Create 12.7 Accessing Bitcoind with Java

12_7_Accessing_Bitcoind_with_Java.md

@@ -0,0 +1,131 @@
+# 12.7: Accessing Bitcoind with Java
+
+> **NOTE:** This is a draft in progress, so that I can get some feedback from early reviewers. It is not yet ready for learning.
+
+Interacting with the `bitcoind` directly and using command-line `curl` can get simple if you understand how it works, but there's a project [JavaBitcoindRpcClient](https://github.com/Polve/JavaBitcoindRpcClient) that provides the functionality in a Java-API level, making it even easier to interact with your Bitcoin Server.
+
+## Setup Dependency
+
+If you use Maven in your Java project, you can include the dependency:
+```xml
+<dependency>
+  <groupId>wf.bitcoin</groupId>
+  <artifactId>JavaBitcoindRpcClient</artifactId>
+  <version>0.9.13</version>
+</dependency>
+```
+
+Or if you use Gradle:
+```groovy
+compile 'wf.bitcoin:JavaBitcoindRpcClient:0.9.13'
+```
+
+### Build Your Connection
+
+To use `JavaBitcoindRpcClient`, you need to create a `BitcoindRpcClient` instance. The arguments in the URL are username, password, IP address and port. You should know this information from your work with `curl` . As you'll recall, the IP address 127.0.0.1 and port 18332 should be correct for the standard testnet setup described in this documents, while you can extract the user and password from `~/.bitcoin/bitcoin.conf`.
+
+```java
+  BitcoindRpcClient rpcClient = new BitcoinJSONRPCClient("http://bitcoinrpc:d8340efbcd34e312044c8431c59c792c@127.0.0.1:18332");
+```
+
+> **MAINNET VS TESTNET:** The port would be 8332 for a mainnet setup.
+
+If `rpcClient` is successfully initialized, you'll be able to send off RPC commands.
+
+Later, when you're all done with your `bitcoind` connection, you should close it:
+```
+rpcClient.stop();
+```
+
+### Making your first RPC Call
+
+In order to use an RPC method using `JavaBitcoindRpcClient`, you'll find that the `BitcoindRpcClient` provides most of the functionality that can be accessed through `bitcloin-cli` or `curl`.
+
+For example, to execute the `getmininginfo`, you should use the `getMiningInfo()` method:
+```java
+MiningInfo info = rpcClient.getMiningInfo();
+System.out.println("Mining Information");
+System.out.println("------------------");
+System.out.println("Chain......: " + info.chain());
+System.out.println("Blocks.....: " + info.blocks());
+System.out.println("Difficulty.: " + info.difficulty());
+System.out.println("Hash Power.: " + new BigDecimal(info.networkHashps()).toPlainString());
+```
+The output for this line should be similar to this:
+```
+Mining Information
+------------------
+Chain......: test
+Blocks.....: 1254920
+Difficulty.: 1.0
+Hash Power.: 6585163152453.466796875
+```
+
+### Creating an Address
+
+You can create a new address attaching a specific label to it, as well as dump the private key for a specific address:
+```java
+  String address = rpcClient.getNewAddress("Learning-Bitcoin-from-the-Command-Line");
+  System.out.println("New Address: " + address);
+
+  String privKey = rpcClient.dumpPrivKey(address);
+  System.out.println("Priv Key: " + privKey);
+```
+Output:
+```
+New Address: mpsFtZ8qTJPRGZy1gaaUw37fHeUSPLkzzs
+Priv Key: cTy2AnmAALsHokYzJzTdsUBSqBtypmWfmSNYgG6qQH43euUZgqic
+```
+
+
+
+### Sending Transactions
+
+You can easily send a transaction using the method `sendToAddress()`.
+
+```java
+String sendToAddress = rpcClient.sendToAddress("mgnNsZj6tPzpd7JwTTidUKnGoDTkcucLT5", 1);
+System.out.println("Send: " + sendToAddress);
+```
+This program will output a transaction id, for example:
+```
+a2d2f629d6666ca6e440169a322850cd9d133f637f7a02a02a0a7477bc5687d4
+```
+
+In case you want to adjust the transaction fee, you can use the `setTxFee` method before sending the output:
+
+```java
+rpcClient.setTxFee(new BigDecimal(0.001).setScale(3, BigDecimal.ROUND_DOWN));
+```
+
+
+### Listening to Transactions or Blocks
+
+You may want to write applications that keep listening the Blockchain, and execute a specific code when something happens, such as a transaction that involves an address in your wallet, or even the generation of a new block in the network.
+To do that, `JavaBitcoindRpcClient` provides support to `BitcoinAcceptor`, where you can attach listeners in the network.
+
+Example:
+```java
+  BitcoinAcceptor acceptor = new BitcoinAcceptor(rpcClient, blockHash, 6, new BitcoinPaymentListener() {
+
+      @Override
+      public void transaction(Transaction tx) {
+          System.out.println("Transaction: " + tx);
+
+      }
+
+      @Override
+      public void block(String block) {
+          System.out.println("Block: " + block);
+
+      }
+  });
+  acceptor.run();
+```
+
+Every time some transaction is sent, or a new block is generated, you should see a similar output in your console:
+```
+Transaction: {account=Tests, address=mhopuJzgmTwhGfpNLCJ9CRknugY691oXp1, category=receive, amount=5.0E-4, label=Tests, vout=1, confirmations=0, trusted=false, txid=361e8fcff243b74ebf396e595a007636654f67c3c7b55fd2860a3d37772155eb, walletconflicts=[], time=1513132887, timereceived=1513132887, bip125-replaceable=unknown}
+
+Block: 000000004564adfee3738314549f7ca35d96c4da0afc6b232183917086b6d971
+```

README.md

@@ -92,6 +92,8 @@ This tutorial assumes that you have some minimal background of how to use the co
   * [12.3: Programming Bitcoind with C](12_3_Programming_Bitcoind_with_C.md) — Needs Editing
   * [12.4: Receiving Bitcoind Notifications with C](12_4_Receiving_Bitcoind_Notifications_with_C.md) — Pending
   * [12.5: Accessing Bitcoind with Other Languages](12_5_Accessing_Bitcoind_with_Other_Languages.md)  — Writing
+  * [12.6: Accessing Bitcoind with Python](12_6_Accessing_Bitcoind_with_Python.md)  — Writing
+  * [12.7: Accessing Bitcoind with Java](12_7_Accessing_Bitcoind_with_Java.md)
 * 13.0: Programming with LibWally
    * 13.1: Programming Transactions
    * 13.2: Programming Scripts