How to Handle \'Cannot Format Object as Date\' Exception in Java?

Cannot Format Object as Date in Java

In Java, when trying to format a given object as a date using the DateFormat.format method, you may encounter the following exception:

java.lang.IllegalArgumentException: Cannot format given Object as a Date

This error occurs when the object you attempt to format is not a Date instance. In your case, you are attempting to format a string ("2012-11-17T00:00:00.000-05:00") as a date using a SimpleDateFormat instance configured with the "mm/yyyy" pattern.

Solution

To address this issue, you should use two SimpleDateFormat objects: one for parsing the input string into a Date instance and another for formatting the resulting Date into the desired format:

<code class="java">import java.text.SimpleDateFormat;
import java.util.Date;

public class DateParser {

    public static void main(String args[]) {
        String monthYear = null;

        // Create input format to parse from "yyy-MM-dd'T'HH:mm:ss.SSSX"
        SimpleDateFormat inputFormat = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSSX");

        // Create output format to format to "MM/yyyy"
        SimpleDateFormat outputFormat = new SimpleDateFormat("MM/yyyy");

        String inputText = "2012-11-17T00:00:00.000-05:00";

        try {
            // Parse the input string into a Date object
            Date date = inputFormat.parse(inputText);

            // Format the parsed Date into the desired format
            monthYear = outputFormat.format(date);

            System.out.println(monthYear);
        } catch (ParseException e) {
            System.err.println("Input string is not a valid date: " + e.getMessage());
        }
    }
}</code>

This approach separates the parsing and formatting operations, ensuring that the input is properly converted to a Date instance before attempting to format it using the specified pattern.

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