EJB Bad Practices: Use of Synchronization Primitives

Description

The Enterprise JavaBeans specification requires that every bean provider follow a set of programming guidelines designed to ensure that the bean will be portable and behave consistently in any EJB container. In this case, the product violates the following EJB guideline: "An enterprise bean must not use thread synchronization primitives to synchronize execution of multiple instances." The specification justifies this requirement in the following way: "This rule is required to ensure consistent runtime semantics because while some EJB containers may use a single JVM to execute all enterprise bean's instances, others may distribute the instances across multiple JVMs."

Demonstrations

The following examples help to illustrate the nature of this weakness and describe methods or techniques which can be used to mitigate the risk.

Note that the examples here are by no means exhaustive and any given weakness may have many subtle varieties, each of which may require different detection methods or runtime controls.

Example One

In the following Java example a Customer Entity EJB provides access to customer information in a database for a business application.

@Entity
public class Customer implements Serializable {


  private String id;
  private String firstName;
  private String lastName;
  private Address address;

  public Customer() {...}

  public Customer(String id, String firstName, String lastName) {...}

  @Id
  public String getCustomerId() {...}

  public synchronized void setCustomerId(String id) {...}

  public String getFirstName() {...}

  public synchronized void setFirstName(String firstName) {...}

  public String getLastName() {...}

  public synchronized void setLastName(String lastName) {...}

  @OneToOne()
  public Address getAddress() {...}

  public synchronized void setAddress(Address address) {...}

}

However, the customer entity EJB uses the synchronized keyword for the set methods to attempt to provide thread safe synchronization for the member variables. The use of synchronized methods violate the restriction of the EJB specification against the use synchronization primitives within EJBs. Using synchronization primitives may cause inconsistent behavior of the EJB when used within different EJB containers.

See Also