Logging method for thrown exception

1
votes

I have methods that are defined as...

public static void myMethod throws IOException ....

how can I use the Logger class to log the exception that is thrown to a file say named "test.log". I've heard of using logger.throwing... but it doesn't seem to work. Could anyone give me a step by step tip on how to do this? I just basically need to log the exception that is thrown (I didn't use try catches). Thank you so much!

3
javaexceptionlogging
Where do you want to log to? To the console? A file? A data base? - Yogu
How do you intend to log the Exception without catching it anywhere? - Peter Lawrey
I want to log to a file named "test.log". - user941401

3 Answers

2
votes

You'll need to add a catch clause. Below is a start for using the java.util.logging.Logger. Note that many projects use an Apache logger which is a bit more powerful and more complicated. Let's say you have a class com.myCompany.Foo that reads some file stuff

typically, at the start of the class in the static field declarations you will have

private static final Logger LOGGER = Logger.getLogger("com.myCompany.Foo");

then, when you have a method that throws exceptions (this is a stupid method!)

int readFirstCharOfFile(File f) throws IOException {
   FileReader reader = null;
   try {
      reader = new FileReader(f);
      return reader.read();
   }
   catch (IOException ioe) {
      // You have a lot of possibilities here, but this seems most reasonable
      LOGGER.log(Level.SEVERE, ioe.getMessage(), ioe);

      // whether you rethrow the Exception "depends" on the contract, but, in our case
      // the method declaration says that we do, so we do.
      throw ioe;
   }
   finally {
      if (reader != null)
         reader.close();
   }
}

The harder part is configuring the Logger to write where you want. IIRC, by default it goes to standard error. There is a lot of "magic" there that I never fully understood so I couldn't explain all the intricacies.

You can Google to get info, here are a couple useful links I found. link1 and link2

0
votes

If you want a more automatic approach than the one given by user949300, you could take a look at Aspect-Oriented Programming (AOP), which allows you to do exception logging for all methods with just a little bit of code. Just google for aspectj log exceptions or java aop log exceptions.

See also question Audit Java: system to detect exceptions thrown / caught (aop?)

0
votes

Try to use jcabi-aspects and its @LogException annotation:

public class Resource {
  @LogExceptions
  public String load(URL url) {
    return url.openConnection().getContent();
  }
}