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SchemaCrawler is an open-source Java API that makes working with database metadata as easy as working with plain old Java objects. SchemaCrawler is also a database schema discovery and comprehension, and schema documentation tool. You can search for database schema objects using regular expressions, and output the schema and data in a readable text format. The output is designed to be diff-ed against other database schemas.

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/*
 *
 * SchemaCrawler
 * http://www.schemacrawler.com
 * Copyright (c) 2000-2016, Sualeh Fatehi.
 *
 * This library is free software; you can redistribute it and/or modify it under the terms
 * of the GNU Lesser General Public License as published by the Free Software Foundation;
 * either version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
 * without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 * See the GNU Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License along with this
 * library; if not, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330,
 * Boston, MA 02111-1307, USA.
 *
 */
package sf.util.graph;


import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Objects;
import java.util.Set;

public class DirectedGraph>
{

  private final String name;
  private final Map> verticesMap;
  private final Set> edges;

  public DirectedGraph(final String name)
  {
    this.name = name;
    verticesMap = new HashMap<>();
    edges = new HashSet<>();
  }

  /**
   * Adds vertices, and a directed edge between them. Simple directed
   * graphs do not allow self-loops.
   * https://en.wikipedia.org/wiki/Loop_(graph_theory)
   *
   * @param from
   *        Vertex value at the start of the edge
   * @param to
   *        Vertex value at the end of the edge
   */
  public void addEdge(final T from, final T to)
  {
    if (!from.equals(to))
    {
      edges.add(new DirectedEdge(addVertex(from), addVertex(to)));
    }
  }

  /**
   * Adds a vertex.
   *
   * @param value
   *        Vertex value
   * @return The newly added vertex
   */
  public Vertex addVertex(final T value)
  {
    final Vertex vertex;
    if (verticesMap.containsKey(value))
    {
      vertex = verticesMap.get(value);
    }
    else
    {
      vertex = new Vertex(value);
      verticesMap.put(value, vertex);
    }
    return vertex;
  }

  public Set> edgeSet()
  {
    return new HashSet<>(edges);
  }

  public Set> getIncomingEdges(final Vertex vertexTo)
  {
    Objects.requireNonNull(vertexTo);

    final Set> incomingEdges = new HashSet<>();
    for (final DirectedEdge edge: edges)
    {
      if (edge.getTo().equals(vertexTo))
      {
        incomingEdges.add(edge);
      }
    }
    return incomingEdges;
  }

  /**
   * @return the name
   */
  public String getName()
  {
    return name;
  }

  public Set> getOutgoingEdges(final Vertex vertexFrom)
  {
    Objects.requireNonNull(vertexFrom);

    final Set> outgoingEdges = new HashSet<>();
    for (final DirectedEdge edge: edges)
    {
      if (edge.getFrom().equals(vertexFrom))
      {
        outgoingEdges.add(edge);
      }
    }
    return outgoingEdges;
  }

  @Override
  public String toString()
  {
    final StringBuilder writer = new StringBuilder(4096);
    writer.append("digraph {\n");
    if (name != null && !name.isEmpty())
    {
      writer.append(String.format("  [label=\"%s\"]\n", name));
    }
    // writer.append(" graph [rankdir=\"LR\"];\n");
    for (final Vertex vertex: verticesMap.values())
    {
      writer.append("  ").append(vertex);
      if (vertex.hasAttribute("fillcolor"))
      {
        writer.append(String.format(" [fillcolor=%s, style=filled]",
                                    vertex.getAttribute("fillcolor")));
      }
      writer.append(";\n");
    }
    for (final DirectedEdge edge: edges)
    {
      writer.append("  ").append(edge).append(";\n");
    }
    writer.append("}\n");
    return writer.toString();
  }

  public Set> vertexSet()
  {
    return new HashSet<>(verticesMap.values());
  }

}