Snake Yaml

[Niraj Dedhia]

Hi Everyone,

I am new to SCALA and this is the first library I am using to read YAML File and map to my class.

I am running following Code.

case class Project(name: String, url: String)

object App {

  def main(args: Array[String]) {
    val yaml = new Yaml(new Constructor(classOf[Project]))
    yaml.setBeanAccess(BeanAccess.FIELD)
    val project = yaml.load("name : abc\nurl : def").asInstanceOf[Project]
    println("YAML READ DATA: " + project)
  }

And getting Following Error:

../Library/Java/JavaVirtualMachines/jdk1.8.0_161.jdk/Contents/Home/bin/java "-javaagent:/Applications/IntelliJ IDEA.app/Contents/lib/idea_rt.jar=57674:/Applications/IntelliJ IDEA.app/Contents/bin" -Dfile.encoding=UTF-8 -classpath /Library/Java/JavaVirtualMachines/jdk1.8.0_161.jdk/Contents/Home/jre/lib/charsets.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_161.jdk/Contents/Home/jre/lib/deploy.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_161.jdk/Contents/Home/jre/lib/ext/cldrdata.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_161.jdk/Contents/Home/jre/lib/ext/dnsns.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_161.jdk/Contents/Home/jre/lib/ext/jaccess.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_161.jdk/Contents/Home/jre/lib/ext/jfxrt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_161.jdk/Contents/Home/jre/lib/ext/localedata.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_161.jdk/Contents/Home/jre/lib/ext/nashorn.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_161.jdk/Contents/Home/jre/lib/ext/sunec.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_161.jdk/Contents/Home/jre/lib/ext/sunjce_provider.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_161.jdk/Contents/Home/jre/lib/ext/sunpkcs11.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_161.jdk/Contents/Home/jre/lib/ext/zipfs.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_161.jdk/Contents/Home/jre/lib/javaws.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_161.jdk/Contents/Home/jre/lib/jce.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_161.jdk/Contents/Home/jre/lib/jfr.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_161.jdk/Contents/Home/jre/lib/jfxswt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_161.jdk/Contents/Home/jre/lib/jsse.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_161.jdk/Contents/Home/jre/lib/management-agent.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_161.jdk/Contents/Home/jre/lib/plugin.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_161.jdk/Contents/Home/jre/lib/resources.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_161.jdk/Contents/Home/jre/lib/rt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_161.jdk/Contents/Home/lib/ant-javafx.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_161.jdk/Contents/Home/lib/dt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_161.jdk/Contents/Home/lib/javafx-mx.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_161.jdk/Contents/Home/lib/jconsole.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_161.jdk/Contents/Home/lib/packager.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_161.jdk/Contents/Home/lib/sa-jdi.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_161.jdk/Contents/Home/lib/tools.jar:/Users/ndedhia/Desktop/apollo/QueryService/target/scala-2.12/classes:/Users/ndedhia/.ivy2/cache/org.joda/joda-convert/jars/joda-convert-1.4.jar:/Users/ndedhia/.ivy2/cache/org.slf4j/slf4j-api/jars/slf4j-api-1.7.12.jar:/Users/ndedhia/.ivy2/cache/org.scala-lang.modules/scala-xml_2.12/bundles/scala-xml_2.12-1.0.6.jar:/Users/ndedhia/.ivy2/cache/org.scala-lang.modules/scala-parser-combinators_2.12/bundles/scala-parser-combinators_2.12-1.1.2.jar:/Users/ndedhia/.ivy2/cache/org.scala-lang/scalap/jars/scalap-2.12.8.jar:/Users/ndedhia/.ivy2/cache/org.scala-lang/scala-reflect/jars/scala-reflect-2.12.8.jar:/Users/ndedhia/.ivy2/cache/org.scala-lang/scala-library/jars/scala-library-2.12.8.jar:/Users/ndedhia/.ivy2/cache/org.scala-lang/scala-compiler/jars/scala-compiler-2.12.8.jar:/Users/ndedhia/.ivy2/cache/org.json4s/json4s-jackson_2.12/jars/json4s-jackson_2.12-3.2.11.jar:/Users/ndedhia/.ivy2/cache/org.json4s/json4s-core_2.12/jars/json4s-core_2.12-3.2.11.jar:/Users/ndedhia/.ivy2/cache/org.json4s/json4s-ast_2.12/jars/json4s-ast_2.12-3.2.11.jar:/Users/ndedhia/.ivy2/cache/com.thesamet.scalapb/scalapb-runtime_2.12/jars/scalapb-runtime_2.12-0.8.4.jar:/Users/ndedhia/.ivy2/cache/com.thesamet.scalapb/scalapb-runtime-grpc_2.12/jars/scalapb-runtime-grpc_2.12-0.8.4.jar:/Users/ndedhia/.ivy2/cache/com.thesamet.scalapb/lenses_2.12/jars/lenses_2.12-0.8.4.jar:/Users/ndedhia/.ivy2/cache/com.lihaoyi/sourcecode_2.12/bundles/sourcecode_2.12-0.1.4.jar:/Users/ndedhia/.ivy2/cache/com.lihaoyi/fastparse_2.12/jars/fastparse_2.12-1.0.0.jar:/Users/ndedhia/.ivy2/cache/com.lihaoyi/fastparse-utils_2.12/jars/fastparse-utils_2.12-1.0.0.jar:/Users/ndedhia/.ivy2/cache/org.codehaus.mojo/animal-sniffer-annotations/jars/animal-sniffer-annotations-1.17.jar:/Users/ndedhia/.ivy2/cache/org.checkerframework/checker-compat-qual/jars/checker-compat-qual-2.5.2.jar:/Users/ndedhia/.ivy2/cache/io.opencensus/opencensus-contrib-grpc-metrics/jars/opencensus-contrib-grpc-metrics-0.18.0.jar:/Users/ndedhia/.ivy2/cache/io.opencensus/opencensus-api/jars/opencensus-api-0.18.0.jar:/Users/ndedhia/.ivy2/cache/io.netty/netty-transport/jars/netty-transport-4.1.32.Final.jar:/Users/ndedhia/.ivy2/cache/io.netty/netty-resolver/jars/netty-resolver-4.1.32.Final.jar:/Users/ndedhia/.ivy2/cache/io.netty/netty-handler-proxy/jars/netty-handler-proxy-4.1.32.Final.jar:/Users/ndedhia/.ivy2/cache/io.netty/netty-handler/jars/netty-handler-4.1.32.Final.jar:/Users/ndedhia/.ivy2/cache/io.netty/netty-common/jars/netty-common-4.1.32.Final.jar:/Users/ndedhia/.ivy2/cache/io.netty/netty-codec-socks/jars/netty-codec-socks-4.1.32.Final.jar:/Users/ndedhia/.ivy2/cache/io.netty/netty-codec-http2/jars/netty-codec-http2-4.1.32.Final.jar:/Users/ndedhia/.ivy2/cache/io.netty/netty-codec-http/jars/netty-codec-http-4.1.32.Final.jar:/Users/ndedhia/.ivy2/cache/io.netty/netty-codec/jars/netty-codec-4.1.32.Final.jar:/Users/ndedhia/.ivy2/cache/io.netty/netty-buffer/jars/netty-buffer-4.1.32.Final.jar:/Users/ndedhia/.ivy2/cache/io.grpc/grpc-stub/jars/grpc-stub-1.18.0.jar:/Users/ndedhia/.ivy2/cache/io.grpc/grpc-protobuf-lite/jars/grpc-protobuf-lite-1.18.0.jar:/Users/ndedhia/.ivy2/cache/io.grpc/grpc-protobuf/jars/grpc-protobuf-1.18.0.jar:/Users/ndedhia/.ivy2/cache/io.grpc/grpc-netty/jars/grpc-netty-1.18.0.jar:/Users/ndedhia/.ivy2/cache/io.grpc/grpc-core/jars/grpc-core-1.18.0.jar:/Users/ndedhia/.ivy2/cache/io.grpc/grpc-context/jars/grpc-context-1.18.0.jar:/Users/ndedhia/.ivy2/cache/com.google.protobuf/protobuf-java/bundles/protobuf-java-3.6.1.jar:/Users/ndedhia/.ivy2/cache/com.google.j2objc/j2objc-annotations/jars/j2objc-annotations-1.1.jar:/Users/ndedhia/.ivy2/cache/com.google.guava/guava/bundles/guava-25.1-android.jar:/Users/ndedhia/.ivy2/cache/com.google.errorprone/error_prone_annotations/jars/error_prone_annotations-2.2.0.jar:/Users/ndedhia/.ivy2/cache/com.google.code.gson/gson/jars/gson-2.7.jar:/Users/ndedhia/.ivy2/cache/com.google.code.findbugs/jsr305/jars/jsr305-3.0.2.jar:/Users/ndedhia/.ivy2/cache/com.google.api.grpc/proto-google-common-protos/jars/proto-google-common-protos-1.12.0.jar:/Users/ndedhia/.ivy2/cache/com.fasterxml.jackson.core/jackson-annotations/bundles/jackson-annotations-2.3.0.jar:/Users/ndedhia/.ivy2/cache/com.fasterxml.jackson.core/jackson-core/bundles/jackson-core-2.3.1.jar:/Users/ndedhia/.ivy2/cache/com.fasterxml.jackson.core/jackson-databind/bundles/jackson-databind-2.3.1.jar:/Users/ndedhia/.ivy2/cache/com.ning/async-http-client/jars/async-http-client-1.9.31.jar:/Users/ndedhia/.ivy2/cache/com.thoughtworks.paranamer/paranamer/jars/paranamer-2.6.jar:/Users/ndedhia/.ivy2/cache/io.netty/netty/bundles/netty-3.10.4.Final.jar:/Users/ndedhia/.ivy2/cache/joda-time/joda-time/jars/joda-time-2.3.jar:/Users/ndedhia/.ivy2/cache/org.yaml/snakeyaml/bundles/snakeyaml-1.21.jar test.yaml.App
Exception in thread "main" Can't construct a java object for tag:yaml.org,2002:test.yaml.Project; exception=java.lang.InstantiationException: NoSuchMethodException:test.yaml.Project.<init>()
 in 'string', line 1, column 1:
    name : abc
    ^

	at org.yaml.snakeyaml.constructor.Constructor$ConstructYamlObject.construct(Constructor.java:314)
	at org.yaml.snakeyaml.constructor.BaseConstructor.constructObjectNoCheck(BaseConstructor.java:204)
	at org.yaml.snakeyaml.constructor.BaseConstructor.constructObject(BaseConstructor.java:193)
	at org.yaml.snakeyaml.constructor.BaseConstructor.constructDocument(BaseConstructor.java:159)
	at org.yaml.snakeyaml.constructor.BaseConstructor.getSingleData(BaseConstructor.java:146)
	at org.yaml.snakeyaml.Yaml.loadFromReader(Yaml.java:524)
	at org.yaml.snakeyaml.Yaml.load(Yaml.java:437)
	at test.yaml.App$.main(scalayaml.scala:14)
	at test.yaml.App.main(scalayaml.scala)
Caused by: org.yaml.snakeyaml.error.YAMLException: java.lang.InstantiationException: NoSuchMethodException:test.yaml.Project.<init>()
	at org.yaml.snakeyaml.constructor.BaseConstructor.newInstance(BaseConstructor.java:277)
	at org.yaml.snakeyaml.constructor.Constructor$ConstructMapping.construct(Constructor.java:145)
	at org.yaml.snakeyaml.constructor.Constructor$ConstructYamlObject.construct(Constructor.java:309)
	... 8 more
Caused by: java.lang.InstantiationException: NoSuchMethodException:test.yaml.Project.<init>()
	at org.yaml.snakeyaml.constructor.BaseConstructor.newInstance(BaseConstructor.java:307)
	at org.yaml.snakeyaml.constructor.BaseConstructor.newInstance(BaseConstructor.java:282)
	at org.yaml.snakeyaml.constructor.BaseConstructor.newInstance(BaseConstructor.java:275)
	

Process finished with exit code 1

Can anyone please help me to get it resolved?:

Thank you,

Niraj Dedhia

[maslovalex]

Hi,

ATM, snakeyaml supports only default constructors.

There are 2 "simple" ways you can go

1. use immutable syntax to load your case instances (see https://bitbucket.org/asomov/snakeyaml/wiki/Documentation#markdown-header-immutable-instances)

case class Project(name: String, url: String)

val yaml = new Yaml()
val project = yaml.loadAs("[abc, def]", classOf[Project])
                       

2. or provide default construtor (maybe even private, but not sure how private will work with some security settings for java)

case class Project(name: String, url: String) {
  private def this() = this("", "")
}

val yaml = new Yaml()
yaml.setBeanAccess(BeanAccess.FIELD)
val read = yaml.loadAs("{name: hello, url: here}", classOf[Project])

-alex