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Understanding EclipseLink, 2.4
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About Weaving

Weaving is a technique of manipulating the byte-code of compiled Java classes. The EclipseLink JPA persistence provider uses weaving to enhance both JPA entities and Plain Old Java Object (POJO) classes for such things as lazy loading, change tracking, fetch groups, and internal optimizations.

Weaving can be performed either dynamically at runtime, when entities are loaded, or statically at compile time by post-processing the entity .class files. By default, EclipseLink uses dynamic weaving whenever possible, including inside a Java EE application server and in Java SE when the EclipseLink agent is configured. Dynamic weaving is recommended as it is easy to configure and does not require any changes to a project's build process.

This section describes the following:

Using Dynamic Weaving

Use dynamic weaving to weave application class files one at a time, as they are loaded at run time. Consider this option when the number of classes to weave is few or when the time taken to weave the classes is short.

If the number of classes to weave is large or the time required to weave the classes is long, consider using static weaving.

Using Static Weaving

Use static weaving to weave all application class files at build time so that you can deliver prewoven class files. Consider this option to weave all applicable class files at build time so that you can deliver prewoven class files. By doing so, you can improve application performance by eliminating the runtime weaving step required by dynamic weaving.

In addition, consider using static weaving to weave in Java environments where you cannot configure an agent.

Weaving POJO Classes

EclipseLink uses weaving to enable the following for POJO classes:

  • Lazy loading

  • Change tracking

  • Fetch groups

EclipseLink weaves all the POJO classes in the JAR you create when you package a POJO application for weaving.

EclipseLink weaves all the classes defined in the persistence.xml file, that is:

  • All the classes you list in the persistence.xml file.

  • All classes relative to the JAR containing the persistence.xml file if element <exclude-unlisted-classes> is false.

Weaving and Java EE Application Servers

The default EclipseLink weaving behavior applies in any Java EE JPA-compliant application server using the EclipseLink JPA persistence provider.To change this behavior, modify your persistence.xml file (for your JPA entities or POJO classes) to use EclipseLink JPA properties, EclipseLink JPA annotations, or both.

Disabling Weaving with Persistence Unit Properties

To disable weaving using EclipseLink persistence unit properties, configure your persistence.xml file with one or more of the following properties set to false:

  • eclipse.weaving; disables all weaving

  • eclipselink.weaving.lazy; disables weaving for lazy loading (indirection)

  • eclipselink.weaving.changetracking; disables weaving for change tracking

  • eclipselink.weaving.fetchgroups; disables weaving for fetch groups

  • eclipselink.weaving.internal; disables weaving for internal optimization

  • eclipselink.weaving.eager; disables weaving for indirection on eager relationships

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