Overview of the EL - The Java EE 6 Tutorial (original) (raw)
2. Using the Tutorial Examples
3. Getting Started with Web Applications
4. JavaServer Faces Technology
Immediate and Deferred Evaluation Syntax
Referencing Objects Using Value Expressions
Referring to Object Properties Using Value Expressions
Where Value Expressions Can Be Used
7. Using JavaServer Faces Technology in Web Pages
8. Using Converters, Listeners, and Validators
9. Developing with JavaServer Faces Technology
10. JavaServer Faces Technology: Advanced Concepts
11. Using Ajax with JavaServer Faces Technology
12. Composite Components: Advanced Topics and Example
13. Creating Custom UI Components and Other Custom Objects
14. Configuring JavaServer Faces Applications
16. Uploading Files with Java Servlet Technology
17. Internationalizing and Localizing Web Applications
18. Introduction to Web Services
19. Building Web Services with JAX-WS
20. Building RESTful Web Services with JAX-RS
21. JAX-RS: Advanced Topics and Example
23. Getting Started with Enterprise Beans
24. Running the Enterprise Bean Examples
25. A Message-Driven Bean Example
26. Using the Embedded Enterprise Bean Container
27. Using Asynchronous Method Invocation in Session Beans
Part V Contexts and Dependency Injection for the Java EE Platform
28. Introduction to Contexts and Dependency Injection for the Java EE Platform
29. Running the Basic Contexts and Dependency Injection Examples
30. Contexts and Dependency Injection for the Java EE Platform: Advanced Topics
31. Running the Advanced Contexts and Dependency Injection Examples
32. Introduction to the Java Persistence API
33. Running the Persistence Examples
34. The Java Persistence Query Language
35. Using the Criteria API to Create Queries
36. Creating and Using String-Based Criteria Queries
37. Controlling Concurrent Access to Entity Data with Locking
38. Using a Second-Level Cache with Java Persistence API Applications
39. Introduction to Security in the Java EE Platform
40. Getting Started Securing Web Applications
41. Getting Started Securing Enterprise Applications
42. Java EE Security: Advanced Topics
Part VIII Java EE Supporting Technologies
43. Introduction to Java EE Supporting Technologies
45. Resources and Resource Adapters
46. The Resource Adapter Example
47. Java Message Service Concepts
48. Java Message Service Examples
49. Bean Validation: Advanced Topics
50. Using Java EE Interceptors
51. Duke's Bookstore Case Study Example
52. Duke's Tutoring Case Study Example
53. Duke's Forest Case Study Example
The EL allows page authors to use simple expressions to dynamically access data from JavaBeans components. For example, the test attribute of the following conditional tag is supplied with an EL expression that compares 0 with the number of items in the session-scoped bean named cart.
<c:if test="${sessionScope.cart.numberOfItems > 0}"> ...
JavaServer Faces technology uses the EL for the following functions:
- Deferred and immediate evaluation of expressions
- The ability to set as well as get data
- The ability to invoke methods
See Using the EL to Reference Managed Beans for more information on how to use the EL in JavaServer Faces applications.
To summarize, the EL provides a way to use simple expressions to perform the following tasks:
- Dynamically read application data stored in JavaBeans components, various data structures, and implicit objects
- Dynamically write data, such as user input into forms, to JavaBeans components
- Invoke arbitrary static and public methods
- Dynamically perform arithmetic operations
The EL is also used to specify the following kinds of expressions that a custom tag attribute will accept:
- Immediate evaluation expressions or deferred evaluation expressions. An immediate evaluation expression is evaluated at once by the underlying technology, such as JavaServer Faces. A deferred evaluation expression can be evaluated later by the underlying technology using the EL.
- Value expression or method expression. A value expression references data, whereas a method expression invokes a method.
- Rvalue expression or lvalue expression. An rvalue expression can only read a value, whereas an lvalue expression can both read and write that value to an external object.
Finally, the EL provides a pluggable API for resolving expressions so custom resolvers that can handle expressions not already supported by the EL can be implemented.
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