We Keep Coding

Java Spring / Reactor send / update flux when underlying database changed

I have a data for candidate "likes", which I'd like to send to client every time the "like" number is changed. I think this is achievable using Spring Flux? But I can't find any example for this. Most flux example is based on specific interval (e.g. every second). This might be a waste, because the transaction is not that much, and a candidate might not get likes in many minutes.
I just want to create dashboard that subscribe to "likes" change, and get updated when certain candidate "likes" number changed.
What is the way to get this?
This is what I did, and it works, but it based on interval (5 seconds), not based on data change.
public Flux<Candidate> subscribeItemChange(String id) {
return Flux.interval(Duration.ofSeconds(5)).map(t -> candidateService.getCandidateDetail(id));
}
The candidateService.getCandidateDetail is basically query database for certain id, so this is more like polling instead of "update on change".
I think I must put something on candidateService.updateLikes() below, but what should I update?
public class CandidateService {
public Candidate getCandidateDetail(String id) {
// query candidate from database
// select * from candidates where id = :id
// and return it
}
public void updateLikes(String id, int likesCount) {
// update candidates set likes_count = :likesCount where id = :id
// ...
// I think I need to write something here, but what?
}
}

You could make use of a dynamic sink, adding a field similar to:
private Sinks.Many<Candidate> likesSink = Sinks.many().multicast().onBackpressureBuffer();
...then you can:
Use sink.tryEmitNext in your updateLikes() method to publish to the sink whenever likes are updated for a candidate;
Implement your subscribeItemChange() method which uses likesSink.asFlux(), which can then be filtered if necessary to only return the stream of "like updates" for a particular candidate.

Based on #Michael Berry guide.
public void updateLikes(String id, int likesCount) {
Candidate c = getCandidateDetail(id);
c.setLikesCount(likesCount);
CandidateDummyDatasource.likesSink.tryEmitNext(c);
}
On subscriber
public Flux<Candidate> subscribeItemChange(String id) {
return CandidateDummyDatasource.likesSink.asFlux()
.filter(c -> c.getId().equals(id))
.map(data -> candidateService.getCandidateDetail(id));
}

How to handle when call requests at same time

I am using Spring boot create a restful for save data to Database.
Now I have problem when you call this service in the same time my data its duplicated in database because previous request not finish yet.
I generate number like 00001 I need to running its from database
I get last from DB
then 00001+1 = 00002
save to Database
but when request same time in database save 00002 for 2 records.
#Transactional
public List<Object> saveData(String data) {
//validate data
//Get Last Data
//set prepare data
//save data
int idLatest = Integer.parseInt(getLatest("7", "8"));
List<Object> objects = autoGenarateEntity(idLatest);
Repository.save(Object);
}
public String getLatest(String idFirst, String idSecond){
Optional<Object> running = Repository.findByBIdStartingWithOrderByBIdDesc(idFirst, idSecond).stream().findFirst();
if(running.isPresent()){
String bId =running.get();
return bId.getBId();
}else {
return "70000000";
}
}
public List<Object> autoGenarateEntity(int idLatest){
List<Object> objects = new ArrayList<>();
IntStream.range(1, 5 + 1).forEach(i -> {
Object obj = new Object();
obj.setBId(Integer.toString(idLatest + i));
obj.add(Object);
});
return objects;
}

Following are the options that can be done in this case:
1.) have unique key constraint for the column having the value of 00001. So that, the second transaction which was trying to commit same value would roll-back.
And you could use Spring-Retry mechanism to execute the second transaction with updated value
2.) Use a custom sequence Generator to increment the value, instead of handling it yourself.

I have a solution for this
#Transactional(isolation = Isolation.SERIALIZABLE)
and use spring retry

How to Iterate Datatable with type List<Class> in Cucumber

I have below feature file with Given annotation
Given user have below credentials
|user |password |
|cucumber1 |cucumber |
|cucumber2 |cucumber |
And i'm created below datamodel
public Class DataModel{
public string user;
public String password;
}
Trying to fetch data into the cucumber stepdefinition as below
Public Class stepdefinition {
#Given("^user have below credentials$")
Public void user_have_below_credintials(List<DataModel> dm){
//Iterator or foreach is required to fetch row,column data from dm
}
}
Please help me how can I Iterate object 'dm' to get row and column values

// The old way
for (int i = 0; i < dm.size(); i++) {
DataModel aDataModel = dm.get(i);
String username = aDataModel.user;
String password = aDataModel.password;
}
// A better way if java5+
for (DataModel aDataModel : dm) {
String username = aDataModel.user;
String password = aDataModel.password;
}
// another way if java8+
dm.forEach(aDataModel -> {
String username = aDataModel.user;
String password = aDataModel.password;
});
Note that the variables won't be available outside the loop with the way I wrote it. Just a demonstration of iterating and accessing the properties of each DataModel in your list.
A thing to keep in mind is that you're describing your list of DataModel objects as a data table. But it's not a table, it's simply a collection of values contained in an object, which you have a list of. You may be displaying it, or choosing to conceptualize it as a data table in your head, but the model that your code is describing isn't that, which means you aren't going to iterate through it quite like a table. Once you access a "row", the "columns" have no defined order, you may access them in any order you want to the same effect.

Creating a endpoint to return a list of objects from a database using Spring

I have a database and I want to use a endpoint to get the data. But I want to filter the data so that only certain values are returned. What I want is to call the endpoint and then get the data that I wanted out of it. I have made two methods one for calling all the data and another for calling only 1 record in the database. they both working good, but I want to now get multiple records from the database. This is what I have so far:
//This get every record
#RequestMapping(
value = API_PREFIX_1_0 + ENDPOINT_coupon + "/getCoupon",
method = RequestMethod.GET)
public Collection<Coupon> couponGetAll()
{
return couponService.getAll();
}
//this get only one record based on the ID of the table
#RequestMapping(
value = API_PREFIX_1_0 + ENDPOINT_coupon + "/{id}",
method = RequestMethod.GET)
public Coupon couponGetById(#PathVariable(value = "id") final long id) {
return couponService.getById(id);
}
What I want to do is use an array or a list of id to get the data from the server.
Thank you for any help with this

The spring CrudRepository already provides a method to find items by a set of ids:
Iterable<T> findAll(Iterable<ID> ids)
this method should be triggered by your service if you are using a CrudRepository in your persistence layer.
Then you could add a request parameter to your couponGetAll() method where to get the ids and send it to your service.
#RequestMapping( value = API_PREFIX_1_0 + ENDPOINT_coupon + "/listOfCoupons", method = RequestMethod.GET)
public Iterable<Coupon> couponGetMine(#RequestParam(name="ids")String ids) {
Iterable<Long> longIds = convertToLong(ids);
return couponService.getAll(ids);
}
The client side url to call would look something like this:
.../listOfCoupons?ids=2,4,7,3
In the endpoint you extract the numbers out of the string. Maybe there is a nicer solution but this is what is in my mind in this short time.
Convert the id string e.g.:
public Iterable<Long> convertToLong(final String ids){
String[] idArray = ids.split(",");
List<Long> idsAsLong = new ArrayList<>();
for (int i = 0; i < idArray.length; i++) {
idsAsLong.add(Long.parseLong(idArray[i]));
}
return idsAsLong;
}

Hibernate caches the query while data is being changed

I'm developing an application which connects to an outside service to fetch new SMS. Theses messages are stored in a local database by Hibernate. My client can search these messages based on numerous parameters such as time, number, and etc.
After calling the search method with a list of parameters called 'List1', I get the desired result without any problems. Though while I'm waiting for this result a new message has arrived.
Soon after, I call the search method with same parameter list again and I'm expecting to get the new message as well, but I get the previous result.
I have checked my database and the new message is present so all I can think of is Hibernate caching. Since both queries are exactly the same, I guess hibernate return the same result set as before.
In case my assumption is correct, how can I overcome this problem? If not, so what exactly is going on?
Edit
here is relevant part of my source code. Following two methods will be invoked when client initiates a search request:
smsService.refresh();
JSONArray result = smsService.retrieveMessages(...);
#Transactional
public JSONArray retrieveMessages(Long periodBegining, Long periodEnd, String order, Integer limit, String profile, Boolean unread, String correspondent) {
List<ShortMessage> messageList = shortMessageDAO.find(beginDate, endDate, order, limit, profile, unread, correspondent);
JSONArray result = new JSONArray();
for (ShortMessage message : messageList)
result.put(message.toJSON());
shortMessageDAO.markRead(messageList);
return result;
}
#Transactional
public void refresh() {
webService.authentication(serviceUsername, servicePassword);
while(webService.hasUnread() > 0) {
SMS sms = webService.retrieveMessage();
ShortMessage message = new ShortMessage(sms.getHash(), sms.getFrom(), sms.getTo(), "DEFAULT", sms.getMessage(), new Date(sms.getTime()), true);
shortMessageDAO.insert(message);
}
}
}
public List<ShortMessage> find(Date beginDate, Date endDate, String order, Integer limit, String profile, Boolean unread, String correspondent) {
Criteria criteria = sessionFactory.getCurrentSession().createCriteria(ShortMessage.class);
criteria.add(Restrictions.ge("time", beginDate));
criteria.add(Restrictions.le("time", endDate));
criteria.add(Restrictions.eq("profile", profile));
if (unread)
criteria.add(Restrictions.eq("unread", true));
if (correspondent != null)
criteria.add(Restrictions.eq("origin", correspondent));
criteria.addOrder(order.equals("ASC") ? Order.asc("time") : Order.desc("time"));
criteria.setMaxResults(limit);
criteria.setCacheMode(CacheMode.IGNORE);
return (ArrayList<ShortMessage>) criteria.list();
}

Yes it looks like hibernate is caching your query and returning cached results.
Please give us a overview of your code to suggest better.
Below listed are two ways of controlling the caching behaviour of queries:-
1) At the main named query level:-
#NamedQuery(
name = "myNamedQuery"
query = "SELECT u FROM USER WHERE u.items is EMPTY"
hints = {#QueryHint(name = "org.hibernate.cacheMode", value = "IGNORE")}
)
2) At individual query level :-
Query q = session.createQuery("from User")
.setCacheMode(CacheMode.IGNORE);

After running numerous test, I found out that this problem is not cache related at all. Upon receiving each message I would have stored the time of arrival based on data provided by SMS panel and not my own machine time.
There was a slight time difference (20 seconds to be exact) between those 2 which was the reason behind the query not returning the new received message.