[postgis] ClassCastException with PostGis Example

[Paul Ramsey]

Silvio wrote:
> 
> Yes, all is ok!
> If I try to retrieve the geometry column as a String and print it the
> example works.
> But, what does strange situation means?
> The database where the program gets the data has three objects. I have
> inserted this object with geometryFromText function.
> Now, this function should record a geometry object on the database but
> instead it records a String object!!!?

This is what happens with JDBC. All the database objects transit from
the db to the JDBC client as text strings. Then, if they are complex
objects, the driver parses the text into object structures. This is how
the internal geometry objects work, and I modelled the extension objects
after them.

If anyone can debug this I would be grateful. I do not have time to do
any PostGIS work for the next month at least.

> Is this a bug? I don't think this but can somebody say me where is the
> error?
> 
> Buffa S.
> 
> ----- Original Message -----
> From: "Paul Ramsey" <pramsey at refractions.net>
> To: <postgis at yahoogroups.com>
> Sent: Tuesday, January 08, 2002 8:27 PM
> Subject: Re: [postgis] ClassCastException with PostGis Example
> 
> > Some tests might help see where things are breaking:
> > - Print out obj.toString() before casting it.
> > - Retrieve the geometry column as a String and print that out too.
> >
> > Silvio wrote:
> > >
> > > Hi,
> > >
> > > I have just installed PostGis with PostGreSql but the PostGis Example
> > > doesn't work.
> > >
> > > This is the example (http://postgis.refractions.net/docs/x441.html)
> > >
> > > 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.PGgeom
> > > etry");
> > >
> > >
> ((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);
> > > ********************CAST ERROR*****************
> > >
> > >           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 compiling phase is ok
> > > After, when I try to run the class I get the following error:
> > >
> > > java.lang.ClassCastException: java.lang.String
> > >         at PostGis.main(PostGis.java:42)
> > >
> > > (the error is referred to the line 42 where I have written "CAST ERROR")
> > >
> > > I hope that somebody can help me!!
> > >
> > > Thanks in advance.
> > >
> > > Silvio B.
> > >

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