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Judul : Don't Role System.Exit() On Coffee Spider Web Application
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Don't Role System.Exit() On Coffee Spider Web Application

I receive got of late come upward across a code snippet, where programmer was using System.exit() if application failed to teach necessary resources afterward dyad of retry. His reasoning was that since, application cannot function, if essential resources similar database is non available or at that topographic point is no disk infinite to write records inwards File system. Ok, I listen you; but System.exit() inwards Java Web application, which runs within either spider web server or application server, which itself is Java programme is non a proficient sentiment at all. Why? because invoking System.exit() kills your JVM, invoking this from Tomcat or Jetty, volition non alone kill your application but most probable server itself. This tin flaming survive potentially dangerous, if that server also host other critical application, which is non uncommon at all. As per my experience, System.exit() calls are quite mutual inwards overly wide try-catch blocks inwards spider web application start-up code that loads environment variables, properties files, connect to MQ Series, establishes database connection, opens socket connections, etc. This is all the same ok, if yous are writing essence Java based server, where each application has their ain JVM, but amongst spider web application deployed on Tomcat, JBoss, WebSphere, Weblogic or whatever other application server, using System.exit() is big mistake. In worst instance tin flaming resultant inwards outage for lots of other critical application. On the other hand, at that topographic point are ways to forestall your spider web application from individual else’s mistake, past times enabling Security Manager. System.exit() as well as Runtime.exit() both goes through the security manager. Enabling Security director volition grab these calls as well as cut down them into an exception rather than shutting downwardly the whole VM. It's non hard to enable the security director inwards most application servers, Tomcat, JBoss both has documented steps to enable security Manager.

Why yous should non exercise System.exit() inwards Java Web application

I holler upward it's good known for senior Java developer that System.exit() shouldn't survive used except inwards e.g. command-line tools; Many beginner Java programmers, though familiar amongst System.exit(), may non know that using them inwards a Servlet/JSP code tin flaming resultant inwards shutdown of server itself, thus if yous receive got of whatever of them inwards your squad them receive got only about fourth dimension to educate them close coding inwards Java spider web application. In fact coding a Java based spider web application is totally dissimilar thus coding a essence Java application e.g. essence concerns similar threading, object pooling, parsing are all done past times Web server as well as it's prohibited for application code to exercise threads. In fact exercise of ThreadLocal variable tin flaming exercise retention leak inwards Java web-app, thus coding inwards web-app require to a greater extent than caution than inwards essence Java application. By the means at that topographic point are other reasons, why using System.exit is absolutely terrible. Especially when yous dealing amongst un-managed resources, if yous don't unloose resources properly as well as promise that OS volition exercise the clean-up for you, thus it could Pb to a temporary resources leak, until OS actually build clean materials created past times your Java application.

What does this all mean? Do System.exit() has whatever legitimate use? Of class at that topographic point are many cases where exercise of System.exit is imperative. Sometime yous actually desire to unopen your JVM in i lawsuit done, specially if it spawned from scheduling software similar Control-M or Autosys. For illustration ascendency describe of piece of occupation Java applications as well as scheduled tasks, tin flaming exercise System.exit(). Ideally, if yous are certain that calling System.exit() volition non receive got whatever side effect, yous tin flaming exercise it. Here is a sample exercise of system.exit() inwards essence Java application :

public static void main( String[] args ){      try     {         processFxRatesFileAndPutIntoDatabase();      }  catch ( Exception e )     {         logError(e);         // if yous demand to leave of absence amongst a failed condition thus System.exit(statusCode) is fine here.         // otherwise programme volition consummate successfully, in i lawsuit it provide from main() method     }   }

Remember, if yous are using Java programme every bit ascendency describe of piece of occupation tool thus yous tin flaming provide System.exit(0) or System.exit(1) every bit whether it succeeded or failed. H5N1 non-zero leave of absence condition code, unremarkably indicates abnormal termination. You tin flaming provide dissimilar error codes to betoken dissimilar errors e.g. bad arguments, can't abide by file, could non connect to database etc. I promise yous notice divergence betwixt using System.exit(1) as well as letting the Java programme consummate successfully. When coffee platform volition terminate amongst System.exit() it volition exercise thus amongst a non-zero condition (as long every bit the primary thread ends as well as at that topographic point are no running daemon threads).


That’s all close Why yous should non exercise System.exit() within Java application. It tin flaming survive unsafe as well as potentially shutdown whole server, which is hosting other critical Java application. For illustration if yous receive got to a greater extent than than i application inwards tomcat as well as i of them telephone weep upward System.exit() thus whole tomcat volition survive shutdown as well as all other spider web application volition also survive shutdown. As a security internet or Insurance, yous must enable Security Manager of your Server. It catches a lot of security problems! Including intentional as well as unintentional telephone weep upward to System.exit() or Runtime.exit(), turning it into an exception rather than shutting downwardly the whole JVM. You are relatively condom to exercise System.exit() inwards ascendency describe of piece of occupation Java application, every bit they run on their ain JVM as well as tin flaming survive used to signal a success as well as failure past times returning dissimilar condition code inwards instance of failure.

Further Learning
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