Created the facilities for transmitting distributed objects and derived

classes over the wire (by inspecting their fields and sending those
directly).


git-svn-id: svn+ssh://src.earth.threerings.net/narya/trunk@8 542714f4-19e9-0310-aa3c-eee0fc999fb1

src/java/com/threerings/presents/io/Marshaller.java

@@ -0,0 +1,113 @@
+//
+// $Id: Marshaller.java,v 1.1 2001/05/30 00:16:00 mdb Exp $
+
+package com.samskivert.cocktail.cher.dobj.net;
+
+import java.io.DataInputStream;
+import java.io.DataOutputStream;
+import java.io.IOException;
+import java.lang.reflect.Field;
+import java.util.Arrays;
+import java.util.Comparator;
+
+import com.samskivert.cocktail.cher.Log;
+import com.samskivert.cocktail.cher.dobj.DObject;
+import com.samskivert.cocktail.cher.io.ObjectStreamException;
+
+/**
+ * The marshaller inspects the class with which it is constructed and
+ * caches the reflection information it needs to marshall and unmarshall
+ * instances of that class.
+ */
+public class Marshaller
+{
+    public Marshaller (Class clazz)
+    {
+        // we introspect on the class and cache the public data members
+        _fields = clazz.getFields();
+        // sort the fields so that they are written and read in the same
+        // order on all VMs
+        Arrays.sort(_fields, FIELD_COMP);
+
+        // now select field marshallers for each of the fields based on
+        // their type
+        _marshallers = new FieldMarshaller[_fields.length];
+        for (int i = 0; i < _fields.length; i++) {
+            _marshallers[i] =
+                FieldMarshallerRegistry.getMarshaller(_fields[i]);
+            // Log.info("Assigned [field=" + _fields[i] +
+            // ", marshaller=" + _marshallers[i] + "].");
+        }
+    }
+
+    /**
+     * Writes out all of the fields of the specified distributed object to
+     * the supplied data output stream.
+     */
+    public void writeTo (DataOutputStream out, DObject dobj)
+        throws IOException
+    {
+        // we simply iterate over our marshallers, writing each field
+        // out in succession
+        for (int i = 0; i < _fields.length; i++) {
+            try {
+                _marshallers[i].writeTo(out, _fields[i], dobj);
+
+            } catch (IllegalAccessException iae) {
+                // this shouldn't happen because we only attempt to marshall
+                // public fields, but we'll pass it on none the less
+                String errmsg = "Unable to marshall dobj field " +
+                    "[field=" + _fields[i].getName() +
+                    ", dobj=" + dobj  + "].";
+                throw new ObjectStreamException(errmsg);
+            }
+        }
+    }
+
+    /**
+     * Reads in all of the fields of the specified distributed object from
+     * the supplied data input stream.
+     */
+    public void readFrom (DataInputStream in, DObject dobj)
+        throws IOException
+    {
+        // we simply iterate over our marshallers, reading each field in
+        // in succession
+        for (int i = 0; i < _fields.length; i++) {
+            try {
+                _marshallers[i].readFrom(in, _fields[i], dobj);
+
+            } catch (IllegalAccessException iae) {
+                // this shouldn't happen because we only attempt to
+                // unmarshall public fields, but we'll pass it on anyway
+                String errmsg = "Unable to unmarshall dobj field " +
+                    "[field=" + _fields[i].getName() +
+                    ", dobj=" + dobj  + "].";
+                throw new ObjectStreamException(errmsg);
+            }
+        }
+    }
+
+    /**
+     * Used to sort object fields into a predictable order.
+     */
+    protected static class FieldComparator implements Comparator
+    {
+        public int compare (Object o1, Object o2)
+        {
+            return ((Field)o1).getName().compareTo(((Field)o2).getName());
+        }
+
+        public boolean equals (Object obj)
+        {
+            // we don't care about comparing this comparator to others
+            return obj == this;
+        }
+    }
+
+    protected Field[] _fields;
+    protected FieldMarshaller[] _marshallers;
+
+    /** We use this to sort the fields into a predictable order. */
+    protected static final FieldComparator FIELD_COMP = new FieldComparator();
+}