运用反射实现ejb动态委派

核心提示：每个bean可能会有很多方法，一般我们通过一个delegate来调用sessionbean中的方法，运用反射实现ejb动态委派，而非直接调用sessionbean,delegate中只是简单的对每个相对应的sessionbean的public方法的简单封装，在调用的时候省去了每次对home的查找和ejb对象的creat

每个bean可能会有很多方法，一般我们通过一个delegate来调用sessionbean中的方法，而非直接调用sessionbean,delegate中只是简单的对每个相对应的sessionbean的public方法的简单封装，在调用的时候省去了每次对home的查找和ejb对象的create,但是可能我们的bean会有很多方法，假如每个bean都写这样一个delegate,这样工作量就会很大，而且也不便于以后系统的移植，比如说，原来使用ejb实现，现在要改用jdo直接操作数据库，而通过运用java的reflect技术，就能较好地实现这些要求。首先，定义了一个FacadeDelegate的抽象类，用来实现对sessionbean的home的查找,代码如下：

import javax.ejb.*;

import testejb.util.common.*;

import testejb.util.resource.*;

public abstract class FacadeDelegate{PRivate static String type = Resource.RemoteType;

public FacadeDelegate() {

}

public EJBHome getHome(String jindiName,Class className)

{

EJBHome home = null;

ServerLocatorAdapter adapter = ServerLocatorAdapter.getInstance();

try

{

home = (EJBHome)adapter.getHome(type, jindiName, className);

}

catch(Exception e)

{

System.err.println(e.getMessage() + jindiName + className.toString());

}

return home;

}}

其中ServerLocatorAdapter是一个用来根据是local还是remote调用ejb对象而通过不同的方法查找home的类，假如type为local则调用LocalServerLocate中的方法，假如type为remote则调用RemoteServerLocate中的方法，获得home。代码如下:

import java.util.*;

import java.lang.reflect.*;

import testejb.util.resource.*;

public class ServerLocatorAdapter {private Map cache;//用来缓存home

private static ServerLocatorAdapter me;

public static ServerLocatorAdapter getInstance()

{if(me == null)

me = new ServerLocatorAdapter();

return me;

}

//取得home

public Object getHome(String type,String jndiHomeName,Class className) throws Exception

{Object home = null;

if(cache.containsKey(jndiHomeName))

return cache.get(jndiHomeName);

if(Resource.LocalType.equals(type))

{

home = getLocalHome(jndiHomeName,className);

cache.put(jndiHomeName,home);

return home;

}

if(Resource.RemoteType.equals(type))

{

home = getRemoteHome(jndiHomeName,className);

cache.put(jndiHomeName,home);

return home;

}

return home;}

//取得local home

private Object getLocalHome(String jndiHomeName,Class className) throws Exception

{

Class myClass = Class.forName(Resource.LocalClass);

// Resource. LocalClass =”testejb.util.common. LocalServerLocator

Method method = myClass.getMethod(Resource.LocalConstractMethod,null);

// Resource. LocalConstractMethod =” getInstance”

LocalServerLocator local = null;

local = (LocalServerLocator)method.invoke(myClass,null);

return local.getLocalHome(jndiHomeName,className);

}

//取得remote home

private Object getRemoteHome(String jndiHomeName,Class className) throws Exception

{

Class myClass = Class.forName(Resource.RemoteClass);

// Resource.RemoteClass =”testejb.util.common.RemoteServerLocator”

Method method = myClass.getMethod(Resource.RemoteConstractMethod,null);

// Resource.RemoteConstractMethod=” getInstance”

RemoteServerLocator remote = null;

remote = (RemoteServerLocator)method.invoke(myClass,null);

return remote.getHome(jndiHomeName,className);

}

private ServerLocatorAdapter() {

// 为cache提供线程安全的保证

cache = Collections.synchronizedMap(new HashMap());

}}

其中Resource为资源类，其中通过对配置文件的读取，取得一些指定的配置信息。

RemoteServerLocator和LocalServerLocator是两个根据不同的调用方式取得home借口的具体实现类，代码如下:

LocalServerLocator：

import javax.naming.*;

import javax.rmi.PortableRemoteObject;

import java.util.*;

import javax.ejb.*;

public class LocalServerLocator {

private Context ic;

private Map cache;//缓存home

private static LocalServerLocator me;

public static LocalServerLocator getInstance()

{if(me == null)

{try

{me = new LocalServerLocator();

}

catch(Exception e)

{System.err.println(e.getCause());

System.err.println(e.getMessage());

}}

return me;

}

public EJBLocalHome getLocalHome(String jndiHomeName, Class className) throws Exception {

EJBLocalHome home = null;

try {if (cache.containsKey(jndiHomeName)) {

home = (EJBLocalHome) cache.get(jndiHomeName);

} else {

Object objref = ic.lookup(jndiHomeName);

home = (EJBLocalHome) objref;

cache.put(jndiHomeName, home);

}

} catch (NamingException ne) {

System.err.println(jndiHomeName);

throw ne;

} catch (Exception e) {

throw e;

}

return home;

}

private LocalServerLocator() throws Exception{

try

{

ic = new InitialContext();

// 为cache提供线程安全的保证

cache = Collections.synchronizedMap(new HashMap());

}

catch(NamingException ne)

{

throw ne;

}

catch(Exception e)

{

throw e;

}

}}