add piston nix pkg for openjdk-java

runtimes/openjdk-java.nix

@@ -0,0 +1,34 @@
+{pkgs, piston, ...}:
+let
+    pkg = pkgs.openjdk;
+in piston.mkRuntime {
+    language = "java";
+    version = pkg.version;
+    runtime = "openjdk";
+    aliases = [];
+
+    run = ''
+        mv $1 $1.java
+        filename=$1.java
+        shift
+        ${pkg}/bin/java $filename "$@"
+    '';
+
+    tests = [
+        (piston.mkTest {
+            files = {
+                "test.java" = ''
+                    public class PrinOK {
+                        public static void main(String[] args) {
+                            System.out.println("OK");
+                        }
+                    }
+                '';
+            };
+            args = [];
+            stdin = "";
+            packages = [];
+            main = "test.java";
+        })
+    ];
+}