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运用反射实现ejb动态委派

发布时间:2019-09-12 18:39:30

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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