Some minor changes:

- Introduce an EmptyMessage class.
 - Make Message.bitcoinSerialize() method final.
 
Patch 1 of the lazy parsing patchset by Steve.

src/com/google/bitcoin/core/AddressMessage.java

@@ -40,4 +40,5 @@ public class AddressMessage extends Message {
         }
         return builder.toString();
     }
+
 }

src/com/google/bitcoin/core/Block.java

@@ -37,7 +37,7 @@ import static com.google.bitcoin.core.Utils.*;
  * or request one specifically using {@link Peer#getBlock(Sha256Hash)}, or grab one from a downloaded {@link BlockChain}.
  */
 public class Block extends Message {
-    private static final Logger log = LoggerFactory.getLogger(Block.class);
+	private static final Logger log = LoggerFactory.getLogger(Block.class);
     private static final long serialVersionUID = 2738848929966035281L;
 
     /** How many bytes are required to represent a block header. */

src/com/google/bitcoin/core/GetAddrMessage.java

@@ -16,7 +16,7 @@
 
 package com.google.bitcoin.core;
 
-public class GetAddrMessage extends Message {
+public class GetAddrMessage extends EmptyMessage {
 	public GetAddrMessage(NetworkParameters params) {
 		super(params);
 	}
@@ -25,4 +25,5 @@ public class GetAddrMessage extends Message {
 	void parse() throws ProtocolException {
     // TODO: Implement this.
 	}
+
 }

src/com/google/bitcoin/core/GetBlocksMessage.java

@@ -16,8 +16,8 @@
 
 package com.google.bitcoin.core;
 
-import java.io.ByteArrayOutputStream;
 import java.io.IOException;
+import java.io.OutputStream;
 import java.util.List;
 
 public class GetBlocksMessage extends Message {
@@ -52,24 +52,19 @@ public class GetBlocksMessage extends Message {
         return b.toString();
     }
 
-    public byte[] bitcoinSerialize() {
-        try {
-            ByteArrayOutputStream buf = new ByteArrayOutputStream();
+    void bitcoinSerializeToStream(OutputStream stream) throws IOException {
             // Version, for some reason.
-            Utils.uint32ToByteStreamLE(NetworkParameters.PROTOCOL_VERSION, buf);
+            Utils.uint32ToByteStreamLE(NetworkParameters.PROTOCOL_VERSION, stream);
             // Then a vector of block hashes. This is actually a "block locator", a set of block
             // identifiers that spans the entire chain with exponentially increasing gaps between
             // them, until we end up at the genesis block. See CBlockLocator::Set()
-            buf.write(new VarInt(locator.size()).encode());
+            stream.write(new VarInt(locator.size()).encode());
             for (Sha256Hash hash : locator) {
                 // Have to reverse as wire format is little endian.
-                buf.write(Utils.reverseBytes(hash.getBytes()));
+            	stream.write(Utils.reverseBytes(hash.getBytes()));
             }
             // Next, a block ID to stop at.
-            buf.write(stopHash.getBytes());
-            return buf.toByteArray();
-        } catch (IOException e) {
-            throw new RuntimeException(e);  // Cannot happen.
-        }
+            stream.write(stopHash.getBytes());
+           
     }
 }

src/com/google/bitcoin/core/Message.java

@@ -20,6 +20,9 @@ import java.io.*;
 import java.math.BigInteger;
 import java.util.Arrays;
 
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
 /**
  * A Message is a data structure that can be serialized/deserialized using both the BitCoin proprietary serialization
  * format and built-in Java object serialization. Specific types of messages that are used both in the block chain,
@@ -28,7 +31,8 @@ import java.util.Arrays;
  * This class is not useful for library users. If you want to talk to the network see the {@link Peer} class.
  */
 public abstract class Message implements Serializable {
-    private static final long serialVersionUID = -3561053461717079135L;
+	private static final Logger log = LoggerFactory.getLogger(Message.class);
+	private static final long serialVersionUID = -3561053461717079135L;
 
     public static final int MAX_SIZE = 0x02000000;
 
@@ -86,7 +90,7 @@ public abstract class Message implements Serializable {
     // are serialized to the wallet.
     abstract void parse() throws ProtocolException;
     
-    public byte[] bitcoinSerialize() {
+    final public byte[] bitcoinSerialize() {
         ByteArrayOutputStream stream = new ByteArrayOutputStream();
         try {
             bitcoinSerializeToStream(stream);
@@ -101,6 +105,7 @@ public abstract class Message implements Serializable {
      * Serializes this message to the provided stream. If you just want the raw bytes use bitcoinSerialize().
      */
     void bitcoinSerializeToStream(OutputStream stream) throws IOException {
+    	log.debug("Warning: {} class has not implemented bitcoinSerializeToStream method.  Generating message with no payload", getClass());
     }
     
     int getMessageSize() {

src/com/google/bitcoin/core/Ping.java

@@ -16,9 +16,10 @@
 
 package com.google.bitcoin.core;
 
-public class Ping extends Message {
+public class Ping extends EmptyMessage {
     @Override
     void parse() throws ProtocolException {
         // nothing to parse
     }
+
 }

src/com/google/bitcoin/core/UnknownMessage.java

@@ -16,7 +16,7 @@
 
 package com.google.bitcoin.core;
 
-public class UnknownMessage extends Message {
+public class UnknownMessage extends EmptyMessage {
     private static final long serialVersionUID = 3614705938207918775L;
     private String name;
 
@@ -33,4 +33,5 @@ public class UnknownMessage extends Message {
     @Override
     public void parse() throws ProtocolException {
     }
+    
 }

src/com/google/bitcoin/core/VersionAck.java

@@ -14,28 +14,25 @@
  * limitations under the License.
  */
 
-
 package com.google.bitcoin.core;
 
 /**
- * The verack message, sent by a client accepting the version message they received from their peer.
+ * The verack message, sent by a client accepting the version message they
+ * received from their peer.
  */
-public class VersionAck
-    extends Message
-{
-    public VersionAck()
-    {
+public class VersionAck extends EmptyMessage {
+	public VersionAck() {
 
-    }
+	}
 
-    // this is needed by the BitcoinSerializer
-    public VersionAck(NetworkParameters params, byte[] payload) {
+	// this is needed by the BitcoinSerializer
+	public VersionAck(NetworkParameters params, byte[] payload) {
 
-    }
+	}
+
+	@Override
+	void parse() throws ProtocolException {
+		// nothing to parse for now
+	}
 
-    @Override
-    void parse() throws ProtocolException
-    {
-        // nothing to parse for now
-    }
 }