package com.yds.model;

 import java.util.Date;

 public class DeviceHistory {

     private int id;

     private Date acq_time; 

     public int getId() {

         return id;

     }

     public void setId(int id) {

         this.id = id;

     }

     public String getDevice_id() {

         return device_id;

     }

     public Date getAcq_time() {

         return acq_time;

     }

     public void setAcq_time(Date acq_time) {

         this.acq_time = acq_time;

     }

 }

import java.util.ArrayList;

import java.util.Date;

import java.util.List;

import net.sf.json.JSONArray;

import com.yds.model.DeviceHistory;

public class Test {

    public static void main(String[] args) {

        List<DeviceHistory> list = new ArrayList<DeviceHistory>();

        DeviceHistory dh = new DeviceHistory();

        dh.setAcq_time(new Date());

        list.add(dh);

        JSONArray json =JSONArray.fromObject(list);

        System.out.println(json.toString());

    }

}

 import java.io.IOException;

 import java.util.ArrayList;

 import java.util.Date;

 import java.util.List;

 import org.codehaus.jackson.JsonGenerationException;

 import org.codehaus.jackson.map.JsonMappingException;

 import org.codehaus.jackson.map.ObjectMapper;

 import com.yds.model.DeviceHistory;

 public class Test {

     public static void main(String[] args) throws JsonGenerationException, JsonMappingException, IOException {

         List<DeviceHistory> list = new ArrayList<DeviceHistory>();

         DeviceHistory dh = new DeviceHistory();

         dh.setAcq_time(new Date());

         list.add(dh);

         ObjectMapper objectMapper = new ObjectMapper();

         String json = objectMapper.writeValueAsString(list);

         System.out.println(json);

     }

 }