This tutorial shows you how build a simple Java application with CockroachDB using a PostgreSQL-compatible driver or ORM.
We have tested the Java jdbc driver and the Hibernate ORM enough to claim beta-level support, so those are featured here. If you encounter problems, please open an issue with details to help us make progress toward full support.
Before You Begin
Make sure you have already installed CockroachDB.
Step 1. Install the Java jdbc driver
Download and set up the Java jdbc driver as described in the official documentation.
Step 2. Start a single-node cluster
For the purpose of this tutorial, you need only one CockroachDB node running in insecure mode:
$ cockroach start \
--insecure \
--store=hello-1 \
--host=localhost
Step 3. Create a user
In a new terminal, as the root user, use the cockroach user command to create a new user, maxroach.
$ cockroach user set maxroach --insecure
Step 4. Create a database and grant privileges
As the root user, use the built-in SQL client to create a bank database.
$ cockroach sql --insecure -e 'CREATE DATABASE bank'
Then grant privileges to the maxroach user.
$ cockroach sql --insecure -e 'GRANT ALL ON DATABASE bank TO maxroach'
Step 5. Run the Java code
Now that you have a database and a user, you'll run code to create a table and insert some rows, and then you'll run code to read and update values as an atomic transaction.
Basic Statements
First, use the following code to connect as the maxroach user and execute some basic SQL statements, creating a table, inserting rows, and reading and printing the rows.
Download the BasicSample.java file, or create the file yourself and copy the code into it.
import java.sql.*;
/*
You can compile and run this example with a command like:
javac BasicSample.java && java -cp .:~/path/to/postgresql-9.4.1208.jar BasicSample
You can download the postgres JDBC driver jar from https://jdbc.postgresql.org.
*/
public class BasicSample {
public static void main(String[] args) throws ClassNotFoundException, SQLException {
// Load the postgres JDBC driver.
Class.forName("org.postgresql.Driver");
// Connect to the "bank" database.
Connection db = DriverManager.getConnection("jdbc:postgresql://127.0.0.1:26257/bank?sslmode=disable", "maxroach", "");
try {
// Create the "accounts" table.
db.createStatement().execute("CREATE TABLE IF NOT EXISTS accounts (id INT PRIMARY KEY, balance INT)");
// Insert two rows into the "accounts" table.
db.createStatement().execute("INSERT INTO accounts (id, balance) VALUES (1, 1000), (2, 250)");
// Print out the balances.
System.out.println("Initial balances:");
ResultSet res = db.createStatement().executeQuery("SELECT id, balance FROM accounts");
while (res.next()) {
System.out.printf("\taccount %s: %s\n", res.getInt("id"), res.getInt("balance"));
}
} finally {
// Close the database connection.
db.close();
}
}
}
Transaction (with retry logic)
Next, use the following code to again connect as the maxroach user but this time execute a batch of statements as an atomic transaction to transfer funds from one account to another, where all included statements are either committed or aborted.
Download the TxnSample.java file, or create the file yourself and copy the code into it.
SERIALIZABLE isolation level, CockroachDB may require the client to retry a transaction in case of read/write contention. CockroachDB provides a generic retry function that runs inside a transaction and retries it as needed. You can copy and paste the retry function from here into your code. Note that, in Java, you access error codes with the getSQLState() method instead of getErrorCode().import java.sql.*;
/*
You can compile and run this example with a command like:
javac TxnSample.java && java -cp .:~/path/to/postgresql-9.4.1208.jar TxnSample
You can download the postgres JDBC driver jar from https://jdbc.postgresql.org.
*/
// Ambiguous whether the transaction committed or not.
class AmbiguousCommitException extends SQLException{
public AmbiguousCommitException(Throwable cause) {
super(cause);
}
}
class InsufficientBalanceException extends Exception {}
class AccountNotFoundException extends Exception {
public int account;
public AccountNotFoundException(int account) {
this.account = account;
}
}
// A simple interface that provides a retryable lambda expression.
interface RetryableTransaction {
public void run(Connection conn)
throws SQLException, InsufficientBalanceException, AccountNotFoundException, AmbiguousCommitException;
}
public class TxnSample {
public static RetryableTransaction transferFunds(int from, int to, int amount) {
return new RetryableTransaction() {
public void run(Connection conn)
throws SQLException, InsufficientBalanceException, AccountNotFoundException, AmbiguousCommitException {
// Check the current balance.
ResultSet res = conn.createStatement().executeQuery("SELECT balance FROM accounts WHERE id = " + from);
if(!res.next()) {
throw new AccountNotFoundException(from);
}
int balance = res.getInt("balance");
if(balance < from) {
throw new InsufficientBalanceException();
}
// Perform the transfer.
conn.createStatement().executeUpdate("UPDATE accounts SET balance = balance - " + amount + " where id = " + from);
conn.createStatement().executeUpdate("UPDATE accounts SET balance = balance + " + amount + " where id = " + to);
}
};
}
public static void retryTransaction(Connection conn, RetryableTransaction tx)
throws SQLException, InsufficientBalanceException, AccountNotFoundException, AmbiguousCommitException {
Savepoint sp = conn.setSavepoint("cockroach_restart");
while(true) {
boolean releaseAttempted = false;
try {
tx.run(conn);
releaseAttempted = true;
conn.releaseSavepoint(sp);
}
catch(SQLException e) {
String sqlState = e.getSQLState();
// Check if the error code indicates a SERIALIZATION_FAILURE.
if(sqlState.equals("40001")) {
// Signal the database that we will attempt a retry.
conn.rollback(sp);
continue;
} else if(releaseAttempted) {
throw new AmbiguousCommitException(e);
} else {
throw e;
}
}
break;
}
conn.commit();
}
public static void main(String[] args) throws ClassNotFoundException, SQLException {
// Load the postgres JDBC driver.
Class.forName("org.postgresql.Driver");
// Connect to the "bank" database.
Connection db = DriverManager.getConnection("jdbc:postgresql://127.0.0.1:26257/bank?sslmode=disable", "maxroach", "");
try {
// We need to turn off autocommit mode to allow for
// multi-statement transactions.
db.setAutoCommit(false);
// Perform the transfer. This assumes the table has
// already been set up as in the "Build a Test App"
// tutorial.
RetryableTransaction transfer = transferFunds(1, 2, 100);
retryTransaction(db, transfer);
// Check balances after transfer.
db.setAutoCommit(true);
ResultSet res = db.createStatement().executeQuery("SELECT id, balance FROM accounts");
while (res.next()) {
System.out.printf("\taccount %s: %s\n", res.getInt("id"), res.getInt("balance"));
}
} catch(InsufficientBalanceException e) {
System.out.println("Insufficient balance");
} catch(AccountNotFoundException e) {
System.out.println("No users in the table with id " + e.account);
} catch(AmbiguousCommitException e) {
System.out.println("Ambiguous result encountered: " + e);
} catch(SQLException e) {
System.out.println("SQLException encountered:" + e);
} finally {
// Close the database connection.
db.close();
}
}
}
After running the code, use the built-in SQL client to verify that funds were transferred from one account to another:
$ cockroach sql --insecure -e 'SELECT id, balance FROM accounts' --database=bank
+----+---------+
| id | balance |
+----+---------+
| 1 | 900 |
| 2 | 350 |
+----+---------+
(2 rows)
What's Next?
Read more about using the Java jdbc driver.
You might also be interested in using a local cluster to explore the following CockroachDB benefits:
- Client Connection Parameters
- Data Replication
- Fault Tolerance & Recovery
- Automatic Rebalancing
- Cross-Cloud Migration
- Follow-the-Workload
- Automated Operations
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