json和jsonNode有什么区别及相互转换

json
json是一个字符串，列如：
String json = "{"username":"tom","company":{"companyName":"中华","address":"北京"},"cars":["奔驰","宝马"]"};
jsonNode
jsonNode是一个对象！
可以将json转换成jsonNode，jsonNode中都是键值对形式，可以根据Key取出对应的值！

JsonNode 和 json 互转示例如下：
`import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;

import java.util.Iterator;

public class JsonPraseTest {

public static void main(String[] args) throws JsonProcessingException {
    String jsonS="{\"basics\":{\n" +
            "                \"instanceName\":\"头像\",\n" +
            "                \"width\":55,\n" +
            "                \"height\":55,\n" +
            "                \"positionX\":0,\n" +
            "                \"positionY\":0,\n" +
            "                \"instanceID\":\"SimpleAvatar621388c2-b3fb-4e07-9160-f40b2a385f6f\",\n" +
            "                \"zIndex\":1,\n" +
            "                \"configurable\":true,\n" +
            "                \"type\":\"simpleAvatar\"\n" +
            "                },\n" +
            "\"avatarStyle\":{\n" +
            "                \"size\":\"50\",\n" +
            "                \"shape\":\"circle\",\n" +
            "                \"color\":\"#628df0\",\n" +
            "                \"backgroundColor\":\"#a1bbf5\",\n" +
            "                \"gap\":4\n" +
            "                },\n" +
            "\"additional\":{\n" +
            "                \"isBadge\":false,\n" +
            "                \"isPhoto\":false\n" +
            "                }\n" +
            "}";
    //JSON ----> JsonNode
    ObjectMapper mapper=new ObjectMapper();
    JsonNode jsonNode = mapper.readTree(jsonS);
    Iterator<String> keys = jsonNode.fieldNames();
    while(keys.hasNext()){
        String fieldName = keys.next();
        System.out.println(fieldName + ": " + jsonNode.path(fieldName).toString());
    }
    //JsonNode ----> JSON  
    System.out.println(mapper.writeValueAsString(jsonNode));
}

}

}
`