Using Apache HTTPClient - how can one see the raw request string before it's being sent?

You can set some environment variables for Apache HttpClient (example tested for 4.3.2).

System.setProperty("org.apache.commons.logging.Log","org.apache.commons.logging.impl.SimpleLog");
System.setProperty("org.apache.commons.logging.simplelog.showdatetime", "true");
System.setProperty("org.apache.commons.logging.simplelog.log.org.apache.http.wire", "DEBUG");

There are also some more variables for debugging:

System.setProperty("org.apache.commons.logging.simplelog.log.org.apache.http.impl.conn", "DEBUG");
System.setProperty("org.apache.commons.logging.simplelog.log.org.apache.http.impl.client", "DEBUG");
System.setProperty("org.apache.commons.logging.simplelog.log.org.apache.http.client", "DEBUG");
System.setProperty("org.apache.commons.logging.simplelog.log.org.apache.http", "DEBUG");