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.containsKey(jindiName))
home = (EJBHome)cache.get(jindiName);
else
{
try
{

home = super.getHome(jindiName, Class.forName(className));//调用父类的的方法取得home

}
catch(Exception e)
{
System.err.println(e.getMessage());
}
cache.put(jindiName,className);
}
try
{
object = home.getClass().getMethod("create", null).invoke(home, null);//调用home的//create方法，取得ejbObject

methodMap = new HashMap();

//将ejbObject中所有的方法存入methodMap中

Method[] aryMethod = object.getClass().getMethods();

if(aryMethod != null && aryMethod.length > 0)
{
for (int i = 0; i < aryMethod.length; i++) {

methodMap.put(aryMethod[i].getName(), aryMethod[i]);
}
}
}
catch(Exception e)
{
System.err.println(e.getMessage());
}
}

//此init方法是对一般java类初始化
public void init(String className,Object[] args)
{

boolean flage = false;

if(cache.get(className) != null)

object = cache.get(className);

else

{

try {
Class myClass = Class.forName(className);
if (args != null && args.length > 0) {
Class[] type = new Class[args.length];
for (int i = 0; i < type.length; i++) {
type[i] = args[i].getClass();

}
Constructor constructor = myClass.getConstructor(type);

object = constructor.newInstance(args);

cache.put(className, object);
}
else {
object = myClass.newInstance();
cache.put(className, object);
}
}

catch (Exception e) {
System.err.println(e.getMessage());
}
}
Method[] methods = object.getClass().getMethods();

methodMap = new HashMap();

for(int i = 0; i< methods.length; i++)
methodMap.put(methods[i].getName(),methods[i]);
}
public Object invoke(String method, Object[] args,String jindiName, String className)
{
if("init".equals(method))
{
this.init(jindiName, className);
return null;
}

if(methodMap == null)
this.init(jindiName, className);
Method tmpMethod = (Method)methodMap.get(method);
if(tmpMethod != null)
{

try
{
return tmpMethod.invoke(object, args);
}

catch(Exception e)
{
System.err.println(e.getMessage());
}
}
return null;
}
public Object invoke(String method, Object[] args, String className)
{

if("init".equals(method))

{
this.init(className,args);
return null;
}
if(methodMap == null)
System.err.println("not init");
Method tmpMethod = (Method)methodMap.get(method);

if(tmpMethod != null)
{
try
{
return tmpMethod.invoke(object, args);
}
catch(Exception e)
{
System.err.println(e.getMessage());
}
}
return null;
}
private FacadeDelegateImp() {
cache = Collections.synchronizedMap(new HashMap());
}
}