目录

• Jackson和JSON Pointer查询解析任何JSON节点
• 1.示例Json文档
• 2. 解析文档
• Jackson 通用解析JSON方法

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

Jackson 通用解析JSON方法

package com.util;
import com.fasterxml.jackson.annotation.JsonAutoDetect;
import com.fasterxml.jackson.annotation.PropertyAccessor;
import com.fasterxml.jackson.databind.DeserializationFeature;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;
import com.fasterxml.jackson.databind.type.TypeFactory;
import com.google.common.collect.Lists;
import lombok.extern.slf4j.Slf4j;
import org.apache.commons.lang3.StringUtils;
import java.io.IOException;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
/**
 * json 解析类，通用于全项目
 * <p/>
 * Created by 刘一波 on 15/7/24.
 * E-Mail:zhanlanstar@163.com
 */
@Slf4j
public class JsonUtils {
    private static ObjectMapper objectMapper = new ObjectMapper();
    static {
        objectMapper.setVisibility(PropertyAccessor.FIELD, JsonAutoDetect.Visibility.ANY);
        objectMapper.configure(SerializationFeature.INDENT_OUTPUT, true);
        objectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
        objectMapper.configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false);
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        objectMapper.setDateFormat(sdf);
    }
    /**
     * 提供给elasticsearch使用，把bean转换成list map 集合类型，否则不能存入索引
     *
     * @param o
     * @return
     */
    public static Object beanToJsonObject(Object o) {
        return jsonStrToList(objectToJsonStr(o), Map.class);
    }
    public static String objectToJsonStr(Object o) {
        try {
            return objectMapper.writeValueAsString(o);
        } catch (IOException e) {
            log.error("object can not objectTranslate to json", e);
        }
        return null;
    }
    public static <T> T jsonStrToObject(String json, Class<T> cls) {
        try {
            return objectMapper.readValue(json, cls);
        } catch (IOException e) {
            log.error("json cant be objectTranslate to object", e);
            return null;
        }
    }
    public static <T> T jsonDataToObject(String jsonStr, Class<T> cls) {
        if (!StringUtils.isEmpty(jsonStr)) {
            T data = JsonUtils.jsonStrToObject(jsonStr, cls);
            return data;
        } else {
            return null;
        }
    }
    public static <T> List<T> jsonStrToList(String jsonStr, Class<?> clazz) {
        List<T> list = Lists.newArrayList();
        try {
            // 指定容器结构和类型（这里是ArrayList和clazz）
            TypeFactory t = TypeFactory.defaultInstance();
            list = objectMapper.readValue(jsonStr,
                    t.constructCollectionType(ArrayList.class, clazz));
        } catch (IOException e) {
            log.error("反序列化序列化attributes，从Json到List报错", e);
        }
        return list;
    }
    public static Map jsonStrToMap(String attributes) {
        try {
            return objectMapper.readValue(attributes, HashMap.class);
        } catch (IOException e) {
            log.error("反序列化序列化attributes，从Json到HashMap报错", e);
        }
        return new HashMap();
    }
}

以上为个人经验，希望能给大家一个参考，也希望大家多多支持自由互联。

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