JAVA中的动态Json解析并找到键和值对？

Question

请记住，JSON 结构事先是未知的，即它是完全任意的，我们只知道它是 JSON 格式。

例如， 以下 JSON

{
  "id": 1,
  "name": "Foo",
  "price": 123,
  "tags": [
    {
    "Bar":"23",
    "Eek":"24"
  }
]
}

---

我们可以这样做来遍历树并跟踪我们想要找出点符号属性名称的深度。

我们如何在编译时获取数据唯一的键，在运行时获取值。

import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.node.ArrayNode;
import com.fasterxml.jackson.databind.node.ObjectNode;
import com.fasterxml.jackson.databind.node.ValueNode;
import java.io.File;
import java.io.IOException;
import java.util.*;

public class Main {
    public static void main(String[] args) {
        File file=new File("src/data.json");
        ObjectMapper mapper=new ObjectMapper();
        try {

            LinkedHashMap<String,String> map= new LinkedHashMap<String, String>();
            JsonNode node =mapper.readTree(file);
            getKeys("",node, map);

            for (Map.Entry<String, String> entry : map.entrySet()) {
                System.out.println("Key:"+entry.getKey() + ""+"   "+" value:" + entry.getValue());
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    public static void getKeys(String currentpath,JsonNode node,LinkedHashMap map){
        if(node.isObject()){
            ObjectNode objectNode=(ObjectNode) node;
            Iterator<Map.Entry<String, JsonNode>> it=objectNode.fields();
            String prefix=currentpath.isEmpty()?"":currentpath+".";
            while (it.hasNext()){
                SortedMap.Entry<String,JsonNode> iter=it.next();
                getKeys(prefix+iter.getKey(),iter.getValue(),map);
            }
        }else if (node.isArray()){
            ArrayNode arrayNode=(ArrayNode) node;
            for(int i=0; i<arrayNode.size(); i++){
                getKeys(currentpath+i,arrayNode.get(i),map);
            }
        }
        else if(node.isValueNode()) {
            ValueNode valueNode=(ValueNode) node;
            map.put(currentpath,valueNode.asText());
        }
    }
}

---

在运行时只显示用户想要的值。

喜欢

输入：地址.street 输出：“23fn3 伦敦”

Answer 1

处理您一无所知的 json 结构并不常见。如果您不知道您在寻找什么值，那么这些数据将如何有用？

在您确实想要遍历整个树的特殊情况下，您将不得不使用递归。因为每个字段 (field) 都可以有一个简单的值 ("field": 1)、一个对象 ("field": {"b": 1}) 或一个数组 ("field": [1, 2, 3])。

下面的代码展示了如何使用Jackson json library 来做到这一点

public static void main(String[] args) throws IOException {
    File file = new File("data.json");
    ObjectMapper mapper = new ObjectMapper();

    JsonNode node = mapper.readTree(file);

    processNode(node);
}

private static void processNode(JsonNode node) {
    if(node.isArray()) {
        // if the node is a list of items,
        //  go through all the items and process them individually
        System.out.println("=== Array start ===");
        for (final JsonNode objInArray : node) {
            System.out.println("--- Array element start ---");
            // process the item in the array
            processNode(objInArray);
            System.out.println("--- Array element end ---");
        }
        System.out.println("=== Array end ===");
    } else if(node.isContainerNode()) {
        // if the node is an object,
        //  go through all fields within the object
        System.out.println("/// Object start ///");
        Iterator<Map.Entry<String, JsonNode>> it = node.fields();
        while (it.hasNext()) {
            Map.Entry<String, JsonNode> field = it.next();
            System.out.println("key: " + field.getKey());
            //process every field in the array
            processNode(field.getValue());
        }
        System.out.println("/// Object end ///");
    } else {
        // if node is a simple value (like string or int) so let's print it
        System.out.println("value: " + node);
    }
}

您提供的示例 json 提供以下输出：

=== Array start ===
--- Array element start ---
/// Object start ///
key: id
value: 1
key: name
value: "Leanne Graham"
key: username
value: "Bret"
key: email
value: "Sincere@april.biz"
key: address
/// Object start ///
key: street
value: " Light"
key: suite
value: "Apt. 556"
key: city
value: "Gwugh"
key: zipcode
value: "93874"
key: geo
/// Object start ///
key: lat
value: "-37.319"
key: lng
value: "81.146"
/// Object end ///
/// Object end ///
key: phone
value: "8031 x56442"
key: website
value: "hilded.org"
key: company
/// Object start ///
key: name
value: "Romra-Crona"
key: catchPhrase
value: " client-server neural-net"
key: bs
value: "harness markets"
/// Object end ///
/// Object end ///
--- Array element end ---
=== Array end ===

Process finished with exit code 0