// This example is from _Java Examples in a Nutshell_. (http://www.oreilly.com)
// Copyright (c) 1997 by David Flanagan
// This example is provided WITHOUT ANY WARRANTY either expressed or implied.
// You may study, use, modify, and distribute it for non-commercial purposes.
// For any commercial use, see http://www.davidflanagan.com/javaexamples
import java.rmi.*;
import java.rmi.server.*;
import java.rmi.registry.*;
import java.sql.*;
import java.io.*;
import java.util.*;
import java.util.Date; // import explicitly to disambiguate from java.sql.Date
import Bank.*;
/**
* This class is another implementation of the RemoteBank interface.
* It uses a database connection as its back end, so that client data isn't
* lost if the server goes down. Note that it takes the database connection
* out of "auto commit" mode and explicitly calls commit() and rollback() to
* ensure that updates happen atomically.
**/
public class RemoteDBBankServer extends UnicastRemoteObject
implements RemoteBank {
Connection db; // The connection to the database that stores account info
/** The constructor. Just save the database connection object away */
public RemoteDBBankServer(Connection db) throws RemoteException {
this.db = db;
}
/** Open an account */
public synchronized void openAccount(String name, String password)
throws RemoteException, BankingException {
// First, check if there is already an account with that name
Statement s = null;
try {
s = db.createStatement();
s.executeQuery("SELECT * FROM accounts WHERE name='" + name + "'");
ResultSet r = s.getResultSet();
if (r.next()) throw new BankingException("Account already exists.");
// If it doesn't exist, go ahead and create it
// Also, create a table for the transaction history of this account and
// insert an initial transaction into it.
s = db.createStatement();
s.executeUpdate("INSERT INTO accounts VALUES ('" + name + "', '" +
password + "', 0)");
s.executeUpdate("CREATE TABLE " + name +
"_history (msg VARCHAR(80))");
s.executeUpdate("INSERT INTO " + name + "_history " +
"VALUES ('Account opened at " + new Date() + "')");
// And if we've been successful so far, commit these updates,
// ending the atomic transaction. All the methods below also use this
// atomic transaction commit/rollback scheme
db.commit();
}
catch(SQLException e) {
// If an exception was thrown, "rollback" the prior updates,
// removing them from the database. This also ends the atomic
// transaction.
try { db.rollback(); } catch (Exception e2) {}
// Pass the SQLException on in the body of a BankingException
throw new BankingException("SQLException: " + e.getMessage() +
": " + e.getSQLState());
}
// No matter what happens, don't forget to close the DB Statement
finally { try { s.close(); } catch (Exception e) {} }
}
/**
* This convenience method checks whether the name and password match
* an existing account. If so, it returns the balance in that account.
* If not, it throws an exception. Note that this method does not call
* commit() or rollback(), so its query is part of a larger transaction.
**/
public int verify(String name, String password)
throws BankingException, SQLException {
Statement s = null;
try {
s = db.createStatement();
s.executeQuery("SELECT balance FROM accounts " +
"WHERE name='" + name + "' " +
" AND password = '" + password + "'");
ResultSet r = s.getResultSet();
if (!r.next())
throw new BankingException("No such account or invalid password");
return r.getInt(1);
}
finally { try { s.close(); } catch (Exception e) {} }
}
/** Close a named account */
public synchronized FunnyMoney closeAccount(String name, String password)
throws RemoteException, BankingException {
int balance = 0;
Statement s = null;
try {
balance = verify(name, password);
s = db.createStatement();
// Delete the account from the accounts table
s.executeUpdate("DELETE FROM accounts " +
"WHERE name = '" + name + "' " +
" AND password = '" + password + "'");
// And drop the transaction history table for this account
s.executeUpdate("DROP TABLE " + name + "_history");
db.commit();
}
catch (SQLException e) {
try { db.rollback(); } catch (Exception e2) {}
throw new BankingException("SQLException: " + e.getMessage() +
": " + e.getSQLState());
}
finally { try { s.close(); } catch (Exception e) {} }
// Finally, return whatever balance remained in the account
return new FunnyMoney(balance);
}
/** Deposit the specified money into the named account */
public synchronized void deposit(String name, String password,
FunnyMoney money)
throws RemoteException, BankingException {
int balance = 0;
Statement s = null;
try {
balance = verify(name, password);
s = db.createStatement();
// Update the balance
s.executeUpdate("UPDATE accounts " +
"SET balance = " + balance + money.amount + " " +
"WHERE name='" + name + "' " +
" AND password = '" + password + "'");
// Add a row to the transaction history
s.executeUpdate("INSERT INTO " + name + "_history " +
"VALUES ('Deposited " + money.amount +
" at " + new Date() + "')");
db.commit();
}
catch (SQLException e) {
try { db.rollback(); } catch (Exception e2) {}
throw new BankingException("SQLException: " + e.getMessage() +
": " + e.getSQLState());
}
finally { try { s.close(); } catch (Exception e) {} }
}
/** Withdraw the specified amount from the named account */
public synchronized FunnyMoney withdraw(String name, String password,
int amount)
throws RemoteException, BankingException {
int balance = 0;
Statement s = null;
try {
balance = verify(name, password);
if (balance < amount) throw new BankingException("Insufficient Funds");
s = db.createStatement();
// Update the account balance
s.executeUpdate("UPDATE accounts " +
"SET balance = " + (balance - amount) + " " +
"WHERE name='" + name + "' " +
" AND password = '" + password + "'");
// Add a row to the transaction history
s.executeUpdate("INSERT INTO " + name + "_history " +
"VALUES ('Withdrew " + amount +
" at " + new Date() + "')");
db.commit();
}
catch (SQLException e) {
try { db.rollback(); } catch (Exception e2) {}
throw new BankingException("SQLException: " + e.getMessage() +
": " + e.getSQLState());
}
finally { try { s.close(); } catch (Exception e) {} }
return new FunnyMoney(amount);
}
/** Return the balance of the specified account */
public synchronized int getBalance(String name, String password)
throws RemoteException, BankingException {
int balance;
try {
// Get the balance
balance = verify(name, password);
// Commit the transaction
db.commit();
}
catch (SQLException e) {
try { db.rollback(); } catch (Exception e2) {}
throw new BankingException("SQLException: " + e.getMessage() +
": " + e.getSQLState());
}
// Return the balance
return balance;
}
/** Get the transaction history of the named account */
public synchronized Vector getTransactionHistory(String name,
String password)
throws RemoteException, BankingException {
Statement s = null;
Vector v = new Vector();
try {
// Call verify to check the password, even though we don't
// care what the current balance is.
verify(name, password);
s = db.createStatement();
// Request everything out of the history table
s.executeQuery("SELECT * from " + name + "_history");
// Get the results of the query and put them in a Vector
ResultSet r = s.getResultSet();
while(r.next()) v.addElement(r.getString(1));
// Commit the transaction
db.commit();
}
catch (SQLException e) {
try { db.rollback(); } catch (Exception e2) {}
throw new BankingException("SQLException: " + e.getMessage() +
": " + e.getSQLState());
}
finally { try { s.close(); } catch (Exception e) {} }
// Return the Vector of transaction history.
return v;
}
/**
* This main() method is the standalone program that figures out what
* database to connect to with what driver, connects to the database,
* creates a RemoteDBBankServer object, and registers it with the registry,
* making it available for client use
**/
public static void main(String[] args) {
try {
// Create a new Properties object. Attempt to initialize it from
// the BankDB.props file or the file optionally specified on the
// command line, ignoring errors.
Properties p = new Properties();
try { p.load(new FileInputStream(args[0])); }
catch (Exception e) {
try { p.load(new FileInputStream("BankDB.props")); }
catch (Exception e2) {}
}
// The BankDB.props file (or file specified on the command line)
// must contain properties "driver" and "database", and may optionally
// contain properties "user" and "password".
String driver = p.getProperty("driver");
String database = p.getProperty("database");
String user = p.getProperty("user", "");
String password = p.getProperty("password", "");
// Load the database driver class
Class.forName(driver);
// Connect to the database that stores our accounts
Connection db = DriverManager.getConnection(database, user, password);
// Configure the database to allow multiple queries and updates
// to be grouped into atomic transactions
db.setAutoCommit(false);
db.setTransactionIsolation(Connection.TRANSACTION_READ_COMMITTED);
// Create a server object that uses our database connection
RemoteDBBankServer bank = new RemoteDBBankServer(db);
// Read a system property to figure out how to name this server.
// Use "SecondRemote" as the default.
String name = System.getProperty("bankname", "SecondRemote");
// Register the server with the name
Naming.rebind(name, bank);
// And tell everyone that we're up and running.
System.out.println(name + " is open and ready for customers.");
}
catch (Exception e) {
System.err.println(e);
if (e instanceof SQLException)
System.err.println("SQL State: " + ((SQLException)e).getSQLState());
System.err.println("Usage: java [-Dbankname=<name>] RemoteDBBankServer "+
"[<dbpropsfile>]");
System.exit(1);
}
}
}
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