Writing any thrown/runtime exception to a '.log' file | Java Community | Help. Code. Learn. | Page 1

median dagger Feb 8, 2023, 2:43 PM

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I have created my own logging class for handling writes to a ".log" file and want to print out any exceptions that are thrown outside my own "try-catch" statements or throw new calls. For example, if an image file in specified URL is not found, it throws a NullPointerExceptionat runtime, which is not handled by me, but by Java itself.

I want to log those runtime exceptions to my logfile, but it does not seem to write them (or perhaps recognise them)

Here is the code to my method that writes to a log file:

  public void writeLog(String message, Throwable t) {
    File logDirectory = FileHelper.createDirectory(FileHelper.workingDirectory, "logs");
    File logFile = new File(logDirectory, this.logFileName);
    if (!logFile.exists()) {
      try {
        boolean created = logFile.createNewFile();
        if (!created) {
          throw new IOException("Failed to create log file");
        }
      } catch (IOException ioe) {
        ioe.printStackTrace();
      }
    }

    try (FileWriter fw = new FileWriter(logFile, true)) {
      if (!this.isSystemMessageWritten(logFile)) {
        this.writeSystemMessage(fw);
      }
      fw.write(String.format("%s%n", message));

      try (PrintWriter pw = new PrintWriter(fw)) {
        t.printStackTrace(pw);
      }
    } catch (IOException ioe) {
      ioe.printStackTrace();
    }
  }

upper stirrupBOT Feb 8, 2023, 2:43 PM

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TIP: Narrow down your issue to simple and precise questions to maximize the chance that others will reply in here.

median dagger Feb 8, 2023, 2:44 PM

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For testing purposes, I decided to intentionally set the wrong filename for the following method:

  public static Image readImageFile(Class<?> clazz, String name) {
    try {
      URL input = clazz.getClassLoader().getResource(name);
      Objects.requireNonNull(input, "input == null!");
      return ImageIO.read(input);
    } catch (IOException ioe) {
      LoggerHelper.logError("Failed to read image", ioe, true);
      return new ImageIcon(new byte[768]).getImage();
    }
  }

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And so when I run the application through a debugger, I get this:

[main] INFO ee.twentyten.config.LauncherConfig - load: "C:\Users\Kasutaja\AppData\Roaming\.twentyten\twentyten.properties"
[main] INFO ee.twentyten.request.HttpsConnectionResponse - getJsonResponse: 204 No Content (https://authserver.mojang.com/validate)
[main] INFO com.mojang.util.YggdrasilHelper - validate: {}
Exception in thread "AWT-EventQueue-0" Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException: input == null!
    at java.util.Objects.requireNonNull(Objects.java:226)
    at ee.twentyten.util.FileHelper.readImageFile(FileHelper.java:34)
    at ee.twentyten.ui.LauncherFrame.<init>(LauncherFrame.java:52)
    at ee.twentyten.ui.LauncherFrame$2.run(LauncherFrame.java:114)
    at java.awt.event.InvocationEvent.dispatch$$$capture(InvocationEvent.java:312)<14 internal lines>

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but it doesn't log the exception

south knot Feb 8, 2023, 2:46 PM

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Why not add a second catch block for a generic exception and log it there?

median dagger Feb 8, 2023, 2:46 PM

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this is outside a catch block though

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this is the JVM runtime exception

south knot Feb 8, 2023, 2:46 PM

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You can still catch null pointer exceptions

median dagger Feb 8, 2023, 2:47 PM

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yeah, but what if some other runtime exception happens?

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i can't just manually try adding each and every one of 'em

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that produces boilerplate

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i'm already handling various try-catch exceptions manually.

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runtime should be based on whichever is being thrown

south knot Feb 8, 2023, 2:48 PM

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all exceptions (usually) are a subclass of Exception (or getting even more generic, Throwable) so a single catch block for exception handles every single kind of exception

median dagger Feb 8, 2023, 2:48 PM

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ooooooooooooooh

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hmmmm

south knot Feb 8, 2023, 2:49 PM

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So if there’s any specific exceptions you care about, you can catch those, and then have a catch Exception at the end as a catch all.

median dagger Feb 8, 2023, 2:49 PM

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i have caught any exception i could think of that is needed in any of my try-catch statements

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i have yet to test if those work

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but the runtime ones i can't seem to figure out

south knot Feb 8, 2023, 2:49 PM

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It’s not super best practice, since someone reading your code might not know what exceptions to expect, but it’ll work.

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All runtime exceptions extend RuntimeExceptiom, so same basic principle

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https://docs.oracle.com/javase/8/docs/api/java/lang/NullPointerException.html

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median dagger Feb 8, 2023, 2:50 PM

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For example, this code manually handles these:

  public static void setLookAndFeel() {
    try {
      UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
    } catch (UnsupportedLookAndFeelException ulafe) {
      LoggerHelper.logError(ulafe.getMessage(), ulafe, true);
    } catch (ClassNotFoundException cnfe) {
      LoggerHelper.logError("Can't find look and feel class", cnfe, true);
    } catch (InstantiationException ie) {
      LoggerHelper.logError("Can't instantiate look and feel class", ie, true);
    } catch (IllegalAccessException iae) {
      LoggerHelper.logError("Can't access look and feel class", iae, true);
    }
  }

I have yet to try if manual try-catch variants work, but that's beside the main problem

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i need a way to report any thrown exception that's outside my control (e.g. JVM runtime)

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and write it onto the file

south knot Feb 8, 2023, 2:51 PM

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If you want to handle an exception, it needs to be in a try catch

median dagger Feb 8, 2023, 2:51 PM

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my logger takes a throwable

south knot Feb 8, 2023, 2:51 PM

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But it works it’s way up the stack trace

median dagger Feb 8, 2023, 2:51 PM

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so "exception instanceof throwable" ?

south knot Feb 8, 2023, 2:52 PM

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Exceptions are Throwable

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median dagger Feb 8, 2023, 2:52 PM

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ah

south knot Feb 8, 2023, 2:53 PM

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It might be worth looking a bit into inheritance and how to use the java api documentation, since it’ll help you solve similar problems a bit better.

median dagger Feb 8, 2023, 2:53 PM

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well, it seems that wrapping anything in my main class in a throwable does not work

south knot Feb 8, 2023, 2:54 PM

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Wrapping with a throwable?

median dagger Feb 8, 2023, 2:54 PM

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try-catch and catch a Throwable

south knot Feb 8, 2023, 2:56 PM

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That’s weird. You should be able to catch a throwable

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What’s your syntax?

median dagger Feb 8, 2023, 2:56 PM

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I don't get it

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what syntax?

south knot Feb 8, 2023, 2:56 PM

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What’s your code

median dagger Feb 8, 2023, 2:57 PM

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where?

south knot Feb 8, 2023, 2:57 PM

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Main

median dagger Feb 8, 2023, 2:57 PM

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  public static void main(String[] args) {
    if (RuntimeHelper.MAX_MEMORY < RuntimeHelper.MIN_MEMORY) {
      List<String> arguments = new ArrayList<>();
      arguments.add(EPlatform.getPlatform() == EPlatform.WINDOWS ? "javaw" : "java");
      arguments.add("-Xmx1024m");
      arguments.add("-Dsun.java2d.d3d=false");
      arguments.add("-Dsun.java2d.opengl=false");
      arguments.add("-Dsun.java2d.pmoffscreen=false");
      arguments.add("-cp");
      arguments.add(System.getProperty("java.class.path"));
      arguments.add(String.valueOf(Launcher.class));

      ProcessBuilder pb = new ProcessBuilder(arguments);
      try {
        Process process = pb.start();

        LoggerHelper.logInfo(pb.command().toString(), true);
        if (process.waitFor() != 0) {
          System.exit(process.exitValue());
        }
      } catch (IOException ioe) {
        JOptionPane.showMessageDialog(null,
            String.format("An error occurred while starting the process:%n%s", ioe.getMessage()),
            "Error", JOptionPane.ERROR_MESSAGE);

        LoggerHelper.logError("Failed to start the process", ioe, true);
      } catch (InterruptedException ie) {
        JOptionPane.showMessageDialog(null,
            String.format("An error occurred while waiting for the process to terminate:%n%s",
                ie.getMessage()), "Error", JOptionPane.ERROR_MESSAGE);

        LoggerHelper.logError("Failed to wait for process to terminate", ie, true);
      }
    } else {
      LauncherFrame.main(args);
    }
  }

I removed the try-catch because it did nothing

south knot Feb 8, 2023, 2:58 PM

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I’m trying to see the try catch

median dagger Feb 8, 2023, 2:58 PM

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it would just be wrapped around

south knot Feb 8, 2023, 2:58 PM

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Since you said it doesn’t work

median dagger Feb 8, 2023, 2:58 PM

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and it makes no difference

south knot Feb 8, 2023, 2:58 PM

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It should, and that’s why I’d like to see why it doesn’t

median dagger Feb 8, 2023, 2:59 PM

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perhaps voice channel for real-time edits while chatting here?

south knot Feb 8, 2023, 2:59 PM

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Can’t right now

median dagger Feb 8, 2023, 2:59 PM

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okay.

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i meant muted but yes

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  public static void main(String[] args) {
    try {
      if (RuntimeHelper.MAX_MEMORY < RuntimeHelper.MIN_MEMORY) {
        List<String> arguments = new ArrayList<>();
        arguments.add(EPlatform.getPlatform() == EPlatform.WINDOWS ? "javaw" : "java");
        arguments.add("-Xmx1024m");
        arguments.add("-Dsun.java2d.d3d=false");
        arguments.add("-Dsun.java2d.opengl=false");
        arguments.add("-Dsun.java2d.pmoffscreen=false");
        arguments.add("-cp");
        arguments.add(System.getProperty("java.class.path"));
        arguments.add(String.valueOf(Launcher.class));

        ProcessBuilder pb = new ProcessBuilder(arguments);
        try {
          Process process = pb.start();

          LoggerHelper.logInfo(pb.command().toString(), true);
          if (process.waitFor() != 0) {
            System.exit(process.exitValue());
          }
        } catch (IOException ioe) {
          JOptionPane.showMessageDialog(null,
              String.format("An error occurred while starting the process:%n%s", ioe.getMessage()),
              "Error", JOptionPane.ERROR_MESSAGE);

          LoggerHelper.logError("Failed to start the process", ioe, true);
        } catch (InterruptedException ie) {
          JOptionPane.showMessageDialog(null,
              String.format("An error occurred while waiting for the process to terminate:%n%s",
                  ie.getMessage()), "Error", JOptionPane.ERROR_MESSAGE);

          LoggerHelper.logError("Failed to wait for process to terminate", ie, true);
        }
      } else {
        LauncherFrame.main(args);
      }
    } catch (Throwable t) {
      JOptionPane.showMessageDialog(null,
          String.format("An error occurred while starting the launcher:%n%s", t.getMessage()),
          "Error", JOptionPane.ERROR_MESSAGE);

      LoggerHelper.logError("Failed to start launcher", t, true);
    }
  }

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it doesn't catch anything

south knot Feb 8, 2023, 3:01 PM

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How did you test that? Is it possible you already have a catch block somewhere catching your test case before it can be caught here?

median dagger Feb 8, 2023, 3:02 PM

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by running the same code

soft hornet Feb 8, 2023, 3:05 PM

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where do you expect the exception to be thrown?

median dagger Feb 8, 2023, 4:02 PM

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well, for testing purposes, it's thrown at exactly here

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well, i partially fixed an issue, and it's got a new problem

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in the log area

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the throwable is null...?

median dagger Feb 8, 2023, 4:32 PM

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ok, i'll try testing it in another way

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not from image input, but in other way

median dagger Feb 8, 2023, 5:07 PM

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Well, I got the main method's throwable working, but the logging is still thinking that the throwable is null

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i don't get it

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Now when doing something, it shows this:

[ERROR] ee.twentyten.request.HttpsConnectionImpl - Failed to write to output stream
java.lang.NullPointerException: t == null!
    at ee.twentyten.log.LauncherLogger.writeLog(LauncherLogger.java:181)
    at ee.twentyten.util.LoggerHelper.logError(LoggerHelper.java:83)
    at ee.twentyten.request.HttpsConnectionImpl.performJsonRequest(HttpsConnectionImpl.java:178)
    at ee.twentyten.util.RequestHelper.performJsonRequest(RequestHelper.java:65)
    at com.mojang.YggdrasilAuthenticationImpl.validate(YggdrasilAuthenticationImpl.java:38)
    at com.mojang.util.YggdrasilHelper.validate(YggdrasilHelper.java:32)
    at com.mojang.util.YggdrasilHelper.isSessionExpired(YggdrasilHelper.java:54)
    at ee.twentyten.ui.LauncherFrame.main(LauncherFrame.java:106)
    at ee.twentyten.Launcher.main(Launcher.java:48)

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I did adjust this just to see if it's null or not:

   try (FileWriter fw = new FileWriter(logFile, true)) {
      if (this.isSystemMessageWritten(logFile)) {
        this.writeSystemMessage(fw);
      }
      fw.write(String.format("%s%n", message));

      try (StringWriter sw = new StringWriter(); PrintWriter pw = new PrintWriter(sw)) {
        if (t == null) {
          t = new NullPointerException("t == null!");
          t.printStackTrace(pw);
        }
        fw.write(String.format("%s%n", sw));
      }
    } catch (IOException ioe) {
      ioe.printStackTrace();
    }

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and I don't get it

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why is it null when I'm passing it over?

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I'm literally trying to catch whatever is being thrown

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so why this?

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It's supposed to throw an IOException for [ERROR] ee.twentyten.request.HttpsConnectionImpl - Failed to write to output stream

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I FIXED IT!

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Let me tell you how

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I went back to my logError code...

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  public static void logError(String message, Throwable t, boolean written) {
    Throwable cause = t.getCause() != null ? t.getCause() : t;
    if (DEBUG_MODE) {
      Logger logger = LoggerFactory.getLogger(LoggerHelper.getCallerClassName());
      logger.error(String.format("%s: %s", LoggerHelper.getCallerMethodName(), message), cause);
    }

    if (written) {
      String outputMessage = String.format("[ERROR] %s - %s", LoggerHelper.getCallerClassName(),
          message);
      LOGGER.writeLog(outputMessage, cause);
    }
  }

And added a ternary condition for the cause

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also moved the "printStackTrace" outside the "if null" statement in the other file

#Writing any thrown/runtime exception to a '.log' file