How to return a list of multiple JSON items in java

问题

I am trying to figure out how to return multiple JSON items. Right now I am able, to return a single JSON like so:

{
    "result": {
        "userId": "abcde123",
        "telephoneNumber": "1-555-5555555"
        },
    "error": null
}

But I would like to return multiple JSON items, like so:

{
    "result": {{
        "userId": "abcde123",
        "telephoneNumber": "1-555-5555555"
        }
        {
        "userId": "fghi456",
        "telephoneNumber": "1-333-3333333"
        }
        },
    "error": null
}

I can view the multiple JSON items as string, like below, but I would like to return it as multiple JSON items, but I don't know how:

[LDAPModel(userId=abcde123, telephoneNumber=1-555-5555555), LDAPModel(userId=fghi456, telephoneNumber=1-333-3333333]

I am a complete beginner in Java, and I don't know the syntax or much in Java. But I was given these codes (including the one below) from SpringBoot; I really don't understand what it is doing, and so I have no idea how create an output of list.

Currently, this is what I was given:

public Optional<LDAPModel> getDirectReports(String cdsID) {
        LdapQuery ldapQuery = LdapQueryBuilder.query()
                .searchScope(SearchScope.SUBTREE)
                .where("objectclass").is("person")
                .and("managerID").like(cdsID);

        List<LDAPModel> ldapModelList = ldapTemplate.search(ldapQuery, (Attributes attrs) ->
                LDAPModel.builder()
                        .userId(getValue(attrs, "userid"))
                        .telephoneNumber(getValue(attrs, "phoneNumber"))
                        .build());
//        for (int ii = 0; ii < ldapModelList.size(); ii++) {
//            Optional.of(ldapModelList.get(ii));
//            ldapModelList.isEmpty() ? Optional.empty() : Optional.of(ldapModelList.get(ii));
//        }
        return ldapModelList.isEmpty() ? Optional.empty() : Optional.of(ldapModelList.get(0));
    }

I tried putting it in a loop (like in the commented out code above), but I don't know how create a list. I tried removing the get(0), but there was a syntax error... There are many things I tried, but it just did not help.

Anyone can help?

Update/Edit: Thank you all for your answers. I posted a follow up question here. If you have a chance, please help me out. Thanks.

回答1:

First of all I would like to point out that your JSON isn't formatted properly. When you want to represent multiple objects in JSON you should use square brackets and separate each object with a comma:

{
    "result": [
        {
          "userId": "abcde123",
          "telephoneNumber": "1-555-5555555"
        },
        {
          "userId": "fghi456",
          "telephoneNumber": "1-333-3333333"
        }
        ],
    "error": null
}

The reason your Java code does not work when you try and remove get(0) is because the method public Optional<LDAPModel> getDirectReports(String cdsID) returns an Optional<LDAPModel> type and by removing get(0) your are effectively trying to return an Optional<List<LDAPModel>>. If you want the method to return a list instead of a single object you can change the return type to Optional<List<LDAPModel>> and then safely remove get(0).

public Optional<List<LDAPModel>> getDirectReports(String cdsID) {
        LdapQuery ldapQuery = LdapQueryBuilder.query()
                .searchScope(SearchScope.SUBTREE)
                .where("objectclass").is("person")
                .and("managerID").like(cdsID);

        List<LDAPModel> ldapModelList = ldapTemplate.search(ldapQuery, (Attributes attrs) ->
                LDAPModel.builder()
                        .userId(getValue(attrs, "userid"))
                        .telephoneNumber(getValue(attrs, "phoneNumber"))
                        .build());

        return ldapModelList.isEmpty() ? Optional.empty() : Optional.of(ldapModelList);
    }

回答2:

The structure looks strange to me. What you have looks like you want result to be an array of objects:

{
    "result": [
        { "userId": "abcde123",
          "telephoneNumber": "1-555-5555555" }
        { "userId": "fghi456",
          "telephoneNumber": "1-333-3333333" }
        ],
    "error": null
}

Given a reasonable JSON library, then the value of the "result" member of the JSON object is a JSON array, from which you can then pick out each element in turn by indexing, and each element is a JSON object with 2 members.

回答3:

I assume you already managed to get all the list/array of LDAPModel i.e. List ldapModelList

If so, you just need to return this ldapModelList in your getDirectReports method.

public List<LDAPModel> getDirectReports(String cdsID) {
    LdapQuery ldapQuery = LdapQueryBuilder.query()
            .searchScope(SearchScope.SUBTREE)
            .where("objectclass").is("person")
            .and("managerID").like(cdsID);

    List<LDAPModel> ldapModelList = ldapTemplate.search(ldapQuery, (Attributes attrs) ->
            LDAPModel.builder()
                    .userId(getValue(attrs, "userid"))
                    .telephoneNumber(getValue(attrs, "phoneNumber"))
                    .build());
    return ldapModelList;
}

Then just use your library to return the json array. I suppose you use jackson. Just make sure in LDAPModel you have

1. getters and setters
2. empty constructor if you add your own constructor having params. But if you don't add any constructor, then no need to add this default empty constructor as java will automatically create it for you.

LDAPModel class is as follows:

public class LDAPModel {
    String userId;
    String telephoneNumber;

    public String getUserId() {
        return userId;
    }

    public void setUserId(String userId) {
        this.userId = userId;
    }

    public String getTelephoneNumber() {
        return telephoneNumber;
    }

    public void setTelephoneNumber(String telephoneNumber) {
        this.telephoneNumber = telephoneNumber;
    }
}
    

For the object to JSON string conversion using Jackson, I assume you already know it or can find out how.

来源：https://stackoverflow.com/questions/63256209/how-to-return-a-list-of-multiple-json-items-in-java