Class AbstractContext

java.lang.Object
org.apache.velocity.context.InternalContextBase
org.apache.velocity.context.AbstractContext
All Implemented Interfaces:
Context, InternalEventContext, InternalHousekeepingContext
Direct Known Subclasses:
DBContext, TreeMapContext, VelocityContext

public abstract class AbstractContext extends InternalContextBase implements Context
This class is the abstract base class for all conventional Velocity Context implementations. Simply extend this class and implement the abstract routines that access your preferred storage method. Takes care of context chaining. Also handles / enforces policy on null keys and values :
  • Null keys and values are accepted and basically dropped.
  • If you place an object into the context with a null key, it will be ignored and logged.
  • If you try to place a null into the context with any key, it will be dropped and logged.
The default implementation of this for application use is org.apache.velocity.VelocityContext. All thanks to Fedor for the chaining idea.
Version:
$Id$
  • Field Details

    • innerContext

      private Context innerContext
      the chained Context if any
  • Constructor Details

    • AbstractContext

      public AbstractContext()
      default CTOR
    • AbstractContext

      public AbstractContext(Context inner)
      Chaining constructor accepts a Context argument. It will relay get() operations into this Context in the even the 'local' get() returns null.
      Parameters:
      inner - context to be chained
  • Method Details

    • internalGet

      public abstract Object internalGet(String key)
      Implement to return a value from the context storage.

      The implementation of this method is required for proper operation of a Context implementation in general Velocity use.
      Parameters:
      key - key whose associated value is to be returned
      Returns:
      object stored in the context
    • internalPut

      public abstract Object internalPut(String key, Object value)
      Implement to put a value into the context storage.

      The implementation of this method is required for proper operation of a Context implementation in general Velocity use.
      Parameters:
      key - key with which to associate the value
      value - value to be associated with the key
      Returns:
      previously stored value if exists, or null
    • internalContainsKey

      public abstract boolean internalContainsKey(String key)
      Implement to determine if a key is in the storage.

      Currently, this method is not used internally by the Velocity engine.
      Parameters:
      key - key to test for existence
      Returns:
      true if found, false if not
    • internalGetKeys

      public abstract String[] internalGetKeys()
      Implement to return an object array of key strings from your storage.

      Currently, this method is not used internally by the Velocity engine.
      Returns:
      array of keys
    • internalRemove

      public abstract Object internalRemove(String key)
      Implement to remove an item from your storage.

      Currently, this method is not used internally by the Velocity engine.
      Parameters:
      key - key to remove
      Returns:
      object removed if exists, else null
    • put

      public Object put(String key, Object value)
      Adds a name/value pair to the context.
      Specified by:
      put in interface Context
      Parameters:
      key - The name to key the provided value with.
      value - The corresponding value.
      Returns:
      Object that was replaced in the the Context if applicable or null if not.
    • get

      public Object get(String key)
      Gets the value corresponding to the provided key from the context. Supports the chaining context mechanism. If the 'local' context doesn't have the value, we try to get it from the chained context.
      Specified by:
      get in interface Context
      Parameters:
      key - The name of the desired value.
      Returns:
      The value corresponding to the provided key or null if the key param is null.
    • containsKey

      public boolean containsKey(String key)
      Indicates whether the specified key is in the context. Provided for debugging purposes.
      Specified by:
      containsKey in interface Context
      Parameters:
      key - The key to look for.
      Returns:
      true if the key is in the context, false if not.
    • getKeys

      public String[] getKeys()
      Get all the keys for the values in the context
      Specified by:
      getKeys in interface Context
      Returns:
      Object[] of keys in the Context. Does not return keys in chained context.
    • remove

      public Object remove(String key)
      Removes the value associated with the specified key from the context.
      Specified by:
      remove in interface Context
      Parameters:
      key - The name of the value to remove.
      Returns:
      The value that the key was mapped to, or null if unmapped.
    • getChainedContext

      public Context getChainedContext()
      returns innerContext if one is chained
      Returns:
      Context if chained, null if not