基于java 8中的匹配属性比较两个不同对象类型的列表

Question

I have two Lists of type:

class User {
    Long userId;
    String userName;
    Long workflowStatusId;
}

class WorkflowStatus {
    Long workflowStatusId;
    String workflowStatusName;
    Long userId;
}

Each user object have workflowStatusId. Similarly, each WorkflowStatus have userId associated with them. I am saving User s first, which is giving me List<User> users where workflowStatusId is set as null for each object. Now for each of these user in users, I am making new entries in WorkflowStatus which is giving me List<WorkflowStatus> workflowStatuses . Now I want to set these newly inserted workflowStatusId in my previously saved User object, so I am trying to match userId property in both and want to set this workflowStatusId once that match is found. I am trying to do something like:

List<User> filteredList = users
                                            .stream()
                                             .filter(user -> workflowStatuses
                                                                .stream()
                                                                .allMatch(user.getUserId().equals(workflowStatus.getUserId())))
                                                                .map(how to set workflowStatusId in user? can i do something like user->user.setWorkflowStatusId((workflowStatus.getWorkflowStatusId)))
                                            .collect(Collectors.toList()); 

Trying to find some solution, if it is possible to do using Java 8 streams . What is the better way to Compare two Lists of different object types based on some common property in java 8?

Answer 1

It is not a good idea to have side effects like setting of properties in the middle of a Stream. A better solution is to just create a Map of your User instances:

Map<Long, User> usersById =
    users.stream().collect(Collectors.toMap(User::getUserId, u -> u));

Now you can simply loop through your WorkflowStatus objects:

for (WorkflowStatus status : workflowStatuses) {
    Long userId = status.getUserId();
    Long statusId = status.getWorkflowStatusId();
    usersById.get(userId).setWorkflowStatusId(statusId);
}

Answer 2

<User> filteredList = users.stream().filter(user -> workflowStatuses
                                                            .stream()
                                                            .allMatch(user.getUserId().equals(workflowStatus.getWorkflowStatusId)))
                                                            .map(how to set workflowStatusId in user? can i do something like user->user.setWorkflowStatusId((workflowStatus.getWorkflowStatusId)))
                                        .collect(Collectors.toList());

On this generate the lamba exprestion loop on java 8

workflowStatus.foreach( data ) -> { user.setworkflowStatusId(data.getWorkflowStatusId);user.setuserId(data.getuserId);}

Or simple replace below

<User> filteredList = users.stream().filter(user -> workflowStatuses
                                                        .stream()
                                                        .allMatch(user.getUserId().equals(workflowStatus.getWorkflowStatusId)))
                                                        .map(workflowStatus.foreach( data ) -> { user.setworkflowStatusId(data.getWorkflowStatusId);user.setuserId(data.getuserId)})
                                    .collect(Collectors.toList());