How can I set the message on an exception in Java?

Question

I want to set a custom exception message. However, I'm unsure of how to do this. Will I need to create a custom exception class or is there an easier way of doing this?

Even java.lang.Exception (http://docs.oracle.com/javase/1.5.0/docs/api/java/lang/Exception.html) has a constructor with a String. — anubhava, Jan 17 '12 at 13:10

score 40 · Answer 1 · answered Jan 17 '12 at 13:07

Most standard exception classes provide a constructor that takes a mesage, for example:

public UnsupportedOperationException(String message) {
    super(message);
}

The above class simply calls its parent's constructor, which calls its parent's constructor, and so on, ultimately culminating in:

public Throwable(String message) {
    ...
}

If you create your own exception class, I think it's a good idea to following this convention.

score 22 · Answer 2 · edited Nov 12 '15 at 09:49

You can only set the message at the creation of the exception. Here is an example if you want to set it after the creation.

public class BusinessException extends RuntimeException{

    private Collection<String> messages;

    public BusinessException(String msg){
        super(msg);
    }


    public BusinessException(String msg, Exception cause){
        super(msg, cause);
    }


    public BusinessException(Collection<String> messages){
        super();
        this.messages= messages;
    }


    public BusinessException (Collection<String> messages, Exception cause){
        super(cause);
        this.messages= messages;
    }

    @Override
    public String getMessage(){
        String msg;

        if(this.messages!=null && !this.messages.isEmpty()){
            msg="[";

            for(String message : this.messages){
                msg+=message+",";
            }

            msg= StringUtils.removeEnd(msg, ",")+"]";

        }else msg= super.getMessage();

        return msg;
    }

}

score 15 · Accepted Answer · answered Jan 17 '12 at 13:08

15

Well, if the API offers an exception that suits your needs (IllegalArgumentException for example), just use it and pass your message in the constructor.

answered Jan 17 '12 at 13:08

quaylar

2,617
1
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31

score 3 · Answer 4 · answered Jan 17 '12 at 13:09

3

The best approach is to wrap the exception.

try {
    my code that throws E;
} catch (final E e) {
    throw new MyE("my message", e);
}

answered Jan 17 '12 at 13:09

Sam

2,939
19
17

score 3 · Answer 5 · edited Sep 01 '20 at 00:50

3

The Exception class (its parent, actually - Throwable) takes a message as an argument in its constructor:

throw new Exception("message") or Exception("message", innerException);

edited Sep 01 '20 at 00:50

Peter Mortensen

30,738
21
105
131

answered Jan 17 '12 at 13:11

baruch dego

101
1
6

score 2 · Answer 6 · edited Sep 01 '20 at 00:51

The root Exception class accepts a String custom message, as do (as far as I can tell) all of derivative classes.

So: no, you don't need to create a custom class. One of the existing exceptions probably covers your case (read their descriptions to find out which). If none of those are really satisfactory, then you can create an extension of Exception (or RuntimeException, etc.) and maintain the custom message constructor.

Sakthikanth · Answer 7 · 2021-09-14T07:59:37.887

1

Try this code:

try{
    throw new Exception("Test String");
}
catch(Exception ex){
    System.out.println(ex.getMessage());
}

edited Sep 14 '21 at 07:59

answered Sep 30 '16 at 10:23

Sakthikanth

139
7

1

An explanation would be in order. Especially as it is very different from the other answers, it would be nice to see a justification for if it really answers the question. For example, what is the idea behind it? – Peter Mortensen Sep 01 '20 at 00:52

score 0 · Answer 8 · answered Jun 07 '22 at 17:09

Another variant

public class MyCustomExceptionWithoutMessageInConstructor extends IllegalArgumentException {
    private static final String ERROR_MESSAGE = "terrible error";

    public MyCustomExceptionWithoutMessageInConstructor() {
        super(ERROR_MESSAGE);
    }
}

How can I set the message on an exception in Java?

8 Answers8