    */
5   
6   package org.infohazard.maverick.flow;
7   
8   import java.io.IOException  ;
9   import javax.servlet.*;
10  
11  import org.apache.commons.logging.Log;
12  import org.apache.commons.logging.LogFactory;
13  
14  /**
15   * <p>
16   * Base class for implementing a Maverick {@link Command}.
17   * Implementors must define {@link #getView}.
18   * </p>
19   * <p>
20   * CommandBase obtains a {@link View} name by calling its Controller's
21   * {@link Controller#go go} method, and then invokes the View's
22   * {@link View#go go} method.
23   * <p>
24   * <p>
25   * The {@link ModelLifetime} interface is honored.
26   * After invoking View.go, if the model object is an instance of
27   * ModelLifetime, its {@link ModelLifetime#discard discard} method is called.
28   *
29   */
30  abstract class CommandBase implements Command
31  {
32      /**
33       * <p>
34       * CommandBase logger.
35       * </p>
36       */
37      private static Log log = LogFactory.getLog(CommandBase.class);
38  
39      /**
40       * <p>
41       * Reference to our {@link Controller}.
42       * </p>
43       */
44      protected Controller controller;
45  
46      /**
47       * <p>
48       * Set reference to out {@link Controller}.
49       * </p>
50       */
51      public CommandBase(Controller ctl)
52      {
53          this.controller = ctl;
54      }
55  
56      /**
57       *
58       */
59      public void go(MaverickContext mctx) throws IOException  , ServletException
60      {
61          Object   model = null;
62          
63          try
64          {
65              // There must be a controller class to distinguish between views
66              String   viewName = this.controller.go(mctx);
67              
68              // Hold on to the model now because chained commands might replace it
69              model = mctx.getModel();
70      
71              if (log.isDebugEnabled())
72                  log.debug("Switching to view:  " + viewName);
73      
74              View target = this.getView(viewName);
75              if (null == target)
76                  throw new ServletException("Controller specified view \"" + viewName
77                                              + "\", but no view with that name is defined.");
78              
79              target.go(mctx);
80          }
81          finally
82          {
83              // Allow the model to manage resources
84              // instanceof returns false if object is null
85              if (model instanceof ModelLifetime)
86                  ((ModelLifetime)model).discard();
87          }
88      }
89  
90      /**
91       */
92      protected abstract View getView(String   name);
93  }
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