title: How do I make a Java app self-update?
body: <p><strong>Problem</strong>: I have a standalone Java app (henceforth known as "the agent") that runs as a service on internal company servers. It acts as a remote agent for some central servers. As the agent gets deployed in more places, managing them is getting more complicated. Specifically: pushing updates is painful because it's a fairly manual process, and getting access to the logs and other info about the environments where the agents are running is problematic, making debugging difficult. The servers under discussion are headless and unattended, meaning that this has to be a fully automated process with no manual intervention, hence <strong>Java Web Start isn't a viable solution</strong>.</p>
  
  <p><strong>Proposed solution</strong>: Make the agent phone home (to the central servers) periodically to provide agent status and check for updates.</p>
  
  <p>I'm open to other suggested solutions to the problem, but I've already got a working prototype for the "status and self-updates" idea, which is what this question is focused on.</p>
  
  <p>What I came up with is actually a separate project that acts as a wrapper for the agent. The wrapper periodically calls the central server via HTTP to check for an updated version of the agent. Upon finding an update, it downloads the new version, shuts down the running agent, and starts the new one. If that seems like an odd or roundabout solution, here are a few other considerations/constraints worth noting:</p>
  
  <ol>
  <li>When the wrapper gets a new version of the agent, there may be new JAR dependencies, meaning class path changes, meaning I probably want to spawn a separate Java process instead of fiddling with ClassLoaders and running the risk of a permanent generation memory leak, which would require manual intervention--exactly what I'm trying to get away from. This is why I ended up with a separate, "wrapper" process to manage the agent updates in my prototype.</li>
  <li>Some servers where the agents are deployed are resource-limited, so any solution needs to be low on CPU and memory usage. That makes me want a solution that doesn't involve spinning up a new JVM and is a stroke against having a separate wrapper process.</li>
  <li>The agent is already deployed to both Windows and RHEL servers, so the solution must be cross-platform, though I wouldn't have a problem duplicating a reasonable amount of the process in batch and bash scripts to get things rolling.</li>
  </ol>
  
  <p><strong>Question</strong>: As stated, I want to know how to make a self-updating Java app. More specifically, are there any frameworks/libraries out there that would help me with this? Can someone with experience in this area give me some pointers?</p>