I am developing a java application that will work peer-to-peer. At any given time, there will be over 5000 clients around the world online. Each of these clients will create small files over time. I would like these files to be distributed amongst all the clients and stored, so that anyone can connect and download the filesdump.
Is there any library that would help with that?
(I'm rephrasing this to make it a little more serious since it's still the only answer)
Try finding a Java bit-torrent library, I just googled and there were a bunch of them--I don't want to list them here because I don't have any personal experience with any of them.
I can tell you that the way it normally operates, bit torrents still require some centralized coordination (The tracker). I'm quite sure that Vues works in a "Trackerless" purely p2p mode so I would look for that specifically when evaluating the libraries.
If this isn't some huge widely-distributed and heavily financed app you are creating I highly recommend looking into some other kind of shared file system like dropbox or even svn, they are not p2p but they are known to work reliably and at least dropbox can work completely in the background, unattended and ignored on any platforms for years without trouble.
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Firstly Cheers to all PROGRAMMERS [ Today = Programmers day :) ]
Secondly,
I'm working on a project where the specifications require using a server as a front end and an application in the back end. The project is an advanced smart home system. The server will handle commands coming from the client through the internet (let's say like a remote control from outside the house) and send them (through a channel of communication) to the application (planning on using JAVA application) which will handle the main logic like controlling hardware stuff (lights ...) , reading from a microphone (local mic) and accessing a database to act as a speech recognition system (offline).
Now I'm still in the planning phase and I'm not sure which technologies are the best for this project. I'm thinking to use Node.js or Apache as the server and a JAVA application as the back end and any SQL database for the application's SRS.
I hope this illustration demonstrates clearly how the system works:
The main question is:
What is the best way to make the Java application communicate with the server (communication channel [must be bidirectional]) ?
and Do you recommend a specific server other than the mentioned ones for this job ?
What crossed my mind so far:
1- JSP and servlets (making the server is the application too). But I don't want a server to handle the offline stuff and I'm not sure if java servlets can access hardware interface. I also want the server to be separate from making critical decisions (different layer for security reasons and since it won't be used as frequently as the local [offline] system).
2- Communication channel :
A- A shared file, but it's a bad idea since I don't want the application to check if the file contents changed (command received) or not from time to time (excessive operations).
B- A an inter-process-communication through a port (socket communication) seems the best solution but I don't know how that would turn in terms of operation cost and communication errors.
OS used : Linux Raspbian
EDIT:
I'm sure ZMQ+Apache is good enough for this task, but how is it in comparison to WebServices (like SOAP) ? Would WebServices be a better solution in terms of standard implementation and security ?
All related suggestions are welcomed, TQ
ZeroMQ is great for internal communications, or any other similar communication solutions.
For specifically your case, I can see that ZeroMQ would be a best fit.
Reasons:
You offline server have to be agnostic to web solution.
Communication can be reliable and bi-directional, possibly another patterns like (pub>sub, req<>res, etc).
Restarting any of sides would not require to restart the sockets (connection) on other side, as messages are queued.
Possibility to scale not just on same hardware, but as well to local area network or even through internet.
Big community of support. It might look a bit hard to get into, but in reality it is dead simple, just go to examples and once concept understood - it is very easy and neat to work with.
ZeroMQ has lots drivers for most popular languages, that includes Java and Node.js.
Considerations:
You need to think over packets and data will be sent. So some popular data protocols like XML or JSON is good way of thinking.
Responsibilities over different services - make sure they are not dependant on each other too much. Or if main offline server - is a core of system, make sure it does not depend on web facing service, so that web face can be removed/replaced/improved etc.
Few more points to think about:
Why Java, and what about modular approach? For example if you want to expand and scale - add more sensors into smart home solutions, then having one giant application would require to change it, it is harder to maintain as well as maintain different clients with own needs. Think modular way - some core functionality for offline stuff, but many aggregator processes that would talk to different sensors. This makes easier to support different setups and environments, as well maintain the system as a whole by improving independent components.
I have a Document Management System that stores documents in a database. I'm looking for a simple way (not too much and complicated protocol to implement) to show the database as a drive in windows (so it can be browsed and manipulated using any windows program, like explorer or office).
I have something in mind that I provide some kind of network share and that can be mounted as a drive in windows. Unfortunately all candidate network protocols for file sharing seem to require substantial effort to implement.
I first considered CIFS, but after reading up on that quickly decided that its BY FAR to complicated for me to implement. Next thougt was NFS, but its not supported by Windows (XP) natively and also seems quite complicated to implement.
FTP might be an option, but implementing an FTP server is again much more complicated than I naively expected.
There might be a simpler protocol to use I haven't thought of.
Is there anything I can (ab)use easily for this purpose?
Ideally I want some kind of (pure Java) premade server where I could easly strip out the part that accesses a local file system and replace it with my own code accessing the database OR a protocol simple enough that I can implement it myself reasonably quickly and more importantly, compatible and reliable.
First, you need to make the correct bindings between your DBS and the database, and define/write an API in your program that will describe an easy access to the needed resources. Writing an API Will allow to maximize inter-operablity of your solution with other services or plugins you might want to add later.
After that, you should serve this services to clients through a permissive and robust protocol such as WebDav which stands for Web-based Distributed Authoring and Versioning. He is natively supported by Windows, you can this way interact with every services implementing WebDav (Windows, most web browsers ...), and you can of course also mount this kind of services as a virtual drive. Plus, it is also supported on Linux and MacOS X, I believe nativ'ely but i'm not sure. In fact, WebDav is an extension to HTTP, and is described in the RFC 4918.
Basically every HTTP (which handles server side response management) library for Java could be used to implement WebDav, if you havé some time and want to do it yourself.
To implement WebDav in a way and with an acceptable effort, I searched for some Java librairies on the web and found these ones, it's now up to you to decide which one really fits your needs :
Milton http://milton.ettrema.com/index.html
A list of some of the existing implementations of the WebDav protocol into open source projects on WebDAV.org (you can find there some pretty amazing projects such as The Jakarta Slide project although I think it is not supported anymore and other projects/librairies that shows the importance of WebDav today). http://www.webdav.org/projects/
I'm well aware of how I can communicate with an outside server using Android. Currently I'm using the relatively new AppEngine Connected Android project to do it, and everything works fairly well. The only thing that I'm concerned with is handling downtime for the server (if at all) and internet loss on the client side.
With that in mind, I have the following questions on an implementation:
What is the standard technique for caching values in a SQLite Database for Android while still trying to constantly receive data from the web-application.
How can I be sure that I have the most up-to-date information when that information is available.
How would I wrap up this logic (of determining which one to pull from and whether or not the data is recent) into a ContentProvider?
Is caching the data even that good of an idea? Or should I simply assume that if the user isn't connected to the internet, then the information isn't readily available.
Good news! There's a android construct built just for doing this kind of stuff, its called a SyncAdapter. This is how all the google apps do database syncing. Plus there's a great google IO video all about using it! It's actually one of my favorites. It gives you a nice really high level overview of how to go about keeping remote resources synced with your server using something called REST.
I'm developing an application for Android, and I'm thinking that it's functionality might be useful on other (Java-running) platforms (say a regular desktop app -- although I hope that the other platform(s) involved are immaterial to the question at hand).
It's unlikely that the UI will be in any way portable (there's just too much of a difference between a good touch-capable, 4in screen UI, and a mouse-and-keyboard 19in screen UI), so I'm happy enough reimplementing that separately.
However, the core "business logic" (ugh, horrid word) and model (data storage) classes could, in theory, be reused in managing the core app. I've noticed that there aren't a lot of classes I'm writing that don't end up referencing some Android-specific bits (I've got XML resources files, images, and SQLite databases, as examples). Basically everything I've written so far has at least one Android-related import.
My question is twofold:
What tools are available out there to help me use Android-related classes and features (eg resources, databases) on non-Android platforms; and
What classes, features, etc of the Android platform should I completely avoid using (for the sake of simplicity, let's exclude UI-related items) due to non-portability, and what should I use instead to improve portability.
Answers that consist of "hahahaha, you're doomed" are OK, as long as there's some rationale provided.
(P.S. I'd make this community wiki if that was still available; this seems like a perfect CW question to me -- a list of Android portability tips and tools)
Looks like you have already identified the key point by keeping UI and biz logic / model separate.
Also sqlite itself is used not only in Android. But of course the way you interact with it (e.g. SQLDBOpenHelper) is different again.
So I guess having the biz logic and model as separate as possible is the way to go.
You can then put a wrapper around it (e.g. "Data Access Object " pattern which talks to the specific DB).
Still keep in mind that the users experience is best when you are as specific to a platform as possible on the UI side.
Example: there is an App (Push & Ride) on the Android market, which seems to run in a J2ME emulator. So screen input does not use the normal soft (or hard) keyboard of the device, but a simulated phone keyboard with the "abc" "def" combos on the number keys, which makes data entry a bit strange.
This app is for sure very portable (and its functionality is really great), but it just does not feel right.
When you want to go multi-platform, you may perhaps also look at things like Appcelerator or Adobe AIR
I started off doing something similar - I wanted to write an app for Android, Blackberry and J2ME. Conceptually, you can layer your design such that platform-specific components (UI, network access, data storage) are separated from the core business logic.
In practice, I don't find this satisfactory. The issues I faced all related to the core version of Java being different in the different platforms (in Blackberry it is based on J2Se 1.4, while Android used Java 6 as base). This led to annoyances like
Not able to reuse code that uses generics
My preferred classes not being available uniformly (for example, forced to use Vector over List)
I have opened discussions regarding this on SO (here and here), but couldn't reach a conclusion.
The logging layer can be made portable by using the Simple Logging Facade for Java(SLF4J) which is available for java/log4j and for android.
Also,you can try this out
http://wp7mapping.interoperabilitybridges.com/Home/Library?source=Android
Contains documentation and tools to map your android app to windows phone
Also read this,even though it contains instructions specific to android - windows phone interop,im sure they apply to other platforms as well
http://windowsphone.interoperabilitybridges.com/media/49652/wp7_guide_for_android_application_developers.pdf
What I do is create a web service outside of the android app which can be used by the android app as well as other systems (websites, windows apps, iphone apps etc).
A simple REST web service which supports JSON is a good example to fetch data and also insert/update data. JSON is particularly suitable because its so lightweight, and doesn't require alot of bandwidth which is great for slow mobile connections.
This way you can store your models/data storage outside of the android app, and it can be used by other apps very easily.
The database layer can be made more portable by using android jdbc or by using a database abstraction layer/object relational mapper/ActiveRecord implementation.
Has anyone tried make android.database(.sqlite) runnable on a non android system?
If you carefully separate business logic from UI and android perks you would be able to reuse it in desktop environment. Android is quite different from it in intialisation and application lifecycle - abstracting creation and setup of BL is also necessary.
Usefull pattern for this purpose would be dependency injection. There are different frameworks around, and some are more suited for android (like roboguice) or desktop (spring or picocontainer or guice).
Android appliactions are very constrained in memory, and this puts limits on what frameworks you can use there. So you may need to abstract data storage as well ( hibernate comes handy on desktop / server side , but too heavy for mobile device)
I'm inclined to suggest trying out the new native extensions for Adobe Air. It allows you to create a device-specific chunk of native code, and connect it to the Air framework, accessing it as you would other objects in Air. (cf. http://www.adobe.com/devnet/air/articles/extending-air.html). This allows you to keep the Android-only code as is, and then replace that code with iOS, Windows DLL, etc. code as needed.
This doesn't solve the problem of translating Java code to other languages/platforms, of course. Still, some of the logic you are doing natively may very well exist already cross-platform in Air. For example, you can access the camera in Air in all supported OSes without writing any device-specific code.
You will probably need to go beyond the current Air classes, so some examples may help:
Android speech-recognition
iOS batttery
Windows and Mac tutorial
NE tutorial
I am currently trying to implement a database compatibility layer for Spring-Boot-JPA/Android-Room:
"compatibility layer" means my Service-layer-code is pure-non-android-code that can be used in android and in spring-boot. The Service-layer-code uses a common java-repository-interface that is either implemented in android-room or in JPA.
Currently i am stuck here:
Howto use methods of CrudRepository<T, ID> (or SimpleJpaRepository<T, ID>) in a Spring-Data-Repository-Fragment method?
My friend and I are planning to build a simple chat client to let people in a (physical, real world) room chat with each other (people chatting over the same wifi network, possibly pinging some external server to organize things by the external IP address of the wifi network). Partly we planned this as a chance to play around with Groovy, which we haven't done much with. But then I thought - damn, how many people have the Java 1.5 runtime? Maybe this is kind of thing where Flash would be better (when I say "Flash" I mean "Flex")? I hate ActionScript and I have very little experience with it, and I've no real interest in using it, but I'm thinking, if we want 9 out of 10 of our friends to be able to use our software, Java is possibly not the way to go?
My concern is in particular with the demographic we have in mind, which will tend to be freelancers and artists and individuals, rather than people at work. I'm aware that Java still has a decent overall market share, but I'm under the impression that its use is heavily concentrated in the computers that people use at work. Folks who don't work at corporations may not have a modern runtime?
I then decided to look up Java market share. It is surprisingly hard to track down info about specific JREs.
There was this on stackOverflow, but its focus is on RIAs, which isn't what I'm talking about:
What's all this business about Flash, Flex, Adobe Air, Java FX and Silverlight?
And then conversations like this make it sound like Flash is the only reasonable choice to make if you want people to be able to use your software without jumping through a lot of hoops:
http://forums.java.net/jive/thread.jspa?messageID=317749&tstart=0
This seemed like a reasonable summary of Java versus Flash issues:
Client Java vs (Adobe) Flash for web applications, what to choose and when
I found it surprisingly hard to track down actual market share data on particular JREs. And I found no easy way to find out if folks who with modern JREs installed are mostly using their computers at work.
So I'm open to hearing some anecdotal information here. If we built our simple chat client in Groovy/Swing, would our target demographic be able to use it? Is Flash the only reliable way to go here?
If portability is your goal, why not go for a JS only approach, perhaps using one of the COMET styles of push? Here's an article to learn more:
http://ajaxian.com/archives/comet-a-new-approach-to-ajax-applications
If a JS RIA isn't what your after. Then Flash/Flex are your next best bet. I'm usually biased towards Java as a technology, but based on your target app and audience I think you'll get more joy using a Flash-based technology.
Adobe understand RIAs better than Sun, which was kinda demonstrated by some high profile Java 2D devs moving to Adobe in 2008/09. Plus with recent Flash Player developments you'll get your app onto more mobile devices.
Obviously server-side in Java ;-)