From a tweet von Gunnar Morling
I learned today that my work on JFR-Doc is used for JfrUnit. In a follow up Gunnar asked me how those JSON-Files are generated and I promised to write up a blog what I hacked together in an evening to get this going.
Get the input
The first and most important thing is to get all JFR-Events (those commands are executed eg in your Java-17-Install-Dir)
./java -XX:StartFlightRecording:filename=/tmp/out-bin.jfr \ -version # Dump JFR Data ./jfr metadata /tmp/out-bin.jfr > /tmp/openjdk-17.jfr
The final file holds content like this
class boolean {
}
class byte {
}
class char {
}
class double {
}
class float {
}
class int {
}
class long {
}
class short {
}
@Name("java.lang.Class")
@Label("Java Class")
class Class {
@Label("Class Loader")
ClassLoader classLoader;
@Label("Name")
String name;
@Label("Package")
Package package;
@Label("Access Modifiers")
int modifiers;
@Label("Hidden")
boolean hidden;
}
...
Looks like these are Java-Classes so one strategy could be to just compile those and use Reflection to extract meta informations but I went another route
Parsing the .jfr-File
Handcrafting a parser is certainly not the way to go. I needed something that could provide me a fairly simple Logical-AST. There are BNF-Definitions for Java but I wanted something much simpler so I fired up my Eclipse IDE and created an Xtext-Project using the wizards and replaced the content in the .xtext-File with
grammar at.bestsolution.jfr.JFRMeta with org.eclipse.xtext.common.Terminals
generate jFRMeta "http://www.bestsolution.at/jfr/JFRMeta"
Model:
classes+=Clazz*;
Clazz:
annotations+=Annotation*
'class' name=ID ( 'extends' super=QualifiedName )? '{'
attributes += Attribute*
'}';
Attribute:
annotations+=Annotation*
type=[Clazz|ID] array?='[]'? name=ID ';'
;
Annotation:
'@' type=[Clazz|ID] ('(' (values+=AnnotationValue |
('{' values+=AnnotationValue
(',' values += AnnotationValue)* '}')) ')')?
;
AnnotationValue:
valueString=STRING | valueBoolean=Boolean | valueNum=INT
;
enum Boolean:
TRUE="true" | FALSE="false"
;
QualifiedName:
ID ('.' ID)*;
That’s all required because the .jfr-File is extremly simple so we don’t need a more complex definition.
How to convert
Well although Xtext is primarily used to develop DSL-Editors for the Eclipse IDE one can run the generated parser in plain old Java. So all now needed is to write a generator who parses the .jfr-File(s) and generate different output from it (HTML, JSON, …) and because although Java now has multiline strings Xtend is the much better choice to write a “code”-generator.
package at.bestsolution.jfr
import org.eclipse.xtext.resource.XtextResourceSet
import org.eclipse.xtext.resource.XtextResource
import java.util.ArrayList
import org.eclipse.emf.common.util.URI
import java.nio.file.Files
import java.nio.file.Paths
import at.bestsolution.jfr.jFRMeta.Model
import java.nio.file.StandardOpenOption
import at.bestsolution.jfr.jFRMeta.Clazz
import static extension at.bestsolution.jfr.GenUtil.*
import at.bestsolution.jfr.jFRMeta.Attribute
class JSONGen {
def static void main(String[] args) {
val versions = createVersionList(Integer.parseInt(args.get(0)))
val injector = new JFRMetaStandaloneSetup().createInjectorAndDoEMFRegistration();
val resourceSet = injector.getInstance(XtextResourceSet);
resourceSet.addLoadOption(XtextResource.OPTION_RESOLVE_ALL, Boolean.TRUE);
val models = new ArrayList
for( v : versions ) {
val resource = resourceSet.getResource(
URI.createURI("file:/Users/tomschindl/git/jfr-doc/openjdk-"+v+".jfr"), true);
val model = resource.getContents().head as Model;
models.add(model)
}
for( pair : models.indexed ) {
val model = pair.value
var version = versions.get(pair.key)
val preModel = pair.key == 0 ? null : models.get(pair.key - 1)
Files.writeString(Paths.get("/Users/tomschindl/git/jfr-doc/openjdk-"+version+".json"),model.generate(preModel,version), StandardOpenOption.TRUNCATE_EXISTING, StandardOpenOption.CREATE)
}
}
def static generate(Model model, Model prevModel, String ver) '''
{
"version": "«ver»",
"distribution": "openjdk",
"events": [
«val evts = model.classes.filter[c|c.super == "jdk.jfr.Event"]»
«FOR e : evts»
«e.generateEvent»«IF e !== evts.last»,«ENDIF»
«ENDFOR»
],
"types": [
«val types = model.classes.filter[c|c.super === null]»
«FOR t : types»
«t.generateType»«IF t !== types.last»,«ENDIF»
«ENDFOR»
]
}
'''
def static generateEvent(Clazz clazz) '''
{
"name": "«clazz.name»",
"description": "«clazz.description»",
"label": "«clazz.label»",
"categories": [
«val cats = clazz.categories»
«FOR cat : cats»
"«cat»"«IF cat !== cats.last»,«ENDIF»
«ENDFOR»
],
"attributes": [
«FOR a : clazz.attributes»
«a.generateAttribute»«IF a !== clazz.attributes.last»,«ENDIF»
«ENDFOR»
]
}
'''
def static generateType(Clazz clazz) '''
{
"name": "«clazz.name»",
"attributes": [
«FOR a : clazz.attributes»
«a.generateAttribute»«IF a !== clazz.attributes.last»,«ENDIF»
«ENDFOR»
]
}
'''
def static generateAttribute(Attribute a) '''
{
"name": "«a.name»",
"type": "«a.type.name»",
"contentType": "«a.contentType»",
"description": "«a.description»"
}
'''
}
All sources are available at https://github.com/BestSolution-at/jfr-doc if you look at this code keep in mind that it was hacked together in an evening
Tomsondev Blog 