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());
}
}
参考文章：EJB 最佳实践：动态委派 作者：O'Reilly and Associates
这是本人第一次再此发表技术性文章，对ejb也是了解不深，如有什么不对处，还请各位高手指教。 
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