如何解析 json 相似的字符串并将其映射到 pojo

Question

我正在尝试使用 Jackson 将以下 JSON 映射到我的 POJO。我有以下 JSON 和以下 POJO。请让我知道如何将 JSON 映射到 POJO。 JSON 字符串：

{
  "Application": {
    "id": "0",
    "name": "MyApp",
    "users": [
      {
        "User": {
          "id": "2",
          "name": "Beth Jones"
        }
      }
    ],
    "groups": [
      {
        "Group": {
          "id": "1",
          "name": "SimpleGroup",
          "users": [
            {
              "User": {
                "id": "2",
                "name": "Beth Jones"
              }
            }
          ]
        }
      }
    ]
  }
}

根据客户端规范的POJO如下：

package com.example.custom;

//import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
import com.example.Application;
import com.example.Group;
import com.example.User;

import java.util.Collection;

//@JsonIgnoreProperties(ignoreUnknown = true)
public class MyApplication extends Application {

    private Collection<User> users;

    private Collection<Group> groups;

    public MyApplication(String id, String name) {

        super(id, name);
    }

    public void setUsers(Collection<User> users) {
        this.users = users;
    }

    public void setGroups(Collection<Group> groups) {

        this.groups = groups;
    }

    @Override
    public Collection<User> getUsers() {

        return this.users;
    }

    @Override
    public User getUser(String userId) {

        for (User user: MyParser.myApp.getUsers()) {
            if (user.getId().equals(userId))
                return user;
        }
        return null;
    }

    @Override
    public Collection<Group> getGroups() {

        return this.groups;
    }

    @Override
    public Group getGroup(String groupId) {

        for (Group group: MyParser.myApp.getGroups()) {
            if (group.getId().equals(groupId))
                return group;
        }
        return null;
    }

    @Override
    public String toString() {
        return "MyApplication{" +
                "users=" + users +
                ", groups=" + groups +
                '}';
    }
}

映射逻辑：

ObjectMapper mapper = new ObjectMapper();
mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
MyParser.myApp = mapper.readValue(rewriter.getText(),MyApplication.class);

生成的对象无法捕获任何内容，因为它全部为空。请帮忙。提前致谢。

Answer 1

我认为你应该正确地建模你的 JSON，在users 列表中你不应该再次指定键是 User，应该假设用户列表将只包含用户，groups 列表也是如此。

恕我直言，JSON 应该是这样的：

{
  "application": {
    "id": "0",
    "name": "MyApp",
    "users": [ . ==> Since this is a user List, it will definitely contains user.
      {
        "id": "2",
        "name": "Beth Jones"
      }
    ],
    "groups": [
      {
        "id": "1",
        "name": "SimpleGroup",
        "users": [
          {
            "id": "2",
            "name": "Beth Jones"
          }
        ]
      }
    ]
  }
}

现在 POJO 也需要一些修改，我只是添加了最低限度的 POJO。

class Application {  <====== Top Level Class
    private Long id;
    private String name;
    private List<User> users;  // Application has some Users
    private List<Group> groups; // Application has some groups
}

class User {   
    private Long id;
    private String name;
}

class Group {
    private Long id;
    private String name;
    private List<User> users;  // Each group has some associated users.
}

现在您可以使用 Java 的任何标准 JSON 库并将您的 JSON 转换为 POJO。这将简化您的结构，并且您不会遇到这种结构的空问题。