ParseException in Java

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In this article, we will learn what is ParseException in Java, its common causes, example, solutions and best practices.
 
ParseException is a checked exception in Java and is a member of java.text package. It signals that an error has been reached unexpectedly while parsing. This usually happens when a string fails to match a required format or pattern. 

ParseException Class Diagram

Java ParseException Example

In this example, we use DateFormat.parse(String source) method which throws a ParseException object.
This parse() method throws ParseException - if the beginning of the specified string cannot be parsed.
Here is a complete code to throw a ParseException exception:
package com.javaguides.corejava;

import java.text.DateFormat;

import java.text.ParseException;
import java.text.SimpleDateFormat;

public class ParseExceptionExample {

    public static void main(String[] args) {

        DateFormat format = new SimpleDateFormat("MM, dd, yyyy");

        try {
            format.parse("01, , 2010");
        } catch (ParseException e) {
            System.err.println("ParseException caught!");
            e.printStackTrace();
        }
    }
}
Output:
ParseException caught!
java.text.ParseException: Unparseable date: "01, , 2010"
 at java.text.DateFormat.parse(DateFormat.java:366)
 at com.javaguides.corejava.ParseExceptionExample.main(ParseExceptionExample.java:15)

Common Causes

Mismatched Formats: Parsing a string that doesn't match the expected format, like in the date example above. 

Unrecognized Symbols: When the string contains characters or symbols that the parser does not recognize. 

Invalid Data: Parsing a logically incorrect value (e.g., 13th month, as seen in the example). 

Solutions and Best Practices 

1. Input Validation 

Before attempting to parse, ensure the input string broadly matches the expected format. This might involve simple checks like verifying the length of a string or using regular expressions for more complex validations. 

2. Detailed Error Messages 

When catching a ParseException, you can access its message to get detailed information about the nature of the error. This can be extremely helpful for debugging or providing feedback to the user. 

3. Alternative Parsing Strategies 

In some scenarios, instead of relying on a single strict format, you might consider using multiple parsers in a chain, attempting to parse with each one until successful. 

4. Use Third-party Libraries 

There are numerous Java libraries that offer enhanced parsing capabilities, often with better error messages and flexible parsing strategies. For date and time parsing, the java.time package (introduced in Java 8) offers superior capabilities compared to the older SimpleDateFormat. 

5. Graceful Fallback 

In some cases, if a string can't be parsed, it might be appropriate to either provide a default value or to ask the user for clarification. 

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