Document Information


Part I Introduction

1.  Overview

2.  Using the Tutorial Examples

Part II The Web Tier

3.  Getting Started with Web Applications

4.  JavaServer Faces Technology

5.  Introduction to Facelets

6.  Expression Language

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

15.  Java Servlet Technology

16.  Uploading Files with Java Servlet Technology

17.  Internationalizing and Localizing Web Applications

Part III Web Services

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

Part IV Enterprise Beans

22.  Enterprise Beans

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

Part VI Persistence

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

Lock Modes

Setting the Lock Mode

Using Pessimistic Locking

Pessimistic Locking Timeouts

38.  Using a Second-Level Cache with Java Persistence API Applications

Part VII Security

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

44.  Transactions

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

Part IX Case Studies

51.  Duke's Bookstore Case Study Example

52.  Duke's Tutoring Case Study Example

53.  Duke's Forest Case Study Example



Overview of Entity Locking and Concurrency

Entity data is concurrently accessed if the data in a data source is accessed at the same time by multiple applications. Special care must be taken to ensure that the underlying data’s integrity is preserved when accessed concurrently.

When data is updated in the database tables in a transaction, the persistence provider assumes the database management system will hold short-term read locks and long-term write locks to maintain data integrity. Most persistence providers will delay database writes until the end of the transaction, except when the application explicitly calls for a flush (that is, the application calls the EntityManager.flush method or executes queries with the flush mode set to AUTO).

By default, persistence providers use optimistic locking, where, before committing changes to the data, the persistence provider checks that no other transaction has modified or deleted the data since the data was read. This is accomplished by a version column in the database table, with a corresponding version attribute in the entity class. When a row is modified, the version value is incremented. The original transaction checks the version attribute, and if the data has been modified by another transaction, a javax.persistence.OptimisticLockException will be thrown, and the original transaction will be rolled back. When the application specifies optimistic lock modes, the persistence provider verifies that a particular entity has not changed since it was read from the database even if the entity data was not modified.

Pessimistic locking goes further than optimistic locking. With pessimistic locking, the persistence provider creates a transaction that obtains a long-term lock on the data until the transaction is completed, which prevents other transactions from modifying or deleting the data until the lock has ended. Pessimistic locking is a better strategy than optimistic locking when the underlying data is frequently accessed and modified by many transactions.

Note - Using pessimistic locks on entities that are not subject to frequent modification may result in decreased application performance.

Using Optimistic Locking

The javax.persistence.Version annotation is used to mark a persistent field or property as a version attribute of an entity. By adding a version attribute, the entity is enabled for optimistic concurrency control. The version attribute is read and updated by the persistence provider when an entity instance is modified during a transaction. The application may read the version attribute, but must not modify the value.

Note - Although some persistence providers may support optimistic locking for entities that do not have version attributes, portable applications should always use entities with version attributes when using optimistic locking. If the application attempts to lock an entity without a version attribute, and the persistence provider doesn’t support optimistic locking for non-versioned entities, a PersistenceException will be thrown.

The @Version annotation has the following requirements:

  • Only a single @Version attribute may be defined per entity.

  • The @Version attribute must be in the primary table for an entity mapped to multiple tables.

  • The type of the @Version attribute must be one of the following: int, Integer, long, Long, short, Short, or java.sql.Timestamp.

The following code snippet shows how to define a version attribute in an entity with persistent fields:

protected int version;

The following code snippet shows how to define a version attribute in an entity with persistent properties:

protected Short getVersion() { ... }