如何使用 Java 8 迭代 Java 对象列表的列表

Question

How to iterate and get through list of list of objects using Java 8 Also need to get the count of distinct customerIds

final List<CustomerIssues> issues = customerIssues.collectList().block();
    
for (final CustomerIssues e : issues) {
    final List<CustomerEditVO> v = e.getData();
    for (final CustomerEditVO edit : v) {
        System.out.println("Id " + edit.getCustomerId());     
    }
    System.out.println("Comments " + e.getComments());
}   

public class CustomerIssues {
    private List<CustomerEditVO> data; 
    private String comments;
}

public class CustomerEditVO { 
    private String customerId;
    private Integer units;
}

CustomerEditVO and CustomerIssues are POJOs

Post Request body --->

{
   "data":[
      {
         "units":"176",
         "CustomerId":"122"
      },
      {
         "units":"400",
         "CustomerId":"1998"
      }
   ],
   "comments" :"Testing"
}

Answer 1

I have created all the given POJO's and created the objects and list for your query.And also overrides the toString() method in order to clearly show the objects in the list output and also extracted and print the list at each operation.

NOTE:: 1) Need to override hashcode and equals method to find the distinct() list and count based on customerId. 2) You can use flatMap to convert listOfList of objects in a single list of objects

import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.List;
import java.util.stream.Collectors;

public class Test {
    public static void main(String[] args) {

        CustomerIssues issues1 =
                new CustomerIssues(Collections.singletonList(new CustomerEditVO("customer1", 100)),"comment1");
        CustomerIssues issues2 =
                new CustomerIssues(Collections.singletonList(new CustomerEditVO("customer2", 200)),"comment2");
        CustomerIssues issues3 =
                new CustomerIssues(Collections.singletonList(new CustomerEditVO("customer3", 300)),"comment3");
        CustomerIssues issues4 =
                new CustomerIssues(Collections.singletonList(new CustomerEditVO("customer4", 400)),"comment4");
        CustomerIssues issues5 =
                new CustomerIssues(Collections.singletonList(new CustomerEditVO("customer5", 500)),"comment5");
        CustomerIssues issues6 =
                new CustomerIssues(Collections.singletonList(new CustomerEditVO("customer5", 600)),"comment6");
        CustomerIssues issues7 =
                new CustomerIssues(Collections.singletonList(new CustomerEditVO("customer5", 700)),"comment7");
        CustomerIssues issues8 =
                new CustomerIssues(Collections.singletonList(new CustomerEditVO("customer1", 800)),"comment8");
        CustomerIssues issues9 =
                new CustomerIssues(Collections.singletonList(new CustomerEditVO("customer2", 900)),"comment9");
        CustomerIssues issues10 =
                new CustomerIssues(Collections.singletonList(new CustomerEditVO("customer3", 1000)),"comment10");

        List<CustomerIssues> customerIssuesList =
                Arrays.asList(issues1,issues2,issues3,issues4,issues5,issues6,issues7,issues8,issues9,issues10);
        System.out.println("Total issues:: " + customerIssuesList + "\n");

        List<List<CustomerEditVO>> listOfListCustomerEditVos =
                customerIssuesList.stream().map(CustomerIssues::getData).collect(Collectors.toList());
        System.out.println("Total listOfListCustomerEditVos:: " + listOfListCustomerEditVos + "\n");

        List<CustomerEditVO> listOfCustomerEditVos =
                listOfListCustomerEditVos.stream().flatMap(Collection::stream).collect(Collectors.toList());
        System.out.println("Total listOfCustomerEditVos:: " + listOfCustomerEditVos + "\n");

        List<String> listOfDistinctCustomerIds = listOfCustomerEditVos.stream().map(CustomerEditVO::getCustomerId)
                .distinct().collect(Collectors.toList());

        System.out.println("List of distinct customer Ids:: " + listOfDistinctCustomerIds + "\n");
        System.out.println("Distinct customer Ids count:: " + listOfDistinctCustomerIds.size() + "\n");

    }
}

import java.util.List;

public class CustomerIssues {

    private List<CustomerEditVO> data;
    private String comments;

    public CustomerIssues(List<CustomerEditVO> data, String comments) {
        this.data = data;
        this.comments = comments;
    }

    public List<CustomerEditVO> getData() {
        return data;
    }

    public void setData(List<CustomerEditVO> data) {
        this.data = data;
    }

    public String getComments() {
        return comments;
    }

    public void setComments(String comments) {
        this.comments = comments;
    }

    @Override
    public String toString() {
        return "CustomerIssues{" +
                "data=" + data +
                ", comments='" + comments + '\'' +
                '}';
    }
}

import java.util.Objects;

public class CustomerEditVO {

    private String customerId;
    private Integer units;

    public CustomerEditVO(String customerId, Integer units) {
        this.customerId = customerId;
        this.units = units;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        CustomerEditVO that = (CustomerEditVO) o;
        return customerId.equals(that.customerId);
    }

    @Override
    public int hashCode() {
        return Objects.hash(customerId);
    }

    public String getCustomerId() {
        return customerId;
    }

    public void setCustomerId(String customerId) {
        this.customerId = customerId;
    }

    public Integer getUnits() {
        return units;
    }

    public void setUnits(Integer units) {
        this.units = units;
    }

    @Override
    public String toString() {
        return "CustomerEditVO{" +
                "customerId='" + customerId + '\'' +
                ", units=" + units +
                '}';
    }
}

Output

Total issues:: [CustomerIssues{data=[CustomerEditVO{customerId='customer1', units=100}], comments='comment1'}, CustomerIssues{data=[CustomerEditVO{customerId='customer2', units=200}], comments='comment2'}, CustomerIssues{data=[CustomerEditVO{customerId='customer3', units=300}], comments='comment3'}, CustomerIssues{data=[CustomerEditVO{customerId='customer4', units=400}], comments='comment4'}, CustomerIssues{data=[CustomerEditVO{customerId='customer5', units=500}], comments='comment5'}, CustomerIssues{data=[CustomerEditVO{customerId='customer5', units=600}], comments='comment6'}, CustomerIssues{data=[CustomerEditVO{customerId='customer5', units=700}], comments='comment7'}, CustomerIssues{data=[CustomerEditVO{customerId='customer1', units=800}], comments='comment8'}, CustomerIssues{data=[CustomerEditVO{customerId='customer2', units=900}], comments='comment9'}, CustomerIssues{data=[CustomerEditVO{customerId='customer3', units=1000}], comments='comment10'}]

Total listOfListCustomerEditVos:: [[CustomerEditVO{customerId='customer1', units=100}], [CustomerEditVO{customerId='customer2', units=200}], [CustomerEditVO{customerId='customer3', units=300}], [CustomerEditVO{customerId='customer4', units=400}], [CustomerEditVO{customerId='customer5', units=500}], [CustomerEditVO{customerId='customer5', units=600}], [CustomerEditVO{customerId='customer5', units=700}], [CustomerEditVO{customerId='customer1', units=800}], [CustomerEditVO{customerId='customer2', units=900}], [CustomerEditVO{customerId='customer3', units=1000}]]

Total listOfCustomerEditVos:: [CustomerEditVO{customerId='customer1', units=100}, CustomerEditVO{customerId='customer2', units=200}, CustomerEditVO{customerId='customer3', units=300}, CustomerEditVO{customerId='customer4', units=400}, CustomerEditVO{customerId='customer5', units=500}, CustomerEditVO{customerId='customer5', units=600}, CustomerEditVO{customerId='customer5', units=700}, CustomerEditVO{customerId='customer1', units=800}, CustomerEditVO{customerId='customer2', units=900}, CustomerEditVO{customerId='customer3', units=1000}]

List of distinct customer Ids:: [customer1, customer2, customer3, customer4, customer5]

Distinct customer Ids count:: 5

I hope this will solve your problem.

Thanks Girdhar

Answer 2

If it is needed to count the number of distinct customerId in CustomerEditVO it may be implemented in a simpler way by flattening the list of CustomerIssues using Stream::flatMap , followed by Stream::distinct and Stream::count :

long distinctCustomerIds = issues.stream() // Stream<CustomerIssues>
        .flatMap(issue -> issue.getData().stream()) // Stream<CustomerEditVO>
        .map(CustomerEditVO::getCustomerId)
        .distinct()
        .count();

To iterate the list of issues using Java 8 facilities may be implemented using Collection::stream or Collection::parallelStream as well as by Iterable::forEach .

Answer 3

You can count them as simple as this:

long count = issues.stream()
                   .map(CustomerIssues::getData) 
                   .flatMap(List::stream)
                   .map(CustomerEditVO::getCustomerId)
                   .distinct()
                   .count();

Or you could even chain your Flux calls with Stream API calls (although that might make the code a little harder to read:

long count = customerIssues.collectList()
                           .block()
                           .stream()
                           .map(CustomerIssues::getData) 
                           .flatMap(List::stream)
                           .map(CustomerEditVO::getCustomerId)
                           .distinct()
                           .count();

Answer 4

Try this:

long i=issues.stream().peek(e->System.out.println(e.getComments()))
    .map(CustomerIssues::getData)
    .collect(ArrayList<CustomerEditVO>::new, (bl, l) -> {
      l.stream().forEach(cev -> System.out.println("Id " + cev.getCustomerId()));
      ((List<CustomerEditVO>)bl).addAll(l);
      }, List::addAll)
     .stream().distinct().count();

System.out.println("distinct customers: " + i);

Also add equals and hashCode to your customer vo like this:

class CustomerEditVO {
    String customerId;
    Integer units;
    
    public CustomerEditVO(String ci, Integer unit) {
        this.customerId = ci;
        this.units = unit;
    }
    public String getCustomerId() {
        return this.customerId;
    }
    @Override
    public boolean equals(Object o) {
        if(o instanceof CustomerEditVO == false) return false;
        return this.customerId.equals(((CustomerEditVO)o).customerId);
    }
    @Override
    public int hashCode() {
        return this.customerId.hashCode(); 
    }
}