java实体类转Json

来源：互联网发布：淘宝分销怎么发货模板编辑：程序博客网时间：2024/05/16 09:25

package com.zsjz.utils.tools;

import java.io.IOException;
import java.io.StringWriter;
import java.util.List;
import javax.servlet.http.HttpServletRequest;
import net.sf.json.JSONArray;
import net.sf.json.JSONObject;
import org.apache.log4j.Logger;
import org.codehaus.jackson.JsonFactory;
import org.codehaus.jackson.JsonGenerator;
import org.codehaus.jackson.JsonNode;
import org.codehaus.jackson.JsonProcessingException;
import org.codehaus.jackson.map.ObjectMapper;

public class JsonUtils {
   private static JsonUtils ju;
   private static JsonFactory jf;
   private static ObjectMapper mapper;

   private static final Logger LOG = Logger.getLogger(JsonUtils.class);

   private JsonUtils(){

   }

   /**
   * 根据传入JSON串返回对应KEY的VALUE
   * @param json JSON字符串
   * @param key KEY
   * @return value
   */
   public static String getJsonByKey(String json,String key){
       mapper = getMapper();
       String nodeStr =null;
       try {
           JsonNode node = mapper.readTree(json);
           node = node.get(key);
           nodeStr = node.toString();
           //如果第一位和最后一位是 "
           if(nodeStr.charAt(0) == '"' && nodeStr.charAt(nodeStr.length()-1) == '"'){
               nodeStr = nodeStr.substring(1,nodeStr.length()-1);
           }
       } catch (Exception e) {
           return null;
       }
       return nodeStr;
   }


   /**
   * 实例化对象，做成了单例
   * @return 生成的实例
   */
   public static JsonUtils getInstance() {
       if(ju==null){
           ju = new JsonUtils();
       }
       return ju;
   }

   /**
   * 获取对象映射器
   * @return 生成的映射器
   */
   public static ObjectMapper getMapper() {
       if(mapper==null) {
           mapper = new ObjectMapper();
       }
       return mapper;
   }

   /**
   * 获取JSON工厂
   * @return JSON工厂
   */
   public static JsonFactory getFactory() {
       if(jf==null){
           jf = new JsonFactory();
       }
       return jf;
   }

   /**
   * 将对象转换成json串
   * @param obj 待转换的对象
   * @return json字符串
   */
   public static String obj2json(Object obj) {
       JsonGenerator jg = null;
       try {
           jf = getFactory();
           mapper = getMapper();
           StringWriter out = new StringWriter();
           jg = jf.createJsonGenerator(out);
           mapper.writeValue(jg, obj);
           return out.toString();
       } catch (IOException e) {
           LOG.error(e.getMessage(), e);
       } finally {
           try {
               if(jg!=null) {
                   jg.close();
               }
           } catch (IOException e) {
               LOG.error(e.getMessage(), e);
           }
       }
       return null;
   }

   /**
   * 将json串转换成对象
   * @param json 待转换的json串
   * @param clz 对象
   * @return 生成的对象
   */
   public static Object json2obj(String json,Class<?> clz) throws IOException {
       mapper = getMapper();
       return mapper.readValue(json,clz);
   }


   /**
   * @param request
   * @param parm
   * @param clz
   * @return
   * @throws IOException
   */
   public static Object initRequestParm2Object(HttpServletRequest request,String parm,Class<?> clz) throws IOException{
       String json = String.valueOf(request.getAttribute(parm));
       return json2obj(json,clz);
   }

   /**
   * 创建一个easyUI_dataGrid可用的JSON
   * @param list
   * @return
   */
   public static JSONObject createDataGrid(List list){
       JSONObject json = new JSONObject();
       json.put("total", list.size());
       JSONArray obj = JSONArray.fromObject(list);
       json.put("rows", obj.toString());
       return json;
   }
   /**
   * 创建一个easyUI_treeGrid可用的JSON
   * 目前与上一方法一样，后期会扩充
   * "_parentId":2   必须数字类型
   * "state":"closed"
   * @param list
   * @return
   */
   public static JSONObject createTreeGrid(List list){
       JSONObject json = new JSONObject();
       json.put("total", list.size());
       JSONArray obj = JSONArray.fromObject(list);
       json.put("rows", obj.toString());
       return json;
   }

}

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