By extending OGSA-DAI's base exception classes you can write exceptions that exploit OGSA-DAI's internationalization functionality.

This page assumes that you are familiar with OGSA-DAI's support for internationalization, message bundles, message IDs and error IDs as described earlier in on Chapter 117, How to register message bundles and on Chapter 118, How to log internationalized messages.

First you should decide whether you wish your exception to be checked or unchecked and declare your exception to extend the appropriate OGSA-DAI class:

For example:

package com.example;

import uk.org.ogsadai.exception.DAIException;

public class MyNewException extends DAIException 
{
    // Exception in progress - see below for more of the body.
}

You should now define an error ID for your exception. We described this already in Section 118.3, “How to define error IDs”

So, our example exception would now look like the following:

package com.example;

import uk.org.ogsadai.exception.DAIException;
import uk.org.ogsadai.exception.ErrorID;

public class MyNewException extends DAIException 
{
    // Declaration of error ID constant whose value is a
    // unique namespace-qualified error key.
    private static final ErrorID MY_NEW_ERROR =
        new ErrorID("com.example.MY_NEW_ERROR");

    // Exception in progress - see below for more of the body.
}

Similarly, you should ensure that your message bundle has an entry for the error key associated with your error ID. For example:

com.example.MY_NEW_ERROR=A bad value was encountered. The value was {0} when I was expecting {1}.

You can now complete your exception by providing a constructor. This should pass the error ID to the super-class constructor and also any parameters required by the associated error key as specified in the message bundle.

Arguments required by the associated error key, as specified in a message bundle, should be provided a java.lang.Object array with the entries in the array in the same order as the placeholders in the message string associated with the error key. For example:

package com.example;

import uk.org.ogsadai.exception.DAIException;
import uk.org.ogsadai.exception.ErrorID;

public class MyNewException extends DAIException 
{
    // Declaration of error ID constant whose value is a
    // unique namespace qualified ID.
    private static final ErrorID MY_NEW_ERROR =
        new ErrorID("com.example.MY_NEW_ERROR");

    public MyNewException(String badValue, String expectedValue)
    {
        // Note how the order of values in the array matches that
        // expected by the message bundle entry for error key
        // com.example.MY_NEW_ERROR shown above.
        super(MY_NEW_ERROR, new Object[] {badValue, expectedValue});
    }
}

To link exceptions into causal chains you can use the standard java.lang.Throwable initCause(Throwable) method, e.g.

package com.example;

import uk.org.ogsadai.exception.DAIException;
import uk.org.ogsadai.exception.ErrorID;

public class MyOtherNewException extends DAIException 
{
    private static final ErrorID MY_OTHER_NEW_ERROR =
        new ErrorID("com.example.MY_OTHER_NEW_ERROR");

    public MyOtherNewException(String badValue, String expectedValue,
                               Throwable cause)
    {
        super(MY_OTHER_NEW_ERROR, new Object[]{badValue, expectedValue});
        // Set up the causal chain.
        super.initCause(cause);
    }
}