Setting default System.exit codes in Java?
And then in the code, something like: Solution 3: Could you abstract out the «system exiting» into a new dependency, so that in your tests you could just have a fake which records the fact that exit has been called (and the value), but use an implementation which calls in the real application? exit codes are exclusively used by parties and applications outside of the program for debugging and handling purposes.
Setting default System.exit codes in Java?
I have a C# app that runs a jar file and uses the System.exit code as a return value. A console window is displayed as a part of this jar, and if the user closes it (thereby terminating the jar) it returns an exit code of 143 . The problem is that 143 (or any positive integer) could be a valid exit code if the jar completes successfully.
I need a way to manually set the System.exit code to a negative integer. Treating 143 as an exception in the C# app is out of the question.
The argument serves as a status code; by convention, a nonzero status code indicates abnormal termination.
If you really want to ignore that, and both the Java and the C# apps are in your hand, an easy workaround is to add 1000 to your System.exit return value in Java, when the jar completes.
Your C# application will recognize the successful execution by a return code >= 1000 and subtract it again. 143 is below 1000 and thus an error.
Acording to the java documentation you can use system.exit(int n), so just put a negative number as a parameter, also by convention, a nonzero status code indicates abnormal termination.
Where does the system.exit() goes to in Java?, The exit status or return code of a process in computer programming is a small number passed from a child process (or callee) to a parent process (or caller) when it has finished executing a specific procedure or delegated task. Here’s a little Java test to demonstrate it
Alternates for System.exit that could send error codes to batch or shell
I have a set of error codes in my java application. Currently I’m using System.exit(code); to return error codes from the application to external applications. Is there any alternatives of System.exit as using this is bad practice because it may shutdown the entire JVM.
I have shared your experience in the past, and tried to engineer out System.exit() . One possibility is to leave a RuntimeException uncaught and you will return 1 to the shell, but ultimately if you want any more versatility than that (and don’t want an ugly stack-trace polluting your output), you must have at least «one» call to System.exit() .
$ java Splat $ echo $? > 0 $ java Splat splat > Exception in thread "main" java.lang.RuntimeException: splat > at Splat.main(Splat.java:9) $ echo $? > 1 My reason for doing this was our organisation started using static analysis results from sonar as a KPI and it was my job to get the numbers down. It’s a terrible reason for doing anything, but an interesting engineering challenge nonetheless .
An approach I tried was throwing a specific class of RuntimeException , with an exit-code instance variable, and catching it at the outer scope. That way you can be sure that when you do murder the VM you’re at the tail of the stack anyway .
public class Splat < public static final class Exit extends RuntimeException < private int exitCode; public Exit(int exitCode) < this.exitCode = exitCode; >> public static void main(String[] args) < try < wrappedMain(args); >catch (Exit e) < System.exit(e.exitCode); >> public static void wrappedMain(String[] args) < if (args.length >0 && "splat".equals(args[0])) < int code = (args.length >1) ? Integer.parseInt(args[1]) : 0; throw new Exit(code); > > > $ java Splat $ java Splat splat $ echo $? > 0 $ java Splat splat 1 $ echo $? > 1 > $ java Splat splat 2 $ echo $? > 2 $ java Splat splat -1 $ echo $? > 127 There are caveats to this approach of course! It is a bit of an odd way to exit and anybody unfamiliar with your constraints will scratch their head. Also, if somebody does catch (Throwable t) later on, then you wont be able to exit. If you are working in a static analysis CI environment then that should be quickly highlighted as a more grievous violation!
As already commented: When you wait for some code in a batch or shell you are actually waiting for the program to finish and that means your java program exits and so does the JVM. And the one and only way is then to use System.exit(code) as you are already doing.
If you are talking about the exit code of a process then System.exit(int) is the way to go since you want the whole process to exit and so the JVM should shutdown as well.
But if you want to send out some error messages to the batch or shell (without exiting the process) then you will have to use System.err.println() . This will write to the error stream instead of the output stream.
When should we call System.exit in Java, System.exit never exits normally because the call will block until the JVM is terminated. It’s as if whatever code is running that has the power plug pulled on it before it can finish. Calling System.exit will initiate the program’s shutdown hooks and whatever thread that calls System.exit will block until program termination.
Why do we have exit codes in Java?
In Java, we use System.exit(int) to exit the program. The reason for an «exit value» in C was that the exit value was used to check for errors in a program. But in Java, errors are reflected by an Exception being thrown, thus they can be handled easily. So why do we have exit values in Java at all?
exit values are returned to the calling program e.g. the shell. An Exception cannot be caught by an external program.
BTW When you throw an Exception it is caught by that thread or that thread dies, the finally blocks are still called for that thread. When you call system.exit(), all threads stop immediately and finally blocks are not called.
exit codes are exclusively used by parties and applications outside of the program for debugging and handling purposes. A super-application can definitely handle a return code better than trying to parse a stack trace.
Also, if you are creating an application for an end-user, you would much rather exit gracefully from your app than post a bunch of stack trace information, for a couple of reasons: one, you will just be scaring them with lots of crazy-looking techno-gibberish, and two, stack traces often reveal sensitive and confidential information about the way the program is structured fundamentally (giving a potential attacker more knowledge about the system).
For a real-world example, I was working on a Java Batch program which used exit codes for its jobs. A user could see whether the job executed successfully or not based on whether the exit code was «0». If it was anything else, they could contact technical support, armed with the additional information of the exit code, and the help desk would have all the necessary information based on that exit code to help them out. It works much nicer than trying to ask a non-technical end-user, «Okay, so what Exception are you getting?»
exit values are returned to the callers to signal the successful or insuccessful completion of the program. The caller may not be able to catch the exception and handle it accordingly.
For eg. 0 exit value means successful completion whereas non-zero return value means some error in execution.
Also, System.exit() will make all the threads in the application to stop at that point itself.
Long story short, Exit codes are simplified signals to the user who encounters an exception while running a Java program. Since we assume that most of the users do not understand stack trace data of an exception, these simple non zero custom code will tell them that something is wrong and this should be reported to the vendor. So the vendor gets the code and he knows the stack trace associated with that code and tries to repair the system. This is an abstraction provided by the programmers so that users don’t have to read and report voluminous stack traces. A very good analogy here is the getErrorCode() method in SqlException Class. This method also closes the current JVM that is running on the client machine. This implies that this terminates all the threads that are in the JVM. This method calls the exit method in the class Java.lang.Runtime. If you go to the documentation of this method, you will understand how virtual machine is shut down.
This is the link http://docs.oracle.com/javase/6/docs/api/java/lang/Runtime.html#exit%28int%29
Java — How to capture System.exit event?, The function Runtime.addShutdownHook (Thread thehook) allows you to register a hook into the Java Virtual Machine. The hook works as an initialized but unstarted thread, which will be called by the JVM on exit. In case you register more than one hook, note that the order in which the hooks are called is …
Dealing with System.exit(0) in JUnit tests
I am implementing some tests for an existing Java Swing application, so that I can safely refactor and extend the code without breaking anything. I started with some unit tests in JUnit, since that seems the simplest way to get started, but now my priority is to create some end-to-end tests to exercise the application as a whole.
I am starting the application afresh in each test by putting each test method in a separate test case, and using the fork=»yes» option in Ant’s junit task. However, some of the use cases I would like to implement as tests involve the user exiting the application, which results in one of the methods calling System.exit(0). This is regarded by JUnit as an error: junit.framework.AssertionFailedError: Forked Java VM exited abnormally .
Is there a way to tell JUnit that exiting with a return code of zero is actually OK?
The library System Rules has a JUnit rule called ExpectedSystemExit. With this rule you are able to test code, that calls System.exit(. ):
public class MyTest < @Rule public final ExpectedSystemExit exit = ExpectedSystemExit.none(); @Test public void systemExitWithArbitraryStatusCode() < exit.expectSystemExit(); /* the code under test, which calls System.exit(. ) * with an arbitrary status */ >@Test public void systemExitWithSelectedStatusCode0() < exit.expectSystemExitWithStatus(0); //the code under test, which calls System.exit(0) >> System Rules needs at least JUnit 4.9.
Full disclosure: I’m the author of System Rules.
How I deal with that is to install a security manager that throws an exception when System.exit is called. Then there is code that catches the exception and doesn’t fail the test.
public class NoExitSecurityManager extends java.rmi.RMISecurityManager < private final SecurityManager parent; public NoExitSecurityManager(final SecurityManager manager) < parent = manager; >public void checkExit(int status) < throw new AttemptToExitException(status); >public void checkPermission(Permission perm) < >> And then in the code, something like:
catch(final Throwable ex) < final Throwable cause; if(ex.getCause() == null) < cause = ex; >else < cause = ex.getCause(); >if(cause instanceof AttemptToExitException) < status = ((AttemptToExitException)cause).getStatus(); >else < throw cause; >> assertEquals("System.exit must be called with the value of " + expectedStatus, expectedStatus, status); Could you abstract out the «system exiting» into a new dependency, so that in your tests you could just have a fake which records the fact that exit has been called (and the value), but use an implementation which calls System.exit in the real application?
If anybody needs this functionality for JUnit 5, I’ve written an extension to do this. This is a simple annotation you can use to tell your test case to expect and exit status code or a specific exit status code.
For example, any exit code will do:
If we want to look for a specific code:
Java — When to use system.exit(0)?, The input to System.exit is your error code. A value of 0 means normal exit. A non zero number will indicate abnormal termination. This number can be up to you. Perhaps if you want to exit if you cannot read a file you could use error code =1, if you cannot read from a socket it could be error code = 2.
Exit codes in Java – System.exit() method
This post will discuss the System exit codes in Java.
The System.exit(int) is the conventional and convenient means to terminate the currently running Java virtual machine by initiating its shutdown sequence. The argument of the exit() method serves as a status code to denotes the termination status. The argument can be either zero or nonzero:
1. Zero
The zero status code should be used when the program execution went fine, i.e., the program is terminated successfully.
2. Non-Zero
A nonzero status code indicates abnormal termination. Java allows us to use different values for different kinds of errors. A nonzero status code can be further positive or negative:
Positive status codes are often used for user-defined codes to indicate a particular exception.
Negative status codes are system generated error codes. They are generated due to some unanticipated exception, system error, or forced termination of the program.
- There are no pre-defined constants in Java to indicate SUCCESS and FAILURE messages.
- We should always use the proper status codes if our application interact with some tools or the program is called within a script.
- System.exit() method internally calls exit() method of the Runtime class. Therefore, the call System.exit(n) is effectively equivalent to the call: Runtime.getRuntime().exit(n) .
That’s all about exit codes in Java.
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