Using java -Djavax.net.debug=… to examine data flows, including TLS

There are different levels you can get from the -Djavax.net.debug option.  You can display its options using -Djavax.net.debug=help .

With this you get

all            turn on all debugging
ssl            turn on ssl debugging

The following can be used with ssl:

    record       enable per-record tracing
    handshake    print each handshake message
    keygen       print key generation data
    session      print session activity
    defaultctx   print default SSL initialization
    sslctx       print SSLContext tracing
    sessioncache print session cache tracing
    keymanager   print key manager tracing
    trustmanager print trust manager tracing
    pluggability print pluggability tracing

    handshake debugging can be widened with:
    data         hex dump of each handshake message
    verbose      verbose handshake message printing

    record debugging can be widened with:
    plaintext    hex dump of record plaintext
    packet       print raw SSL/TLS packets

and your program exits.

You can use

-Djavax.net.debug=ssl:record or -Djavax.net.debug=ssl:handshake

To display specific levels of detail.