ajanta.agent
Class Agent

java.lang.Object
  |
  +--ajanta.agent.Agent

All Implemented Interfaces:

java.io.Serializable

Direct Known Subclasses:

ItinAgent, ReportableAgent, SecureAgent

public abstract class Agent

extends java.lang.Object

implements java.io.Serializable

The Agent class is the generic mobile agent. It serves as the base class for all agents. Application-specific agents should be programmed as sub-classes of Agent.

See Also:

Credentials, AgentStatus, Serialized Form

Field Summary

byte[]	creatorSignature signature of the credential signed by creator of the agent
ajanta.agent.Credentials	cred Credentials of the agent
ajanta.server.AgentEnv	host host is the object reference to the current server's environment object.
java.lang.Object	myRef
ajanta.naming.URN	name URN ( name ) of the agent
byte[]	ownerSignature signature of the credential signed by owner of the agent
ajanta.agent.AgentStatus	status status object is modified whenever a recall request is pending.

Constructor Summary

Agent()
Default constructor of the agent which assigns cred, host, ownerSignature and creatorSignature as null

Agent(ajanta.agent.Credentials cred)
It assigns host, ownerSignature and creatorSignature as null.

Agent(ajanta.agent.Credentials cred, ajanta.server.AgentEnv host)
It assigns ownerSignature and creatorSignature as null.

Method Summary

void	agentEntry() It system defined entry protocol and is the first method to be automatically executed every time an agent arrives at a server.
void	agentExit() Agent's server executes this method just before it is sent off to another server.
abstract void	arrive() The arrive() method represents an entry protocol.
void	colocate(ajanta.naming.URN target) This method is called to relocate the agent at the server where a specified "target" object is currently resident.
void	colocate(ajanta.naming.URN target, ajanta.util.MethodSpec as) This method is called to relocate the agent at the server where a specified "target" object is currently resident.
abstract void	depart() The depart() method represents an exit protocol.
void	meet(ajanta.naming.URN reportTo, ajanta.util.MethodSpec as) This method acts as the starting point of execution for an agent when it is relocated at a server.
void	recallCommand(ajanta.naming.URN whoInvoked, ajanta.naming.URN reportTo) This method is executed by the agent server currenlty hosting this agent when it receives a recall request for this agent.
void	run() It is a empty method which can be overridden in subclasses.
void	signCreator(ajanta.naming.URN serverURN, ajanta.server.AgentEnv host) It signs the credentials byte of the agent with specified server's ( creator) private keys and store it in creatorSignature
void	signOwner() It signs the credentials byte of the agent with owner's private keys and store it in ownerSignature
void	start(ajanta.server.AgentEnv host, ajanta.naming.URN dest, ajanta.util.MethodSpec action) After agent has been created this method is called to launch the agent to appropriate server.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

name

public ajanta.naming.URN name

URN ( name ) of the agent

cred

public ajanta.agent.Credentials cred

Credentials of the agent

ownerSignature

public byte[] ownerSignature

signature of the credential signed by owner of the agent

creatorSignature

public byte[] creatorSignature

signature of the credential signed by creator of the agent

host

public transient ajanta.server.AgentEnv host

host is the object reference to the current server's environment object.

status

public ajanta.agent.AgentStatus status

status object is modified whenever a recall request is pending. This information is checked in the agentExit method, which is executed when the agent is about to leave a server.

myRef

public java.lang.Object myRef

Constructor Detail

Agent

public Agent()

Default constructor of the agent which assigns cred, host, ownerSignature and creatorSignature as null

Agent

public Agent(ajanta.agent.Credentials cred)

It assigns host, ownerSignature and creatorSignature as null. cred is assigned to the Credentials passed as argument.

Agent

public Agent(ajanta.agent.Credentials cred,
             ajanta.server.AgentEnv host)

It assigns ownerSignature and creatorSignature as null. cred is assigned to the Credentials object passed as argument and host to AgentEnv object.

Method Detail

agentEntry

public final void agentEntry()

It system defined entry protocol and is the first method to be automatically executed every time an agent arrives at a server.

arrive

public abstract void arrive()

The arrive() method represents an entry protocol. It is automatically executed every time an agent arrives at a server. It is an abstract method, and must be overridden in subclasses to define the application-specific entry protocol.

depart

public abstract void depart()

The depart() method represents an exit protocol. It is automatically executed every time an agent leaves a server. It is an abstract method, and must be overridden in subclasses to define the application-specific exit protocol.

agentExit

public final void agentExit()

Agent's server executes this method just before it is sent off to another server. It checks agent's status to find whether a recall is pending or not. If a recall is pending then it colocate the agent to returnTo server set in recall command . If returnTo is not set then it is colocated to guardian of the agent.

run

public void run()

It is a empty method which can be overridden in subclasses. This is the default method which get executed on a server if no other method is specified

start

public void start(ajanta.server.AgentEnv host,
                  ajanta.naming.URN dest,
                  ajanta.util.MethodSpec action)
           throws LaunchFailedException,
                  java.net.UnknownHostException

After agent has been created this method is called to launch the agent to appropriate server.

Parameters:

host - AgentEnv instance representing server's environment

dest - URN of the destination server

action - MethodSpec representing the method to be executed on the server if null then run method is executed

LaunchFailedException

java.net.UnknownHostException

colocate

public void colocate(ajanta.naming.URN target)

This method is called to relocate the agent at the server where a specified "target" object is currently resident.

Parameters:

target - URN of the target object

colocate

public void colocate(ajanta.naming.URN target,
                     ajanta.util.MethodSpec as)

This method is called to relocate the agent at the server where a specified "target" object is currently resident. It execute the meet method on the server. Meet method execute the specified method in the MethodSpec

Parameters:

target - URN of the target object

as - MethodSpec representing the method to be executed by meet method

meet

public void meet(ajanta.naming.URN reportTo,
                 ajanta.util.MethodSpec as)
          throws java.lang.Exception

This method acts as the starting point of execution for an agent when it is relocated at a server. The meet method contains the specification of the actions to be performed by the agent when it is relocated.

java.lang.Exception

recallCommand

public void recallCommand(ajanta.naming.URN whoInvoked,
                          ajanta.naming.URN reportTo)

This method is executed by the agent server currenlty hosting this agent when it receives a recall request for this agent. It set the recallPending status of the agent to true.

Parameters:

whoInvoked - URN of the recaller

reportTo - URN of object with whom agent has to colocate on recall

signCreator

public void signCreator(ajanta.naming.URN serverURN,
                        ajanta.server.AgentEnv host)

It signs the credentials byte of the agent with specified server's ( creator) private keys and store it in creatorSignature

Parameters:

serverURN - URN of the creator of the agent

signOwner

public void signOwner()

It signs the credentials byte of the agent with owner's private keys and store it in ownerSignature