How to set up nginx server to proxy to a java application

you need to be running a web server that has the .jar file running at all times.  A jar file by itself is simply a file that contains instructions for use by java

And the Java application is listening on port 80?

you can verify the listening port by using
netstat -antp  

on the server where the java application is active....
(there is a <pid>/java at the end of the line)

And then stop this server and use netstat -antp again to verfy the ports used.
And if listening on port 80, and using http you should be able to verify it's working by using a browser to that addresses.

I commented out the root line and add a new one.

server {
        listen       80 default_server;
        listen       [::]:80 default_server;
        # server_name  localhost;
        # root         /usr/share/nginx/html;

        server_name  localhost;
        #root         /usr/share/nginx/html;

        # Load configuration files for the default server block.
        include /etc/nginx/default.d/*.conf;

        location / {
        proxy_pass http://10.104.0.104:80;
        }

        # redirect server error pages to the static page /40x.html
        #
        error_page 404 /404.html;
            location = /40x.html {
        }

        # redirect server error pages to the static page /50x.html
        #
        error_page 500 502 503 504 /50x.html;
            location = /50x.html {

I found the solution.