使用Jackson和JSON Pointer查询解析任何JSON节点

JSON Pointer是字符串表达式，用于标识JSON文档特定节点。RFC 6901规范有定义，用于查询复杂Json文档结构。

1.示例Json文档

{ 
    "firstName": "John", 
    "lastName": "Doe", 
    "address": { 
        "street": "21 2nd Street", 
        "city": "New York", 
        "postalCode": "10021-3100", 
        "coordinates": { 
            "latitude": 40.7250387, 
            "longitude": -73.9932568 
        } 
    }, 
    "phone": [ 
        "139", 
        "137" 
    ], 
    "grade": [ 
        { 
            "name": "math", 
            "score": 99 
        }, 
        { 
            "name": "english", 
            "score": 97 
        } 
    ] 
} 

该文档包括复杂的嵌套，其中嵌套类型有对象，数组，数组对象。下面使用JSON Pointer进行解析。

2. 解析文档

使用Jackson的核心对象ObjectMapper，首先解析json字符串未JsonNode。

    String json = "{\n" + 
            "    \"firstName\": \"John\",\n" + 
            "    \"lastName\": \"Doe\",\n" + 
            "    \"address\": {\n" + 
            "      \"street\": \"21 2nd Street\",\n" + 
            "      \"city\": \"New York\",\n" + 
            "      \"postalCode\": \"10021-3100\",\n" + 
            "      \"coordinates\": {\n" + 
            "        \"latitude\": 40.7250387,\n" + 
            "        \"longitude\": -73.9932568\n" + 
            "      }\n" + 
            "    },\n" + 
            "    \"phone\":[\"139\",\"137\"],\n" + 
            "    \"grade\":[\n" + 
            "        {\"name\":\"math\",\"score\":99},\n" + 
            "        {\"name\":\"english\",\"score\":97}\n" + 
            "    ]\n" + 
            "  }"; 
 
    ObjectMapper mapper = new ObjectMapper(); 
    JsonNode node = mapper.readTree(json); 

2.1 获取属性

    JsonNode firstName = node.at("/firstName"); 
    print("firstName",firstName.toString()); 

必须以/开头，表示当前起始节点。
输出结果：

firstName:"John" 

2.2 获取对象属性

    JsonNode coordinatesNode = node.at("/address/coordinates"); 
    print("coordinatesNode",coordinatesNode.toString()); 

输出结果：

coordinatesNode:{"latitude":40.7250387,"longitude":-73.9932568} 

2.3 获取数组属性

    JsonNode phoneNode = node.at("/phone"); 
    print("phoneNode", phoneNode.toString()); 

输出结果：

phoneNode:["139","137"] 

2.4 获取数组属性元素

    JsonNode phone1Node = node.at("/phone/0"); 
    print("phone1Node",phone1Node.toString()); 

输出结果：

phone1Node:"139" 

2.4 获取数组对象属性

    JsonNode nameNode = node.at("/grade/0/name"); 
    print("name",nameNode.toString()); 
 
    JsonNode scoreNode = node.at("/grade/0/score"); 
    print("score",scoreNode.toString()); 

输出结果：

name:"math" 
score:99 

3. 总结

本文介绍了JSON Pointer是字符串表达式，可以非常方便解析复杂JSON节点值。

本文参考链接：https://blog.csdn.net/neweastsun/article/details/106530134