如何从Java中的JSON文件中删除键值对

问题描述：

我想知道是否有人可以帮助我或提示我如何使用Java编辑附加的虚拟JSON文件.

I was wondering if anyone can help me or hint me towards how to edit the attached dummy JSON file in Java.

如您所见，我有一个head对象，其中包含许多值和遵循相同模式的子代.

As you can see I have a head object that contains many values and children that follow the same pattern.

我想知道是否有一种方法可以删除所有值为-1的键.

I wanted to know if there was a way to remove all the keys where the value is -1.

以下是我在许多使用 jackson 的网站上尝试的内容:

Following is what I was trying based on many websites using jackson:

try {
            // create object mapper instance
            ObjectMapper mapper = new ObjectMapper();

            // convert JSON file to map
            Map<?, ?> map = mapper.readValue(Paths.get("test.json").toFile(), Map.class);

            // print map entries
            for (Map.Entry<?, ?> entry : map.entrySet()) {
                isInteger = main.isObjectInteger(entry.getValue());

                
//              System.out.println("if value is all: " + entry.getKey() + "=" + entry.getValue());
//

上面的代码将显示文件的结构，但是我的问题是达到子代内部的-1值并将其删除.

The above code will display the structure of the file, however my problem is reaching the -1 values inside the children and removing them.

使用.getClass和.simpleName方法，我知道它是一个arrayList，但是我对如何搜索它感到困惑.

Using the .getClass and .simpleName methods I know that it is an arrayList but I am confused as to how to search through it.

任何帮助将不胜感激！

答

在 Jackson 中，您可以将整个 JSON 有效负载读取为 JsonNode 并进行迭代在所有属性上检查给定条件.如果满足条件，则可以删除给定的字段.为此，您需要实现递归方法.看下面的例子:

In Jackson you can read whole JSON payload as JsonNode and iterate over all properties check given condition. In case condition is met you can remove given field. To do that you need to implement recursive method. Take a look on below example:

import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;
import com.fasterxml.jackson.databind.node.ArrayNode;
import com.fasterxml.jackson.databind.node.ObjectNode;

import java.io.File;
import java.io.IOException;
import java.util.Iterator;
import java.util.Map;
import java.util.Objects;
import java.util.function.Predicate;

public class JsonRemoveSomeFieldsApp {

    public static void main(String[] args) throws IOException {
        File jsonFile = new File("./resource/test.json").getAbsoluteFile();

        ObjectMapper mapper = new ObjectMapper();
        mapper.enable(SerializationFeature.INDENT_OUTPUT);
        JsonNode root = mapper.readTree(jsonFile);

        JsonCleaner jsonCleaner = new JsonCleaner(root, (node) -> node.isNumber() && node.numberValue().intValue() == -1);
        JsonNode result = jsonCleaner.removeAll();

        // write to file
        mapper.writeValue(System.out, result);
    }
}

class JsonCleaner {

    private final JsonNode root;
    private final Predicate<JsonNode> toRemoveCondition;

    JsonCleaner(JsonNode node, Predicate<JsonNode> toRemoveCondition) {
        this.root = Objects.requireNonNull(node);
        this.toRemoveCondition = Objects.requireNonNull(toRemoveCondition);
    }

    public JsonNode removeAll() {
        process(root);
        return root;
    }

    private void process(JsonNode node) {
        if (node.isObject()) {
            ObjectNode object = (ObjectNode) node;
            Iterator<Map.Entry<String, JsonNode>> fields = object.fields();
            while (fields.hasNext()) {
                Map.Entry<String, JsonNode> field = fields.next();
                JsonNode valueToCheck = field.getValue();
                if (valueToCheck.isContainerNode()) {
                    process(valueToCheck);
                } else if (toRemoveCondition.test(valueToCheck)) {
                    fields.remove();
                }
            }
        } else if (node.isArray()) {
            ArrayNode array = (ArrayNode) node;
            array.elements().forEachRemaining(this::process);
        }
    }
}

对于以下 JSON 有效负载:

{
  "name": "Head",
  "missed": -1,
  "covered": -1,
  "children": [
    {
      "name": "project1",
      "missed": -1,
      "covered": -1,
      "children": [
        {
          "name": "project1",
          "missed": 10,
          "covered": 11
        }
      ]
    },
    {
      "name": "project1",
      "missed": -1,
      "covered": 12,
      "children": [
        {
          "name": "project1",
          "missed": 10,
          "covered": -1
        }
      ]
    }
  ]
}

以上代码打印:

{
  "name" : "Head",
  "children" : [ {
    "name" : "project1",
    "children" : [ {
      "name" : "project1",
      "missed" : 10,
      "covered" : 11
    } ]
  }, {
    "name" : "project1",
    "covered" : 12,
    "children" : [ {
      "name" : "project1",
      "missed" : 10
    } ]
  } ]
}

另请参阅:

在Java中平整3级嵌套JSON字符串

如何从Java中的JSON文件中删除键值对

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