FetchBlock example: Enhance this example to be able to connect DNS discovered peers so that you don't need to install bitcoind locally.
package org.bitcoinj.examples;
+import joptsimple.OptionException;
+import joptsimple.OptionParser;
+import joptsimple.OptionSet;
import org.bitcoinj.core.*;
+import org.bitcoinj.net.discovery.DnsDiscovery;
import org.bitcoinj.params.TestNet3Params;
import org.bitcoinj.store.BlockStore;
import org.bitcoinj.store.MemoryBlockStore;
import org.bitcoinj.utils.BriefLogFormatter;
import java.net.InetAddress;
+import java.util.List;
import java.util.concurrent.Future;
/**
- * Downloads the block given a block hash from the localhost node and prints it out.
+ * <p>Downloads the block given a block hash from the remote or localhost node and prints it out.</p>
+ * <p>When downloading from localhost, run bitcoind locally: bitcoind -testnet -daemon.
+ * After bitcoind is up and running, use command: org.bitcoinj.examples.FetchBlock --localhost &lt;blockHash&gt; </p>
+ * <p>Otherwise, use command: org.bitcoinj.examples.FetchBlock &lt;blockHash&gt;, this command will download blocks from a peer generated by DNS seeds.</p>
*/
public class FetchBlock {
public static void main(String[] args) throws Exception {
BriefLogFormatter.init();
+ // Parse command line arguments
+ OptionParser parser = new OptionParser();
+ OptionSet opts = null;
+ List<String> nonOpts = null;
+ try {
+ parser.accepts("localhost", "Connect to the localhost node");
+ parser.accepts("help", "Displays program options");
+ opts = parser.parse(args);
+ if (opts.has("help")) {
+ System.out.println("usage: org.bitcoinj.examples.FetchBlock [--localhost] <blockHash>");
+ parser.printHelpOn(System.out);
+ return;
+ }
+ nonOpts = opts.nonOptionArguments();
+ if (nonOpts.size() != 1) {
+ throw new IllegalArgumentException("Incorrect number of block hash, please provide only one block hash.");
+ }
+ } catch (OptionException | IllegalArgumentException e) {
+ System.err.println(e.getMessage());
+ System.err.println("usage: org.bitcoinj.examples.FetchBlock [--localhost] <blockHash>");
+ parser.printHelpOn(System.err);
+ return;
+ }
+
+ // Connect to testnet and find a peer
System.out.println("Connecting to node");
final NetworkParameters params = TestNet3Params.get();
-
BlockStore blockStore = new MemoryBlockStore(params);
BlockChain chain = new BlockChain(params, blockStore);
PeerGroup peerGroup = new PeerGroup(params, chain);
- peerGroup.start();
+ if (!opts.has("localhost")) {
+ peerGroup.addPeerDiscovery(new DnsDiscovery(params));
+ } else {
PeerAddress addr = new PeerAddress(params, InetAddress.getLocalHost());
peerGroup.addAddress(addr);
+ }
+ peerGroup.start();
peerGroup.waitForPeers(1).get();
Peer peer = peerGroup.getConnectedPeers().get(0);
- Sha256Hash blockHash = Sha256Hash.wrap(args[0]);
+ // Retrieve a block through a peer
+ Sha256Hash blockHash = Sha256Hash.wrap(nonOpts.get(0));
Future<Block> future = peer.getBlock(blockHash);
System.out.println("Waiting for node to send us the requested block: " + blockHash);
Block block = future.get();
