Read a YAML file in Groovy

Question

I am trying to load an existing YAML file (which uses snakeYaml library) in my Groovy project. I have a class called YamlTape.groovy which contains method to load the YAML file using the following code.

static YamlTape readFrom(Reader reader) {
    try {
        println "YamlTape : inside readFrom reader.size() = "+reader+" YamlTape: "+YamlTape

        yaml.loadAs(reader, YamlTape)
        println "YamlTape : after readfrom"
    } catch (YAMLException e) {
        println "YamlTape : inside catch block"
        throw new TapeLoadException('Invalid tape', e)
    }
}

and trying to call this method from another groovy class.

Code:

    YamlTape loadTape(String name) {
    println "YamlTapeLoader : inside loadTape"
    def file = fileFor(name)
    println "YamlTapeLoader : inside loadTape filename -name: "+name
    println "YamlTapeLoader : inside loadTape filename -file: "+file

    file.setReadable(true);
    file.setWritable(true);

    if (file.isFile()) {
        println "YamlTapeLoader : inside file.isFile() : "+file.isFile()
        def tape = file.withReader(FILE_CHARSET) { reader ->
            YamlTape.readFrom(reader)

            println "YamlTapeLoader : inside readFrom : "+reader
        }
        println "YamlTapeLoader : tape : "+tape


        tape
    } else {
        println "YamlTapeLoader : inside ELSE : "
        new YamlTape(name: name)
    }
}

But the tape variable in load tape method always returns null. I have added some logs and found the code is able to access the yaml file but unable to parse Yaml document and return as Java Object.

Logs are :

YamlTapeLoader : inside loadTape
YamlTapeLoader : inside loadTape filename -name: kar
YamlTapeLoader : inside loadTape filename -file: /Users/Shared/AATest/Record/kar.yaml
YamlTapeLoader : inside file.isFile() : true
YamlTape : inside readFrom reader.size() = java.io.LineNumberReader@34189cab YamlTape: class co.freeside.betamax.tape.yaml.YamlTape
YamlTape : inside getYaml 
YamlTape : representer = co.freeside.betamax.tape.yaml.TapeRepresenter@201a503f
YamlTape : constructor = org.yaml.snakeyaml.constructor.Constructor@16e7eec9
YamlTape : dumperOption = org.yaml.snakeyaml.DumperOptions@39d7af3
YamlTape : after readfrom
YamlTapeLoader : inside readFrom : java.io.LineNumberReader@34189cab
YamlTapeLoader : tape : null

Answer 1

The withReader block implicitly returns the last line of the closure, which in your case is:

        println "YamlTapeLoader : inside readFrom : "+reader

And println returns null , so change the code to:

    def tape = file.withReader(FILE_CHARSET) { reader ->
        def ret = YamlTape.readFrom(reader)
        println "YamlTapeLoader : inside readFrom : "+reader
        ret // Return the result of YamlTape.readFrom
    }

And it should work

Edit

Your readFrom method has the same error... Change it to:

static YamlTape readFrom(Reader reader) {
  try {
    println "YamlTape : inside readFrom reader.size() = "+reader+" YamlTape: "+YamlTape

    def ret = Yaml.loadAs(reader, YamlTape)
    println "YamlTape : after readfrom"

    ret // Return the YamlTape
  } catch (YAMLException e) {
    println "YamlTape : inside catch block"
    throw new TapeLoadException('Invalid tape', e)
  }
}