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Jboss Ejb3.0 Entity Bean

王朝java/jsp·作者佚名 2006-01-31

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Order.java

package org.jboss.tutorial.entity.bean;

import javax.persistence.CascadeType;

import javax.persistence.Entity;

import javax.persistence.FetchType;

import javax.persistence.GeneratorType;

import javax.persistence.Id;

import javax.persistence.OneToMany;

import javax.persistence.Table;

import javax.persistence.Id;

import javax.persistence.CascadeType;

import javax.persistence.FetchType;

import java.util.ArrayList;

import java.util.Collection;

@Entity

@Table(name = "PURCHASE_ORDER")

//If the table name isn't specified it defaults to the bean name

//of the class. For instance, the LineItem EJB would be mapped to

//the LINEITEM table

public class Order implements java.io.Serializable

{

private int id;

private double total;

private Collection<LineItem> lineItems;

@Id(generate = GeneratorType.AUTO)

public int getId()

{

return id;

}

public void setId(int id)

{

this.id = id;

}

public double getTotal()

{

return total;

}

public void setTotal(double total)

{

this.total = total;

}

public void addPurchase(String product, int quantity, double price)

{

if (lineItems == null) lineItems = new ArrayList<LineItem>();

LineItem item = new LineItem();

item.setOrder(this);

item.setProduct(product);

item.setQuantity(quantity);

item.setSubtotal(quantity * price);

lineItems.add(item);

total += quantity * price;

}

//CascadeType.ALL specifies that when an Order is created,

//any LineItems held in the lineItems collection will be created

//as well (CascadeType.PERSIST). If the Order is delete from

//persistence storage, all related LineItems will be

//deleted (CascadeType.REMOVE). If an Order instance is

//reattached to persistence storage, any changes to the

//LineItems collection will be merged with persistence

//storage (CascadeType.MERGE).

//FetchType.EAGER specifies that when the Order is loaded

//whether or not to prefetch the relationship as well.

//If you want the LineItems to be loaded on demand, then specify FetchType.LAZY.

// The mappedBy attribute specifies that this is a bi-directional

//relationship that is managed by the order property on the LineItem entity bean.

@OneToMany(cascade = CascadeType.ALL, fetch = FetchType.EAGER, mappedBy="order")

public Collection<LineItem> getLineItems()

{

return lineItems;

}

public void setLineItems(Collection<LineItem> lineItems)

{

this.lineItems = lineItems;

}

加了不少英文注释，希望能看得懂。

@Table(name = "PURCHASE_ORDER")

指名数据库（jboss的数据库为hsqldb）中对应得表的名字，默认为class的名字，比如下面的LineItem就没有@table。（order.java , LineItem.java都为o/r映射，值得互相对照）

@Id(generate = GeneratorType.AUTO)

递增，同数据库里的相同。必须在getter方法上标注。

@OneToMany(cascade = CascadeType.ALL, fetch = FetchType.EAGER, mappedBy="order")

关系：order和LineItem为1对多的关系。在这里CascadeType.ALL是指明当建立一个Order被实例化后，都应该同时同时建立LineItem。注释里的就是根据两者建立时间的不同，定义了不同的CascadeType。

LineItem.java

package org.jboss.tutorial.entity.bean;

import javax.persistence.Entity;

import javax.persistence.GeneratorType;

import javax.persistence.Id;

import javax.persistence.JoinColumn;

import javax.persistence.ManyToOne;

import javax.persistence.Entity;

@Entity

public class LineItem implements java.io.Serializable

{

private int id;

private double subtotal;

private int quantity;

private String product;

private Order order;

@Id(generate = GeneratorType.AUTO)

public int getId()

{

return id;

}

public void setId(int id)

{

this.id = id;

}

public double getSubtotal()

{

return subtotal;

}

public void setSubtotal(double subtotal)

{

this.subtotal = subtotal;

}

public int getQuantity()

{

return quantity;

}

public void setQuantity(int quantity)

{

this.quantity = quantity;

}

public String getProduct()

{

return product;

}

public void setProduct(String product)

{

this.product = product;

}

//The @JoinColumn specifies the foreign key column within the LineItem table.

@ManyToOne

@JoinColumn(name = "order_id")

public Order getOrder()

{

return order;

}

public void setOrder(Order order)

{

this.order = order;

}

ShoppingCart.java

package org.jboss.tutorial.entity.bean;

import javax.ejb.Remote;

import javax.ejb.Remove;

@Remote

public interface ShoppingCart

{

void buy(String product, int quantity, double price);

Order getOrder();

@Remove void checkout();

}

ShoppingCartBean.java

package org.jboss.tutorial.entity.bean;

import javax.persistence.EntityManager;

import javax.ejb.Inject;

import javax.ejb.Remove;

import javax.ejb.Stateful;

@Stateful

public class ShoppingCartBean implements ShoppingCart

{

@Inject

private EntityManager manager; //The EntityManager is used to do querying,

//creating, find by primary key, and removal of entity beans.

private Order order;

public void buy(String product, int quantity, double price)

{

if (order == null) order = new Order();

order.addPurchase(product, quantity, price);

}

public Order getOrder()

{

return order;

}

@Remove

public void checkout()

{

manager.persist(order);

}

EntityManager的作用可大了，可以用于查询，创建，删除实体Bean,这里插入个EntityManager,主要是在最后用户离开时，在数据库里保存数据，相当于保存个object。运行完Client.java后就可以在hsqldb上看到有purchase_order 和 LineItem 的两张表。HypersonicDatabase ，找到startDatabaseManager然后下面有个invoke,点击就可以访问hsqldb了。

Client.java

package org.jboss.tutorial.entity.client;

import org.jboss.tutorial.entity.bean.LineItem;

import org.jboss.tutorial.entity.bean.Order;

import org.jboss.tutorial.entity.bean.ShoppingCart;

import javax.naming.InitialContext;

public class Client

{

public static void main(String[] args) throws Exception

{

InitialContext ctx = new InitialContext();

ShoppingCart cart = (ShoppingCart) ctx.lookup(ShoppingCart.class.getName());