How to feed SQL script to psql from a Java programme?

Question

I need to feed a SQL script to a Postgres database. I am creating a Process instance that executes psql with the script path as argument. The core of the code:

public static void main(final String[] args) 
{
    ProcessBuilder pb = new ProcessBuilder("psql", "-d base", "-U user", "-f path/new_schema.sql");
    Map<String, String> env = pb.environment();
    env.put("PGPASSWORD", "pass");
    pb.redirectErrorStream(true);

    try
    {
         Process p = pb.start();
         InputStream stdout = p.getInputStream ();
         BufferedReader reader = new BufferedReader (new InputStreamReader(stdout));

         String line;
         while ((line = reader.readLine ()) != null) 
         {
             System.out.println ("Stdout: " + line);
        }
    }
    catch (Exception ex)
    {
        System.out.println("Something went wrong: " + ex.getMessage());
    }
}

This way authentication fails with this message:

psql: FATAL: Peer authentication failed for user "user"

Other users report the same error in other contexts, apparently Postgres 9.3 no longer uses the PGPASSWORD environment variable.

Therefore I tried the alternative route using a .pgpass file with these contents:

localhost:5432:*:user:pass

Then added a new environment variable before launching the Process instance:

env.put("PGPASSFILE", "/home/user/.pgpass");

Still, I receive back the "authentication failed" message.

The .pgpass file has the correct permissions (0600) and is doing its job if I invoke psql directly from the shell.

What am I missing?