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());
}
}
来自:csdn 作者:skyjiang
参考文章：ejb 最佳实践：动态委派 作者：o'reilly and associates
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