We have a VPN network and at a central point we have kept a java application (.jar file). We are allowing users of the VPN system to use this application- What are the cons of using this solution?
As for pros -
Easy to update to a new version
Storing the files in relative location helps save files in a central location
EDIT
Is it possible to access the COM ports using JWS since our app runs inside a sandbox?
I think what you describe would work well with Java Web Start - advantages I can think of
reduced bandwidth usage (JWS will only download files if they have been updated, if not it will use a local cached copy).
possibility to use specific JVM parameters.
automatic check of the client configuration (for example, JRE version must be at least xxxx, if not download it).
There are probably more.
It's okay. For a customer project, we choosed this solution too.
Its okay, if you have a good bandwith and, on traffic producing apps, a low latency at runtime.
For a test, I build a Sql-Wrapper, to add a simulated latency to each call to our database. So we're got a feeling for the application at runtime without a real vpn connection.
Related
I would like to implement a java application (server application) that can download a new version (.jar file) from a given url, and then update itself at runtime.
What is the best way to do this and is it possible?
I guess that the application can download a new .jar file and start it. But how should I do the handover, e.g. know when the new application is started and then exit. Or is there a better way to do this?
The basic structure of a solution is as follows:
There is a main loop responsible for repeatedly loading the latest version of the app (if required) and launching it.
The application does its thing, but periodically checks the download URL. If it detects a new version it exits back to the launcher.
There are a number of ways you could implement this. For example:
The launcher could be a wrapper script or binary application that starts a new JVM to run the application from a JAR file that gets replaced.
The launcher could be a Java application that creates a classloader for the new JAR, loads an entrypoint class and calls some method on it. If you do it this way, you have to watch for classloader storage leaks, but that's not difficult. (You just need to make sure that no objects with classes loaded from the JAR are reachable after you relaunch.)
The advantages of the external wrapper approach are:
you only need one JAR,
you can replace the entire Java app,
any secondary threads created by the app, etc will go away without special shutdown logic, and
you can also deal with recovery from application crashes, etc.
The second approach requires two JARs, but has the following advantages:
the solution is pure Java and portable,
the changeover will be quicker, and
you can more easily retain state across the restart (modulo leakage issues).
The "best" way depends on your specific requirements.
It should also be noted that:
There are security risks with auto-updating. In general, if the server that provides the updates is compromised, or if the mechanisms for providing the updates are susceptible to attack, then auto-updating can lead to a compromise of the client(s).
Pushing a update to a client that cause damage to the client could have legal risks, and risks to your business' reputation.
If you can find a way to avoid reinventing the wheel, that would be good. See the other answers for suggestions.
I am currently developing a JAVA Linux Daemon and also had the need to implement an auto-update mechanism. I wanted to limit my application to one jar file, and came up with a simple solution:
Pack the updater application in the update itself.
Application: When the application detects a newer version it does the following:
Download update (Zipfile)
Extract Application and ApplicationUpdater (all in the zipfile)
Run updater
ApplicationUpdater: When the updater runs it does the following:
Stop the Application (in my case a daemon via init.d)
Copy the downloaded jar file to overwrite current Application
Start the Application
Cleanup.
Hope it helps someone.
I've recently created update4j which is fully compatible with Java 9's module system.
It will seamlessly start the new version without a restart.
This is a known problem and I recommend against reinventing a wheel - don't write your own hack, just use what other people have already done.
Two situations you need to consider:
App needs to be self-updatable and keep running even during update (server app, embedded apps). Go with OSGi: Bundles or Equinox p2.
App is a desktop app and has an installer. There are many installers with update option. Check installers list.
I've written a Java application that can load plugins at runtime and start using them immediately, inspired by a similar mechanism in jEdit. jEdit is open source so you have the option of looking to see how it works.
The solution uses a custom ClassLoader to load files from the jar. Once they're loaded you can invoke some method from the new jar that will act as its main method. Then the tricky part is making sure you get rid of all references to the old code so that it can be garbage collected. I'm not quite an expert on that part, I've made it work but it wasn't easy.
First way: use tomcat and it's deploy facilities.
Second way: to split application on two parts (functional and update) and let update part replace function part.
Third way: In your server appliction just download new version, then old version releases bound port, then old version runs new version (starts process), then old version sends a request on application port to the new version to delete old version, old version terminates and new version deletes old version. Like this:
This isn't necessarily the best way, but it might work for you.
You can write a bootstrap application (ala the World of Warcraft launcher, if you've played WoW). That bootstrap is responsible for checking for updates.
If an update is available, it will offer it to the user, handle the download, installation, etc.
If the application is up to date, it will allow the user to launch the application
Optionally, you can allow the user to launch the application, even if it isn't up to date
This way you don't have to worry about forcing an exit of your application.
If your application is web based, and if it is important that they have an up to date client, then you can also do version checks while the application runs. You can do them at intervals, while performing normal communication with the server (some or all calls), or both.
For a product I recently worked on, we did version checks upon launch (without a boot strapper app, but before the main window appeared), and during calls to the server. When the client was out of date, we relied on the user to quit manually, but forbid any action against the server.
Please note that I don't know if Java can invoke UI code before you bring up your main window. We were using C#/WPF.
If you build your application using Equinox plugins, you can use the P2 Provisioning System to get a ready-made solution to this problem. This will require the server to restart itself after an update.
I see a security problem when downloading a new jar (etc.), e.g., a man in the middle attack. You always have to sign your downloadable update.
On JAX2015, Adam Bien told about using JGit for updating the binaries.
Sadly I could not find any tutorials.
Source in German.
Adam Bien created the updater see here
I forked it here with some javaFX frontend. I am also working on an automatic signing.
Some relevant background:
My application is a Java app compiled into a .exe via JSmooth. The anticipated user base would likely be a few hundred users, but could grow well beyond that, as it's a community specific application.
How it works:
2 .jar files, one that preforms initial checks, another with the meat of the application.
Ideally, the init jar displays the splash, checks the version in desktop.txt against server.txt, if they differ, it prompts the user to update.
What I need to figure out:
1) What is a cheap, scalable hosting service that I could use as the file host for updates?
2) How can I create an "updater" to actually preform the jar replacement? My current solution is simply writing an updater in Java, but I was hoping for something like the installers people are more familiar with.
All of the research I've done has resulted in lackluster results, as 99% of hosting searches result in site hosting results. I just need an update repository with reasonable security. i.e., decent DDoS resistance and not left wide open to the Internet.
Edit: formatting
Easy to do and very foolish cheap with Amazon S3 or Joyent Manta as both support time-limited signed URLs and headers (which can contain a SHA-1 of the file) to check to see if the update is needed before downloading
On startup your app would check the update URL to see if it has changed. If it has changed, download the JARs. Do this before the app loads classes from those JARs. Updating the updater itself will be trickier so consider that an update might need a new update URL to prevent expiry.
I've got an applet that is rather large (4MB) on a web page used by a few thousand users scattered across a WAN. Bandwidths to these users range from a paltry 128Kbps to 10Mbps.
The problem occurs when a new version of the applet is made available; it is downloaded automatically by all the users browsers effectively chocking the network.
They really hate 'release day' morning around here :)
Is there any strategy to work around this problem?
Edit: I can only serve this applet centrally from one pair of servers. I cannot make any modifications to the hosting or network infrastructure.
Here are some ideas:
Divide your user community into N equal groups, and provide a different applet URL for each for group. Then stagger the times at which each group's copy of the applet is updated.
Put the applet on a server that has been tweaked to lie about the applet's modification date, and use this to (crudely) throttle the rate at which browsers fetch the updated applet.
Push the applet to locations on the local networks of large groups of users. Have the central server issue HTTP redirects so that each browser picks up the applet from a "close" location.
Deploy caching HTTP proxies & autoproxy files on the local networks, and block direct access to the applet forcing the users to get the applet via the proxies.
The last option is probably the best.
Apart from what Stephen C mentions, I'd like to add another strategy that you should consider.
Consider breaking your applet codebase into different modules (archives)
These modules are updated instead of the entire 4MB applet. You can have a special classloader that checks if a new version of a given module is available.
For patches have a separate "patch" archive that loads before any other archives so that any updated classes are loaded from the patch archive instead of the older already downloaded archives.
The java web start already does some of these things to avoid entire updates. You can take a look the link (developer documentation) for a few pointers.
If you can put a .htaccess in the directory you can add expiresByType so that the client doesn't ask the server everytime.
Have you looked at pack200? and (pack200 + .htaccess)
Have you looked at indexed Jar?
Anthony
So, I've develop a simple hello world midlet using the Samsung SDK 1.1.2 and I've Packaged the midlet. Now I have two files (a JAR/JAD) combination. How do I get these installed on my phone?
As you can tell from the question, I'm new to phone development. Trying to deploy to a Samsung handset on ATT.
I'm trying to test out the entire development cycle - the emulators work great for writing code but I really need to make sure the Midlet works as expected on the target phone.
Suggest you read up a little on OTA delivery of applications, for background.
You have a number of options for deployment, here's a few.
Connect your handset to a computer via bluetooth, cable, or wifi and copy the JAR file over.
I'm not sure if Samsung support this, but other handset manufacturers certainly provide 'manager' software you can download and install on a computer to do this. If your app relies on user data in the JAD this may not be an idea option, or you could include default data in the JAR.
Place your JAD and JAR file on a web server you have access to, from which they can be downloaded to your phone. You'll need to ensure that the MIME types for the JAD and JAR files are set correctly, they may not be by default. Exactly how you do this depends on your server - here's an example method. (Presumably you have a web/data access service from AT&T.) If all is well you can fetch the JAD file from the phone's browser and the handset will then prompt you to confirm you wish to proceed and download the full JAR and install. Mobile Network Operators have a variable attitude to supporting JAD and JAR access, for example you may find you have to run your server on port 80 or 8080 for it to work in some cases.
Join a service that will host an application for you. One I'm aware of is GetJar. I'm not sure of the details, but doing this will mean you don't have to run your own web server.
Apart from basic deployment you might consider signing your application - a process that basically allows you to assert your 'true' identity to a handset. The advantage of doing this is that signed applications can present fewer network access confirmation dialogs and the like to the handset owner. Also, when the application is being deployed, the user will see a message about unsignedness that might include the word 'untrusted' or similar, and that can be off-putting. (Having said that, some major applications out there have been unsigned.)
Hope that gets you started.
You can certainly copy the jar/jad over via usb or bluetooth, but the Samsung devices I've used will not install a file that's been manually copied over.
Unfortunately the other methods are significantly more work.
Internet Explorer has a file download limit of 4GB (2 GB on IE6). Firefox does not have this problem (haven't tested safari yet)
(More info here: http://support.microsoft.com/kb/298618)
I am working on a site that will allow the user to download very large files (up to and exceeding 100GB)
What is the best way to do this without using FTP. The end user must be able to download the file from there browser using HTTP. I don't think Flash or Silverlight can save files to the client so as far as I know they won't cut it.
I'm guessing we will need an ActiveX or Java applet to pull this off. Something like the download manager that MSDN uses.
Does anyone know of a commercial (or free) component that will do that? We do not want the user to have to install a "browser wide" download manager (like GetRight), we want it to only work with downloading on our site.
Update: Here is some additional info to help clarify what I'm trying to do. Most of the files above the 4GB limit would be large HD video files (its for a video editing company). These will be downloaded by users across the internet, this isn't going to be people on a local network. We want the files to be available via HTTP (some users are going to be behind firewalls that aren't going to allow FTP, Bittorrent, etc.). The will be a library of files the end user could download, so we aren't talking about a one time large download. The will be download different large files on a semi-regular basis.
So far Vault that #Edmund-Tay suggested is the closest solution. The only problem is that it doesn't work for files larger than 4GB (it instantly fails before starting the download, they are probably using a 32bit integer somewhere which is exceeded/overflown by the content length of the file).
The best solution would be a java applet or ActiveX component, since the problem only exist in IE, that would work like the article #spoulson linked to. However, so far I haven't had any luck finding a solution that does anything like that (multipart downloads, resume, etc.).
It looks like we might have to write our own. Another option would be to write a .Net application (maybe ClickOnce) that is associated with an extension or mime type. Then the user would actually be downloading a small file from the web server that opens in the exe/ClickOnce app that tells the application what file to download. That is how the MSDN downloader works. The end user would then only have to download/install an EXE once. That would be better than downloading an exe every time they wanted to download a large file.
#levand:
My actual preference, as a user, in these situations is to download a lightweight .exe file that downloads the file for you.
That's a dealbreaker for many, many sites. Users either are or should be extremely reluctant to download .exe files from websites and run them willy-nilly. Even if they're not always that cautious, incautious behaviour is not something we should encourage as responsible developers.
If you're working on something along the lines of a company intranet, a .exe is potentially an okay solution, but for the public web? No way.
#TonyB:
What is the best way to do this without using FTP.
I'm sorry, but I have to ask why the requirement. Your question reads to me along the lines of "what's the best way to cook a steak without any meat or heat source?" FTP was designed for this sort of thing.
bittorrent?
There have been a few web-based versions already (bitlet, w3btorrent), and Azureus was built using java, so it's definitely possible.
Edit: #TonyB is it limited to port 80?
Please don't use ActiveX... I am so sick of sites that are only viewable in IE.
My actual preference, as a user, in these situations is to download a lightweight .exe file that downloads the file for you.
Can you split the files into pieces and then rejoin them after the download?
If you don't want to write java code in-house, there are commercial applet solutions available:
Vault
MyDownloder
Both of them have eval versions that you can download and test.
A few ideas:
Blizzard use a light-weight .exe BitTorrent wrapper for their patches. I'm not entirely sure how it is done, but it looks like a branded version of the official BitTorrent client.
Upload to Amazon S3, provide the torrent link of the file (all S3 files are automatically BitTorrent-enabled), plus the full HTTP download link as alternative. See S3 documentation
What about saying "We recommend that you install Free Download Manager to download this file. You will have the added benefit of being able to resume the file and accelerate the download."
Personally I never download anything using the built in browser download tool unless I have to (e.g. Gmail attachments)
#travis
Unfortunately It has to be over HTTP inside the users browser.
I'll update the question to be more clear about that.
#levand
The problem only exist in IE (it works in Firefox) so while ActiveX would only work on IE, IE is the only one we need the work around for.
#travis - interesting idea. Not sure if it will work for what I need but I'll keep it in mind. I'm hoping to find something to integrate with the existing site instead of having to go out to a third party. It would also require me to setup a bittorrent tracker which wouldn't be as easy as it sounds for this application because different users will have different access to different files.
#jjnguy
I'm looking for a java applet or ActiveX component that will do that for me. These are non-technical users so we really just want to have them click download and the full file ends up in the specified location
#ceejayoz
I totally agree but its part of the requirement for our client. There will be FTP access but each user will have the option of downloading via HTTP or FTP. There are some users that will be behind corporate firewalls that don't permit FTP
I have seen other sites do this in the past (MSDN, Adobe) so I was hoping there is something out there already instead of having to make one in house (and learning java and/or ActiveX)
I say click-once installed download manager, similar to msdn.
But becoming a CDN without a more optimized protocol for the job is no easy task. I can't imagine a business model that can be worthwhile enough to have such large file downloads as a core competency unless you are doing something like msdn. If you create a thick client, you at least get the chance to get some more face time with the users, for advertising or some other revenue model, since you will probably be paying in the hundreds of thousands of dollars to host such a service.
The problem with the applet approach mentioned is that unless you have the end user modify their java security properties your applet will not have permission to save to the hard drive.
It may be possible using Java Web Start (aka JNLP). I think that if it is a signed app it can get the extra permission to write to the hard drive. This is not too different from the download an exe approach. The problem with this is that the user has to have the correct version of Java installed and has to have the Java Web Start capability setup correctly.
I would recommend the exe approach as it will be the easiest for the non-technical users to use.
There are some users that will be behind corporate firewalls that don't permit FTP...
Are users with restrictive firewalls like that likely to be permitted to install and run a .exe file from your website?
Take a look at cURL. This article describes how to do a multi-part simultaneous download via HTTP. I've used cURL in the past to manage FTP downloads of files over 300GB.
Another tip: You can boost download times even more if you increase the size of the TCP Window on the client's NIC configuration. Set it as high as the OS allows and you should see up to 2x improvement depending on your physical network. This worked for me on Windows 2000 and 2003 when FTPing over a WAN. The down side is it may increase overhead for all other network traffic that wants only a few KB for a network packet, but is now forced to send/recv in 64KB packets. Your mileage may vary.
Edit: What exactly is this you're trying to accomplish? Who is the audience? I'm assumed for a bit that you're looking to do this over your own network; but you seem to imply the client side is someone on the internet. I think we need clearer requirements.
Create a folder of files to be downloaded on the server where the document service is running (either using Linux commands or using java to execute shell commands)
Write the file to be downloaded to this folder (using Linux command or Java shell command is OK). Considering the efficiency of program execution, WGet command is used here
Package the downloaded folder as a zip file (using shell command), configure nginx agent, return the access file path of nginx to the front end, and then download from the front end.