Add a PeerMonitor example. I'll extend it later.

examples/src/main/java/com/google/bitcoin/examples/PeerMonitor.java

@@ -0,0 +1,133 @@
+/*
+ * Copyright 2012 Google Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.bitcoin.examples;
+
+import com.google.bitcoin.core.AbstractPeerEventListener;
+import com.google.bitcoin.core.NetworkParameters;
+import com.google.bitcoin.core.Peer;
+import com.google.bitcoin.core.PeerGroup;
+import com.google.bitcoin.discovery.DnsDiscovery;
+import com.google.bitcoin.utils.BriefLogFormatter;
+
+import javax.swing.*;
+import javax.swing.table.AbstractTableModel;
+import java.awt.*;
+import java.util.List;
+
+/**
+ * Shows connected peers in a table view, so you can watch as they come and go.
+ */
+public class PeerMonitor {
+    private NetworkParameters params;
+    private PeerGroup peerGroup;
+    private PeerTableModel peerTableModel;
+
+    public static void main(String[] args) throws Exception {
+        BriefLogFormatter.init();
+        new PeerMonitor();
+    }
+
+    public PeerMonitor() {
+        setupNetwork();
+        setupGUI();
+    }
+
+    private void setupNetwork() {
+        params = NetworkParameters.prodNet();
+        peerGroup = new PeerGroup(params, null /* no chain */);
+        peerGroup.setUserAgent("PeerMonitor", "1.0");
+        peerGroup.addPeerDiscovery(new DnsDiscovery(params));
+        peerGroup.addEventListener(new AbstractPeerEventListener() {
+            @Override
+            public void onPeerConnected(Peer peer, int peerCount) {
+                refreshUI();
+            }
+
+            @Override
+            public void onPeerDisconnected(Peer peer, int peerCount) {
+                refreshUI();
+            }
+        });
+        peerGroup.start();
+    }
+
+    private void refreshUI() {
+        // Tell the Swing UI thread to redraw the peers table.
+        SwingUtilities.invokeLater(new Runnable() {
+            public void run() {
+                peerTableModel.fireTableDataChanged();
+            }
+        });
+    }
+
+    private void setupGUI() {
+        JFrame window = new JFrame("Network monitor");
+        window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
+        JLabel instructions = new JLabel("Peers shown below. Download peer is in bold.");
+        window.getContentPane().add(instructions, BorderLayout.NORTH);
+        peerTableModel = new PeerTableModel();
+        JTable peerTable = new JTable(peerTableModel);
+        JScrollPane scrollPane = new JScrollPane(peerTable);
+        window.getContentPane().add(scrollPane, BorderLayout.CENTER);
+        window.pack();
+        window.setSize(640, 480);
+        window.setVisible(true);
+    }
+
+    private class PeerTableModel extends AbstractTableModel {
+        private final int IP_ADDRESS = 0;
+        private final int PROTOCOL_VERSION = 1;
+        private final int USER_AGENT = 2;
+        private final int CHAIN_HEIGHT = 3;
+
+        public int getRowCount() {
+            return peerGroup.numConnectedPeers();
+        }
+
+        @Override
+        public String getColumnName(int i) {
+            switch (i) {
+                case IP_ADDRESS: return "IP address";
+                case PROTOCOL_VERSION: return "Protocol version";
+                case USER_AGENT: return "User Agent";
+                case CHAIN_HEIGHT: return "Chain height";
+                default: throw new RuntimeException();
+            }
+        }
+
+        public int getColumnCount() {
+            return 4;
+        }
+
+        public Object getValueAt(int row, int col) {
+            List<Peer> peers = peerGroup.getConnectedPeers();
+            Peer peer = peers.get(row);
+            switch (col) {
+                case IP_ADDRESS:
+                    return peer.getAddress().getAddr().getHostAddress();
+                case PROTOCOL_VERSION:
+                    return Integer.toString(peer.getPeerVersionMessage().clientVersion);
+                case USER_AGENT:
+                    return peer.getPeerVersionMessage().subVer;
+                case CHAIN_HEIGHT:
+                    return peer.getBestHeight();
+
+                default: throw new RuntimeException();
+            }
+        }
+    }
+}