Groovy compiler fails with unexpected token on readObject - serialization

Question

My Gradle project has a mix of Java and Groovy classes. All source is under src/main/groovy. One of my Groovy classes contains a Map that I have created from reading a JSON string via JsonSlurper.parseText(). This class is marked Serializable.
To avoid a NotSerializableException, I have implemented my own writeObject() and readObject() methods, but my code is not compiling. I didn't find many Groovy examples, but various Java references and tutorials told me to use these signatures:
private void writeObject(java.io.ObjectOutputStream out)
throws IOException
private void readObject(java.io.ObjectInputStream in)
throws IOException, ClassNotFoundException
My class looks like this:
import groovy.json.JsonBuilder
import groovy.json.JsonSlurper
class GroovyJSONMap implements Serializable {
private static final long serialVersionUID = 20150902L
Map myJSON = [:]
GroovyJSONMap() {
//no op
}
GroovyJSONMap(String json) {
if (json) {
try {
setJSON(json)
} catch (any) {
println "WHOOPS! Not a JSON object...."
myJSON = ["invalid": true]
}
}
}
GroovyJSONMap(Map json) {
if (json) {
setJSON(json)
}
}
final void setJSON(String json) {
myJSON = new JsonSlurper().parseText(json)
}
String getJSON() {
new JsonBuilder(myJSON).toString()
}
#Override
String toString() {
getJSON()
}
private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException {
setJSON((String)in.readObject())
}
private void writeObject(ObjectOutputStream out) throws IOException {
out.writeObject(getJSON())
}
}
The compiler error:
:clean
:compileJava UP-TO-DATE
:compileGroovy
startup failed:
c:\path\to\src\main\groovy\GroovyJSONMap.groovy: 44: unexpected token: ObjectInputStream # line 110, column 29.
private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException {
^
1 error
:compileGroovy FAILED
I have moved the readObject() method to various positions in the source, but it still is not compiling. The compiler does not complain about writeObject(), only readObject(). Why is my code not compiling?

Answer 1

The compiler points to ObjectOutputStream, but the problem is really at in.
The word in is a reserved word in Groovy and cannot be used for a variable or method name.
The solution is to rename in to any non-Groovy-reserved word, such as stream (also changed writeObject() for consistency):
private void readObject(ObjectInputStream stream) throws IOException, ClassNotFoundException {
setJSON((String)stream.readObject())
}
private void writeObject(ObjectOutputStream stream) throws IOException {
stream.writeObject(getJSON())
}