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SPEL OVERVIEW

Origin and Purpose​

  • A part of the Spring Framework
  • Specifically designed for use within Spring applications.
  • It provides powerful features for querying and manipulating object graphs at runtime

Features​

  • Integration with Spring: Seamlessly integrates with Spring beans, allowing for
    • Dynamic evaluation of bean properties, method calls, and more.
  • EL Support: Supports the standard Unified EL syntax used in JSP and JSF.
  • Templating: Allows for template expressions to be embedded within strings.
  • Type Conversion: Built-in support for type conversion and property access.

Syntax and Usage​

  • SpEL has a syntax that is an extension of the Unified EL syntax, which makes it familiar to those who have worked with JSP or JSF.
  • It supports more advanced features like calling methods, accessing properties, and even working with collections and arrays.
ExpressionParser parser = new SpelExpressionParser();
Expression exp = parser.parseExpression("'Hello ' + name");

StandardEvaluationContext context = new StandardEvaluationContext();
context.setVariable("name", "World");

String message = (String) exp.getValue(context);

System.out.println(message); // Outputs "Hello World"

Key Differences​

  1. Integration and Use Cases:

    • MVEL: Typically used in applications requiring a lightweight, high-performance expression language, such as rule engines and templating engines.
    • SpEL: Designed specifically for Spring applications, providing deep integration with Spring's features and infrastructure.

  2. Syntax and Features:

    • MVEL: More concise and dynamic, designed for simplicity and speed.
    • SpEL: More powerful in terms of integration with Spring, supports a wider range of features such as method invocation, collection handling, and more.

  3. Performance:

    • MVEL: Generally faster and lighter, suitable for high-performance scenarios.
    • SpEL: While powerful and flexible, it may not be as fast as MVEL due to its broader feature set and deeper integration with Spring.

Summary​

  • MVEL is a general-purpose expression language known for its speed and simplicity, often used in rule engines and templating.
  • SpEL is tailored for Spring applications, providing powerful features for dynamic property access and method invocation within the Spring context.
  • The choice between MVEL and SpEL depends on the specific requirements of your application and whether you need tight integration with Spring features.

References​