java - 使用 Jackson 创建包含数组和自定义字段的有效 JSON

Question

下面的代码使用 Jackson 生成 JSON，就数据而言很好，但它不是 JSON

生成的 JSON 未通过 JSONLint ，因为它的方括号周围有引号，逗号周围有引号。它还有我从中删除的反斜杠 - 但我很确定我在下面所做的事情有问题

这是我正在尝试做的事情:

JSON 应该如下所示(除了我在此处添加的 skip 字段以突出显示在序列化时它将从对象中省略):

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

users 键是一个用户数组 - 上面显示的 2 个元素。跳过字段不应该是最终 json 的一部分，而应该是每个“用户”对象的一部分

添加了 URI 字段

我的代码如下。它成功地跳过了“skip”字段，并且如果消除了奇怪的格式，它会成功构建一个几乎是 JSON 的字符串。但我承认这段代码很糟糕，而且还可以做得更好(尽管我不知道如何做，因为我是新手)

您问的奇怪格式是什么？

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. 引号，(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(用于跳过字段逻辑)

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

Answer 1

我认为你可以使用Hashmap<String, Object> 。 Jackson 将了解如何将过滤器应用于 Object在数组中，并且只会跳过它找到的任何其他对象(字符串/数组)。这是适合我的演示:

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"
}