This is "Hello World" Example for Java.

The structure HelloWorld package is like this:

example.java.helloworld/
|-- HelloWorld
|   `-- Main.java
|-- LICENSE
|-- Manifest.txt
`-- README.md

For compile the main class for package, execute the follow command:

javac HelloWorld/Main.java

This generate the Main.class file into HelloWorld directory.

For run the main class for package, execute the follow command:

java -cp . HelloWorld.Main

This show the Hello world message.

For pack the main class for package as a JAR file, execute the follow command:

jar cfme Main.jar Manifest.txt HelloWorld.Main HelloWorld/Main.class

For run the JAR file packed, execute the follow command:

java -jar Main.jar

This show the Hello world message.

To sign the jar you need to create a keystore, you acn do this with next command:

keytool -genkeypair \
  -alias signFiles \
  -validity 300 \
  -keystore keystore.jks

To export the public certificate use:

keytool -export -keystore keystore.jks -alias signFiles -file public.cer

For the actual signing of the jar file:

jarsigner -signedjar \
  signed-HelloWorld.jar HelloWorld.jar signFiles \
  -tsa http://sha256timestamp.ws.symantec.com/sha256/timestamp \
  -keystore keystore.jks

In order to verify the jar is correctly signed:

jarsigner -verify signed-HelloWorld.jar -keystore tmp-keystore.jks

If someone else wants to verify he should first import you public certificate:

keytool -importcert \
  -file public.cer \
  -storepass tmptmp \
  -noprompt \
 -keystore tmp-keystore.jks

All these steps have also been automated for you in a [Makefile](makefile) .

You can simply run make in the directory to:

• compile the Main.java class
• bundle it into a jar
• create a keystore and prompt for password and info
• sign the jar
• export the public certificate

Other useful commands are clean to remove all generated files, and verify to create a new keystore, import the public certificate and verify the signed jar using that new keystore.

• java - How to run a JAR file - Stack Overflow.
• Setting an Application's Entry Point (The Java™ Tutorials > Deployment > Packaging Programs in JAR Files).
• hello world project: https://github.com/macagua/example.java.helloworld
• Gist used as reference for makefile: https://gist.github.com/isaacs/62a2d1825d04437c6f08
• using java keytool: https://docs.oracle.com/javase/8/docs/technotes/tools/unix/keytool.html
• how to fix the timestamp error: https://stackoverflow.com/questions/21695520/tsa-or-tsacert-timestamp-for-applet-jar-self-signed