I've encountered several serializable exceptions, and I did some searching on Flink's internet and doc; there are some famous solutions like transient, extends Serializable etc. Each time the origin of exception is very clear, but in my case, i am unable to find where exactly it is not serialized.
Q: How should i debug this kind of Exception?
A.scala:
class executor ( val sink: SinkFunction[List[String]] {
def exe(): Unit = {
xxx.....addSink(sinks)
}
}
B.scala:
class Main extends App {
def createSink: SinkFunction[List[String]] = new StringSink()
object StringSink {
// static
val stringList: List[String] = List()
}
// create a testing sink
class StringSink extends SinkFunction[List[String]] {
override def invoke(strs: List[String]): Unit = {
// add strs into the variable "stringList" of the compagin object StringSink
}
}
new executor(createSink()).exe()
// then do somethings with the strings
}
The exception is:
The implementation of the SinkFunction is not serializable. The
object probably contains or references non serializable fields.
Two suspicious points that I found:
The instance of StringSink is passed into another file.
In the class of StringSink, it uses a static variable stringList
of its compagin object.
I faced similar problems. It used to take longtime to find out what member/object is not serializable. The exception logs are not really helpful.
What helped me is the following JVM option, which enables more details in exception trace.
Enable this option...
-Dsun.io.serialization.extendedDebugInfo=true
My first guess would be the you don't have a no argument constructor in StringSink
Rules for POJO types Clipped from here
Flink recognizes a data type as a POJO type (and allows “by-name” field referencing) if the following conditions are fulfilled:
The class is public and standalone (no non-static inner class)
The class has a public no-argument constructor
All non-static, non-transient fields in the class (and all superclasses) are either public (and non-final) or have a public getter- and a setter- method that follows the Java beans naming conventions for getters and setters.
Just add a no argument constructor and try again
class StringSink extends SinkFunction[List[String]] {
public StringSink() {
}
#override def invoke(strs: List[String]): Unit = {
// add strs into the variable "stringList" of the compagin object StringSink
}
}
Related
I need to dynamically assign values of cacheResolver for #Cacheable in runtime because cacheResolver has the same value for #Cacheable in every method. Hence, I use Spring AOP to dynamically assign the value but then Spring does not recognize the newly added value for cacheResolver.
Seems that AOP load #Cacheable value at the beginning.
Anyone knows how to make it work?
My AOP code:
#Aspect
#Component
#Order(1)
public class CacheableAspect {
#Pointcut("#annotation(org.springframework.cache.annotation.Cacheable)")
public void cacheablePointCut() {}
#Before("cacheablePointCut()")
public void addCacheableResolver(JoinPoint joinPoint) {
Annotation cacheableAnnotation = getCacheableAnnotation(joinPoint);
Object handler = Proxy.getInvocationHandler(cacheableAnnotation);
Field f;
try {
f = handler.getClass().getDeclaredField("memberValues");
} catch (NoSuchFieldException | SecurityException e) {
throw new IllegalStateException(e);
}
f.setAccessible(true);
Map<String, Object> memberValues;
try {
memberValues = (Map<String, Object>) f.get(handler);
} catch (IllegalArgumentException | IllegalAccessException e) {
throw new IllegalStateException(e);
}
memberValues.put("cacheResolver", "cacheableResolver");
}
private Annotation getCacheableAnnotation(JoinPoint joinPoint) {
MethodSignature signature = (MethodSignature) joinPoint.getSignature();
Method method = signature.getMethod();
return method.getAnnotation(Cacheable.class);
}
}
My #Cacheable code in which i want cacheResolver is dynamically assigned a value:
#Cacheable(value = "test")
public int test() {
System.out.println("xxx");
return 10;
}
OK, so you are trying to dynamically change an annotation representation in the JVM during runtime. Not only is that ugly, but it probably does not work as you hope it would. It seems you found out that specific annotations are represented by a dynamic proxy instance during runtime, then you are successfully manipulating one of its field values. But annotations are meant to be immutable, aber depending on when e.g. Spring scans the annotations while wiring the application, your approach to modify the proxy fields later, while being a nice try, just comes too late.
How about a more canonical approach to use multiple cache managers and/or a resolver which dynamically does what you need to begin with? As much as I love AOP, it is not the answer to everyhing.
By the way, even though your aspect is kind of useless in this case, at least we can use it as an example of how to bind annotation values to advice methods parameters, i.e. you do not need to fetch the annotation from the method by reflection next time you write an aspect:
#Pointcut("#annotation(cacheable)")
public void cacheablePointCut(Cacheable cacheable) {}
#Before("cacheablePointCut(cacheable)")
public void addCacheableResolver(JoinPoint joinPoint, Cacheable cacheable) {
Object handler = Proxy.getInvocationHandler(cacheable);
// (...)
}
In my project, I'd like to get all the range class related to the given class by an restricted(somevaluefrom or allvalues from) objectproperties. I can get the restricted subclassofAxioms expressions including the given class, but how can I get the range class in these expressions? In other word, how can I get all the related classes to the given class excluding inherited subclass.
For example:
public static void printSubClassOfAxioms(OWLOntology ontology,OWLReasoner reasoner,OWLClass owlClass){
for(OWLSubClassOfAxiom ax:ontology.getSubClassAxiomsForSubClass(owlClass)){
OWLClassExpression expression=ax.getSuperClass();
System.out.println(ax);
System.out.println(expression);
}
}
The results are:
SubClassOf(<#FourCheesesTopping> <#CheeseTopping>)
SubClassOf(<#FourCheesesTopping> ObjectSomeValuesFrom(<#hasSpiciness> <#Mild>))
SubClassOf(<#FourCheesesTopping> ObjectAllValuesFrom(<#hasCountryOfOrigin> #Country>))
How can I just get the range classes #Country and #Mild
Thank you for your attention!
Write an OWLObjectVisitor and override the visit(OWL... Type) for the restrictions you're interested in. At that point,
type.getFiller()
will yield the class you're after.
Examples are in the documentation: https://github.com/owlcs/owlapi/wiki/Documentation
public class RestrictionVisitor extends OWLClassExpressionVisitor {
#Override
public void visit(#Nonnull OWLObjectSomeValuesFrom ce) {
// This method gets called when a class expression is an existential
// (someValuesFrom) restriction and it asks us to visit it
}
}
I found the following use of a wrapper class, and was wondering if it is a good practice or whether its just duplication of code for no reason.
//Class:
public class SomeClass{
public Integer someInt;
public String someString;
}
//Callout Class:
public class CalloutClass{
public SomeClass someMethod(){
//...code to do a callout to an api
SomeClass someClassObj = (SomeClass)JSON.Deserialize(APIResponse.getBody(), SomeClass.class);
return someClassObj;
}
}
//Controller:
public class SomeController {
public SomeController(){
someClassObj = calloutClassObj.someMethod();
SomeWrapper wrapperObj = new SomeWrapper();
for(SomeClass iterObj : someClassObj){
wrapperObj.someWrapperInt = iterObj.someInt;
wrapperObj.someWrapperString = iterObj.someString;
}
}
public class someWrapper{
public Integer someWrapperInt{get;set;}
public String someWrapperString{get;set;}
}
}
The wrapper class "someWrapper" could be eliminated if we just use getters and setters ({get;set;}) in "SomeClass."
Could anyone explain if there could be a reason for following this procedure?
Thanks,
James
My assumption (because, code in controller is extra pseudo) is
SomeClass is a business entity, purpose of which is to store/work with business data. By work I mean using it's values to display it (using wrapper in controller), to calculate smth in other entities or build reports... Such kind of object should be as lightweight as possible. You usually iterate through them. You don't need any methods in such kind of objects. Exception is constructor with parameter(s). You might want to have SomeObject__c as parameter or someWrapper.
someWrapper is a entity to display business entity. As for wrapper classes in controllers. Imagine, that when you display entity on edit page and enter a value for someWrapperInt property, you want to update someWrapperString property (or you can just put validation there, for example, checking if it is really Integer). Usually, as for business entity, you don't want such kind of functionality. But when user create or edit it, you may want smth like this.
I'm using app engine datastore so I have entity like this.
#PersistenceCapable
public class Author {
#PrimaryKey
#Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
#JsonProperty("id")
#JsonSerialize(using = JsonKeySerializer.class)
#JsonDeserialize(using = JsonKeyDeserializer.class)
private Key key;
....
}
When the model is sent to view, it will serialize the Key object as an Id value. Then, if I send data back from view I want to deserialize the Id back to Key object by using JsonKeyDeserializer class.
public class JsonKeyDeserializer extends JsonDeserializer<Key> {
#Override
public Key deserialize(JsonParser jsonParser, DeserializationContext deserializeContext)
throws IOException, JsonProcessingException {
String id = jsonParser.getText();
if (id.isEmpty()) {
return null;
}
// Here is the problem because I have several entities and I can't fix the Author class in this deserializer like this.
// I want to know what class is being deserialized at runtime.
// return KeyFactory.createKey(Author.class.getSimpleName(), Integer.parseInt(id))
}
}
I tried to debug the value in deserialize's parameters but I can't find the way to get the target deserialized class. How can I solve this?
You may have misunderstood the role of KeySerializer/KeyDeserializer: they are used for Java Map keys, and not as generic identifiers in database sense of term "key".
So you probably would need to use regular JsonSerializer/JsonDeserializer instead.
As to type: it is assumed that handlers are constructed for specific types, and no extra type information is passed during serialization or deserialization process: expected type (if handlers are used for different types) must be passed during construction.
When registering general serializers or deserializers, you can do this when implementing Module, as one of the arguments is type for which (de)serializer is requested.
When defining handlers directly for properties (like when using annotations), this information is available on createContextual() callback of interface ContextualSerializer (and -Deserializer), if your handler implements it: BeanProperty is passed to specify property (in this case field with annotation), and you can access its type. This information needs to be stored to be used during (de)serialization.
EDIT: as author pointed out, I actually misread the question: KeySerializer is the class name, not annotation.
I created one table using Inheritance concept to sore data into google app engine datastore. It contained following coding but it shows error.How to user Inheritance concept.What error in my program
Program 1:
#Entity
#Inheritance(strategy = InheritanceType.JOINED)
public class calender {
#Id
private String EmailId;
#Basic
private String CalName;
#Basic
public void setEmailId(String emailId) {
EmailId = emailId;
}
public String getEmailId() {
return EmailId;
}
public void setCalName(String calName) {
CalName = calName;
}
public String getCalName() {
return CalName;
}
public calender(String EmailId, String CalName) {
this.EmailId = EmailId;
this.CalName = CalName;
}
}
Program 2:
#Entity
public class method extends calender {
#Id
private String method;
public void setMethod(String method) {
this.method = method;
}
public String getMethod() {
return method;
}
public method(String method) {
this.method = method;
}
}
My constraint is I want output like this
Calendartable contain
Emailid
calendarname
and method table contain
Emailid
method
How to achieve this?
It shows the following error in this line public method(String method)
java.lang.Error: Unresolved compilation problem:
Implicit super constructor calender() is undefined. Must explicitly invoke another constructor
According to Using JPA with App Engine, the JOINED inheritance strategy is not supported.
Your code doesn't compile, add a default constructor in Calendar.
I don't think you should annotate the method field with #Id.
The datastore of GAE/J is not an RDBMS so consequently the only "inheritance strategy" that makes any sense is TABLE_PER_CLASS. I would expect GAE/J to throw an exception if you specify that strategy, and if it doesn't then you ought to raise an issue against them
Your error "constructor calender() is undefined" is rather straightforward. You should create constructor without parameters in calendar class (you can make it private if you don't want to use it). That's because compiler can create default constructor by himself only if there aren't another constructors in the class.