Java clients can access PostGIS "geometry" objects in the PostgreSQL database either directly as text representations or using the JDBC extension objects bundled with PostGIS. In order to use the extension objects, the "postgis.jar" file must be in your CLASSPATH along with the "postgresql.jar" JDBC driver package.
import java.sql.*; import java.util.*; import java.lang.*; import org.postgis.*; public class JavaGIS { public static void main(String[] args) { java.sql.Connection conn; try { /* * Load the JDBC driver and establish a connection. */ Class.forName("org.postgresql.Driver"); String url = "jdbc:postgresql://localhost:5432/database"; conn = DriverManager.getConnection(url, "postgres", ""); /* * Add the geometry types to the connection. Note that you * must cast the connection to the pgsql-specific connection * implementation before calling the addDataType() method. */ ((org.postgresql.Connection)conn).addDataType("geometry","org.postgis.PGgeometry"); ((org.postgresql.Connection)conn).addDataType("box3d","org.postgis.PGbox3d"); /* * Create a statement and execute a select query. */ Statement s = conn.createStatement(); ResultSet r = s.executeQuery("select AsText(geom) as geom,id from geomtable"); while( r.next() ) { /* * Retrieve the geometry as an object then cast it to the geometry type. * Print things out. */ PGgeometry geom = (PGgeometry)r.getObject(1); int id = r.getInt(2); System.out.println("Row " + id + ":"); System.out.println(geom.toString()); } s.close(); conn.close(); } catch( Exception e ) { e.printStackTrace(); } } } |
The "PGgeometry" object is a wrapper object which contains a specific topological geometry object (subclasses of the abstract class "Geometry") depending on the type: Point, LineString, Polygon, MultiPoint, MultiLineString, MultiPolygon.
PGgeometry geom = (PGgeometry)r.getObject(1); if( geom.getType() = Geometry.POLYGON ) { Polygon pl = (Polygon)geom.getGeometry(); for( int r = 0; r < pl.numRings(); r++ ) { LinearRing rng = pl.getRing(r); System.out.println("Ring: " + r); for( int p = 0; p < rng.numPoints(); p++ ) { Point pt = rng.getPoint(p); System.out.println("Point: " + p); System.out.println(pt.toString()); } } } |
The JavaDoc for the extension objects provides a reference for the various data acessor functions in the geometric objects.