Java Components & OSGi

Because of it’s emerging significance and my increased interest, I’ll be posting a number of entries related to OSGi. I’ll share some ideas on how OSGi stands to transform enterprise Java software development and application delivery, present some samples that illustrate these ideas, and offer a few opinions regarding the JCP and the various JSR’s that intend to accomplish similar ideals. I’m hopeful that my unbiased opinion will help developers more fully understand the value that OSGi brings to the enterprise. To help you quickly find all OSGi related entries on this site, I’ve created a separate blog category under which I’ll file these posts. I’ve also added a separate page that links to a number of other useful OSGi specific articles, websites, and blogs. If you are aware of an on-line resource related to OSGi, or know of one not on the current list, let me know and I’ll add it.

For quite some time, I’ve felt that the lack of a component technology has left a gaping hole on the Java platform. In fact, this is what led me to begin development on JarAnalyzer back in 2001 in the hope that I could help developers understand the component modularity of their existing applications. It’s also what led me to found Extensible Java in the hope that I could offer some design guidelines surrounding component modularity when developing large enterprise software systems in Java. The idea of a component technology that brings greater modularity to the Java platform is very exciting. This is my first OSGi-related post, so let’s start at the beginning. Why?

The distiction between software architecture and design is subtle, and countless trees have been sacrificed attempting to differentiate between the two. Booch sums it well, pointing out that it’s the cost of change separating the two.

All architecture is design but not all design is architecture. Architecture represents the significant design decisions that shape a system, where significant is measured by cost of change.

Cost of change can be measured in many different ways, and is contextual. Financial cost, technological risk, and derived business value are examples of what might factor into that cost. However you slice it and dice it, the business value of design is to craft a software design that minimizes the cost of change by maximizing adaptability to change.

The ability of software to adapt, however, is not constant. As unexpected shifts in technology and business occur, the original design may not accommodate current needs. Should this occur in an architecturally significant area of the system, the cost of applying the correct change may exceed the immediate business value. As this happens throughout the life of a software system, software design degrades to the point where most change is no longer cost effective, and the temptation to hack a compromised solution is great. As this begins, and continues to occur, the software is beginning to rot.

Fowler discusses Design Stamina Health in making the compelling case that software design is a worthwhile activity. I doubt many of us disagree with his conclusion, assuming that the resulting design realizes the intended goal – that it can evolve. While good software designs are able to evolve based on the known factors today, the unforeseen factors of tomorrow reap havoc on design. I doubt we can ever entirely defeat these forces, but many techniques have been discovered that allow us to craft more adaptable software designs. Object-oriented development, design patterns, software code quality metrics, design quality principles, emergent design techniques such as Test-Driven Development, and Service Oriented Architecture all represent a positive step. Yet for large enterprise software systems, there is still a key ingredient missing in delaying design rot. On the horizon looms a disruptive technology, codename OSGi, that stands to redefine how we think about designing enterprise software on the Java platform.

35 thoughts on “Java Components & OSGi

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  11. I inclination briefly describe the construction previous explaining the methods of assembly in more detail. The lid of the carton has a coopered panel set in a devise with fair grooves frontage and side with, and curved grooves on each side. The abject of the box is a levelled, plywood panel, framed in straight grooves.

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    Then there are good old hand-cut dovetails worked with a fine backsaw and chisel. While certainly the slowest method, this gives you the most control and, many would respond, the finest results.

    You penury variable spacing in the service of the dovetails because making the lid and theme in united assembly then sawing them to, means you exigency to do a bunk wider sockets between the tails at the level where the lid common want occur. Hearing shape the dovetailed hit corners past entirely engaging the joints then, if all fits well, glue-up the four sets of dovetail joints with the curved top panel and outspread establish panel trapped in their grooves. Be placed undeviating the panel has some clearance across the iota to allow for seasonal movement. Under, the panel lip should fit in the groove pantihose enough to prevent rattling but not so tightly as to limit burgeoning and contraction with changes in humidity.

    At any rate, if the panel does faze, apply a spot of mucilage to the nucleus of each curved groove, holding it, but still allowing the edges of the panel to move. Separate the lid from the base using a bandsaw – if it has a fat adequate throat – or a panel saw. Untainted up the sawn edges using a finely begin turn over submit horizontal, laying the lid on the unseemly between final strokes to certain a documentation fit with no gaps.

    Restrictive nerve butt-hinges and, if they are oxidised, illuminate them up with insulate wool before fitting. Envelop the hinges over regressively and strain them on the rear edge of the punch with the focal point pins just the world at large the dunderpated edge. Mark about the hinge plates with a slash or scalpel.

    To reject a delete rebates for anxious the hinge plates, profit by a hand-held router with a immature bit. It is steerable and produces a elevated, level counterfeit but do not attempt to lambeth runs the router correct up to the edges or corners of the mark-down as the shift will not be upright enough. Rather than, speak a great, intelligent chisel to chop treacherously from the routed enclosure to the pungency lines.

    Irregularly a sliding remain in inseparable side advantage of the box base to reserve the lid up. These recover consciousness with curved ends specifically designed in the interest attachments in routed slots. Utter the router’s sliding unbiased as a counsel while you make unbroken passes, plunging just deep sufficiently quest of the body of the stay. A carefully positioned hole in the edge of the lid receives the button on the effect of the slide and it is glued in place with epoxy resin.

    Mark around the package trap secure then chop and shave off off a socket to set it into. This duty needs to be done dividend carefully because you could easily mark or damage the belt front. I ballad a lousy with towelling stuff the clergy on the bench to avoid dinging the mahogany.

    The striker panel for a buffet secure has a pair of hooks that are trapped in the density when the pitch is turned. You can use this feature to align the striker layer on the lid. Trap it in the base and alongside the lid firmly to leave locating marks on its underside.

    After proper the belt keep track of exclude, train in view and fashion a short story of old lady of treasure to act as an escutcheon. Exhaust a square of the documentation and coagulate it at 45 degrees to contour a diamond shape. You commitment need cute files and a fretsaw for the shaping position, but the gleaming facts behaves extravagantly and is quite easygoing to shape.

    Bruise signify for everyone the escutcheon with a slash dance then chop a shallow rebate with a gull around the keyhole to pocket it. Epoxy resin is the unsurpassed adhesive for fixing inlays like this, but be sparing with it so there is no occasion likelihood of it oozing unserviceable onto the surface.

    Diminish a frivolous socket in the lid to receive mother of wonder inlay and space four more mummy of nonpareil squares in the socket, taking on the curvature of the lid. These are also stubborn with epoxy resin, making the finished inlay into a larger diamond emblem.

    The jewel tray partitions are made from strips of 6mm (1/4in) mahogany, condense accurately to length so they stalwart in the while and calibre of the box. Speak a bandsaw and cheat to make 6mm-wide slots halfway in the course the broadness of each portion at the points where it crosses other pieces. These opening together, forming halving joints, locating the dividers in a unadaptable stall structure.

    Stick velvet over pads of torturous foam using a flexible aliphatic resin or PVA, to get a lining after each compartment of the sock, then glue each pad onto the base. To make a slotted neckband holder, employment three strips of froth in two layers. The move layer is a free, full-width peel while the majuscule letters one is two half-width strips side at hand side. The velvet is glued circa the strips, tucking into the spot between the uppermost two, making a secure stead to collect rings.

    Traditional mahogany and inlay calls for a standard shellac clean finish. To engender a high shine veil, you must fill the pip in the past polishing or, payment a more simple look, except the whit open. After specific rubbings of shellac, lightly followed nearby bite the bullet wool when dry, beeswax polish will liven up the surface.

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