Develop Reference

How do you specify/figure out which minimum JDK is required for running the fat jar?

I used sbt-assembly on a project where I have some java 14 jars, and my local machine has JDK 8 as the default JDK.
The sbt assembly task was successful and produced a fat jar.
When I run it with JDK 8, I get the error:
Exception in thread "main" java.lang.UnsupportedClassVersionError: javafx/event/EventTarget has been compiled by a more recent version of the Java Runtime (class file version 55.0), this version of the Java Runtime only recognizes class file versions up to 52.0
JDK 11 (version 55.0) is the one I need. And sure enough, when I set JDK 11 on my shell, I can run the fat jar.
Is there a way to be explicit about the target JDK version in the build.sbt file?
Also, I'm surprised that even though I have Java 14 jars in the dependency, the application runs fine on JDK 11. Is it just an example of Java's supreme backwards compatibility in action? I would like to know what else could be at work.
This is what my build.sbt looks like
name := "scalafx-app"
version := "0.1"
scalaVersion := "2.13.3"
scalacOptions += "-Ymacro-annotations"
useCoursier := false
assemblyMergeStrategy in assembly := {
case "module-info.class" => MergeStrategy.concat
case x =>
val oldStrategy = (assemblyMergeStrategy in assembly).value
oldStrategy(x)
}
lazy val scalaTest = "org.scalatest" %% "scalatest" % "3.1.1"
lazy val osName = System.getProperty("os.name") match {
case n if n.startsWith("Linux") => "linux"
case n if n.startsWith("Mac") => "mac"
case n if n.startsWith("Windows") => "win"
case _ => throw new Exception("Unknown platform!")
}
lazy val javaFXModules = Seq("base", "controls", "fxml", "graphics", "media", "web")
lazy val root = (project in file("."))
.settings(
libraryDependencies += scalaTest % Test,
// scalafx
libraryDependencies += "org.scalafx" %% "scalafx" % "14-R19",
libraryDependencies ++= javaFXModules.map(m =>
"org.openjfx" % s"javafx-$m" % "14.0.1" classifier(osName) withJavadoc()
),
libraryDependencies += "org.scalafx" %% "scalafxml-core-sfx8" % "0.5",
// javafx custom components
libraryDependencies += "com.jfoenix" % "jfoenix" % "9.0.9",
libraryDependencies += "org.kordamp.ikonli" % "ikonli-javafx" % "11.4.0",
libraryDependencies += "org.kordamp.ikonli" % "ikonli-material-pack" % "11.4.0",
// json parsing
libraryDependencies += "com.typesafe.play" %% "play-json" % "2.9.0",
libraryDependencies += "com.squareup.moshi" % "moshi" % "1.9.3",
// logging
libraryDependencies += "com.typesafe.scala-logging" %% "scala-logging" % "3.9.2",
libraryDependencies += "ch.qos.logback" % "logback-classic" % "1.2.3",
)

A JAR is just like a zip of classes, each class is the one that you can check with javap to see which JDK version they need by looking at the value of the "major version" field; see this.
If you want to ensure the classes are compiled to a specific Java version, you can use the release & target scalac options.
Like this:
// Ensure the compiler emits Java 8 bytecode.
scalacOptions ++= Seq("-release", "8", "-target:8")
release is used to specify which Java sdtlib is used.
target is used t specify which bytcode version is emitted.

Spark does not find Scala specific methods

The problem is that every job fails with the following exception:
Exception in thread "main" java.lang.NoSuchMethodError: scala.Predef$.refArrayOps([Ljava/lang/Object;)[Ljava/lang/Object;
at ps.sparkapp.Classification$.main(Classification.scala:35)
at ps.sparkapp.Classification.main(Classification.scala)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.apache.spark.deploy.SparkSubmit$.org$apache$spark$deploy$SparkSubmit$$runMain(SparkSubmit.scala:743)
at org.apache.spark.deploy.SparkSubmit$.doRunMain$1(SparkSubmit.scala:187)
at org.apache.spark.deploy.SparkSubmit$.submit(SparkSubmit.scala:212)
at org.apache.spark.deploy.SparkSubmit$.main(SparkSubmit.scala:126)
at org.apache.spark.deploy.SparkSubmit.main(SparkSubmit.scala)
This exception meas that the task can not find the method. I develop using the intelij community edition. I have no problems compiling the package. All dependencies are packaged correctly. Here my build.sbt:
name := "SparkApp"
version := "1.0"
scalaVersion := "2.11.6"
libraryDependencies += "org.apache.spark" % "spark-core_2.11" % "2.1.1"
libraryDependencies += "org.apache.spark" % "spark-mllib_2.11" % "2.1.1"
scala -version
Scala code runner version 2.11.6 -- Copyright 2002-2013, LAMP/EPFL
I found out that this error has somehow to do with scala because it only happens when I use functionality that is native to scala, e.g scala for loop, .map or .drop(2).
The class and everything is still written in scala, but if i avoid functionality like .map or drop(2) then everything works fine.
import org.apache.spark.ml.feature.VectorAssembler
import org.apache.spark.sql.SparkSession
import org.apache.spark.ml.linalg.Vector
object Classification {
def main(args: Array[String]) {
...
//df.printSchema()
var dataset = df.groupBy("user_id","measurement_date").pivot("rank").min()
val col = dataset.schema.fieldNames.drop(2) // <- here the error happens
// take all features and put them into one vector
val assembler = new VectorAssembler()
.setInputCols(col)
.setOutputCol("features")
val data = assembler.transform(dataset)
data.printSchema()
data.show()
sc.stop()
}
}
As said if I do not use .drop(2) everything works perfectly, but avoiding these methods is no option since that is very painful..
I could not find any solution on the web, any ideas?
BTW: I can use these methods within the spark-shell, which i find strange.
Thanks in advance.
NOTE 1)
I use:
SPARK version 2.1.1
Using Scala version 2.11.8 (OpenJDK 64-Bit Server VM, Java 1.8.0_131)

Try adding the actual Scala libraries etc as a project dependency. E.g.:
libraryDependencies += "org.scala-lang" % "scala-library" % "2.11.6"

Cannot use a method returning play.mvc.WebSocket as a Handler for requests in Play?

GET /status controllers.Application.handleWebSocketConnection()
Here is the relevant source code.
public WebSocket handleWebSocketConnection() {
return WebSocket.withActor(new F.Function<ActorRef, Props>() {
#Override
public Props apply(ActorRef actorRef) throws Throwable {
return UserActor.props(actorRef, "");
}
});
}
here is my build.sbt
import play.routes.compiler.InjectedRoutesGenerator
import play.sbt.PlayScala
name := "hello"
version := "1.0"
lazy val `dashboard` = (project in file(".")).enablePlugins(PlayScala)
scalaVersion := "2.11.8"
libraryDependencies ++= Seq(
jdbc ,
cache ,
ws ,
specs2 % Test,
"io.netty" % "netty-all" % "4.0.0"
)
unmanagedResourceDirectories in Test <+= baseDirectory ( _ /"target/web/public/test" )
resolvers ++= Seq(
"scalaz-bintray" at "https://dl.bintray.com/scalaz/releases"
)
routesGenerator := InjectedRoutesGenerator
fork in run := true
I am using Play version 2.4.2 and all the source code is in java 8. I get the following error. I am not sure what is going with my routes and the controller. I followed the link here.
[error] /Users/hello/Documents/java/test_app/conf/routes:8: Cannot use a method returning play.mvc.WebSocket[?0] as a Handler for requests
[error] GET /status controllers.Application.handleWebSocketConnection()
[error] /Users/hello/Documents/java/test_app/conf/routes:8: not enough arguments for method createInvoker: (implicit hif: play.core.routing.HandlerInvokerFactory[play.mvc.WebSocket[?0]])play.core.routing.HandlerInvoker[play.mvc.WebSocket[?0]].
[error] two errors found
[error] (compile:compile) Compilation failed
any ideas?

I don't have the rep needed to add a comment... so here we go:
I'm wondering if specifying the type of messages handled by your websocket would fix the problem, try:
public WebSocket<String> handleWebSocketConnection()
This is of course assuming your websocket is expecting Strings coming in from the browser as welle as send Strings back.

Unable to import com.google.firebase.FirebaseApplication in Play Frame work application

I am trying to add Firebase in my play framework project. I followed the following link
https://medium.com/#RICEaaron/scala-firebase-da433df93bd2#.m1fwlvc8l
I am done with following steps
created project in firebase developer console
generated private server key and downloaded the json file
Added firebase server sdk dependency in build.sbt
This is my build.sbt code:
name := """NeutrinoRPM"""
version := "1.0-SNAPSHOT"
lazy val root = (project in file(".")).enablePlugins(PlayJava)
scalaVersion := "2.11.1"
resolvers += Resolver.sonatypeRepo("snapshots")
libraryDependencies ++= Seq(
javaJdbc,
cache,
javaWs,
javaCore,
"ws.securesocial" %% "securesocial" % "3.0-M3",
"org.julienrf" %% "play-jsmessages" % "1.6.2",
javaJpa.exclude("org.hibernate.javax.persistence", "hibernate-jpa-2.0-api"),
"org.hibernate" % "hibernate-entitymanager" % "4.3.4.Final",
"mysql" % "mysql-connector-java" % "5.1.9",
"com.typesafe.play" %% "play-mailer" % "2.4.0",
"com.nimbusds" % "nimbus-jose-jwt" % "3.8.2",
"com.wordnik" %% "swagger-play2" % "1.3.12",
"org.webjars" % "swagger-ui" % "2.1.8-M1",
"com.google.api-client" % "google-api-client" % "1.21.0",
"com.google.apis" % "google-api-services-analytics" % "v3-rev127-1.21.0",
"com.google.code.gson" % "gson" % "2.6.2",
"com.google.http-client" % "google-http-client-gson" % "1.21.0",
"org.apache.pdfbox" % "pdfbox" % "2.0.1",
"com.google.firebase" % "firebase-server-sdk" % "3.0.1"
)
Now I am trying to initialize the Firebase server SDK with this code snippet:
FileInputStream serviceAccount = new FileInputStream("path/to/serviceAccountKey.json");
FirebaseOptions options = new FirebaseOptions.Builder()
.setCredential(FirebaseCredentials.fromCertificate(serviceAccount))
.setDatabaseUrl("https://<DATABASE_NAME>.firebaseio.com/")
.build();
FirebaseApp.initializeApp(options);
But when i try to import
com.google.firebase.FirebaseApplication
com.google.firebase.FirebaseOptions
com.google.firebase.database
I get this error: The import com.google.firebase.FirebaseApplication can not be resolved
I spent too many hours on google to search the solution to my problem but ended up with no help. Please help me.

Your dependency on the Firebase server SDK is old:
"com.google.firebase" % "firebase-server-sdk" % "3.0.1"
For new Firebase projects created through firebase.google.com, you should be using the Firebase Admin SDK when running in the JVM. The maven dependency is com.google.firebase:firebase-admin:4.1.0.
There is no FirebaseApplication in that SDK - perhaps you are instead looking for FirebaseApp?

Mysterious Play 2.4 Injection exception

Recently upgraded to Play 2.4 and I'm still learning all the little quirks and such. I'm trying to just get my index page working and I'm having a hard time of it, and I know it's something small I'm missing. Here is the error
CreationException: Unable to create injector, see the following errors:
1) Error in custom provider, Configuration error: Configuration error[Cannot connect to database [default]]
while locating play.api.db.DBApiProvider
while locating play.api.db.DBApi
for parameter 0 at play.db.DefaultDBApi.<init>(DefaultDBApi.java:28)
at play.db.DefaultDBApi.class(DefaultDBApi.java:28)
while locating play.db.DefaultDBApi
while locating play.db.DBApi
for field at play.db.DBModule$NamedDatabaseProvider.dbApi(DBModule.java:61)
while locating play.db.DBModule$NamedDatabaseProvider
at com.google.inject.util.Providers$GuicifiedProviderWithDependencies.initialize(Providers.java:149)
at play.db.DBModule.bindings(DBModule.java:40):
And my configuration information (yes that port number for mysql is correct)
application.conf
db.default.driver=com.mysql.jdbc.Driver
db.default.url="jdbc:mysql:localhost:33060/coffee_bean"
db.default.username=
db.default.password=""
ebean.default = ["models.*"]
Main controller
public Result index() {
ObjectNode response = Json.newObject();
Configuration config = Play.application().configuration();
response.put(config.getString("coffee.bean.message.key"),config.getString("coffee.bean.success.message"));
response.put(config.getString("version"), config.getString("coffee.bean.version"));
return ok(response);
}
built.sbt
name := """coffee-bean"""
version := "1.0-SNAPSHOT"
lazy val root = (project in file(".")).enablePlugins(PlayJava)
scalaVersion := "2.11.6"
libraryDependencies ++= Seq(
javaJdbc,
cache,
javaWs,
"mysql" % "mysql-connector-java" % "5.1.36",
evolutions
)
// Play provides two styles of routers, one expects its actions to be injected, the
// other, legacy style, accesses its actions statically.
routesGenerator := InjectedRoutesGenerator
lazy val myProject = (project in file("."))
.enablePlugins(PlayJava, PlayEbean)
plugins.sbt
// The Play plugin
addSbtPlugin("com.typesafe.play" % "sbt-plugin" % "2.4.2")
// Web plugins
addSbtPlugin("com.typesafe.sbt" % "sbt-coffeescript" % "1.0.0")
addSbtPlugin("com.typesafe.sbt" % "sbt-less" % "1.0.6")
addSbtPlugin("com.typesafe.sbt" % "sbt-jshint" % "1.0.3")
addSbtPlugin("com.typesafe.sbt" % "sbt-rjs" % "1.0.7")
addSbtPlugin("com.typesafe.sbt" % "sbt-digest" % "1.1.0")
addSbtPlugin("com.typesafe.sbt" % "sbt-mocha" % "1.1.0")
// Play enhancer - this automatically generates getters/setters for public fields
// and rewrites accessors of these fields to use the getters/setters. Remove this
// plugin if you prefer not to have this feature, or disable on a per project
// basis using disablePlugins(PlayEnhancer) in your build.sbt
addSbtPlugin("com.typesafe.sbt" % "sbt-play-enhancer" % "1.1.0")
// Play Ebean support, to enable, uncomment this line, and enable in your build.sbt using
// enablePlugins(SbtEbean). Note, uncommenting this line will automatically bring in
// Play enhancer, regardless of whether the line above is commented out or not.
addSbtPlugin("com.typesafe.sbt" % "sbt-play-ebean" % "1.0.0")
addSbtPlugin("com.typesafe.play" % "sbt-plugin" % "2.4.0")
Anything else you need to see?
So far I've tried just reimporting dependencies, double checking to make sure version are right, going through the documentation again, and so far nothing has worked. I'm expecting a certain user will have all the answers :)

Database connection configuration is missing.
Define it in conf\application.conf:
db.default.driver=com.mysql.jdbc.Driver
db.default.url="jdbc:mysql://localhost/playdb"
db.default.username=playdbuser
db.default.password="a strong password"

My config:
<persistence xmlns="http://xmlns.jcp.org/xml/ns/persistence"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence http://xmlns.jcp.org/xml/ns/persistence/persistence_2_1.xsd"
version="2.1">
<persistence-unit name="defaultPersistenceUnit" transaction-type="RESOURCE_LOCAL">
<provider>org.hibernate.jpa.HibernatePersistenceProvider</provider>
<non-jta-data-source>caribbeanDS</non-jta-data-source>
<properties>
<property name="hibernate.dialect" value="org.hibernate.dialect.H2Dialect"/>
<property name="hibernate.hbm2ddl.auto" value="update"/>
</properties>
</persistence-unit>
</persistence>
My code:
version := "1.0-SNAPSHOT"
lazy val root = (project in file(".")).enablePlugins(PlayJava)
scalaVersion := "2.11.6"
libraryDependencies ++= Seq(
javaJdbc,
cache,
javaWs,
javaJpa,
"org.hibernate" % "hibernate-entitymanager" % "4.3.10.Final" // replace by your jpa implementation
)
// Play provides two styles of routers, one expects its actions to be injected, the
// other, legacy style, accesses its actions statically.
routesGenerator := InjectedRoutesGenerator
fork in run := true
# Default database configuration using MySQL database engine
# Connect to playdb as playdbuser
db.caribbean.driver=com.mysql.jdbc.Driver
db.caribbean.url="jdbc:mysql://localhost:8889/bahamasnet"
db.caribbean.username=root
db.caribbean.password="root"
db.caribbean.jndiName=caribbeanDS
jpa.default=defaultPersistenceUnit