一个JDBC连接数据库的例子

 过程域对象BusinessService的程序，它提供了customer对象的持久化方法。
saveCustomer() 把customer域对象永久的保存到数据库中。
updateCustomer() 更新数据库中Customer域对象的状态。
deleteCustomer() 从数据库中删除Customer域对象。
loadCustomer() 根据特定的OID，把一个Customer域对象从数据库中加载到内存中。
findCustomerByName() 根据特定的顾客名字，把符合条件的customer域对象从数据库中加载到内存中。

public class BusinessService{
 private String url ="jdbc:mysql://localhost:3306/SAMPLEDB";
 private String user ="test";
 private String password ="test";
 
 public BusinessService() throws Exception{
  //加载mysql数据库驱动程序
  Class.forName("com.mysql.jdbc.Driver"); 
 }
 
 public Connection getConnection()throws Excepiton{
  return java.sql.DriverManager.getConnection(url,user,password);
 }
 
 /**保存参数制定的Customer对象，并且级联保存与它相关的order对象。
 *如果customer，或者order为空，则抛出异常。
 */
 public void saveCustomer(Customer customer) throws Exception{
  Connection conn = null ;
  PreparedStatement stmt = null ;
  try{
   conn = getConnection();
   conn.setAutoCommit(false);
   if (customer.getName() == null){
    throw new BusinessExcepiton("客户姓名不能为空！");
   }
   long customerId = getNextId(conn,"CUSTOMERS");
   stmt = conn.preparedStatement("insert into CUSTOMERS(id,name,age) values(?,?,?)");
   stmt.setLong(1,customerId);
   stmt.setString(2,customer.getName());
   stmt.setInt(3,customer.getAge());
   stmt.execute();
   
   Iterator it = customer.getOrders().iterator();
   while(it.hasNext()){
    Order order = (order)it.next();
    if(order.getOrderName == null){
     throw new BusinessException("订单编号不允许为空！");
    }
    Long orderId = getNextId(conn,"ORDERS");
    stmt = conn.preparedStatement("insert into ORDERS(id,order_number,price,customer_id)"
                   +"values(?,?,?,?,?)"
                   );
    stmt.setLong(1,orderId);
    stmt.setString(2,order.getOrderNumber());
    stmt.setDouble(3,order.getPrice());
    stmt.setLong(4,customerId);
    stmt.execute();
   }
   conn.commit();
  }catch(Excepiton e){
   try{
    conn.rollback();
   }catch(SQLExcepiton e){
    e.printStackTrace(System.out);
   }
   throw e ;
  }finally{
   try{
    stmt.close();
    conn.close();
   }catch(Exception e){
    e.printStackTrace();
   }
  }
  
 }
 /**
 *更新指定参数的customer对象
 */
 public void updateCustomer(Customer customer)throws Exception{
  Connection conn = null ;
  PreparedStatement stmt = null ;
  try{
   conn = getConnection();//获得数据库连接
   conn.setAutoCommit(false);
   stmt = conn.prepareStatement("update customer set name=?,age=? where id =?");
   stmt.setString(1,customer.getName());
   stmt.setInt(2,customer.getAge());
   stmt.setLong(3,customer.getId().LongValue());
   stmt.execute();
   stmt.commit();
  }catch(Exception e){
   try{
    conn.rollback();
   }catch(SQLException sqlex){
    sqlex.printStackTrace(System.out);
   }
   throw e ;
  }finally{
   stmt.close();
   conn.close();
  }
 }
 /**删除指定的customer对象，并且删除与它关联的order对象。
 *
 */
 public void deleteCustomer(Customer customer) throws Exception{
  Connection conn = null ;
  PreparedStatement stmt = null ;
  try{
   conn = getConnection();
   conn.setAutoCommit(false);
   stmt = conn.prepareStatement("delete from Orders where customer_id =?");
   stmt.setLong(1,customer.getID().LongValue());
   stmt.executeUpdate();
   
   stmt = conn.prepareStatement("delete from Customers where id =?");
   stmt.setLong(1,customer.getID().LongValue());
   stmt.executeUpdate();
   
   stmt.commit ;
  }catch(Exception e){
   try{
    conn.rollback();
   }catch(SQLException sqlex){
    sqlex.printStackTrace(System.out);
   }
   throw e ;
  }finally{
   try{
    stmt.close();
    conn.close();
   }catch(Exception e){
    e.printStackTrace();
   }
  }
 }

 /**根据OID加载一个Customer对象
 *
 */ 
 public Customer LoadCustomer(long customerId)throws Exception{
  Connection conn = null ;
  PreparedStatement stmt = null ;
  ResultSet rs = null ;
  try{
   conn = getConnection();
   stmt = conn.prepareStatement("select id,name,age from customers where id=?");
   stmt.setLong(1,customerId);
   rs = stmt.executeQuery();
   if(rs.next()){
    Customer customer = new Customer();
    customer.setId(new long(rs.getLong(1)));
    customer.setName(rs.getString(2));
    customer.setAge(rs.getInt(3));
    return customer ;
   }else{
    throw new BusinessException("OID为"+customerId+"的Customer对象不存在！");
   }       
  }finally{
   try{
    rs.close();
    conn.close();
    stmt.close();
   }catch(Exception ex){
    ex.printStackTrace();
   }
  }
 }
 
 /**
 *根据姓名查询满足条件的客户
 */
 public List findCustomerByName(String name)throws Exception{
  HashMap map = new HashMap();
  List result = new ArrayList();
  
  Connection conn = null;
  PreparedStatement stmt = null ;
  ResultSet rs = null ;  
  try{
   conn = getConnection();
      
   String sqlString =" select c.id customer_id,c.name,c.age,o.id order_id,o.order_number,o.price "
            +" from customers c ,orders o where c.id = o.id(+) and c.name=? " ;
   stmt = conn.prepareStatement(sqlString);
   stmt.setString(1,name);
   rs = stmt.executeQuery();
   while(rs.next()){
    //遍历jdbc resutlset结果
    Long customerId = new Long(rs.getLong(1));
    String customerName = rs.getString(2);
    int customerAge = rs.getInt(3);
    Long orderId  = new Long(rs.getLong(4));
    String orderNumber = rs.getString(5);
    double price = rs.getDouble(6);
    
    Customer customer = null ;
    if(map.containsKey(customerId)){
     //如果在map中已经存在OID匹配的Customer对象，就获得此对象的引用，这样就避免创建重复的对象
     customer = (Customer)map.get(customerId);
    }else{
     customer =new Customer();
     customer.setId(customerId);
     customer.setName(customerName);
     customer.setAge(customerAge);
     map.put(customerId,customer);
    }
    //映射order对象
    Order order = new Order();
    order.setId(orderId);
    order.setOrderName(orderName);
    order.setPrice(price);
    //建立customer与order关系
    customer.getOrders().add(order);
    order.setCustomer(customer);
    //把map中所有的customer对象加入到result中
    Iterator iter = map.values().iterator();
    while(iter.hasnext()){
     result.add(iter.next());
    }
    return result ;
   }finally{
    try{
     rs.close();
     stmt.close();
     conn.close();
    }catch(Exception ex){
     e.printStackTrace();
    }
   }   
  }
 }

 /**
 *生成一个新的主键值，为表的最大主键值＋1，如果不存在，则为1
 */ 
 private long getNextId(Connection conn,String tablename)throws Exception{
  long nextId ;
  PreparedStatement stmt = null ;
  ResultSet rs = null ;
  try{
   stmt = conn.prepareStatement("select max(id) from "+tablename);
   rs = stmt.executeQuery();
   if(rs.next()){
    nextId = rs.getLong(1)+1;
    if(rs.wasNull()) nextId = 1;
   }else{
    nextId = 1;
   }
   return nextId ;
  }finally{
   try{
    rs.close();
    stmt.close();
   }catch(Exception ex){
    ex.printStackTrace();
   }
  }
 }
}