使用包含数组和自定义字段的Jackson创建有效的JSON [英] Create a valid JSON using Jackson that contains an array and a custom field

问题描述

下面的代码使用Jackson生成JSON，就数据而言是好的，但它不是JSON

My code below to generate a JSON using Jackson, is fine as far as the data is concerned, but its not a JSON

生成的JSON没有传递 JSONLint ，因为它的引号括号和逗号周围的引号。它也反击了我从它中删除了 - 但我很确定我在下面做的事情有问题

The generated JSON doesnt pass JSONLint, because its got quotes around the square brackets and quotes around commas. It also backslashes which I hacked out of it - but Im pretty sure there's something wrong with what Im doing below

这是我正在尝试做的事情：

Here is what I'm trying to do:

JSON应该如下所示（除了 skip 字段，我在此处添加了该字段以突出显示它序列化时将从Object中省略）：

The JSON is supposed to look as follows (with the exception of the skip field which I have added here to highlight that it will be omitted from the Object when serialized):

{
    "users": [{
        "foo": "abc1",
        "bar": "def1",
        "skip": "this field is skipped"
    }, {
        "foo": "abc2",
        "bar": "def2",
        "skip": "this field is skipped"
    }],
    "uri": "/users"
}

用户密钥是一组用户 - 上面显示了2个元素。 skip字段不应该是最终json的一部分，但它是每个'user'对象的一部分

The users Key is an array of users - 2 elements shown above. The skip field shouldnt be part of the final json, but its part of each 'user' object

添加URI字段

我的代码如下。它成功跳过'skip'字段，如果消除了奇怪的格式，它就成功构建了几乎是JSON的String。但我承认这段代码很可怕而且它可能会更好（虽然我不知道我是怎么做到这一点）

My code is below. It successfully skips the 'skip' field and it successfully builds a String that is almost a JSON if the weird formatting is eliminated. But I admit this code is horrid and it can be better (although I dont know how since Im new to this)

你问的奇怪格式是什么？

What is the weird formatting you ask?

1. 反斜杠（你可以看到我已经使用hackey正则表达式消除了）


2. 引用[和]


3. 行情，（逗号）

代码：

get("/users", (request, response) -> {
    //this is the array of objects
    Object[] allUsers = listenUp.get_all_users();

    //Ignore this field per ListenUpUser object
    String[] ignorableFieldNames = { "skip" };

    ObjectMapper mapper = new ObjectMapper();
    mapper.enable(SerializationFeature.INDENT_OUTPUT);

    mapper.addMixIn(Object.class, PropertyFilterMixIn.class);
    FilterProvider filters = new SimpleFilterProvider()
            .addFilter("filter properties by name",
                    SimpleBeanPropertyFilter.serializeAllExcept(
                            ignorableFieldNames));
    ObjectWriter writer = mapper.writer(filters);

    ArrayNode array = mapper.createArrayNode();

    for(int i = 0; i < allUsers.length; i++) {
        array.add(writer.writeValueAsString(allUsers[i]));
    }

    JsonNodeFactory nodeFactory = JsonNodeFactory.instance;
    ObjectNode child = mapper.createObjectNode();
    child.put("users", array.toString());
    child.put("uri", "/users");
    response.status(200);
    response.type("application/json");
    String a = child.toString().replaceAll("\\\\", "");
    return a;
});

这已在文件顶部定义（对于跳过字段逻辑）

This has been defined at the top of the file (for the skip field logic)

@JsonFilter("filter properties by name")
class PropertyFilterMixIn {}

推荐答案

我认为你可以使用 Hashmap< String，Object> 。 Jackson将了解如何将过滤器应用于数组中的 Object ，并且只会跳过它找到的任何其他对象（String / array）。这是演示，适用于我：

I think you can use Hashmap<String, Object>. Jackson will understand how to apply filter to the Object in array and will just skip any other object(String/array) it finds. Here is demo, that works for me:

import com.fasterxml.jackson.annotation.JsonFilter;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;
import com.fasterxml.jackson.databind.ser.FilterProvider;
import com.fasterxml.jackson.databind.ser.impl.SimpleBeanPropertyFilter;
import com.fasterxml.jackson.databind.ser.impl.SimpleFilterProvider;
import org.json.JSONException;

import java.io.IOException;
import java.util.HashMap;

public class test12 {
    public static void main(String[] args) throws IOException, JSONException {
        Object[] allUsers = get_all_users();

        String[] ignorableFieldNames = {"skip"};

        ObjectMapper mapper = new ObjectMapper();
        mapper.enable(SerializationFeature.INDENT_OUTPUT);

        mapper.addMixIn(Object.class, PropertyFilterMixIn.class);
        FilterProvider filters = new SimpleFilterProvider()
                .addFilter("filter properties by name",
                        SimpleBeanPropertyFilter.serializeAllExcept(
                                ignorableFieldNames));
        mapper.setFilterProvider(filters);

        HashMap<String, Object> map = new HashMap<String, Object>();
        map.put("users", allUsers);
        map.put("uri", "/users");
        String result = mapper.writeValueAsString(map);

        System.out.println(result);
    }

    @JsonFilter("filter properties by name")
    public static class PropertyFilterMixIn {
    }

    private static Object[] get_all_users() {
        User user1 = new User();
        user1.foo = "abc1";
        user1.bar = "def1";
        user1.skip = "this field is skipped";
        User user2 = new User();
        user2.foo = "abc2";
        user2.bar = "def2";
        user2.skip = "this field is skipped";
        return new Object[]{user1, user2};
    }

    public static class User {
        public String foo;
        public String bar;
        public String skip;
    }
}

结果：

{
  "users" : [ {
    "foo" : "abc1",
    "bar" : "def1"
  }, {
    "foo" : "abc2",
    "bar" : "def2"
  } ],
  "uri" : "/users"
}

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