Package org.apache.velocity.tools.generic

Class FieldTool

  • @DefaultKey("field")
public class FieldTool
extends SafeConfig

    This is a simple tools class to allow easy access to static fields in a class, such as string constants from within a template. Velocity will not introspect for class fields (and won't in the future :), but writing setter/getter methods to do this is a pain, so use this if you really have to access fields. 

     Example uses in a template:
   ## here we access a constant in a class include in the configuration
     $field.COUNTER_NAME

   ## here we dynamically lookup a class' fields to find another constant
     $field.in("org.com.SomeClass").ANOTHER_CONSTANT

   ## here we pass an object instance in (an Integer in this case) and
   ## retrieve a static constant from that instance's class
     $field.in(0).MIN_VALUE

   ## by default, once we've searched a class' fields, those fields stay
   ## available in the tool (change this by storeDynamicLookups="false")
   ## so here we get another constant from the Integer class
     $field.MAX_VALUE


 Example tools.xml config:
 <tools>
   <toolbox scope="application">
     <tool class="org.apache.velocity.tools.generic.FieldTool"
              include="org.apache.velocity.runtime.RuntimeConstants,com.org.MyConstants"/>
   </toolbox>
 </tools>

    Right now, this tool only gives access to public static fields. It seems that anything else is too dangerous. This is for convenient access to 'constants'. If you have fields that aren't static, handle them by explicitly placing them into the context or writing a getter method.

    Since:
    VelocityTools 2.0
    Version:
    $Id: FieldTool.java 463298 2006-10-12 16:10:32Z henning $
    Author:
    Geir Magnusson Jr., Nathan Bubna

    • Field Detail

      • INCLUDE_KEY

        public static final String INCLUDE_KEY
        The key used for specifying which classes should be inspected for public static methods to be made available.
        See Also:
        Constant Field Values

      • STORE_DYNAMIC_KEY

        public static final String STORE_DYNAMIC_KEY
        The key used for specifying whether or not the tool should store fields in classes dynamically looked up from within a template. The default value is true.
        See Also:
        Constant Field Values

      • log

        protected org.apache.velocity.runtime.log.Log log

      • storage

        protected HashMap storage

      • storeDynamicLookups

        protected boolean storeDynamicLookups

    • Constructor Detail

      • FieldTool

        public FieldTool()

    • Method Detail

      • configure

        protected void configure​(ValueParser values)
        Description copied from class: SafeConfig
        Does the actual configuration. This is protected, so subclasses may share the same ValueParser and call configure at any time, while preventing templates from doing so when configure(Map) is locked.
        Overrides:
        configure in class SafeConfig

      • get

        public Object get​(String name)
        Returns the value for the specified field name as found in the stored Map of field names to values (or placeholders). Returns null if there is no matching field.

      • in

        public FieldTool.FieldToolSub in​(String classname)
        Returns a FieldTool.FieldToolSub holding a Map of all the public static field names to values (or a placeholder if the value is not final) for the specified class(name). If the Class with the specified name cannot be loaded, this will return null, rather than throw an exception.
        See Also:
        in(Class clazz)

      • inspect

        protected Map<String,​Object> inspect​(Class clazz)
        Looks for all public, static fields in the specified class and stores their value (if final) or else a FieldTool.MutableField for in a Map under the fields' names. This will never return null, only an empty Map if there are no public static fields.

      • retrieve

        protected static Object retrieve​(Field field,
                                 Class clazz,
                                 org.apache.velocity.runtime.log.Log log)
        Retrieves and returns the value of the specified Field in the specified Class. If Log is provided, then access errors will be logged, otherwise this will fail silently and return null.