Package org.apache.commons.configuration2.interpol

Class ConstantLookup

java.lang.Object
org.apache.commons.configuration2.interpol.ConstantLookup
All Implemented Interfaces:
Lookup
public class ConstantLookup extends Object implements Lookup

Looks up constant fields in classes.

Variable names passed in must be of the form mypackage.MyClass.FIELD. The lookup() method will split the passed in string at the last dot, separating the fully qualified class name and the name of the constant (i.e. static final) member field. Then the class is loaded and the field's value is obtained using reflection.

Once retrieved values are cached for fast access. This class is thread-safe. It can be used as a standard (i.e. global) lookup object and serve multiple clients concurrently.

Since:
1.4

  • Constructor Details

  • Method Details

    • lookup

      public Object lookup(String var)
      Looks up a variable. The passed in variable name is interpreted as the name of a static final member field of a class. If the value has already been obtained, it can be retrieved from an internal cache. Otherwise this method will invoke the resolveField() method and pass in the name of the class and the field.
      Specified by:
      lookup in interface Lookup
      Parameters:
      var - the name of the variable to be resolved
      Returns:
      the value of this variable or null if it cannot be resolved

    • clear

      public static void clear()
      Clears the shared cache with the so far resolved constants.

    • resolveField

      protected Object resolveField(String className, String fieldName) throws Exception
      Determines the value of the specified constant member field of a class. This implementation will call fetchClass() to obtain the Class object for the target class. Then it will use reflection to obtain the field's value. For this to work the field must be accessible.
      Parameters:
      className - the name of the class
      fieldName - the name of the member field of that class to read
      Returns:
      the field's value
      Throws:
      Exception - if an error occurs

    • fetchClass

      protected Class<?> fetchClass(String className) throws ClassNotFoundException
      Loads the class with the specified name. If an application has special needs regarding the class loaders to be used, it can hook in here. This implementation delegates to the getClass() method of Commons Lang's ClassUtils.
      Parameters:
      className - the name of the class to be loaded
      Returns:
      the corresponding class object
      Throws:
      ClassNotFoundException - if the class cannot be loaded