Module org.jgrapht.io
Package org.jgrapht.nio.gml

Class GmlImporter<V,E>

java.lang.Object
org.jgrapht.nio.BaseEventDrivenImporter<V,E>
org.jgrapht.nio.gml.GmlImporter<V,E>
Type Parameters:
V - the vertex type
E - the edge type
All Implemented Interfaces:
GraphImporter<V,E>
public class GmlImporter<V,E> extends BaseEventDrivenImporter<V,E> implements GraphImporter<V,E>
Imports a graph from a GML file (Graph Modeling Language).

For a description of the format see http://www.infosun.fmi.uni-passau.de/Graphlet/GML/.

Below is small example of a graph in GML format. 

 graph [
   node [ 
     id 1
   ]
   node [
     id 2
     label "Node 2 has an optional label"
   ]
   node [
     id 3
   ]
   edge [
     source 1
     target 2 
     weight 2.0
     label "Edge between 1 and 2"
   ]
   edge [
     source 2
     target 3
     weight 3.0
     label "Edge between 2 and 3"
   ]
 ]

In case the graph is weighted then the importer also reads edge weights. Otherwise edge weights are ignored. The importer also supports reading additional string attributes such as label or custom user attributes. String attributes are unescaped as if they are Java strings.

The parser completely ignores elements from the input that are not related to vertices or edges of the graph. Moreover, complicated nested structures are simply returned as a whole. For example, in the following graph 

 graph [
   node [ 
     id 1
   ]
   node [ 
     id 2
   ]
   edge [
     source 1
     target 2 
     points [ x 1.0 y 2.0 ]
   ]
 ]
the points attribute of the edge is returned as a string containing "[ x 1.0 y 2.0 ]".

The graph vertices and edges are build using the corresponding graph suppliers. The id of the vertices in the original file are reported as a vertex attribute named "ID".

The default behavior of the importer is to use the graph vertex supplier in order to create vertices. The user can also bypass vertex creation by providing a custom vertex factory method using setVertexFactory(Function). The factory method is responsible to create a new graph vertex given the vertex identifier read from file.

Author:
Dimitrios Michail

  • Field Details

    • DEFAULT_VERTEX_ID_KEY

      public static final String DEFAULT_VERTEX_ID_KEY
      Default key used for vertex ID.
      See Also:

  • Constructor Details

    • GmlImporter

      public GmlImporter()
      Constructs a new importer.

  • Method Details

    • importGraph

      public void importGraph(Graph<V,E> graph, Reader input)
      Import a graph.

      The provided graph must be able to support the features of the graph that is read. For example if the GML file contains self-loops then the graph provided must also support self-loops. The same for multiple edges.

      If the provided graph is a weighted graph, the importer also reads edge weights. Otherwise edge weights are ignored.

      Specified by:
      importGraph in interface GraphImporter<V,E>
      Parameters:
      graph - the output graph
      input - the input reader
      Throws:
      ImportException - in case an error occurs, such as I/O or parse error

    • getVertexFactory

      public Function<Integer,V> getVertexFactory()
      Get the user custom vertex factory. This is null by default and the graph supplier is used instead.
      Returns:
      the user custom vertex factory

    • setVertexFactory

      public void setVertexFactory(Function<Integer,V> vertexFactory)
      Set the user custom vertex factory. The default behavior is being null in which case the graph vertex supplier is used. If supplied the vertex factory is called every time a new vertex is encountered in the file. The method is called with parameter the vertex identifier from the file and should return the actual graph vertex to add to the graph.
      Parameters:
      vertexFactory - a vertex factory