org.springframework.beans

## Class CachedIntrospectionResults

- java.lang.Object
- - org.springframework.beans.CachedIntrospectionResults

-     public class CachedIntrospectionResults
      extends Object

  Internal class that caches JavaBeans `PropertyDescriptor` information for a Java class. Not intended for direct use by application code.

  Necessary for own caching of descriptors within the application's ClassLoader, rather than rely on the JDK's system-wide BeanInfo cache (in order to avoid leaks on ClassLoader shutdown).

  Information is cached statically, so we don't need to create new objects of this class for every JavaBean we manipulate. Hence, this class implements the factory design pattern, using a private constructor and a static `forClass(Class)` factory method to obtain instances.

  Note that for caching to work effectively, some preconditions need to be met: Prefer an arrangement where the Spring jars live in the same ClassLoader as the application classes, which allows for clean caching along with the application's lifecycle in any case. For a web application, consider declaring a local `IntrospectorCleanupListener` in `web.xml` in case of a multi-ClassLoader layout, which will allow for effective caching as well.

  In case of a non-clean ClassLoader arrangement without a cleanup listener having been set up, this class will fall back to a weak-reference-based caching model that recreates much-requested entries every time the garbage collector removed them. In such a scenario, consider the `IGNORE_BEANINFO_PROPERTY_NAME` system property.

  Since:
    05 May 2001
  Author:
    Rod Johnson, Juergen Hoeller
  See Also:
    `acceptClassLoader(ClassLoader)`, `clearClassLoader(ClassLoader)`, `forClass(Class)`

- - ### Field Summary

    Fields
    Modifier and Type | Field and Description
    --- | ---
    `static String` | `IGNORE_BEANINFO_PROPERTY_NAME` System property that instructs Spring to use the `Introspector.IGNORE_ALL_BEANINFO` mode when calling the JavaBeans `Introspector`: "spring.beaninfo.ignore", with a value of "true" skipping the search for `BeanInfo` classes (typically for scenarios where no such classes are being defined for beans in the application in the first place).

  - ### Method Summary

    Methods
    Modifier and Type | Method and Description
    --- | ---
    `static void` | `acceptClassLoader(ClassLoader classLoader)` Accept the given ClassLoader as cache-safe, even if its classes would not qualify as cache-safe in this CachedIntrospectionResults class.
    `static void` | `clearClassLoader(ClassLoader classLoader)` Clear the introspection cache for the given ClassLoader, removing the introspection results for all classes underneath that ClassLoader, and removing the ClassLoader (and its children) from the acceptance list.

    - ### Methods inherited from class java.lang.Object

      `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- - ### Field Detail

    - #### IGNORE_BEANINFO_PROPERTY_NAME

          public static final String IGNORE_BEANINFO_PROPERTY_NAME

      System property that instructs Spring to use the `Introspector.IGNORE_ALL_BEANINFO` mode when calling the JavaBeans `Introspector`: "spring.beaninfo.ignore", with a value of "true" skipping the search for `BeanInfo` classes (typically for scenarios where no such classes are being defined for beans in the application in the first place).

      The default is "false", considering all `BeanInfo` metadata classes, like for standard `Introspector.getBeanInfo(Class)` calls. Consider switching this flag to "true" if you experience repeated ClassLoader access for non-existing `BeanInfo` classes, in case such access is expensive on startup or on lazy loading.

      Note that such an effect may also indicate a scenario where caching doesn't work effectively: Prefer an arrangement where the Spring jars live in the same ClassLoader as the application classes, which allows for clean caching along with the application's lifecycle in any case. For a web application, consider declaring a local `IntrospectorCleanupListener` in `web.xml` in case of a multi-ClassLoader layout, which will allow for effective caching as well.

      See Also:
        `Introspector.getBeanInfo(Class, int)`, Constant Field Values

  - ### Method Detail

    - #### acceptClassLoader

          public static void acceptClassLoader(ClassLoader classLoader)

      Accept the given ClassLoader as cache-safe, even if its classes would not qualify as cache-safe in this CachedIntrospectionResults class.

      This configuration method is only relevant in scenarios where the Spring classes reside in a 'common' ClassLoader (e.g. the system ClassLoader) whose lifecycle is not coupled to the application. In such a scenario, CachedIntrospectionResults would by default not cache any of the application's classes, since they would create a leak in the common ClassLoader.

      Any `acceptClassLoader` call at application startup should be paired with a `clearClassLoader(java.lang.ClassLoader)` call at application shutdown.

      Parameters:
        `classLoader` - the ClassLoader to accept

    - #### clearClassLoader

          public static void clearClassLoader(ClassLoader classLoader)

      Clear the introspection cache for the given ClassLoader, removing the introspection results for all classes underneath that ClassLoader, and removing the ClassLoader (and its children) from the acceptance list.
      Parameters:
        `classLoader` - the ClassLoader to clear the cache for