bookbean.java

< J2EE应用开发详解>>一书全部的源代码. 本书基于J2EE 1．4平台

package com.j2ee14.ch17;

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

/**
 * 演示 Bean-Managed Persistent Entity Bean.
 * 这个实体Bean代表了Book信息.
 */
public class BookBean implements EntityBean {

	protected EntityContext ctx;

	// Bean管理的字段。
	private String bookID;	// PK
	private String bookName;
	private double price;

	public BookBean() {
		System.out.println("New Bank Book Entity Bean Java Object created by EJB Container.");
	}

    //业务逻辑方法

	/**
	 * 增加图书的价格.
	 */
	public void increasePrice(double amt) throws BookException {
		System.out.println("deposit(" + amt + ") called.");

		price += amt;
	}

	/**
	 * 减少图书的价格
	 * @throw BookException thrown in amt < available price
	 */
	public void decreasePrice(double amt) throws BookException {
		System.out.println("withdraw(" + amt + ") called.");

		if (amt > price) {
			throw new BookException("the  price is " + price + "!  You cannot decrease " + amt + "!");
		}

		price -= amt;
	}

	// getter和setter方法。

	public double getPrice() {
		System.out.println("getBalance() called.");
		return price;
	}

	public void setBookName(String name) {
		System.out.println("setbookName() called.");
		bookName = name;
	}

	public String getBookName() {
		System.out.println("getbookName() called.");
		return bookName;
	}

	public String getBookID() {
		System.out.println("getBookID() called.");
		return bookID;
	}

	public void setBookID(String id) {
		System.out.println("setBookID() called.");
		this.bookID = id;
	}

	
	//
	// 以下是和EJB相关的方法。它们被容器调用。
	//
	public void ejbActivate() {
		System.out.println("ejbActivate() called.");
	}
    
    //删除EJB，将删除数据库中对应的对象。
	public void ejbRemove() throws RemoveException {
		System.out.println("ejbRemove() called.");

		BookPK pk = (BookPK) ctx.getPrimaryKey();
		String id = pk.bookID;

		PreparedStatement pstmt = null;
		Connection conn = null;
		try {
			/*
			 * 1) 获得JDBC连接
			 */
			conn = getConnection();

			/*
			 * 2) 从数据库中删除book
			 */
			pstmt = conn.prepareStatement("delete from book where id = ?");
			pstmt.setString(1, id);

			/*
			 * 3)如果发生异常，则抛出
			 */
			if (pstmt.executeUpdate() == 0) {
				throw new RemoveException("Book " + pk + " failed to be removed from the database");
			}
		}
		catch (Exception ex) {
			throw new EJBException(ex.toString());
		}
		finally {
			/*
			 * 4) 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) {}
		}
	}

	/**
	 * 由容器调用，释放占有的资源。.
	 */
	public void ejbPassivate() {
		System.out.println("ejbPassivate () called.");
	}

	/**
	 * 由容器调用，使得内存中的数据和数据库一致。
	 */
	public void ejbLoad() {
		System.out.println("ejbLoad() called.");

		/*
		 * Again, query the Entity Context to get the current
		 * Primary Key, so we know which instance to load.
		 */
		BookPK pk = (BookPK) ctx.getPrimaryKey();
		String id = pk.bookID;

		PreparedStatement pstmt = null;
		Connection conn = null;
		try {
			
			conn = getConnection();			
			pstmt = conn.prepareStatement("select bookName, price from book where id = ?");
			pstmt.setString(1, id);
			ResultSet rs = pstmt.executeQuery();
			rs.next();
			bookName = rs.getString("bookName");
			price = rs.getDouble("price");
		}
		catch (Exception ex) {
			throw new EJBException("Book " + pk + " failed to load from database", ex);
		}
		finally {			
			try { if (pstmt != null) pstmt.close(); }
			catch (Exception e) {}
			try { if (conn != null) conn.close(); }
			catch (Exception e) {}
		}

	}

	/**
	 * 由容器调用，使得内存中的数据和数据库一致。
	 */
	public void ejbStore() {
		System.out.println("ejbStore() called.");

		PreparedStatement pstmt = null;
		Connection conn = null;
		try {		
			conn = getConnection();
			pstmt = conn.prepareStatement("update book set bookName = ?, price = ? where id = ?");
			pstmt.setString(1, bookName);
			pstmt.setDouble(2, price);
			pstmt.setString(3, bookID);
			pstmt.executeUpdate();

		}
		catch (Exception ex) {
			throw new EJBException("Book " + bookID + " failed to save to database", ex);
		}
		finally {		
			try { if (pstmt != null) pstmt.close(); }
			catch (Exception e) {}
			try { if (conn != null) conn.close(); }
			catch (Exception e) {}
		}
	}

	/**
	 * 由容器调用设置Bean的上下文信息。
	 */
	public void setEntityContext(EntityContext ctx) {
		System.out.println("setEntityContext called");
		this.ctx = ctx;
        }

	/**
	 * 由容器调用，取消上下文信息。
	 */
	public void unsetEntityContext() {
		System.out.println("unsetEntityContext called");
		this.ctx = null; 
        }

	/**
	 * 在ejbCreate()方法后调用。
	 */
	public void ejbPostCreate(String bookID, String bookName) {
	}

	/**
	 * 创建一个实体Bean。它和Home接口的create方法对应。
	 * @return The primary key for this book
	 */
	public BookPK ejbCreate(String bookID, String bookName) throws CreateException {

		PreparedStatement pstmt = null;
		Connection conn = null;
		try {
			System.out.println("ejbCreate() called.");
			this.bookID = bookID;
			this.bookName = bookName;
			this.price = 0;
			conn = getConnection();

		    //把数据添加到数据库
			pstmt = conn.prepareStatement("insert into book (id, bookName, price) values (?, ?, ?)");
			pstmt.setString(1, bookID);
			pstmt.setString(2, bookName);
			pstmt.setDouble(3, price);
			pstmt.executeUpdate();

			/*
			 *产生一个主键，然后返回。
			 */
			return new BookPK(bookID);
		}
		catch (Exception e) {
			throw new CreateException(e.toString());
		}
		finally {
			/*
			 * 释放数据连接。
			 */
			try { if (pstmt != null) pstmt.close(); }
			catch (Exception e) {}
			try { if (conn != null) conn.close(); }
			catch (Exception e) {}
		}
	}

	/**
	 * 按照主键查找图书。
	 */
	public BookPK ejbFindByPrimaryKey(BookPK key) throws FinderException {
		PreparedStatement pstmt = null;
		Connection conn = null;
		try {
			System.out.println("ejbFindByPrimaryKey(" + key + ") called");

			/*
			 *获得数据库连接。
			 */
			conn = getConnection();

			/*
			 * 在数据库中查找实体。
			 */
			pstmt = conn.prepareStatement("select id from book where id = ?");
			pstmt.setString(1, key.toString());
			ResultSet rs = pstmt.executeQuery();
			rs.next();

			/*
			 *如果查找到，则返回主键。
			 */
			return key;
		}
		catch (Exception e) {
			throw new FinderException(e.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) {}
		}
	}

	/**
	 * 按照图书的名字查找。
	 */
	public Collection ejbFindByBookName(String name) throws FinderException {
		PreparedStatement pstmt = null;
		Connection conn = null;
		Vector v = new Vector();

		try {
			System.out.println("ejbFindBybookName(" + name + ") called");

			/*
			 * 获得数据库连接
			 */
			conn = getConnection();

			/*
			 * 按照图书的名字在数据库中查找。
			 */
			pstmt = conn.prepareStatement("select id from book where bookName = ?");
			pstmt.setString(1, name);
			ResultSet rs = pstmt.executeQuery();

			/*
			 * 把每个匹配的记录放在Vector中。
			 */
			while (rs.next()) {
				String id = rs.getString("id");
				v.addElement(new BookPK(id));
			}

			/*
			 *返回查找的结果
			 */
			return v;
		}
		catch (Exception e) {
			throw new FinderException(e.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) {}
		}
	}

	/**
	 * 从连接池中获得一个连接。	 *
	 * @return The JDBC connection
	 */
	public Connection getConnection() throws Exception {
		try {
			Context ctx = new InitialContext();
			javax.sql.DataSource ds = (javax.sql.DataSource) ctx.lookup("java:comp/env/jdbc/ejbPool");
			return ds.getConnection();
		}
		catch (Exception e) {
			System.err.println("Could not locate datasource!  Reason:");
			e.printStackTrace();
			throw e;
		}
	}
}