Service Proxies

To prevent direct access to the System Agent it has to publish its methods for accessing the resources through the use of a proxy.

The first step to take for creating a proxy is to define an interface used for the Agents and other parts of the System to access the resource. This interface will be used by the user of the service to look for it. When the interface is created, the next step is to implement this interface in the proxy. The proxy has also to implement the ProxyIFace which contains the clone methods. As described in the proxy will be cloned by the System before given to the requester. For example has the class definition of the MAFFinderProxy the following content:

public class MAFFinderProxy implements MAFFinderIFace, ProxyIFace

The proxy needs some variables, the service behind it and the ID of the Agent when cloned. The reference to the service can be addressed by the interface used for the proxy, which should also be implemented by the System Agent behind. The AgentID is null for the primary proxy and contains the ID of the Agent which requested the proxy when cloned. To prevent the proxy to be clone again by the Agent it uses a boolean variable which indicates if the proxy is a clone and may not be cloned again. This leads to the following variable definitions in the MAFFinderProxy:

/** The service to use. */

private MAFFinderIFace service = null;

 

/** The AgentID of the Agent using this Proxy. */

private AgentID agentid = null;

 

/** Is true if this proxy is a clone. */

boolean isClone = false;

When created (constructed) the proxy needs the reference to the service as parameter for the constructor. The MAFFinderProxy has the following main constructor:

public MAFFinderProxy(MAFFinderIFace service) {

   this.service = service;

}

For the ProxyIFace it has to implement two methods, clone and isClone. The method clone is called by the platform when a request for that proxy came in and the proxy has to be cloned for the caller. It should return an object that implements also the ProxyIFace. In fact it should return a new instance of the same proxy with some different variables. The clone method gets the AgentID as parameter to know for which Agent to make the clone and which Agent the clone uses. For cloning it should use the following mechanism (it is free to use another, but this is recommended). The proxy contains a private constructor which gets the AgentID and the service reference as parameter. It is private so it can only be called from inside of the proxy. The constructor sets the isClone variable to true, preventing a new cloning. It has now the AgentID to make security calls when a method of the proxy is called. The constructor of the MAFFinderProxy looks like this:

private MAFFinderProxy(MAFFinderIFace service, AgentID agentid) {

   this.service = service;

   this.agentid = agentid;

   isClone = true;

}

And the method to clone and to check if it is a clone are in the following way implemented:

public ProxyIFace clone(AgentID agentid) {

   if(!isClone)

      return new MAFFinderProxy(service, agentid);

   else

      return null;

 }

 

 public boolean isClone() {

    return isClone;

} 

These methods can be taken over by any proxy without big changes making the creation of a proxy as easy as possible.