Java objects and JSON are converted to each other

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package com.lecast.json.until;

import java.lang.reflect.Type;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.List;
import java.util.Map;

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.JsonDeserializationContext;
import com.google.gson.JsonDeserializer;
import com.google.gson.JsonElement;
import com.google.gson.JsonParseException;
import com.google.gson.JsonPrimitive;
import com.google.gson.JsonSerializationContext;
import com.google.gson.JsonSerializer;

/**
 * json 简单操作的工具类
 * @author lee.li
 *
 */
public class JsonUtil{

	private static Gson gson=null;
	static{
		if(gson==null){
			gson=new Gson();
		}
	}
	private JsonUtil(){}
	/**
	 * 将对象转换成json格式
	 * @param ts
	 * @return
	 */
	public static String objectToJson(Object ts){
		String jsonStr=null;
		if(gson!=null){
			jsonStr=gson.toJson(ts);
		}
		return jsonStr;
	}
	/**
	 * 将对象转换成json格式(并自定义日期格式)
	 * @param ts
	 * @return
	 */
	public static String objectToJsonDateSerializer(Object ts,final String dateformat){
		String jsonStr=null;
		gson=new GsonBuilder().registerTypeHierarchyAdapter(Date.class,new JsonSerializer<Date>() {
			public JsonElement serialize(Date src,Type typeOfSrc,JsonSerializationContext context) {
				SimpleDateFormat format = new SimpleDateFormat(dateformat);
				return new JsonPrimitive(format.format(src));
			}
		}).setDateFormat(dateformat).create();
		if(gson!=null){
			jsonStr=gson.toJson(ts);
		}
		return jsonStr;
	}
	/**
	 * 将json格式转换成list对象
	 * @param jsonStr
	 * @return
	 */
	public static List<?> jsonToList(String jsonStr){
		List<?> objList=null;
		if(gson!=null){
			java.lang.reflect.Type type=new com.google.gson.reflect.TypeToken<List<?>>(){}.getType();
			objList=gson.fromJson(jsonStr,type);
		}
		return objList;
	}
	/**
	 * 将json格式转换成map对象
	 * @param jsonStr
	 * @return
	 */
	public static Map<?,?> jsonToMap(String jsonStr){
		Map<?,?> objMap=null;
		if(gson!=null){
			java.lang.reflect.Type type=new com.google.gson.reflect.TypeToken<Map<?,?>>(){}.getType();
			objMap=gson.fromJson(jsonStr,type);
		}
		return objMap;
	}
	/**
	 * 将json转换成bean对象
	 * @param jsonStr
	 * @return
	 */
	public static Object  jsonToBean(String jsonStr,Class<?> cl){
		Object obj=null;
		if(gson!=null){
			obj=gson.fromJson(jsonStr,cl);
		}
		return obj;
	}
	/**
	 * 将json转换成bean对象
	 * @param jsonStr
	 * @param cl
	 * @return
	 */
	@SuppressWarnings("unchecked")
	public static <T> T  jsonToBeanDateSerializer(String jsonStr,Class<T> cl,final String pattern){
		Object obj=null;
		gson=new GsonBuilder().registerTypeAdapter(Date.class,new JsonDeserializer<Date>() {
			public Date deserialize(JsonElement json,Type typeOfT,JsonDeserializationContext context)
					throws JsonParseException {
					SimpleDateFormat format=new SimpleDateFormat(pattern);
					String dateStr=json.getAsString();
				try {
					return format.parse(dateStr);
				} catch (ParseException e) {
					e.printStackTrace();
				}
				return null;
			}
		}).setDateFormat(pattern).create();
		if(gson!=null){
			obj=gson.fromJson(jsonStr,cl);
		}
		return (T)obj;
	}
	/**
	 * 根据
	 * @param jsonStr
	 * @param key
	 * @return
	 */
	public static Object  getJsonValue(String jsonStr,String key){
		Object rulsObj=null;
		Map<?,?> rulsMap=jsonToMap(jsonStr);
		if(rulsMap!=null&&rulsMap.size()>0){
			rulsObj=rulsMap.get(key);
		}
		return rulsObj;
	}
	
}

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