Description
Woong Gyu La opened DATAMONGO-884 and commented
Revised upon request by Thomas Darimont:
NullPointerException occurs when calling overriden Object method of the field with "@DBRef(lazy=true)"
Assume class B has override toString method as below:
public class B
{
@Id
private String id;
private String value;
@Override
public String toString(){
return String.format("B[id='%s', value='%s']",id,value);
}
}
Assume class A contains class B as a field with annotation "DBRef(lazy=true)" as below:
public class A
{
@Id
private String id;
@DBRef(lazy=true)
public B b;
@Override
public String toString()
{
return String.format("A[b='%s']",b);
}
}
When a class A object has queried from MongoTemplate and calls to println as below:
A obj = mongoTemplate().findOne(new Query(...), A.class);
System.out.println(obj);
The above code raised exception in "LazyLoadingInterceptor" class within "DefaultDbRefResolver" class:
@Override
public Object intercept(Object obj, Method method, Object[] args, MethodProxy proxy) throws Throwable {
return ReflectionUtils.isObjectMethod(method) ? method.invoke(obj, args) : method.invoke(ensureResolved(), args);
}
It seems that ReflectionUtils.isObjectMethod(method) returns "true" for even the method is an overriden method, so results to call
method.invoke(obj, args); // which result NullPointerException since obj is null.
where it should actually call
method.invoke(ensureResolved(), args);
p.s. It seems obj is always "null" within the function "DefaultDbRefResolver::LazyLoadingInterceptor::intercept()." I was wondering if there is any reason for checking if the method is an Object method by "ReflectionUtils.isObjectMethod(method)," since whether it is object method or not, method.invoke(obj,args) will always result NullPointerException due to obj is "null."
Original Message:
DefaultDbRefResolver.intercept function only check if the method is originally from Object class, but does not check if the method is an override method of Object. when the method is an override method of Object then it should call ensureResolved() instead of just calling method.invoke(obj,args).
For example.
When @DBRef(lazy=true) is used and toString method is override, it result NullPointerException.
public class B
{
@Id
private String id;
private String value;
@Override
public String toString(){
return String.format("B[id='%s', value='%s']",id,value);
}
}
public class A
{
@DBRef(lazy=true)
public B b;
@Override
public String toString()
{
return String.format("A[b='%s']",b);
}
}
So in DefaultDbRefResolver.intercept method should change as below
@Override
public Object intercept(Object obj, Method method, Object[] args, MethodProxy proxy) throws Throwable {
return ReflectionUtils.isObjectMethod(method) && method.getDeclaringClass()==Object.class ? method.invoke(obj, args) : method.invoke(ensureResolved(), args);
}
Affects: 1.4.1 (Codd SR1)
Referenced from: pull request #158
Backported to: 1.4.2 (Codd SR2)