/*
* GeoTools - The Open Source Java GIS Toolkit
* http://geotools.org
*
* (C) 2002-2008, Open Source Geospatial Foundation (OSGeo)
*
* 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;
* version 2.1 of the License.
*
* 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.
*/
package org.geotools.graph.io.standard;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;
import java.util.Iterator;
import org.geotools.graph.build.GraphGenerator;
import org.geotools.graph.structure.Edge;
import org.geotools.graph.structure.Graph;
import org.geotools.graph.structure.Node;
/**
* An implementation of GraphReaderWriter used for reading and writing graph
* objects to and from a database. <BR>
* <BR>
* Upon reading, the database is queried using
* the getQuery() template method, and a representation of the objects to be
* modelled by the graph are returned through a standard ResultSet. From each
* tuple in the result set, the object is recreated via the template method
* readInternal(ResultSet). The object is then passed to an underlying
* graph generator and the graph components used to model the object are
* constructed.<BR>
* <BR>
* Upon writing, the graph is read component by component based
* on set properties. If the NODES property is set, nodes will be written. If
* the EDGES property is set, edges will be written as well. As each component
* is processed, it is passed to the repspective template methods
* writeNode(Statement,Node) and writeEdge(Statement,Edge). The methods then
* execute a statement to create the database representation of the graph
* component.
*
* @author Justin Deoliveira, Refractions Research Inc, jdeolive@refractions.net
*
*
* @source $URL$
*/
public abstract class DBReaderWriter extends AbstractReaderWriter {
/** JDBC driver class name key **/
public static final String DRIVERCLASS = "DRIVERCLASS";
/** JDBC driver url **/
public static final String DRIVERURL = "DRIVERURL";
/** Database server key **/
public static final String SERVER = "SERVER";
/** Database port key **/
public static final String PORT = "PORT";
/** Database name key **/
public static final String DBNAME = "DBNAME";
/** User name key **/
public static final String USERNAME = "USERNAME";
/** Table key **/
public static final String TABLENAME = "TABLENAME";
/**
* Performs a graph read by querying the database and processing each tuple
* returned in the query. As each tuple is processed, the graph components
* represented by the tuple are created by an underlying GraphGenerator.
*
* @see org.geotools.graph.io.GraphReaderWriter#read()
*/
public Graph read() throws Exception {
//get underlying generator
GraphGenerator generator = (GraphGenerator)getProperty(GENERATOR);
//create database connection
Connection conn = getConnection();
//query database to obtain graph information
Statement st = conn.createStatement();
ResultSet rs = st.executeQuery(getQuery());
// System.out.println(getQuery());
while(rs.next()) {
generator.add(readInternal(rs));
}
//close database connection
rs.close();
st.close();
conn.close();
return(generator.getGraph());
}
/**
* Performs a write on the graph out to the database. If the NODES property
* is set, the nodes of the graph will be written, and if the EDGES property
* is set, the edges of the graph will be written.
*
* * @see GraphGenerator#write()
*/
public void write(Graph g) throws Exception {
//get database connection
Connection conn = getConnection();
Statement st = conn.createStatement();
//write nodes if property set
if (getProperty(NODES) != null) {
for (Iterator itr = g.getNodes().iterator(); itr.hasNext();) {
writeNode(st, (Node)itr.next());
}
}
//write edges if property set
if (getProperty(EDGES) != null) {
for (Iterator itr = g.getEdges().iterator(); itr.hasNext();) {
writeEdge(st, (Edge)itr.next());
}
}
//close database connection
st.close();
conn.close();
}
/**
* Opens a connection to the database, based on set properties.
*
* @return Connection to the database.
*
* @throws Exception
*/
protected Connection getConnection() throws Exception {
//read database + driver properties
String driverclass = (String)getProperty(DRIVERCLASS);
String driverurl = (String)getProperty(DRIVERURL);
String server = (String)getProperty(SERVER);
String port = (String)getProperty(PORT);
String dbname = (String)getProperty(DBNAME);
String username = (String)getProperty(USERNAME);
Class.forName(driverclass);
return(
DriverManager.getConnection(
driverurl + server+":"+port+"/"+dbname+"?user="+username
)
);
}
/**
* Template method used to write a node into the database.
*
* @param st Statement used to execute write statement.
* @param node Node to write.
*/
protected void writeNode(Statement st, Node node) {}
/**
* Template method used to write an edge into the database.
*
* @param st Statement used to execute write statement.
* @param edge Edge to write.
*/
protected void writeEdge(Statement st, Edge edge) {}
/**
* Template method which returns the query to execute in order to read
* a graph from the database.
*
* @return SQL query.
*/
protected abstract String getQuery();
/**
* Template method used to create the object represented by a tuple returned
* by the database query.
*
* @param rs ResultSet of query.
*
* @return Object represented by current tuple of result set.
*/
protected abstract Object readInternal(ResultSet rs) throws Exception;
}