运用反射实现ejb动态委派

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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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