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NetBeans Meta Update Server

A simple standalone update server for NetBeans and NetBeans Platform application plugins.

Just run it using java -jar. It will serve whatever plugins you tell it about, and automatically check for updates. Download it from

Your users can simply get updates using Tools | Plugins, with no additional steps.

The server will generate and serve a plugin which registers it with Tools | Plugins in NetBeans. That's generated for you on startup and is always-up-to-date.


  • You give it URLs where your plugin (NBM) files live on the web.
  • It downloads them and serves them.
  • It processes metadata in the downloaded NBM files and uses that to figure out the rest.
  • It periodically checks for new versions and updates what it is serving automatically.
  • Automatically generates and serves a NetBeans plugin which registers your server as an update server - your users install that, and from then on the IDE/application will automatically check your server for updates
  • Logs hit and download statistics using in easily analyzed bunyan-compatible JSON using bunyan-java

Usage fairly self-explanatory - start it and navigate to it in a browser. Try the demo server to see what it does.

It serves NBM (NetBeans module) files with appropriate metadata so that the NetBeans update center (Tools | Plugins) can download plugins from it. It give you a way to distribute updates, where simply publishing a new version at the same URL will make the new version automatically available to your users.

Use Case

This was written to scratch an itch. I have a Jenkins continuous integration server which builds modules. I want to publish them to users so it is easy for them to get updates. And I want no manual steps for me to provide them.

I briefly considered writing a Jenkins extension like its Maven Repository plugin, which would serve this stuff. Then I thought, why be tied to Jenkins at all? This solution will serve whatever you want, wherever it is.

If you use this with Jenkins, one small change is useful to your Maven pom.xml - this server relies on the download URLs for modules not changing, but by default Maven includes the version in the NBM name. To fix this, add <finalName>YourModuleName</finalName> to the configuration section for both the nbm-maven-plugin and the maven-jar-plugin.


Plugins are added to the server by adding remote URLs to NBM files via a web form on the home page the server serves. The primary use-case is wanting to distribute some modules built by a continuous build.

Once a plugin is added, its URL is polled once per-hour to check for updates (this will use the If-Modified-Since HTTP header to avoid excessive downloading). If an update is found, it is downloaded; if its specification verion is greater than an existing copy on the server, the old one is replaced.

The primary use-case is continuous builds - in fact, it came out of a discussion of writing a Jenkins/Hudson plugin for this purpose. This project accomplishes the same thing in a simpler way. So, this is an update server which serves nbm files which are available elsewhere via HTTP. It has a small HTTP web api which lets you add new NBMs.

The server uses Acteur, an asynchronous server framework based on Netty. HTTP downloads from remote servers are also asynchronous - meaning that this tiny web application can serve a lot of traffic while consuming minimal system resources.

Running The Server

Build it or download a binary. Run it with java -jar

If no directory path is passed to it, it will store and serve data from /tmp/nbmserver

In a web browser, navigate to / to see a web page containing a list of all modules served and an upload form. Uploading requires HTTP basic authentication - for the password, either pass --password on the command line, or make a note of the generated password logged on startup.

Web API / Adding NBMs

The server has an extremely simple web API:

  • An HTTP GET to /modules lists the modules being served in XML, using the NetBeans autoupdate DTD
    • Add ?json=true to get this data in JSON format instead, if you want to get this data in a usable form for client-side Javascript
  • An HTTP GET/PUT/POST to /add with the parameter url set to the remote URL of an NBM file
    • This call requires HTTP Basic authentication
  • An HTTP GET to /download/$CODE_NAME/$HASH.nbm will download the cached copy of an NBM file

There is one caveat: If the URL to an NBM incorporates the version number of that NBM, and an update will have a different version number, then you will need to manually add the new URL every time you publish an update. For automatic updates, change your build script not to do that. HTTP does not do wild-cards, so there really is no other fix.

Configuring The Server

All of the following properties can be set via the command-line by prefixing the property name with -- - for example

java -jar nbmserver-standalone.jar --port 3572 --external.port 80 --password hoohah

The system will also look for, and load if present, the following files:

  • /etc/
  • ~/
  • ./

any duplicates in the previous one being overridden in the next; command-line arguments override them all.

The following are useful properties

  • nbm.dir - the path to the folder to store NBM files in. Will be created if non-existent. If not set, uses /tmp/nbmserver or OS-specific equivalent.
  • port - the port to run on
  • external.port - if you are running it behind a reverse proxy such as NginX, this sets what port URLs to files this server is serving should have - the module catalogue it serves includes download URLs, which must be canonicalized.
  • password - the password used to authenticate the administrator (needed to add URLs to the system). If not set, a random one is generated on startup and logged.
  • hostname - the host name to use in external URLs in the module catalog
  • basepath - path to prepend to all URLs served and in the module catalog
  • workerThreads, backgroundThreads - control the size of thread pools used for servicing events and background tasks
    • See note below
  • download.threads - how many concurrent downloads from remote update/build servers should be attempted simultaneously
    • See note below
  • poll.interval.minutes - the interval in minutes between checks of remote servers for newer versions of the NBMs served. The default is hourly.
  • - sets the user name expected for basic authentication for adding modules. The default is admin.
  • log.file - the file to log stats and other information to - default is nbmserver.log in the process' working directory
  • log.level - defaults to info - see bunyan-java for details

See the documentation for Acteur for additional settings. The properties are loaded using Giulius and follow its rules for what overrides what.

Note: Since Netty and Acteur are asynchronous, threads are used much more efficiently - a single thread can simultaneously service hundreds or thousands of connections.

If you use files instead of command-line arguments, the server periodically checks and reloads these. To guarantee changes are picked up, restart the server (it starts very fast!).

The Generated Update Center Module

On startup, the server generates a NetBeans module on-the-fly which can be installed and will register your server as an update server. Once a user has done that, NetBeans will automatically check back with your server for updates.

Some care is taken to ensure the generated module is not updated unless something has changed, but is if something has:

  • The implementation version is a SHA-1 hash of the sorted keys and values used to generate it
  • The package name and module code name are derived from the server's update catalogue URL, so multiple servers can be hosted on one domain but will generate unique modules
  • The module's specification version incorporates
    • The version of the server
    • A munged timestamp from the first time the server was run
    • A number which is incremented every time the generated bits differ from the preceding run

This does mean you should take some care choosing your host name and base path, as the module will not know if you change them later (a new one will be generated, but the old one will be broken).

The following settings can be set as described above, and affect only the module:

  • update.url.https - use https for the update URL
  • serverDisplayName - what the server is called in descriptions (e.g. "Joe Blow's modules")
  • - the name to show for the module author; uses System.getProperty("") if unset

Build and Run

Build with Maven and run the JAR. Builds can be downloaded here. Requires JDK 7 or greater.

The build creates a merged JAR file which contains all of the project's dependencies, called nbmserver-standalone.jar which is suitable for deployment and can be run with java -jar.

Security & Reverse Proxy Setup

Calls which modify server state use HTTP Basic Authentication and require the administrator user name and password (see configuration below).

Basic authentication is not secure unless you use HTTPs. The standard way to do that is to run the server behind a reverse proxy such as NginX.

The following is an example NginX configuration which reverse-proxies the application and redirects secured requests to HTTPS:

location	 /modules {
	proxy_set_header	X-Real-IP	$remote_addr;
	proxy_set_header	X-Forwarded-For $proxy_add_x_forwarded_for;
	proxy_set_header	X-Forwarded-Host $host;
	proxy_set_header	Host $http_host;
	proxy_pass	http://localhost:8959;
	proxy_redirect	off;
    location        /modules/add {
            if ($scheme = http) {
                    rewrite  ^/(.*)$$1  permanent;
            proxy_set_header        X-Real-IP       $remote_addr;
            proxy_set_header        X-Forwarded-For $proxy_add_x_forwarded_for;
            proxy_set_header        X-Forwarded-Host $host;
            proxy_set_header        Host $http_host;
            proxy_buffering         off;
            proxy_pass      http://localhost:8959;
            proxy_redirect  off;

Replace with the actual host name of the server. To use this configuration, you would want to start the server with --hostname so that generated URLs will be correct.

Here is an example set of arguments for a Debian launch script (start from /etc/init.d/skeleton):

    /home/tim/nbmserver-standalone.jar --password somepassword --basepath modules 
    --nbm.dir /var/nbmserver --port 8959 
    --hostname --external.port 80"

The salient details of what this does:

  • Save and load NBM files using the folder /var/nbmserver
  • Use port 8859
  • Use the hostname in generated URLs in its module catalog
  • Set the ports used in generated URLs (we are behind a reverse proxy, so we don't want to ask normal users to connet over port 8859)


The server stores files in the folder specified by the property/argument nbm.dir. This is laid out as follows:

  • nbm.dir
      • nbm-sha1-hash.json - JSON representation of the information in the module's Info/info.xml file, plus the original URL, download time, etc.
      • nbm-sha1-hash.nbm - the actual nbm file
      • ...

So, each module is stored in a directory with the module's code name as its name. A version of a module is represented by a JSON file and an NBM file. The name portion of each file is the SHA-1 hash of the nbm file's bits.

The version of the module served is the one with the highest specification version in its manifest. If there is more than one build of the same version, the most recently downloaded is used.

Caveat: The above algorithm does mean that if you add url-to-nbm A pointing to 1.2 and later you add url-to-nbm B pointing to 1.0, the version served will be 1.2.

The server honors the If-Modified-Since and If-None-Match headers to reduce server load.


The server logs simple stats as lines of JSON to stats.log in the folder NBMs are served from. The activity can be identified by the combination of property names.

  • {"ref"="-", "addr"="/0:0:0:0:0:0:0:1:51328", "time"="Sun, 14 Jul 2013 06:46:31 GMT"} - an index page hit with referrer
  • {"id"="abcd", "addr"="/0:0:0:0:0:0:0:1:51328", "time"="Sun, 14 Jul 2013 06:46:39 GMT"} - a request for the NBM catalog, possibly with an installation ID identifying a unique user
  • {"pth"="", "addr"="/0:0:0:0:0:0:0:1:51288", "time"="Sun, 14 Jul 2013 06:37:29 GMT"} - a download of an NBM

Server start and shutdown events are also logged.


  • Repack jars using pack200
  • Automatically sign JARs if a certificate is provided
  • More admin UI for configuring some of the settings described above
  • Auto-generate version numbers and repack (and possibly re-sign) NBM bits as described here so that even if the remote bits version didn't change, if the bits did, it increments


Logging is done in a format compatible with bunyan. Bunyan is quite useful for monitoring and filtering logs in real time.

A couple of scripts are included in the project root directory for analyzing logs to determine the geographic distribution of users. They require NodeJS, bunyan and geoiplookup to be available on the path. For a simple geographic distribution, tweak the uniqueAddresses script to point to your nbmserver.log is and run ./uniqueAddresses | ./listaddrs.


An update server for NetBeans Plugins which serves remotely built NBM files




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