How to print the build target in Java?

Question

Say we have a class PrintTarget with main() inside of it.

Can we build/compile such that , somehow we should be able to send the build-target-name inside of the main. and when the main() is called it will print the build-target name.

I dont want the target name WHILE building. we all know how to do that. I want the generated JAR to remember the target name. Say we created the jar printTarget.jar And executed the jar #>java printTarget.jar I want this invocation to print the target name.

Answer 1

To pass data from build time to run time you need to write the data into a file that is stored in the JAR, e.g.

<jar destfile="printTarget.jar">
  <fileset dir="${classes.dir}" />
  <manifest>
    <attribute name="Main-Class" value="com.example.Main" />
  </manifest>
  <!-- This is just a way to create a zip entry from inline text in the build
       file without having to <echo> it to a real file on disk first -->
  <mappedresources>
    <mergemapper to="com/example/buildinfo.properties"/>
    <string encoding="ISO-8859-1"># this is a generated file, do not edit
      targetname=custom-build-1
    </string>
  </mappedresources>
</jar>

which you can then read in your main method

package com.example;
import java.io.*;
import java.util.Properties;

public class Main {
  public static void main(String[] args) throws Exception {
    Properties buildInfo = new Properties();
    InputStream is = Main.class.getResourceAsStream("buildinfo.properties");
    try {
      buildInfo.load(is);
    } finally {
      is.close();
    }

    System.out.println("Build target was " +
       buildInfo.getProperty("targetname", "<unknown>"));
  }
}

This should print

Build target was custom-build-1