I'm having hard time with understanding of Optional class.
So, I have a task where I need to replace every null initialization with Optional class.
e.g.
I have a class Client
So I made object like this:
Client chosen = null;
How am I supposed to replace that null initialization with Optional?
Your initialization could look like the following:
Optional<Client> chosen = Optional.empty();
or if you want to assign an initial value:
Client client = new Client();
Optional<Client> chosen = Optional.of(client);
You have two simple solutions to initialize the Optional in your case:
Initialize the Optional directly to empty, as described by
cwschmidt:
Optional<Client> chosen = Optional.empty();
Initialize the Optional, after the POJO has been initialized or not:
Optional<Client> chosen = Optional.ofNullable(client)
--> If client is null, the Optional chosen will be inititialized to empty, and if client has a value it will be initialized.
Related
I have a class :
class Con {
private List<Ind> inds;
}
I am using Gson in the usual way to convert a JSON string to this class object. so in case, the JSON doesn't have the key inds present this variable inds is assigned a null value. Is there a way to assign inds an empty ArrayList instead?
My Thoughts:
One straightforward way could be once the Gson object is built. Go over all the null objects and assign them to the new ArrayList<>(). Is there a better approach?
public List<Ind> getInds() {
return inds;
}
Currently I am using the above getter in a code like : con.getInds().stream() which is causing NullPointerException.
I am not sure what would be a good way to resolve this. Instead of List Should I return an Optional or Should I modify this getter like
public List<Ind> getInds() {
inds==null?new ArrayList<>():inds;
}
The above will also resolve the NullPointerException. Not sure if there are pros and cons to using this approach. Although now there is no way to identify if the Json has a key with name inds or not. For the current code that I am writing this may not be required. But there is a meaning loss here certainly.
One solution to this would be to assign default values to the fields, for example:
class Con {
private List<Ind> inds = new ArrayList<>();
}
Gson will keep this default value; only if the field is present in the JSON data it will reassign the field value.
There are however a few things to keep in mind:
Your class needs a no-args constructor (implicit or explicit); otherwise Gson might create instances without invoking the initializer blocks of the class, and therefore the field will be null
If the field is present in JSON but has a JSON null value, then Gson will still set that as value
You cannot tell afterwards whether the field was present in JSON but had an empty JSON array as value, or whether it was missing
Scenario
I need to create a Kotlin class that can receive up to 4 arguments for its constructor, but only requires at least 1 out of a set of 3 (the fourth being entirely optional). To illustrate:
class Pie {
// Completely optional, the constructor should use it if present, otherwise it may be null.
var topping: String?
// Of these three [fillingA, fillingB, fillingC] 1 or more must be present.
var fillingA: String?
var fillingB: String?
var fillingC: String?
}
Thoughts
I've attempted to use Kotlin init{} blocks for validation, or telescoping constructors, but it gets ugly fast and I've yet to solve the issue. I have not found anything in the kotlinlang.org docs on primary/secondary constructors that is more elegant, though. My preference would be to find something similar to the #Size or #NotNull annotations, but I have failed to locate anything close.
It is important to note that I am using this class as a model for an API response.
Question
What is the most concise way to validate that a Kotlin class has at least 1 of a set of arguments passed to its constructor?
Are this fillings interchangeable? You could assume that fillingA is always required and the other ones are optional, something like this:
class Pie constructor(
val fillingA: String,
val fillingB: String? = null,
val fillingC: String? = null,
val topping: String? = null
){...}
I am trying to use Optional instead of standard null checks in java
#Data
public class InputObj {
private Double savings;
}
#Data
public class Result {
private String outputSavings;
}
public Result convertInputObjToResult(InputObj inputObj){
Result result = new Result();
Optional<InputObj> optionalInputObj = Optional.ofNullable(inputObj);
optionalInputObj.map(InputObj::getSavings).map(value -> util.convertRoundAndAbs(value,true)).ifPresent(result::setOutputSavings);
return result;
}
which is equivalent of below
public Result convertInputObjToResult(InputObj inputObj){
Result result = new Result();
if(inputObj != null){
if(inputObj.getSavings() != null){
result.setOutputSavings(util.convertRoundAndAbs(inputObj.getSavings(),true));
}
}
return result;
}
I wrote some test cases and I do not get any Null Pointer Exception but I am unable to understand that ifPresent condition is at end and map is before but still I don't get any NPE. Do you see any thing wrong with this code or how it can be improved? This is part of a spring boot application and #Data annotation is used for lombok.
Here's a link to further describe how the map operation works for the Java Optional class.
If a value is present, apply the provided mapping function to it, and if the result is non-null, return an Optional describing the result. Otherwise return an empty Optional.
So in a case where you have a null value from the map method, it will automatically be converted to Optional.empty().
Then, taking a look at the ifPresent method
If a value is present, invoke the specified consumer with the value, otherwise do nothing.
So this is why you aren't getting any NPE's; the map operations are able to map null results or passed values to Optional.empty(), and the ifPresent operation doesn't execute if passed an empty Optional.
There is no issue with the code except for the typo “ optionalMembershipDetails”. Assuming you meant to use “ optionalInputObj”.
You need to read about java streams to understand the full concept. In a nutshell, operations are evaluated in lazy manner. So ifPresent call will trigger operations which appear before it. In this case, the object is wrapped inside optional, so each intermediate operation will pass another optional to the next operation. Having Optional prevents you getting NPE.
Is it possible to get the method parameter value based on parameter name in Spring AOP.
MethodSignature signature = (MethodSignature) proceedingJoinPoint.getSignature();
Method method = signature.getMethod();
method.getParameters().getName()
// possible to get the paramater names
This approach will get parameter names, not value.
proceedingJoinPoint.getArgs()
will return values not names
Then is it possible to get the value based on a parameter name?
As I searched everywhere does not exist a function that gives parameter value by name and I wrote a simple method that makes this work.
public Object getParameterByName(ProceedingJoinPoint proceedingJoinPoint, String parameterName) {
MethodSignature methodSig = (MethodSignature) proceedingJoinPoint.getSignature();
Object[] args = proceedingJoinPoint.getArgs();
String[] parametersName = methodSig.getParameterNames();
int idx = Arrays.asList(parametersName).indexOf(parameterName);
if(args.length > idx) { // parameter exist
return args[idx];
} // otherwise your parameter does not exist by given name
return null;
}
I searched for the same thing when I had to use AOP for logging function arguments and their values but it seems there is no direct way to get value based on argument name.
What I noticed however us that value returned by method.getParameters().getName() and proceedingJoinPoint.getArgs() was always in sync., i.e., for function
public void foo(String a, String b)
called as
foo("hello", "world");
method.getParameters().getName() returned ["a", "b"] and proceedingJoinPoint.getArgs() returned ["hello", "world"], in order. So you can iterate over the array by index and for each index i, the i'th argument name would correspond to i'th argument value.
I couldn't find a supporting documentation for this behavior but hey, this code has been running on production servers for about an year it never has produced incorrect result. Though I'd be glad if someone can link to a documentation of this behavior. You may even dig into reflectiion's code to verify this behavior.
I have the following running code to determine if a user can edit Object Namespace
com.tivoli.mts.PDPrincipal whoIsit = new PDPrincipal(userId,configURL);
com.tivoli.mts.PDPermission whatTheyWant = new PDPermission(objectSpaceName,GMTConstants.tamPermissions);
boolean haveAccess = whoIsit.implies(whatTheyWant);
The problem is that the implies method from com.tivoli.mts.PDPrincipal class has been deprecated.
This has been replaced by
com.tivoli.pd.jazn.PDPrincipal.implies(javax.security.auth.Subject subject)
Question is how do i construct this Subject object. Secondly, can i continue to use the deprecated clas and method?
I was able to work out a solution for this hence sharing it here so that anyone else facing the same issue can use this code.
I found that the new com.tivoli.pd.jazn.PDPermission class has a method implies which takes in a PdAuthorization context and a com.tivoli.pd.jazn.PDPrincipal object which does the same authorization checks that the previous class com.tivoli.mts.PDPrincipal use to do.
Mentioned below is how the same authorization can be done. With this code you need not implement the JAAS code.
First construct the PdAuthorizationContext as shown below. Make sure to define a static PdAuthorizationContext object so that it can be reused untill you close it. Constructing PDAuthorizationContext for every authorization check is resource intensive and not recommended. close the context at the end of your logic
URL configURL = new URL("file:" + String locationToTamConfigFile);
PDAuthorizationContext pdAuthCtx = new PDAuthorizationContext(configURL);
Next Construct the new PDPrincipal and the PdPermission objects as shown below and call the implies method
com.tivoli.pd.jazn.PDPrincipal pdPrincipal = new com.tivoli.pd.jazn.PDPrincipal(pdAuthCtx,userId);
com.tivoli.pd.jazn.PDPermission pdPermission = new com.tivoli.pd.jazn.PDPermission(objectSpaceName,"TbvA");
boolean newimpliesTry = pdPermission.implies(pdAuthCtx,pdPrincipal);