Package freemarker.ext.beans

Class BeansWrapperBuilder

java.lang.Object
freemarker.ext.beans.BeansWrapperConfiguration
freemarker.ext.beans.BeansWrapperBuilder
All Implemented Interfaces:
Cloneable
public class BeansWrapperBuilder extends BeansWrapperConfiguration
Gets/creates a BeansWrapper singleton instance that's already configured as specified in the properties of this object; this is recommended over using the BeansWrapper constructors. The returned instance can't be further configured (it's write protected).

The builder meant to be used as a drop-away object (not stored in a field), like in this example: 

    BeansWrapper beansWrapper = new BeansWrapperBuilder(Configuration.VERSION_2_3_21).build();

Or, a more complex example:

    // Create the builder:
    BeansWrapperBuilder builder = new BeansWrapperBuilder(Configuration.VERSION_2_3_21);
    // Set desired BeansWrapper configuration properties:
    builder.setUseModelCache(true);
    builder.setExposeFields(true);
    
    // Get the singleton:
    BeansWrapper beansWrapper = builder.build();
    // You don't need the builder anymore.

Despite that builders aren't meant to be used as long-lived objects (singletons), the builder is thread-safe after you have stopped calling its setters and it was safely published (see JSR 133) to other threads. This can be useful if you have to put the builder into an IoC container, rather than the singleton it produces.

The main benefit of using a builder instead of a BeansWrapper constructor is that this way the internal object wrapping-related caches (most notably the class introspection cache) will come from a global, JVM-level (more precisely, freemarker.jar-class-loader-level) cache. Also the BeansWrapper singletons themselves are stored in this global cache. Some of the wrapping-related caches are expensive to build and can take significant amount of memory. Using builders, components that use FreeMarker will share BeansWrapper instances and said caches even if they use separate FreeMarker Configuration-s. (Many Java libraries use FreeMarker internally, so Configuration sharing is not an option.)

Note that the returned BeansWrapper instances are only weak-referenced from inside the builder mechanism, so singletons are garbage collected when they go out of usage, just like non-singletons.

About the object wrapping-related caches:

  • Class introspection cache: Stores information about classes that once had to be wrapped. The cache is stored in the static fields of certain FreeMarker classes. Thus, if you have two BeansWrapper instances, they might share the same class introspection cache. But if you have two freemarker.jar-s (typically, in two Web Application's WEB-INF/lib directories), those won't share their caches (as they don't share the same FreeMarker classes). Also, currently there's a separate cache for each permutation of the property values that influence class introspection: expose_fields, and exposure_level, and BeansWrapperConfiguration.setMemberAccessPolicy(MemberAccessPolicy) member_access_policy}. So only BeansWrapper where those properties are the same may share class introspection caches among each other.

  • Model caches: These are local to a BeansWrapper. BeansWrapperBuilder returns the same BeansWrapper instance for equivalent properties (unless the existing instance was garbage collected and thus a new one had to be created), hence these caches will be re-used too. BeansWrapper instances are cached in the static fields of FreeMarker too, but there's a separate cache for each Thread Context Class Loader, which in a servlet container practically means a separate cache for each Web Application (each servlet context). (This is like so because for resolving class names to classes FreeMarker uses the Thread Context Class Loader, so the result of the resolution can be different for different Thread Context Class Loaders.) The model caches are:

Note that what this method documentation says about BeansWrapper also applies to DefaultObjectWrapperBuilder.

Since:
2.3.21

  • Constructor Details

  • Method Details

    • build

      public BeansWrapper build()
      Returns a BeansWrapper instance that matches the settings of this builder. This will be possibly a singleton that is also in use elsewhere, not necessarily a new object.