What is the recommended way to escape HTML symbols in plain Java?

java

html-escaping

string-builder

security

byNikita Barsukov·Dec 16, 2024

To escape HTML symbols in Java, use StringEscapeUtils.escapeHtml4() from Apache Commons Text. This method turns characters such as <, >, &, " into <, >, &, " respectively. This way, you can protect your application from XSS attacks and ensure accurate HTML rendering.

Here's a quick example:

String safeHtml = StringEscapeUtils.escapeHtml4("<p>Example</p>");
System.out.println(safeHtml);  // Outputs: &lt;p&gt;Example&lt;/p&gt;

Exploring additional methods for HTML escaping

Efficient escaping using StringBuilder

If your application deals with mutable strings frequently, utilizing StringBuilder in combination with the escapeHTML method can significantly optimize string manipulation.

public static String escapeHtmlWithBuilder(String text) {
    StringBuilder escapedText = new StringBuilder();
    for (char c : text.toCharArray()) {
        // Do the 'switchy-switchy', escaping characters
        switch (c) {
            case '<': escapedText.append("&lt;"); break; // Transform '<' to '&lt;'
            case '>': escapedText.append("&gt;"); break; // Transform '>' to '&gt;'
            // Remember to escape '&', '"', etc.
            default: escapedText.append(c);
        }
    }
    // Ta-da! Your string is now safe to use.
    return escapedText.toString();
}

Choosing suitable libraries

Java developers are spoilt for choice when it comes to libraries providing HTML escaping utilities:

Spring Framework: For those already using Spring, HtmlUtils.htmlEscape(String input) provides consistent HTML escaping.
Google Guava: Offers HtmlEscapers.htmlEscaper(), useful for projects already relying on Guava.

Focusing on security and manual replacements

Replacing characters manually might seem straightforward, but it's less secure and more prone to mistakes. Always adhere to HTML specification and use comprehensive libraries to ward off unexpected surprises (ahem... XSS attacks).

Defense against potential threats

Mitigating HTML injection issues

Employing correct HTML escaping methods like escapeHtml from Apache Commons or equivalent functions in other libraries helps to thwart HTML injection attacks. It's like your application is a bouncer, stopping malicious code from crashing the party.

Picking the right library

Consider your project's requirements and existing technology stack when choosing a HTML escaping library. Some libraries like Apache are known for relevance across various document types. On the other hand, Spring's built-in tool excels in Spring-based applications, while Google Guava is a handy choice for projects already leveraging it.

Up-to-date knowledge

Keeping up with HTML specifications and library updates ensures optimal security. Remember, you're a developer. You have to outsmart the hackers. Having the correct version of StringEscapeUtils is also vital:

For Apache Commons Lang 2:

import static org.apache.commons.lang.StringEscapeUtils.escapeHtml;

For Apache Commons Lang 3:

import static org.apache.commons.lang3.StringEscapeUtils.escapeHtml4;

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