Java: Display request of an HttpURLConnection before sending

Question

I want to make some API calls to a server using HttpURLConnection. But the requests are not successful, returning:

Answer 1

Use something like tcpdump, which can dump the actual network packets that are emitted or received by your computer.

Answer 2

You can put the HttpURLConnection in debug mode by enabling java.logging with

-Djava.util.logging.config.file=logging.properties

and put in logging.properties (by default in JRE_HOME\lib) the following property

sun.net.www.protocol.http.HttpURLConnection.level = ALL

Answer 3

tcpdump will work, but it can be hard to make it do what you want. NetCat is more user-friendly (here's the project page: http://netcat.sourceforge.net/ - most Unix platforms already include it).

nc -l 9999

This will listen on TCP port 9999, and when an HTTP client connects, it'll print out the full text of the request.