Class NodeTreeWalker

java.lang.Object
org.apache.commons.configuration2.tree.NodeTreeWalker

public class NodeTreeWalker extends Object

A class providing different algorithms for traversing a hierarchy of configuration nodes.

The methods provided by this class accept a ConfigurationNodeVisitor and visit all nodes in a hierarchy starting from a given root node. Because a NodeHandler has to be passed in, too, arbitrary types of nodes can be processed. The walk() methods differ in the order in which nodes are visited. Details can be found in the method documentation.

An instance of this class does not define any state; therefore, it can be shared and used concurrently. The INSTANCE member field can be used for accessing a default instance. If desired (e.g. for testing purposes), new instances can be created.

Since:
2.0
  • Field Details

    • INSTANCE

      public static final NodeTreeWalker INSTANCE
      The default instance of this class.
  • Constructor Details

    • NodeTreeWalker

      public NodeTreeWalker()
  • Method Details

    • walkDFS

      public <T> void walkDFS(T root, ConfigurationNodeVisitor<T> visitor, NodeHandler<T> handler)
      Visits all nodes in the hierarchy represented by the given root node in depth first search manner. This means that first ConfigurationNodeVisitor.visitBeforeChildren(Object, NodeHandler) is called on a node, then recursively all of its children are processed, and eventually ConfigurationNodeVisitor.visitAfterChildren(Object, NodeHandler) gets invoked.
      Type Parameters:
      T - the type of the nodes involved
      Parameters:
      root - the root node of the hierarchy to be processed (may be null, then this call has no effect)
      visitor - the ConfigurationNodeVisitor (must not be null)
      handler - the NodeHandler (must not be null)
      Throws:
      IllegalArgumentException - if a required parameter is null
    • walkBFS

      public <T> void walkBFS(T root, ConfigurationNodeVisitor<T> visitor, NodeHandler<T> handler)
      Visits all nodes in the hierarchy represented by the given root node in breadth first search manner. This means that the nodes are visited in an order corresponding to the distance from the root node: first the root node is visited, then all direct children of the root node, then all direct children of the first child of the root node, etc. In this mode of traversal, there is no direct connection between the encounter of a node and its children. Therefore, on the visitor object only the visitBeforeChildren() method gets called!.
      Type Parameters:
      T - the type of the nodes involved
      Parameters:
      root - the root node of the hierarchy to be processed (may be null, then this call has no effect)
      visitor - the ConfigurationNodeVisitor (must not be null)
      handler - the NodeHandler (must not be null)
      Throws:
      IllegalArgumentException - if a required parameter is null
    • dfs

      private static <T> void dfs(T node, ConfigurationNodeVisitor<T> visitor, NodeHandler<T> handler)
      Recursive helper method for performing a DFS traversal.
      Type Parameters:
      T - the type of the nodes involved
      Parameters:
      node - the current node
      visitor - the visitor
      handler - the handler
    • bfs

      private static <T> void bfs(T root, ConfigurationNodeVisitor<T> visitor, NodeHandler<T> handler)
      Helper method for performing a BFS traversal. Implementation node: This method organizes the nodes to be visited in structures on the heap. Therefore, it can deal with larger structures than would be the case in a recursive approach (where the stack size limits the size of the structures which can be traversed).
      Type Parameters:
      T - the type of the nodes involved
      Parameters:
      root - the root node to be navigated
      visitor - the visitor
      handler - the handler
    • checkParameters

      private static <T> boolean checkParameters(T root, ConfigurationNodeVisitor<T> visitor, NodeHandler<T> handler)
      Helper method for checking the parameters for the walk() methods. If mandatory parameters are missing, an exception is thrown. The return value indicates whether an operation can be performed.
      Type Parameters:
      T - the type of the nodes involved
      Parameters:
      root - the root node
      visitor - the visitor
      handler - the handler
      Returns:
      true if a walk operation can be performed, false otherwise
      Throws:
      IllegalArgumentException - if a required parameter is missing