process builder to run multi-platform postgres import

We saw how to clone a postgresql database for testing cleanly in an earlier blog post. The next step is to do so from Java so it can be part of an integration test.

How to run each of 4 DDLs:
Running a DDL file is easy which is good since we have four of them.

importDdlOrSqlFile("initialJForumSchema.ddl");
importDdlOrSqlFile("javaranchCustom.ddl");
importDdlOrSqlFile("users.ddl");
importDdlOrSqlFile("databaseChangesAfterMostRecentInstall.txt");

Ok. So maybe it is easy because all the functional code is in another method.

What is Process Builder?

Process Builder was introduced in Java 5.  The Runtime.exec JavaDoc says

ProcessBuilder.start() is now the preferred way to start a process with a modified environment.

Since I need to set two system properties, this is perfect.

How to create the Process Builder

On Windows, you just pass the command to run at the DOS prompt.  The actual command was shown in the closing a postgresql database blog post.  On UNIX/Mac/etc, you need to create a new shell and pass the command that way.  Luckily, it is easy to check for a Windows operating system:


private ProcessBuilder createProcessBuilder(String command) {
String os = System.getProperty("os.name").toLowerCase();
if (os.contains("win")) {
return new ProcessBuilder(command);
}
return new ProcessBuilder("sh", "-c", command);
}

How to set system properties

I need to set the user id and password as operating system properties so postgresql doesn’t prompt for them interactively.  Using process builder, I can call environment() to get a map of environmental properties for my process.  Then setting them is simply a matter of setting them in the map.


private void importDdlOrSqlFile(String fileName) throws Exception {
String command = importToPostgresCommand(fileName);
System.out.println(command);
ProcessBuilder processBuilder = createProcessBuilder(command);
Map<String, String> env = processBuilder.environment();
env.put("PGUSER",   SystemGlobals.getValue(DATABASE_CONNECTION_USERNAME));
env.put("PGPASSWORD",  SystemGlobals.getValue(DATABASE_CONNECTION_PASSWORD));
processBuilder.redirectErrorStream(true);
runProcess(fileName, processBuilder);
}

How to run the Process Builder

All ready to run it!   start() kicks it off.  I think read all the output from the commands via the process builder’s input stream and output it to the console.  (I do this since many commands are run and the developer can see what it is up to.)  Finally, I check the error code.  After all, if the database didn’t get created properly, there isn’t much point in having a whole pile of failing tests.


private void runProcess(String fileName, ProcessBuilder processBuilder) throws IOException, InterruptedException {
Process proc = processBuilder.start();
Scanner scanner = new Scanner(proc.getInputStream());
while (scanner.hasNext()) {
String line = scanner.nextLine();
System.out.println("importing data: " + line);
}
int exitVal = proc.waitFor();
System.out.println("Completed loading " + fileName + " Exit value: " + exitVal);
if (exitVal != 0) {
System.out.println("Please fix error in database script and re-run.");
System.exit(1);
}

}

Testing

This code was tested on multiple developer’s machines including Windows and Mac.

Leave a Reply

Your email address will not be published.