Update example02.sc to use more efficient reading through memory mapped files

Author: plokhotnyuk

jsoniter-scala-examples/README.md

@@ -125,5 +125,48 @@ Expected output:
 
 ## RFC-8259 validation (example02)
 
-An example of a command line application that reads the system input, parses and validates JSON according to the latest
-specification and in case of any error prints it to the system error output
+An example of a command line application that reads the provided file, parses and validates JSON according to the latest
+specification and in case of any error prints it to the system error output.
+
+For faster JSON validation the example uses reading through memory mapped files which are not supported by Scala.js.
+
+### Build uber jar, print its size, and measure its start up time
+
+```sh
+scala-cli --power package --assembly example02.sc --force -o example02.jar
+ls -l ./example02.jar
+time ./example02.jar test.json 2> /dev/null
+```
+Expected output:
+```text
+real	0m0.096s
+user	0m0.138s
+sys 	0m0.017s
+```
+### Build GraalVM native image, print its size, and measure its start up time
+
+```sh
+scala-cli --power package --jvm graalvm --native-image example02.sc --force -o example02_graalvm.bin 
+ls -l ./example02_graalvm.bin
+time ./example02_graalvm.bin test.json 2> /dev/null
+```
+Expected output:
+```text
+real	0m0.003s
+user	0m0.000s
+sys 	0m0.002s
+```
+
+### Build Scala Native image, print its size, and measure its start up time
+
+```sh
+scala-cli --power package --native-version 0.4.16 --native example02.sc --force -o example02_native.bin
+ls -l ./example02_native.bin
+time ./example02_native.bin test.json 2> /dev/null
+```
+Expected output:
+```text
+real	0m0.003s
+user	0m0.000s
+sys 	0m0.003s
+```

jsoniter-scala-examples/example02.sc

@@ -1,13 +1,15 @@
 //> using dep "com.github.plokhotnyuk.jsoniter-scala::jsoniter-scala-core::2.28.2"
 
 import com.github.plokhotnyuk.jsoniter_scala.core._
+import java.io.RandomAccessFile
+import java.nio.channels.FileChannel
 
 val jsonCodec: JsonValueCodec[Unit] = new JsonValueCodec[Unit] {
   override def decodeValue(in: JsonReader, default: Unit): Unit = decode(in, 1024) // Max depth is 1024
 
   override def encodeValue(x: Unit, out: JsonWriter): Unit = ???
 
-  override def nullValue(): Unit = ()
+  override def nullValue: Unit = ()
 
   private[this] def decode(in: JsonReader, depth: Int): Unit = {
     val b = in.nextToken()
@@ -43,10 +45,14 @@ val jsonCodec: JsonValueCodec[Unit] = new JsonValueCodec[Unit] {
         }) ()
         if (!in.isCurrentToken('}')) in.objectEndOrCommaError()
       }
-    } else in.readNullOrError(nullValue(), "expected JSON value")
+    } else in.readNullOrError(nullValue, "expected JSON value")
   }
 }
 
-try readFromStream(System.in)(jsonCodec) catch {
+try {
+  val fileChannel = new RandomAccessFile(args(0), "rw").getChannel
+  val mappedByteBuffer = fileChannel.map(FileChannel.MapMode.READ_WRITE, 0, fileChannel.size)
+  readFromByteBuffer(mappedByteBuffer)(jsonCodec)
+} catch {
   case ex: Throwable => ex.printStackTrace(System.err)
 }

jsoniter-scala-examples/test.json

@@ -0,0 +1 @@
+{"x:123}