获取 Complex JSON Object (Java 8) 中的键列表

Question

我正在处理一个看起来像这样的 JSON :-

{
"key1": {
    "key1.1": {
        "nestedkey1": "something",
        "nestedkey2": "something",
        "nestedkey3": "Something"
    },
    "key1.2": {
        "nestedkey1": "something",
        "nestedkey2": "something",
        "nestedkey3": "Something"
    }
},
"key2": {
    "key2.1": {
        "nestedkey1": "something",
        "nestedkey2": "something",
        "nestedkey3": "Something"
    },
    "key2.2": {
        "nestedkey1": "something",
        "nestedkey2": "something",
        "nestedkey3": "Something"
    }
}...

而且我不知道所有的键。我希望获得所有密钥，以便我可以从中创建一个 Map 。该地图应该类似于 ("key1" -> Corresponding object)...

在 Java 中有没有简单的方法来做到这一点？

Answer 1

使用 Jackson JSON 库，这个 json 可以被解析为 Map<String, Object> 使用 TypeReference:

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.core.type.TypeReference;
import com.fasterxml.jackson.databind.ObjectMapper;
import java.util.Map;

public class JsonTest {

    public static void main(String[] args) throws JsonProcessingException {
        String json = "{\n"
                + "\"key1\": {\n"
                + "    \"key1.1\": {\n"
                + "        \"nestedkey1\": \"something\",\n"
                + "        \"nestedkey2\": \"something\",\n"
                + "        \"nestedkey3\": \"Something\"\n"
                + "    },\n"
                + "    \"key1.2\": {\n"
                + "        \"nestedkey1\": \"something\",\n"
                + "        \"nestedkey2\": \"something\",\n"
                + "        \"nestedkey3\": \"Something\"\n"
                + "    }\n"
                + "},\n"
                + "\"key2\": {\n"
                + "    \"key2.1\": {\n"
                + "        \"nestedkey1\": \"something\",\n"
                + "        \"nestedkey2\": \"something\",\n"
                + "        \"nestedkey3\": \"Something\"\n"
                + "    },\n"
                + "    \"key2.2\": {\n"
                + "        \"nestedkey1\": \"something\",\n"
                + "        \"nestedkey2\": \"something\",\n"
                + "        \"nestedkey3\": \"Something\"\n"
                + "    }\n"
                + "}}"; // make sure the json is valid and closing } is available

        ObjectMapper mapper = new ObjectMapper();

        Map<String, Object> map = mapper.readValue(json, new TypeReference<>() {});

        System.out.println(map);
    }
}

要获取所有键的列表，需要实现一个递归方法来遍历top-level映射的条目并添加键：

public static List<String> getKeys(Map<String, Object> map) {
    List<String> keys = new ArrayList<>();
    for (Map.Entry<String, Object> entry : map.entrySet()) {
        keys.add(entry.getKey());
        if (entry.getValue() instanceof Map) {
            Map<String, Object> nested = (Map<String, Object>) entry.getValue();
            keys.addAll(getKeys(nested));
        }
    }
    return keys;
}

同样，可以创建“前缀”键列表：

public static List<String> getPrefixedKeys(String prefix, Map<String, Object> map) {
    List<String> keys = new ArrayList<>();
    for (Map.Entry<String, Object> entry : map.entrySet()) {
        String key = prefix + entry.getKey();
        keys.add(key);
        if (entry.getValue() instanceof Map) {
            Map<String, Object> nested = (Map<String, Object>) entry.getValue();
            keys.addAll(getPrefixedKeys(key + "/", nested));
        }
    }
    return keys;
}

// test
System.out.println(getPrefixedKeys("/", map));

输出:

[/key1, /key1/key1.1, /key1/key1.1/nestedkey1, /key1/key1.1/nestedkey2, /key1/key1.1/nestedkey3, 
/key1/key1.2, /key1/key1.2/nestedkey1, /key1/key1.2/nestedkey2, /key1/key1.2/nestedkey3, 
/key2, /key2/key2.1, /key2/key2.1/nestedkey1, /key2/key2.1/nestedkey2, /key2/key2.1/nestedkey3, 
/key2/key2.2, /key2/key2.2/nestedkey1, /key2/key2.2/nestedkey2, /key2/key2.2/nestedkey3]

Answer 2

String filePath ="src/main/resources/json/1.json";
FileReader reader = new FileReader(filePath);

JSONParser parser = new JSONParser();
JSONObject jsonObject = (JSONObject) parser.parse(reader);

Set<String> setKeys= jsonObject.keySet();
Map<String,Object> yourMap= new HashMap<>();
for (String key:setKeys) {
yourMap.put(key,jsonObject.get(key));
}

您的地图已准备就绪！

Answer 3

计算任务是输出JSON条不定级记录中各级字段名。如果您尝试在 Java.

中处理这种情况，代码将会很长

在 open-source Java 包 SPL 中这样做很方便。三行代码就够了：

	A	B
1	=i=0,json(file("records.json").read())
2	func recurse(r)	>i+=1,r.fno().run(tmp=eval("r.#"/~),B1=B1.to(:i-1)\|r.fname(~),output(B1.concat("->")),if(ifr(tmp),func(recurse,tmp),(B1=B1\|tmp)))
3	=func(recurse,A1)

SPL 提供 JDBC 驱动程序供 Java 调用。只需将上面的 SPL 脚本存储为 jsonkeys.splx 并在调用存储过程时在 Java 中调用它：

…
Class.forName("com.esproc.jdbc.InternalDriver");
con= DriverManager.getConnection("jdbc:esproc:local://");
st = con.prepareCall("call jsonkeys()");
st.execute();
…

获取 Complex JSON Object (Java 8) 中的键列表

Get list of keys in Complex JSON Object (Java 8)

java

json

hashmap

key-value

spring-boot