从 JSON 多维数组中按键获取值答案

【问题标题】：Get values by key from JSON Multi-dimensional Array从 JSON 多维数组中按键获取值
【发布时间】：2022-07-07 21:56:06
【问题描述】：

JSON：

[{"id":141741,"name":"Group","nodeTypeId":3,"deleted":false,"hasNodeAccesses":false,"children": [{"id":141742,"name":"Division","nodeTypeId":14,"deleted":false,"hasNodeAccesses":false,"children":[{"id":141743,"name":"Site 1","nodeTypeId":4,"deleted":false,"hasNodeAccesses":false,"children":[{"id":141746,"name":"Converting","nodeTypeId":5,"deleted":false,"hasNodeAccesses":false,"children":[]}]},{"id":141744,"name":"Site 2","nodeTypeId":4,"deleted":false,"hasNodeAccesses":false,"children":[{"id":141748,"name":"Converting","nodeTypeId":5,"deleted":false,"hasNodeAccesses":false,"children":[]}]},{"id":141745,"name":"Site 3","nodeTypeId":4,"deleted":false,"hasNodeAccesses":false,"children":[{"id":141750,"name":"Converting","nodeTypeId":5,"deleted":false,"hasNodeAccesses":false,"children":[]}]},{"id":141752,"name":"ML1","nodeTypeId":12,"deleted":false,"hasNodeAccesses":false,"children":[{"id":141755,"nodeTypeId":4,"deleted":false,"hasNodeAccesses":false,"children":[]}]},{"id":141753,"name":"ML2","nodeTypeId":12,"deleted":false,"hasNodeAccesses":false,"children":[{"id":141756,"nodeTypeId":4,"deleted":false,"hasNodeAccesses":false,"children":[]}]},{"id":141754,"name":"ML3","nodeTypeId":12,"deleted":false,"hasNodeAccesses":false,"children":[{"id":141757,"nodeTypeId":4,"deleted":false,"hasNodeAccesses":false,"children":[]}]}]}]}]

代码：

public List<String> getCapexStrategyNodeNames() {
        JsonNode capexStrategyNodeList = client.getCapexStrategyNodes();
        JSONArray nodes = capexStrategyNodeList.getArray();
        List<JSONObject> nodeList = nodes.toList();
        return retrieveValues(nodeList, "name");
    }

private List<String> retrieveValues(List<JSONObject> list, String key) {
    return list.stream()
            .map(val -> val.getString(key))
            .collect(Collectors.toList());
}

输出：

[Group]

我只检索第一个值
如何从嵌套的 JSON 数组中检索所有名称值？

提前致谢！

【问题讨论】：

标签： java json rest multidimensional-array

【解决方案1】：

使用您当前的实现，您将获得 JsonNode 对象并且您正在读取它的 name 属性，但您没有读取该属性，因为它是 chlildren（内部对象）。

您必须递归查询所有嵌套对象并获取字段name 的值。

在我看来，最简单的方法是使用JsonPath。

在 pom.xml 文件中添加这个依赖：

<dependency>
    <groupId>com.jayway.jsonpath</groupId>
    <artifactId>json-path</artifactId>
    <version>2.4.0</version>
</dependency>

这里是代码 sn-p:

public static void main(String[] args) throws JsonProcessingException {
        String json = "[{\"id\":141741,\"name\":\"Group\",\"nodeTypeId\":3,\"deleted\":false,\"hasNodeAccesses\":false,\"children\": [{\"id\":141742,\"name\":\"Division\",\"nodeTypeId\":14,\"deleted\":false,\"hasNodeAccesses\":false,\"children\":[{\"id\":141743,\"name\":\"Site 1\",\"nodeTypeId\":4,\"deleted\":false,\"hasNodeAccesses\":false,\"children\":[{\"id\":141746,\"name\":\"Converting\",\"nodeTypeId\":5,\"deleted\":false,\"hasNodeAccesses\":false,\"children\":[]}]},{\"id\":141744,\"name\":\"Site 2\",\"nodeTypeId\":4,\"deleted\":false,\"hasNodeAccesses\":false,\"children\":[{\"id\":141748,\"name\":\"Converting\",\"nodeTypeId\":5,\"deleted\":false,\"hasNodeAccesses\":false,\"children\":[]}]},{\"id\":141745,\"name\":\"Site 3\",\"nodeTypeId\":4,\"deleted\":false,\"hasNodeAccesses\":false,\"children\":[{\"id\":141750,\"name\":\"Converting\",\"nodeTypeId\":5,\"deleted\":false,\"hasNodeAccesses\":false,\"children\":[]}]},{\"id\":141752,\"name\":\"ML1\",\"nodeTypeId\":12,\"deleted\":false,\"hasNodeAccesses\":false,\"children\":[{\"id\":141755,\"nodeTypeId\":4,\"deleted\":false,\"hasNodeAccesses\":false,\"children\":[]}]},{\"id\":141753,\"name\":\"ML2\",\"nodeTypeId\":12,\"deleted\":false,\"hasNodeAccesses\":false,\"children\":[{\"id\":141756,\"nodeTypeId\":4,\"deleted\":false,\"hasNodeAccesses\":false,\"children\":[]}]},{\"id\":141754,\"name\":\"ML3\",\"nodeTypeId\":12,\"deleted\":false,\"hasNodeAccesses\":false,\"children\":[{\"id\":141757,\"nodeTypeId\":4,\"deleted\":false,\"hasNodeAccesses\":false,\"children\":[]}]}]}]}]";
        List<Object> expensive = JsonPath.parse(json)
                .read("$..name"); //Recursive descent: Searches for the/specified property name recursively and returns an array of all values with this property name. Always returns a list, even if just one property is found.

        System.out.println(expensive);

    }

如果您运行此代码，您将看到如下输出：

["Group","Division","Site 1","Converting","Site 2","Converting","Site 3","Converting","ML1","ML2","ML3"]

【讨论】：

【解决方案2】：

您的 json 只有一个对象，因此您的输出只有一项是正确的。

这是第一级数组中唯一存在的对象

[{
    "id": 141741,
    "name": "Group",
    "nodeTypeId": 3,
    "deleted": false,
    "hasNodeAccesses": false,
    "children": [...]
}]

所以你的代码应该返回 ["Group"] 并且它是正确的。可能您需要浏览孩子，并可能递归地浏览任何嵌套的孩子。在这种情况下，您需要更改算法

【讨论】：