Jdk 11 new features

Sumary

• Testing a single-file source program
• A Maven project: jdbc and csv export

Today Oracle just released JDK 12. Like most developers, I am still using JDK 1.7 or 1.8. But I am curious about it. So I spent some time on JDK 11.

Single-file source code

• Basically you do not need to compile first before you run.
• Java single-source has no dependency management: you still have to set up classpath just like you run a compiled Java class file.
• Groovy can do this long time ago and has a dependency management tool called Grape

• Both Go and dotnet core have built-in dependency management

  // java ./Hello.java
  
  import picocli.CommandLine;
  import picocli.CommandLine.Option;
  import picocli.CommandLine.Parameters;
  
  import java.io.File;
  
  public class Hello implements Runnable 
  {
  @Option(names = { "-v", "--verbose" }, description = "Verbose mode. Helpful for troubleshooting. " +
  "Multiple -v options increase the verbosity.")
  private boolean[] verbose = new boolean[0];
  
  @Option(names = { "-h", "--help" }, usageHelp = true,
  description = "Displays this help message and quits.")
  private boolean helpRequested = false;
  
  @Parameters(arity = "1..*", paramLabel = "FILE", description = "File(s) to process.")
  private File[] inputFiles;
  
  public void run() {
      if (verbose.length > 0) {
          System.out.println(inputFiles.length + " files to process...");
      }
      if (verbose.length > 1) {
          for (File f : inputFiles) {
              System.out.println(f.getAbsolutePath());
          }
      }
  }
  
  public static void main(String[] args) {
      CommandLine.run(new Hello(), args);
  }
  }

It does work

Check my github repo for more examples

A sample Maven project

In Maven project, first step is to properly set it up the plugins for compiling and packaging.

In my Maven project, I tested accessing Postgres db and creating csv file from a query.