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，如果每个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，如果type为local则调用localserverlocate中的方法，如果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;

}

}}

remoteserverlocator

import javax.naming.*;

import javax.rmi.portableremoteobject;

import java.util.*;

import javax.ejb.*;

public class remoteserverlocator{private context ic;

private map cache;

private static remoteserverlocator me;

public static remoteserverlocator getinstance()

{

if(me == null)

{try

{

me = new remoteserverlocator();

}

catch(exception e)

{

system.err.println(e.getmessage());

}}

return me;

}

public ejbhome gethome(string jndihomename, class classname) throws exception {

ejbhome home = null;

try {

if (cache.containskey(jndihomename)) {

home = (ejbhome) cache.get(jndihomename);

} else {

object objref = ic.lookup(jndihomename);

object obj = portableremoteobject.narrow(objref, classname);

home = (ejbhome) obj;

cache.put(jndihomename, home);

}

} catch (namingexception ne) {

system.err.println(jndihomename);

throw ne;

} catch (exception e) {throw e;

}

return home;

}private remoteserverlocator() throws exception{

try {

ic = getinitialcontext();

// 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;

}}

private javax.naming.context getinitialcontext() throws namingexception {

java.util.hashtable jndiparm = new java.util.hashtable();

jndiparm.put(context.provider_url, "your server address");

jndiparm.put(context.initial_context_factory, "org.jnp.interfaces.namingcontextfactory");

return new initialcontext(jndiparm);

}}

对上面这些调用机制有个了解之后，下面就是来具体的实现动态委派了，再此定义了一个facadedelegateimp类，继承了facadedelegate类。先看一下代码，然后对此作解释，这样比较清楚一些

import testejb.delegate.common.*;

import javax.ejb.*;

import java.lang.reflect.*;

import java.util.*;

public class facadedelegateimp extends facadedelegate {private static facadedelegateimp me;

private map cache;

private hashmap methodmap;

private object object;

public static facadedelegateimp getinstance()

{if(me == null)

me = new facadedelegateimp();

return me;

}

//init方法是在调用invoke之前对要调用的sessionbean进行初始化

public void init(string jindiname, string classname) {

ejbhome home = null;

if(cache.c