前提是需要加Jar包：

gson-2.2.2.jar

package utils;

import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.Reader;
import java.io.StringReader;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import model.dll.WebServiceParams;

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.reflect.TypeToken;
import com.google.gson.stream.JsonReader;

public class GSonUtils {
 /**
  * 将List<Map<String,Object>>转换成JSON字符串
  *
  * @param o
  * @return
  */
 public static String parseListMap2JSon(Object o) {
  Gson gson = new GsonBuilder().create();
  return gson.toJson(o, new TypeToken<List<Map<String, Object>>>() {
  }.getType());
 }

/**
  * 将JSON格式转换成Map
  *
  * @param json
  * @return
  */
 public static Map<String, Object> parseJSON2Map(String json) {
  Map<String,Object> map = new HashMap<String, Object>();
  Gson gson = new GsonBuilder().create();
  JsonReader reader = new JsonReader(new StringReader(json));
  map = gson.fromJson(reader, new TypeToken<Map<String, Object>>() {
  }.getType());
  return map;
 }

/**
  * 将JSON转成List<Map>
  *
  * @param json
  * @return
  */
 public static List<Map<String, Object>> parseJSON2ListMap(String json) {
  List<Map<String,Object>> rst = new ArrayList<Map<String,Object>>();
  Gson gson = new Gson();
  JsonReader reader = new JsonReader(new StringReader(json));
  rst = gson.fromJson(reader, new TypeToken<List<Map<Object,String>>>() {
  }.getType());
  return rst;
 }

/**
  * 将对象转换成JSON格式
  * @param o
  * @return
  */
 public static String parse2JSON(Object o) {
  if(o == null){
   return "";
  }
  Gson g = new GsonBuilder().create();
  String json = g.toJson(o,o.getClass());
  return json;
 }
 
 /**
  * 将json字符串转换成指定类型的对象
  * @param json
  * @param typeToken
  * @return
  */
 public static <T> T parseJson2(String json, TypeToken<T> typeToken){
  Gson gson = new Gson();
  JsonReader reader = new JsonReader(new StringReader(json));
  return gson.fromJson(reader, typeToken.getType());
 }
 
 public static WebServiceParams parseJson2WebServiceParams(String json){
  return GSonUtils.parseJson2(json, new TypeToken<WebServiceParams>(){});
 }
}

================demo案例json互转类型===============================

String infos = test();//json map类型格式:{"pubuser":"{\"code\":\"test\",\"dateRegister\":\"2013-09-24 14:11:46.0\",\"password\":\"c4ca4238a0b923820dcc509a6f75849b\",\"id\":\"e6ee44f3-98ab-4446-bd9b-db2e525d3b24\",\"serialNum\":148,\"status\":0}","info":"{\"dbVersion\":22}"}
   
   //解析json map格式
   Map<String, String> map = parseJson2(infos,new TypeToken<Map<String, String>>() {});// json==》map

String pubuser = map.get("pubuser");
   Pubuser pubs = parseJson2(pubuser, new TypeToken<Pubuser>() {
   });// json==》Pubuser(实体对象)

//实体对象转换成json map格式
   public String test(){
    Map<String,String> map = new HashMap<String,String>();
    Tradings data = new Tradings();//实体对象
      data.setId(UUID.randomUUID().toString());
      data.setCost(19.2);
      map.put("trading", parse2JSON(data));
      return parse2JSON(map);
     }

/**
    * 将对象转换成JSON格式
    *
    * @param o
    * @return
    */
   public static String parse2JSON(Object o) {
    if (o == null) {
     return "";
    }
    Gson g = new GsonBuilder().create();
    String json = g.toJson(o, o.getClass());
    return json;
   }

/**
    * 将json字符串转换成指定类型的对象
    *
    * @param json
    * @param typeToken
    * @return
    */
   public static <T> T parseJson2(String json, TypeToken<T> typeToken) {
    Gson gson = new Gson();
    JsonReader reader = new JsonReader(new StringReader(json));
    return gson.fromJson(reader, typeToken.getType());
   }

/**
    * 将JSON转成List<Map>
    *
    * @param json
    * @return
    */
   public static List<Map<String, Object>> parseJSON2ListMap(String json) {
    List<Map<String, Object>> rst = new ArrayList<Map<String, Object>>();
    Gson gson = new Gson();
    JsonReader reader = new JsonReader(new StringReader(json));
    rst = gson.fromJson(reader, new TypeToken<List<Map<Object, String>>>() {
    }.getType());
    return rst;
   }