URL encoding is a method that ensures your URL only contains valid characters so that the receiving server can correctly interpret it. According to the RFC 3986 standard, URIs (which are a superset of URLs) only contain a limited set of characters consisting of digits, letters, and a few graphic symbols, all within the ASCII character set. If a URL contains characters outside this limited set, the characters must be percent-encoded. Percent-encoding means a character is converted into a two-digit hexadecimal representation of eight bits with the % escape character ahead of them. The purpose of URL encoding is not to hide parts of a URL from an outside observer but rather to ensure that the URL is easily and unequivocally interpretable by the receiving server; and to prevent manipulation of the URL by the user of the client that is constructing and sending the URL. Failure to encode a URL can result in various issues, including your application being unable to compose the URL to send it to the server, or the server receiving the URL may be unable to parse it correctly, leading to an error response. Not encoding URL parameters can expose your application to potential security threats. Each programming language provides one or more APIs for encoding and decoding URLs. In Java, URL encoding and decoding are important for processing free-form data that a visitor enters in an HTML form, constructing calls to an external API from code by adding query parameters to a base URL, and constructing calls to an API gateway used for further request routing to internal services. The process of encoding URLs in Java typically involves using the java.net.URLEncoder class and its encode() method, which ensures all alphanumeric characters are intact and converts other characters into percent-encoded hexadecimal representations. There are three overloads of the encode() method, including one that allows explicitly setting the encoding scheme as a string and another that uses the StandardCharsets.UTF_8 constant to eliminate typos and checked exceptions. URL decoding in Java can be done using the java.net.URLDecoder.decode() method, which converts percent-encoded characters back to their original form. Best practices for URL handling in Java include not skipping URL encoding, explicitly encoding parameter values when constructing new URLs, and using standard libraries like URLEncoder and URLDecoder for reliable encoding and decoding. Additionally, validating user data, including user data coming via URLs on the server-side, concerning both syntax and semantics is crucial to ensure the security of your application. The Snyk Security extension for IntelliJ IDEA can help identify issues with unsanitized input from URL parameters, potentially leading to cross-site scripting (XSS), command injection, server-side request forgery (SSRF), or open redirect vulnerabilities.