Class CombinedLocationStrategy

All Implemented Interfaces:

public class CombinedLocationStrategy extends Object implements FileLocationStrategy

A specialized implementation of a FileLocationStrategy which encapsulates an arbitrary number of FileLocationStrategy objects.

A collection with the wrapped FileLocationStrategy objects is passed at construction time. During a [locate() operation the wrapped strategies are called one after the other until one returns a non null URL. This URL is returned. If none of the wrapped strategies is able to resolve the passed in FileLocator, result is null. This is similar to the chain of responsibility design pattern.

This class, together with the provided concrete FileLocationStrategy implementations, offers a convenient way to customize the lookup for configuration files: Just add the desired concrete strategies to a CombinedLocationStrategy object. If necessary, custom strategies can be implemented if there are specific requirements. Note that the order in which strategies are added to a CombinedLocationStrategy matters: sub strategies are queried in the same order as they appear in the collection passed to the constructor.

  • Constructor Details

    • CombinedLocationStrategy

      Creates a new instance of CombinedLocationStrategy and initializes it with the provided sub strategies. The passed in collection must not be null or contain null elements.
      subs - the collection with sub strategies
      IllegalArgumentException - if the collection is null or has null elements
  • Method Details

    • getSubStrategies

      Gets a (unmodifiable) collection with the sub strategies managed by this object.
      the sub FileLocationStrategy objects
    • locate

      public URL locate(FileSystem fileSystem, FileLocator locator)
      Tries to locate the specified file. The method also expects the FileSystem to be used. Note that the FileLocator object may also contain a FileSystem, but this is optional. The passed in FileSystem should be used, and callers must not pass a null reference for this argument. A concrete implementation has to evaluate the properties stored in the FileLocator object and try to match them to an existing file. If this can be done, a corresponding URL is returned. Otherwise, result is null. Implementations should not throw an exception (unless parameters are null) as there might be alternative strategies which can find the file in question. This implementation tries to locate the file by delegating to the managed sub strategies.
      Specified by:
      locate in interface FileLocationStrategy
      fileSystem - the FileSystem to be used for this operation
      locator - the object describing the file to be located
      a URL pointing to the referenced file if location was successful; null if the file could not be resolved