Spring Tutorials

The Spring Expression Language is a powerful expression language that supports querying and manipulating an object graph at runtime. SpEL expressions can be used with XML or annotation based configuration metadata for defining BeanDefinitions. In both cases the syntax to define the expression is of the form:

#{ <expression string>}

There are several existing expression languages like MVEL, OGNL and JBoss EL. Every EL is developed with some purpose in mind. SpEL is created to help the Spring porfolio products. The syntax used for the SpEL is same like Unified EL.

SpEL serves as the foundation for expression evaluation within the Spring portfolio, it is not directly tied to Spring and can be used independently. In order to be self contained, many of the examples in this chapter use SpEL as if it were an independent expression language. This requires creating a few bootstrapping infrastructure classes such as the parser.

Another advantage of SpEL is it can work independently without depending on the Spring environment. In the following sections, you will read the complete details on SpEL API and Features the Spring Expression Language.

The SpEL API provides many interfaces and classes. They are as follows:

1. Expression interface
2. SpelExpression class
3. ExpressionParser interface
4. SpelExpressionParser class
5. EvaluationContext interface
6. StandardEvaluationContext class

There are several features exist with SpEL. The expression language supports the following functionality as given below.

1. Literal expressions
2. Boolean and relational operators
3. Regular expressions
4. Class expressions
5. Accessing properties, arrays, lists, maps
6. Method invocation
7. Relational operators
8. Assignment
9. Calling constructors
10. Bean references
11. Array construction
12. Inline lists
13. Ternary operator
14. Variables
15. User defined functions
16. Collection projection
17. Collection selection
18. Templated expressions
19. Inline maps