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

//
// $Id: Marshaller.java,v 1.2 2001/05/30 23:58:31 mdb Exp $

package com.threerings.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.threerings.cocktail.cher.Log;
import com.threerings.cocktail.cher.dobj.DObject;
import com.threerings.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();
}