How to convert List to Map - Key of Map should be a combination of multiple keys
#AllArgsConstructor
#NoArgsConstructor
#Data
#Builder
public class Student {
private long id;
private String firstName;
private String lastName;
private String street;
private String city;
public static void main(String[] args) {
List<Student> students = Arrays.asList(
Student.builder().id(1).firstName("John").lastName("Doe").build(),
Student.builder().id(1).firstName("Jane").lastName("Doe").build(),
Student.builder().id(1).firstName("Mike").lastName("Doe").build(),
Student.builder().id(1).firstName("Jack").lastName("Doe").build()
);
LinkedHashMap<Long, String> collect = students.stream()
.collect(Collectors.toMap(
Student::getId, Student::getFirstName, (x, y) -> x + ", " + y, LinkedHashMap::new));
System.out.println(collect);
// Answer I am expecting is Ex: {1johnDoe=[id=1,firstName=John, lastName=Doe]}
}
}
Using Java 17
I have implemented the below code using some of the latest java features apart from Java 8.
Records in java 14 : As of JDK 14, we can replace our data classes with records. Records are immutable classes that require only the type and name of fields. We do not need to create constructor, getters, setters, override toString() methods, override hashcode and equals methods.
List.of() in java 9: It is a static method that returns the immutable list of elements passed as arguments. Here in the below scenario, we will get the list of four student objects.
public class Test {
public static void main(String[] args) {
record Student(long id, String firstName, String lastName,String street, String city){}
Student s1 = new Student(1,"F1","L1","S1","C1");
Student s2 = new Student(2,"F2","L2","S2","C2");
Student s3 = new Student(3,"F3","L3","S3","C3");
Student s4 = new Student(4,"F4","L4","S4","C4");
Map<String,Student> output =
List.of(s1,s2,s3,s4).stream().collect(Collectors.toMap(x -> x.id() + x.firstName(),
Function.identity(), (k, v) -> k, LinkedHashMap::new));
System.out.println(output);
}
}
Output:
{1F1=Student[id=1, firstName=F1, lastName=L1, street=S1, city=C1], 2F2=Student[id=2, firstName=F2, lastName=L2, street=S2, city=C2], 3F3=Student[id=3, firstName=F3, lastName=L3, street=S3, city=C3], 4F4=Student[id=4, firstName=F4, lastName=L4, street=S4, city=C4]}
You can do as follows
LinkedHashMap<String, Student> collect = students.stream()
.collect(
Collectors.toMap(
student->(String.join("", Long.toString(student.getId()),student.getFirstName(),student.getLastName())),
student->student,
(v1,v2)->v1,
LinkedHashMap::new));
collect.forEach((k,v)->System.out.println(k+"="+v));
I think, you want key as String and value as Student into map
I have spring boot application which is integrated with Redis cache. Have to implement caching for one of the method call. That method argument is an object with multiple params which is external Request object. This object params will vary for each request also based on that param and its values output of the method is varies. I need to create a cache key using that Request object field/param values. How to achieve it.
We can use SimpleKeyGenerator only when method params are static?
UserService.java
#Cacheable(value = "usercache", keyGenerator="customKeyGenerator")
public UserResponse getUserResp(User user){
//Some backend calls
return user
}
User.java
public class User {
private String firstname;
private String lastname;
private Integer age;
private Date dob;
private Address address;
// Another 10 params
}
In this method implementation User object is dynamic. I have to create a cache key based on User object fields which is having valid non null values. How to achieve it.
I have implemented as like below.
User.java
public class User implements Serializable {
private String firstname;
private String lastname;
private Integer age;
private Date dob;
private Address address;
// Another 10 params
#Override
public int hashCode() {
final int prime = 31;
//Add necessary fields
}
#Override
public boolean equals(Object obj) {
if (this == obj)
return true;
//Add necessary fields
}
}
public class UserKeyGenerator implements KeyGenerator{
private static final String UNDERSCORE_DELIMITER = "_";
#Override
public Object generate(Object target, Method method, Object... params) {
String cacheKey = null;
if(params.length > 0) {
StringJoiner paramStrJoiner = new StringJoiner(UNDERSCORE_DELIMITER);
User userReq = (User) params[0];
paramStrJoiner.add(target.getClass().getSimpleName());
paramStrJoiner.add(method.getName());
paramStrJoiner.add(String.valueOf(userReq.hashCode()));
cacheKey = paramStrJoiner.toString();
}
return cacheKey;
}
I have a class in my domain called Activity that looks like the following
#JsonIdentityInfo(generator=ObjectIdGenerators.PropertyGenerator.class, property="id")
#NodeEntity
public class Activity {
#GraphId
private Long id;
private String title;
private String description;
#Relationship(type = "RELATED_TO", direction = Relationship.UNDIRECTED)
private List<Activity> relatedActivities = new ArrayList<>();
public Activity() {
}
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public String getTitle() {
return title;
}
public String getDescription() {
return description;
}
public Collection<Activity> getRelatedActivities() {
System.out.println("getting relatedActivities");
System.out.println(relatedActivities);
return relatedActivities;
}
public void addRelatedActivity(Activity activity) {
this.relatedActivities.add(activity);
}
}
I create relationships using the following repository class:
#RepositoryRestResource(collectionResourceRel = "relationships", path = "relationships")
public interface RelationshipRepository extends GraphRepository<Relationship> {
#Query("MATCH (a1:Activity), (a2:Activity) " +
"WHERE a1.title = {0} AND a2.title = {1}" +
"CREATE (a1)-[:RELATED_TO]->(a2)")
void addRelationship(String a1Title, String a2Title);
}
I have verified that this code works using the neo4j browser, which lets me see existing nodes and relationships between them. However, when I access getRelatedActivities() on an Activity object, it's always an empty array, even if that Activity has other Activity nodes related to it, clearly visible in neo4j.
How can I get the relatedActivites on an Activity to automatically populate based on its relationships correctly?
The problem in your code is that you define the "target" as an Activity here
#Relationship(type = "RELATED_TO", direction = Relationship.UNDIRECTED)
private List<Activity> relatedActivities = new ArrayList<>();
but you also have a RelationshipEntity class in your code base: Relationship with the same type RELATED_TO.
When OGM gets the result it tries to match every field but since it converts the relationship type RELATED_TO to the RelationshipEntity and not an Activity object, it does not fill the list in the Activity class.
i want to group the item element according to date such that , if item object's date is greater than present date then , it will fall into futuredate group and if date is less than present date then it will fall into pastdate
and then i want to reduce on these group so that i can get aggregate qty,price of these group, further aggregate value returned from pastdate group shold sit in oldPrice and oldQty of object
public class Item {
private String name;
private int qty;
private int oldQty;
private BigDecimal price;
private BigDecimal oldPrice;
Private Date date;
//constructors, getter/setters
}
Map<String, List<Item>> groupByP =
items.stream().collect(Collectors.groupingBy((row)->{
//logic to seperate items into two group based on date
}));
How to proceed after this
There are two ways to this, the first is first partition and later compute:
(this partitions, then return a Pair that holds the sum of all quantities and an average of the price)
Map<Boolean, List<Item>> partioned = items.stream()
.collect(Collectors.partitioningBy(item -> item.getDate().compareTo(now) > 0));
partioned.get(Boolean.FALSE).stream()
.map(item -> new AbstractMap.SimpleEntry<>(item.getOldQty(), item.getOldPrice()))
.reduce((entry1, entry2) -> {
int sum = entry1.getKey() + entry2.getKey();
BigDecimal averagePrice = entry1.getValue().add(entry2.getValue()).divide(BigDecimal.valueOf(2));
return new AbstractMap.SimpleEntry<>(sum, averagePrice);
}).get();
The second us writing a custom collector, but I doubt it will be more clear.
If you want to split items into to groups you need to use partitioningBy collector.
#AllArgsConstructor
#Getter
public static class Item {
private String name;
private int qty;
private int oldQty;
private BigDecimal price;
private BigDecimal oldPrice;
private Date date;
}
public static void main(String [] args) {
List<Item> items = Lists.newArrayList();
Map<Boolean, List<Item>> partitionedItems = items.stream()
.collect(Collectors.partitioningBy(item -> item.getDate().after(new Date())));
}
In this case you'll get
Map<Boolean, List<Item>>
Now you can:
map.get(true)
returns a list of items that match the condition
map.get(false)
returns a list of items that don't match the condition
Having those two lists you can make any reduction you want.
I am trying to use AutoMapper for the first time and have some problems with it.
My code is below and I get error below. Maybe someone could show how to map the list of models?
cannot convert from 'System.Linq.IQueryable<AnonymousType#1>' to 'Entity.Product' C:\Users\Administrator\Projects\PC\trunk\PC\Controllers\AdminController.cs 37 100 PC
public class ProductViewModel
{
public int Id { get; set; }
public string Name { get; set; }
public int UsersCount { get; set; }
}
var products = _repository.GetProducts(true).Select(p=> new
{
p.Id,
p.Name,
UsersCount = 0
});
Mapper.CreateMap<Product, ProductViewModel>();
ViewData["Products"] = Mapper.Map<IEnumerable<Product>, IEnumerable<ProductViewModel>>(products); //Error appears on products object
//Product domain model(linq2sql generated model)
public partial class Product : INotifyPropertyChanging, INotifyPropertyChanged
{
private static PropertyChangingEventArgs emptyChangingEventArgs = new PropertyChangingEventArgs(String.Empty);
private int _Id;
private bool _Active;
private System.Nullable<int> _Sort;
private System.Nullable<int> _Category;
private string _Name;
private int _ProductTypeId;
private decimal _Price;
private System.Nullable<int> _Months;
private System.Nullable<int> _Credits;
private string _Features;
private string _BlockReason;
private string _BuyUrl1;
private string _BuyUrl2;
private bool _UsersManager;
}
In your LINQ query you select an anonymous object. Make sure you select a Product which is your source type (or more specifically IEnumerable<Product>):
IEnumerable<Product> products = _repository.GetProducts(true);
IEnumerable<ProductViewModel> productsViewModel = Mapper.Map<IEnumerable<Product>, IEnumerable<ProductViewModel>>(products);
return View(productsViewModel);
Also do not call Mapper.CreateMap<TSource, TDest> inside your controller action. This must be called only once in the lifetime of the AppDomain, ideally in your Application_Start.
Also notice that I have gotten rid of ViewData which is a great thing. You don't need ViewData. You are working with view models. That's what they are supposed to do. Contain information that will be needed by your view in a strongly typed manner.