Json工具类

在工程中定义此类，方便以后进行json数据转换逻辑操作。

package com.example.demo.util;

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.JavaType;
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.node.ArrayNode;
import com.fasterxml.jackson.databind.node.JsonNodeFactory;
import com.fasterxml.jackson.databind.node.ObjectNode;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

public class JsonUtil {
    private static ObjectMapper objectMapper = new ObjectMapper();

    private JsonUtil() {

    }

    public static ObjectNode createObject() { //大括号
        return objectMapper.createObjectNode();
    }

    public static ArrayNode createArray() { //中括号
        return objectMapper.createArrayNode();
    }

    public static JsonNodeFactory getFactory() {
        return objectMapper.getNodeFactory();
    }

    public static String toJson(Object obj) {
        String json = null;
        try {
            json = objectMapper.writeValueAsString(obj);
        } catch (JsonProcessingException e) {
            throw new RuntimeException(e);
        }
        return json;
    }

    public static JsonNode fromJson(String json) {
        JsonNode jsonNode = null;
        try {
            jsonNode = objectMapper.readValue(json, JsonNode.class);
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
        return jsonNode;
    }

    public static ObjectNode fromObject(String json) {
        return (ObjectNode) fromJson(json);
    }

    public static <T> T fromObject(String json, Class<T> tClass) {
        try {
            return objectMapper.readValue(json, tClass);

        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }

    public static <T> T fromObject(ObjectNode node, Class<T> tClass) {
        return fromObject(toJson(node), tClass);
    }

    public static ArrayNode fromArray(String json) {
        return (ArrayNode) fromJson(json);
    }

    public static <T> List<T> fromArray(String json, Class<T> tClass) {
        JavaType javaType = getCollectionType(ArrayList.class, tClass);
        List<T> list = null;
        try {
            list = objectMapper.readValue(json, javaType);
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
        return list;
    }

    public static <T> List<T> fromArray(ArrayNode node, Class<T> tClass) {
        return fromArray(toJson(node), tClass);
    }

    private static JavaType getCollectionType(Class<?> collectionClass, Class<?>... elementClasses) {
        return objectMapper.getTypeFactory().constructParametricType(collectionClass, elementClasses);
    }
}