EJB设计模式(1)
第一个设计模式非常简单。一个公司和雇员的Entity Bean和下面给出的Entity Bean的代码片断是类似的。它们是由jbuilder4的 EntityBean模版生成的。所有的字段都声明为public的cmp字段。
Code snippet for Company Entity Bean
public class CompanyBean implements EntityBean {
EntityContext entityContext;
public Integer comId; //the primary key
public String comName; //the company name
public String comDescription //basic description
public Timestamp mutationDate //eXPlained later
public Integer ejbCreate(<params>) throws
CreateException {
return null;
}
//various get() and set() for every column/field
// which are exposed in the Remote Interface as well
Code snippet for Employee Entity Bean
public class EmployeeBean implements EntityBean {
EntityContext entityContext;
public Integer empId; //the primary key
public Integer comId; //the company foreign key
public String empFirstName; //the employee firstname
public String empLastName // the employee lastname
public Timestamp mutationDate //explained later
public Integer ejbCreate(<params>) throws
CreateException {
return null;
}
//various get() and set() for every column/field
// which are exposed in the Remote Interface as well
这个设计模式虽然很简单,但是却有很多缺点,比如,对每一个字段的访问都会导致对get()和set()方法的一次远程调用。而远程过程调用(RPCs)是非常耗费资源的,并且,对于在实际中通
常要求的组合的访问会导致一系列的远程调用。可以说,这个模式在实际中可用性很差。上面展示的设计模式可以作为其他设计模式的基础,比如RAD,原型设计,测试等。这时,那个代表雇员的Employee Entity Bean并没有展示出在雇员和公司之间有何关系。(未完待续)