Fixing java.lang.IllegalArgumentException: Illegal Base64 character 3C

When working with Java applications, you may encounter the java.lang.IllegalArgumentException: Illegal Base64 character 3C error. This error occurs when trying to decode a Base64-encoded string containing an illegal character. In this post, we’ll discuss the causes of this error and provide solutions to fix it.

Understanding java.lang.IllegalArgumentException: Illegal Base64 character 3C

The java.lang.IllegalArgumentException is a subclass of the RuntimeException class, indicating that an illegal argument has been passed to a method. When decoding a Base64-encoded string, the Illegal Base64 character 3C error occurs if the string contains an illegal character, such as ‘<‘ (represented as 3C in hexadecimal).

Causes

There are several reasons why this error may occur, including:

• Manual modification of a Base64-encoded string, introducing an illegal character.
• Data corruption during transmission or storage, resulting in an illegal character.
• An improperly generated Base64-encoded string from a third-party library or service.

How to Fix java.lang.IllegalArgumentException: Illegal Base64 character 3C

To fix this error, follow these steps:

1. Identify the source of the Base64-encoded string, and ensure it is generated correctly and has not been manually modified.
2. Verify the integrity of the data during transmission and storage to prevent data corruption.
3. Use proper error handling, such as try–catch blocks, to handle IllegalArgumentException errors gracefully when decoding Base64-encoded strings.

Here is an example of using proper error handling when decoding a Base64-encoded string:

import java.nio.charset.StandardCharsets;
import java.util.Base64;

public class Main {

 public static void main(String[] args) {
 String encodedString = "aGVsbG8gd29ybGQh"; // A valid Base64-encoded string

 try {
 byte[] decodedBytes = Base64.getDecoder().decode(encodedString);
 String decodedString = new String(decodedBytes, StandardCharsets.UTF_8);
 System.out.println("Decoded string: " + decodedString);
 } catch (IllegalArgumentException e) {
 System.err.println("Error: Illegal Base64 character encountered: " + e.getMessage());
 // Additional error handling actions as needed}
    }
}

By handling the IllegalArgumentException error properly, you can prevent the application from crashing and provide a better user experience.

Best Practices to Prevent

Follow these best practices to avoid encountering the java.lang.IllegalArgumentException: Illegal Base64 character 3C error in your Java applications:

• Use reliable libraries or services to generate Base64-encoded strings.
• Never manually modify Base64-encoded strings.
• Validate the integrity of data during transmission and storage.
• Implement proper error handling when decoding Base64-encoded strings.

Conclusion

In this post, we’ve learned about the java.lang.IllegalArgumentException: Illegal Base64 character 3C error, its causes, and how to fix it. By following best practices and understanding the error’s origin, you can prevent it from occurring in your Java applications and ensure smooth execution.

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