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Networkable solutions

Networkable solutions. Using sockets we can pass objects back and forth between client and server, but we’re limited Cannot call methods on objects between client/server, only send objects and respond to protocols Conceivably we’ll run into firewall problems

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Networkable solutions

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  1. Networkable solutions • Using sockets we can pass objects back and forth between client and server, but we’re limited • Cannot call methods on objects between client/server, only send objects and respond to protocols • Conceivably we’ll run into firewall problems • RMI, Remote Method Invocation, can fix both these problems • Clients call methods across machines, on objects running in other JVMs • Built on top of HTTP, so can (in theory) be used through firewalls • Different in 1.1/1.2, requires a fair amount of bookkeeping overhead to set up

  2. Object streams, passing objects • ObjectInputStream and ObjectOutputStream provide mechanisms for passing objects between clients • Wrap streams around/in other streams, e.g., socket streams via stream decorator pattern • Send copies of objects, different from standard Java object model where everything is a reference • Objects sent must implement Serializable interface • Flag interface, no methods • All fields (object graph) written, objects not written more than once, references used for already-written objects • Possible to customize how objects are serialized using writeObject/readObject or Externalizable interface • Fields labeled as transient are not written

  3. RMI ideas • Think of clients and servers, though this distinction is blurred • In jdk 1.2, server-side objects can call client object methods, so really distributed computing • Still, an initial server/rmiregistry begins the RMI process • JVMs on different machines execute, objects communicate with each other between JVMs • Sockets used underneath, either TCP/IP or HTTP or … customizable e.g., SSL • Classes can either be located in all JVMs, or transferred/downloaded using HTTP codebase • Codebase is also used in applets, but restricted to original web page as root

  4. Applet codebase • JVM executing in browser has different capabilities than “regular” JVM • Looks in codebase as its CLASSPATH, also uses client/browser side CLASSPATH • Codebase is relative to location of web page originating the applet for security reasons • Implications for downloading swing.jar?

  5. RMI information/basics • http://java.sun.com/products/1.2/docs/guide/rmi/codebase.html • http://java.sun.com/docs/books/tutorial/rmi/

  6. Downloading code in RMI

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