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A Java template engine for generating HTML, email, configuration files, and source code from templates.
Apache FreeMarker is a Java-based template engine first released in 1999, now maintained under the Apache Software Foundation. It generates text output — HTML pages, emails, configuration files, source code, and more — by combining templates with data models provided by Java applications. FreeMarker follows a strict MVC separation, keeping presentation logic in templates and business logic in Java code. The template language supports variables, conditionals, loops, macros, functions, and string operations, providing enough power for complex rendering without crossing into general-purpose programming.
FreeMarker has been a cornerstone of the Java web ecosystem for over two decades, used extensively in frameworks like Apache Struts, Spring MVC, and various CMS platforms. Its auto-escaping capabilities help prevent XSS vulnerabilities in HTML output, while its configurable template loading supports classpath, file system, and database-backed template storage. The engine processes templates with high performance through compiled template caching and lazy evaluation. FreeMarker supports multiple output formats beyond HTML, including XML, RTF, and plain text, making it versatile for document generation workflows.
Enterprise applications commonly use FreeMarker for automated email systems, PDF report generation, and configuration file templating. The template language's error handling provides clear messages that pinpoint issues to specific template lines, simplifying debugging in production environments.
FreeMarker template diffs are high-stakes because changes directly affect user-facing output across emails, web pages, and generated documents. Misplaced interpolation syntax, broken macro calls, or altered conditional logic can produce malformed HTML or incorrect content served to thousands of users.
Teams should compare templates carefully when modifying loop structures, null-handling directives, and auto-escaping settings that guard against XSS vulnerabilities.
UtraDiff compares FreeMarker template files with syntax highlighting that distinguishes template directives like <#if>, <#list>, and <#macro> from HTML output and interpolation expressions like ${variable}. Side-by-side view separates template logic changes from markup modifications, making it clear whether a diff affects rendering behavior or static content.
Inline view consolidates nested directive changes, and Alt+arrow navigation jumps between modified template blocks.
Supported extensions: .ftl .ftlh .ftlx