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

Solution

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)
  }
}

Comments

[Warrior]

Still the def tape is returning null. Actually i am trying to load an existing .yaml file using snakeYaml in my groovy project. I have a class called YamlTape.groovy which contains method to load the Yaml file

[tim_yates]

Are you actually using betamax, or are you just using it as sideways way to load yaml? If you're just trying to load yaml, you don't need to import the whole of betamax

[tim_yates]

@Warrior actually, you're doing the same in your readFrom method...see edit

[Warrior]

We are using betamax to record the restful service in the yaml file. I am able to record it but when try to reload the yaml file it crashes.