Source for gnu.java.beans.decoder.ObjectHandler

   1: /* gnu.java.beans.decoder.ObjectHandler
   2:    Copyright (C) 2004 Free Software Foundation, Inc.
   3: 
   4: This file is part of GNU Classpath.
   5: 
   6: GNU Classpath is free software; you can redistribute it and/or modify
   7: it under the terms of the GNU General Public License as published by
   8: the Free Software Foundation; either version 2, or (at your option)
   9: any later version.
  10: 
  11: GNU Classpath is distributed in the hope that it will be useful, but
  12: WITHOUT ANY WARRANTY; without even the implied warranty of
  13: MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14: General Public License for more details.
  15: 
  16: You should have received a copy of the GNU General Public License
  17: along with GNU Classpath; see the file COPYING.  If not, write to the
  18: Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
  19: 02110-1301 USA.
  20: 
  21: Linking this library statically or dynamically with other modules is
  22: making a combined work based on this library.  Thus, the terms and
  23: conditions of the GNU General Public License cover the whole
  24: combination.
  25: 
  26: As a special exception, the copyright holders of this library give you
  27: permission to link this library with independent modules to produce an
  28: executable, regardless of the license terms of these independent
  29: modules, and to copy and distribute the resulting executable under
  30: terms of your choice, provided that you also meet, for each linked
  31: independent module, the terms and conditions of the license of that
  32: module.  An independent module is a module which is not derived from
  33: or based on this library.  If you modify this library, you may extend
  34: this exception to your version of the library, but you are not
  35: obligated to do so.  If you do not wish to do so, delete this
  36: exception statement from your version. */
  37: 
  38: package gnu.java.beans.decoder;
  39: 
  40: import java.beans.ExceptionListener;
  41: 
  42: import org.xml.sax.Attributes;
  43: 
  44: /** An ObjectHandler parses the <object> tag and thereby creates various
  45:  * Context implementations.
  46:  *
  47:  * @author Robert Schuster
  48:  *
  49:  */
  50: public class ObjectHandler extends AbstractElementHandler
  51: {
  52:   /**
  53:    * XXX: Can all results be stored with an object id?
  54:    *
  55:    *
  56:    * @param PersistenceParser
  57:    */
  58:   ObjectHandler(ElementHandler parent)
  59:   {
  60:     super(parent, true);
  61:   }
  62: 
  63:   protected Context startElement(Attributes attributes, ExceptionListener exceptionListener)
  64:     throws AssemblyException
  65:   {
  66:     String className = attributes.getValue("class");
  67:     String methodName = attributes.getValue("method");
  68:     String fieldName = attributes.getValue("field");
  69:     String index = attributes.getValue("index");
  70:     String propertyName = attributes.getValue("property");
  71:     String id = attributes.getValue("id");
  72:     String idRef = attributes.getValue("idref");
  73: 
  74:     /* first check if we just want to access an existing object (idref present)
  75:      *
  76:      * note: <object idref="foo" method="bar"/> is not valid to call method "bar"
  77:      * on the object with id "foo". Instead this should return the object "foo"
  78:      * itself. The right way to this is:
  79:      * <object idref="foo">
  80:      *         <object method="bar"/>
  81:      * </object>
  82:      *
  83:      * This means that if idref is present class, method, field, index and
  84:      * property are obsolete.
  85:      */
  86:     if (idRef != null)
  87:       // reactivates an existing object and giving it another name if id exists
  88:       return new ObjectContext(id, getObject(idRef));
  89: 
  90:     // decides whether we are in a static (className present) or dynamic context
  91:     if (className != null)
  92:       {
  93:         try
  94:           {
  95:             Class klass = instantiateClass(className);
  96: 
  97:             // class name exists which means that we are in a static context.
  98:             // so we may want to ...
  99:             // access a static field if the fieldName exists
 100:             if (fieldName != null)
 101:               {
 102:                 try
 103:                   {
 104:                     return new ObjectContext(id,
 105:                                              klass.getField(fieldName).get(null));
 106:                   }
 107:                 catch (NoSuchFieldException nsfe)
 108:                   {
 109:                     throw new AssemblyException(nsfe);
 110:                   }
 111:                 catch (IllegalAccessException iae)
 112:                   {
 113:                     throw new AssemblyException(iae);
 114:                   }
 115:               }
 116: 
 117:             // (falling through is important!)
 118:             // run a constructor if methodName is "new" or null
 119:             if (methodName == null || methodName.equals("new"))
 120:               return new ConstructorContext(id, klass);
 121: 
 122:             // (falling through is important!)
 123:             // run a static method on the given class (if methodName exists, which is implied already)
 124:             return new StaticMethodContext(id, klass, methodName);
 125:             // XXX: should fail if unexpected attributes are present?
 126:           }
 127:         catch (ClassNotFoundException cnfe)
 128:           {
 129:             throw new AssemblyException(cnfe);
 130:           }
 131:       }
 132:     else
 133:       {
 134:         // className does not exist which means we are in the context of
 135:         // some object and want to ...
 136:         // access the get(int index) method if index != null
 137:         if (index != null)
 138:           {
 139:             try
 140:               {
 141:                 // Note: http://java.sun.com/products/jfc/tsc/articles/persistence3/ says
 142:                 // that <void index="4"/> will make up a get()-call. But this is wrong because
 143:                 // <void/> tags never return values (to the surrounding context)
 144:                 return new IndexContext(id, Integer.parseInt(index));
 145:               }
 146:             catch (NumberFormatException nfe)
 147:               {
 148:                 throw new AssemblyException(nfe);
 149:               }
 150:           }
 151: 
 152:         // access a method if methodName exists
 153:         if (methodName != null)
 154:           return new MethodContext(id, methodName);
 155: 
 156:         // (falling through is important!)
 157:         // access a property if a propertyName exists
 158:         if (propertyName != null && propertyName.length() > 0)
 159:           // this is reported as an ordinary method access where the propertyName is
 160:           // converted into a 'getter'-method name: convert first character of property name
 161:           // to upper case and prepend 'get'
 162:           // Note: This will be a getter-method because the <object> tag implies that a return
 163:           // value is expected.
 164:           return new PropertyContext(id, propertyName);
 165:       }
 166: 
 167:     throw new AssemblyException(new IllegalArgumentException("Wrong or missing attributes for <object> tag."));
 168:   }
 169: }