import com.alibaba.fastjson.JSON;
import com.alibaba.fastjson.JSONArray;
import com.alibaba.fastjson.JSONObject;
import com.alibaba.fastjson.serializer.SerializerFeature;
import com.alibaba.fastjson.serializer.SimplePropertyPreFilter;

import java.util.ArrayList;
import java.util.List;


public class JsonUtils {

	/**
	 * 对象转字符串
	 *
	 * @param object
	 * @return
	 */
	public static String objectToString(Object object) {
		return JSON.toJSONString(object, SerializerFeature.WriteNullStringAsEmpty);
	}

	/**
	 * 字符串转对象
	 *
	 * @param jsonString
	 * @return
	 */
	public static Object stringToObject(String jsonString, Class cla) {
		JSONObject jsonObject = JSON.parseObject(jsonString);
		Object obj = JSON.toJavaObject(jsonObject, cla);
		return obj;
	}

	/**
	 *  截取对象中需要的字段
	 * @param t 需要的截取的对象 可以是List
	 * @param properties 需要的字段
	 * @return 返回需要的字段的object对象
	 */
	public  static <T> Object  PropertyPreFilter(T t,String... properties){
		//如果对象为null
		if (t==null)
		{
			return  "";
		}
		SimplePropertyPreFilter filter = new SimplePropertyPreFilter(t.getClass(),properties);
		if(t instanceof List){
			if(((List) t).size()==0) {
				return new ArrayList<>();
			}
			SimplePropertyPreFilter listFilter = new SimplePropertyPreFilter(((List)t).get(0).getClass(),properties);
           String s = JSONArray.toJSONString(t,listFilter, SerializerFeature.WriteMapNullValue,
				   // 将String类型的null转成""
				   SerializerFeature.WriteNullStringAsEmpty,
				   // 将Number类型的null转成0
				   SerializerFeature.WriteNullNumberAsZero,
				   // 将List类型的null转成[]
				   SerializerFeature.WriteNullListAsEmpty,
				   // 将Boolean类型的null转成false
				   SerializerFeature.WriteNullBooleanAsFalse,
				   // 避免循环引用
				   SerializerFeature.DisableCircularReferenceDetect);
        return JSONArray.parseArray(s);
		}

		return JSONObject.parseObject(JSON.toJSONString(t,filter,
				SerializerFeature.WriteMapNullValue,
				// 将String类型的null转成""
				SerializerFeature.WriteNullStringAsEmpty,
				// 将Number类型的null转成0
				SerializerFeature.WriteNullNumberAsZero,
				// 将List类型的null转成[]
				SerializerFeature.WriteNullListAsEmpty,
				// 将Boolean类型的null转成false
				SerializerFeature.WriteNullBooleanAsFalse,
				// 避免循环引用
				SerializerFeature.DisableCircularReferenceDetect));

	}
	/**
	 * 从标准Json字符串中获取String值
	 *
	 * @param jsonString
	 * @param key
	 * @return
	 */
	public static String getStringValue(String jsonString, String key) {
		JSONObject jsonObject = JSON.parseObject(jsonString);
		boolean b = jsonObject.containsKey(key);
		if (b) {
			return jsonObject.getString(key);
		} else {
			return "";
		}
	}

	/**
	 * 从Json对象中获取String值
	 * @param jsonObject
	 * @param key
	 * @return
	 */
	public static String getJsonObjectValue(JSONObject jsonObject, String key) {
		boolean b = jsonObject.containsKey(key);
		if (b) {
			return jsonObject.getString(key);
		} else {
			return "";
		}
	}

	/**
	 * json字符串转成List<T>对象
	 *
	 * @param jsonString
	 * @param cla
	 * @return
	 */
	public static <T> List<T> stringToList(String jsonString, Class cla) {
		List<T> list = new ArrayList<T>();
		list = JSON.parseArray(jsonString, cla);
		return list;
	}

	/**
	 * list集合转json字符串
	 *
	 * @param list
	 * @return
	 */
	public static <T> String listToJsonString(List<T> list) {
		String jsonString = JSONArray.toJSONString(list);
		return jsonString;

	}

	/**
	 * 从Json字符串中获取int值
	 *
	 * @param jsonString
	 * @param key
	 * @return
	 */
	public static int getIntValue(String jsonString, String key) {
		JSONObject jsonObject = JSON.parseObject(jsonString);
		boolean b = jsonObject.containsKey(key);
		if (b) {
			return jsonObject.getIntValue(key);
		} else {
			return 10000;
		}
	}

	public static Boolean existsKey(JSONObject jsonObject, String key) {
		return jsonObject.containsKey(key);
	}

	/**
	 * 构建单个键值对的Json字符串
	 *
	 * @param key
	 * @param value
	 * @return
	 */
	public static String keyValueToString(String key, Object value) {
		JSONObject json = new JSONObject();
		json.put(key, value);
		return json.toJSONString();
	}

	/**
	 * 构建含有两个键值对的Json字符串
	 *
	 * @param key1
	 * @param value1
	 * @param key2
	 * @param value2
	 * @return
	 */
	public static String keyValueToString2(String key1, Object value1, String key2, Object value2) {
		JSONObject json = new JSONObject();
		json.put(key1, value1);
		json.put(key2, value2);
		return json.toJSONString();
	}

	public static String addToJson(String jsonString, String key, Object date) {
		JSONObject jsonObject = JSONObject.parseObject(jsonString);
		jsonObject.put(key, date);
		return jsonObject.toJSONString();
	}
}

fastJson 小工具