accountbean.java

Java2程序设计150例德源代码

package account;
import java.sql.*;
import javax.ejb.*;
import java.util.*;
import javax.naming.*;

// 这个管理持久化实体Bean表示一个银行账户
public class AccountBean implements EntityBean {
	protected EntityContext ctx;
	// Bean的状态域
	private String accountID; // 本例中的主键
	private String ownerName;
	private double balance;
	public AccountBean() {
	}
	// 商务逻辑方法
	//存款
	public void deposit(double amt) throws AccountException {
		balance += amt;
	}
	// 取款，如果amt>余额，抛出异常
	public void withdraw(double amt) throws AccountException {
		if (amt > balance) {
			throw new AccountException("余额不够");
		}
		balance -= amt;
	}
	// 实体Bean上的获得器/设置器方法
	public double getBalance() {
		System.out.println("getBalance()");
		return balance;
	}
	public void setOwnerName(String name) {
		System.out.println("setOwnerName()" + accountID);
		ownerName = name;
	}
	public String getOwnerName() {
		System.out.println("getOwnerName() on" + accountID);
		return ownerName;
	}
	public String getAccountID() {
		System.out.println("getAccountID() on" + accountID);
		return accountID;
	}
	public void setAccountID(String id) {
		System.out.println("setAccountID() on " + accountID);
		this.accountID = id;
	}
	// 返回所有账户的余额
	public double ejbHomeGetTotalBankValue() throws AccountException {
		PreparedStatement pstmt = null;
		Connection conn = null;
		try {
			// 和数据库连接
			conn = getConnection();
			// 执行查询操作，得到所有账户余额总和
			pstmt =
				conn.prepareStatement(
					"select sum(balance) as total from accounts");
			ResultSet rs = pstmt.executeQuery();
			if (rs.next()) {
				return rs.getDouble("total");
			}
		} catch (Exception e) {
			e.printStackTrace();
			throw new AccountException(e);
		} finally { // 释放数据库资源
			try {
				if (pstmt != null)
					pstmt.close();
			} catch (Exception e) {
			}
			try {
				if (conn != null)
					conn.close();
			} catch (Exception e) {
			}
		}
		throw new AccountException("Error!");
	}
	// EJB必须实现的方法 
	public void ejbActivate() {
		System.out.println("ejbActivate()");
	}
	// 从数据库中移除实体Bean
	public void ejbRemove() throws RemoveException {
		System.out.println("ejbRemove()");
		//  一个实体Bean可以表示不同的数据实例
		//  我们应该通过主键来判断删除哪个数据实例
		AccountPK pk = (AccountPK) ctx.getPrimaryKey();
		String id = pk.accountID;
		PreparedStatement pstmt = null;
		Connection conn = null;
		try {
			// 获得新的数据库连接
			conn = getConnection();
			// 从数据库中删除账号
			pstmt = conn.prepareStatement("delete from accounts where id = ?");
			pstmt.setString(1, id);
			// 操作数据库失败，抛出一个系统级错误
			if (pstmt.executeUpdate() == 0) {
				throw new RemoveException(
					"Account "
						+ pk
						+ " failed to be removed from the database");
			}
		} catch (Exception ex) {
			throw new EJBException(ex.toString());
		} finally { // 释放数据库连接
			try {
				if (pstmt != null)
					pstmt.close();
			} catch (Exception e) {
			}
			try {
				if (conn != null)
					conn.close();
			} catch (Exception e) {
			}
		}
	}
	// 钝化，为了挂起释放的资源
	public void ejPassivate() {
		System.out.println("ejbPassivate ()on " + accountID);
	}
	// 更新内存中的实体Bean对象，反映数据库中的当前值
	public void ejbLoad() {
		System.out.println("ejbLoad() on " + accountID);
		// 得到实体主键，这样我们知道那个实例被加载
		AccountPK pk = (AccountPK) ctx.getPrimaryKey();
		String id = pk.accountID;
		PreparedStatement pstmt = null;
		Connection conn = null;
		try {
			// 获得新的数据库连接
			conn = getConnection();
			// 通过ID查询，得到数据库中的账号
			pstmt =
				conn.prepareStatement(
					"select ownerName, balance from accounts where id = ?");
			pstmt.setString(1, id);
			ResultSet rs = pstmt.executeQuery();
			rs.next();
			ownerName = rs.getString("ownerName");
			balance = rs.getDouble("balance");
		} catch (Exception ex) {
			throw new EJBException(
				"Account " + pk + " failed to load from database",
				ex);
		} finally { // 释放数据库连接
			try {
				if (pstmt != null)
					pstmt.close();
			} catch (Exception e) {
			}
			try {
				if (conn != null)
					conn.close();
			} catch (Exception e) {
			}
		}
	}
	// 更新数据库，反映当前内存中的值
	public void ejbStore() {
		System.out.println("ejbStore() on " + accountID);
		PreparedStatement pstmt = null;
		Connection conn = null;
		try {
			// 获得新的数据库连接
			conn = getConnection();
			// 往数据库存储账户
			pstmt =
				conn.prepareStatement(
					"update accounts set ownerName = ?, balance = ? where id = ?");
			pstmt.setString(1, ownerName);
			pstmt.setDouble(2, balance);
			pstmt.setString(3, accountID);
			pstmt.executeUpdate();
		} catch (Exception ex) {
			throw new EJBException(
				"Account " + accountID + " failed to save to database",
				ex);
		} finally { // 释放数据库连接
			try {
				if (pstmt != null)
					pstmt.close();
			} catch (Exception e) {
			}
			try {
				if (conn != null)
					conn.close();
			} catch (Exception e) {
			}
		}
	}
	// 把一个Bean实例和一个特定的环境对象关联起来
	public void setEntityContext(EntityContext ctx) {
		System.out.println("setEntityContext called");
		this.ctx = ctx;
	}
	// 把一个Bean和它的环境变量分离
	public void unsetEntityContext() {
		System.out.println("unsetEntityContext called on " + accountID);
		this.ctx = null;
	}
	// 在ejbCreate()调用后，Bean可以从它的环境中提取EJB对象
	// 并当作一个this参数传递
	public void ejbPostCreate(String accountID, String ownerName) {
	}
	// 此方法对应Home中的create()方法
	// 当客户端调用本地对象(Home)的create()方法时，
	// 本地对象调用ejbCreate()方法
	public AccountPK ejbCreate(String accountID, String ownerName)
		throws CreateException {
		PreparedStatement pstmt = null;
		Connection conn = null;
		try {
			System.out.println("ejbCreate() called on " + accountID);
			this.accountID = accountID;
			this.ownerName = ownerName;
			this.balance = 0;
			// 获得数据库的连接
			conn = getConnection();
			// 插入账号
			pstmt =
				conn.prepareStatement(
					"insert into accounts (id, ownerName, balance) values (?, ?, ?)");
			pstmt.setString(1, accountID);
			pstmt.setString(2, ownerName);
			pstmt.setDouble(3, balance);
			pstmt.executeUpdate();
			// 产生一个主键，并返回
			return new AccountPK(accountID);
		} catch (Exception e) {
			throw new CreateException(e.toString());
		} finally { //释放数据库的连接
			try {
				if (pstmt != null)
					pstmt.close();
			} catch (Exception e) {
			}
			try {
				if (conn != null)
					conn.close();
			} catch (Exception e) {
			}
		}
	}
	// 通过主键找到一个账号
	public AccountPK ejbFindByPrimaryKey(AccountPK key)
		throws FinderException {
		PreparedStatement pstmt = null;
		Connection conn = null;
		try {
			System.out.println("ejbFindByPrimaryKey(" + key + ") called");
			// 数据库连接
			conn = getConnection();
			// 在数据库中查找这个实体
			pstmt =
				conn.prepareStatement("select id from accounts where id = ?");
			pstmt.setString(1, key.toString());
			ResultSet rs = pstmt.executeQuery();
			rs.next();
			// 返回主键
			return key;
		} catch (Exception e) {
			throw new FinderException(e.toString());
		} finally { // 释放数据库
			try {
				if (pstmt != null)
					pstmt.close();
			} catch (Exception e) {
			}
			try {
				if (conn != null)
					conn.close();
			} catch (Exception e) {
			}
		}
	}
	// 通过名字查找所有账号
	public Collection ejbFindByOwnerName(String name) throws FinderException {
		PreparedStatement pstmt = null;
		Connection conn = null;
		Vector v = new Vector();
		try {
			System.out.println("ejbFindByOwnerName(" + name + ") called");
			// 获得数据库连接
			conn = getConnection();
			// 在数据库中找这个主键
			pstmt =
				conn.prepareStatement(
					"select id from accounts where ownerName = ?");
			pstmt.setString(1, name);
			ResultSet rs = pstmt.executeQuery();
			// 把找到的主键放到Vector中
			while (rs.next()) {
				String id = rs.getString("id");
				v.addElement(new AccountPK(id));
			}
			// 返回一个找到的主键的列举
			return v;
		} catch (Exception e) {
			throw new FinderException(e.toString());
		} finally { // 释放数据库
			try {
				if (pstmt != null)
					pstmt.close();
			} catch (Exception e) {
			}
			try {
				if (conn != null)
					conn.close();
			} catch (Exception e) {
			}
		}
	}

	//返回JDBC连接
	public Connection getConnection() throws Exception {
		try {
			Context ctx = new InitialContext();
			javax.sql.DataSource ds =
				(javax.sql.DataSource) ctx.lookup("java:/MSSQLDS");
			//这里要注意一致
			return ds.getConnection();
		} catch (Exception e) {
			System.out.println("Couldn't get dataSource!");
			e.printStackTrace();
			throw e;
		}

	}
}