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: }