Rule to prohibit local variables by specific type

[dgroup]

ObjectMapper is better to have as field than a local variable due to performance reasons

[dykov]

//LocalVariableDeclaration/Type/ReferenceType/ClassOrInterfaceType
[pmd-java:typeIs('xxx')]
(: or for list of strings (property type="List[String]" name="classes"):
[some $class in $classes satisfies pmd-java:typeIs($class)]
:)

[dykov]

@dgroup , should we check cases when a ObjectMapper comes as a method parameter? Or should it be a separate rule?

import com.fasterxml.jackson.databind.ObjectMapper;             
public class Foo {
    public void bar(ObjectMapper objectMapper) {}
}

[dykov]

@dgroup , also, should we check the following cases?

String str = new ObjectMapper().writeValueAsString(obj);

[dgroup]

Yes, we need.