写在前面：开发中经常用到json和对象的相互转换，下面将列出FastJson中ObjectMapper对象的API的使用

一、maven工程中pom导入

        
     
      com.fasterxml.jackson.core
         
     
      jackson-databind
         
     
      2.8.3
     
    

二、使用

1、创建对象

public static ObjectMapper mapper = new ObjectMapper();

2、初始化

static {    // 转换为格式化的json    mapper.enable(SerializationFeature.INDENT_OUTPUT);    // 如果json中有新增的字段并且是实体类类中不存在的，不报错    mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);    //修改日期格式    mapper.setDateFormat(new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"));}

3、对象转为字符串

String jsonStr = mapper.writeValueAsString(user);System.out.println("对象转为字符串：" + jsonStr);

4、对象转为byte数组

byte[] byteArr = mapper.writeValueAsBytes(user);System.out.println("对象转为byte数组：" + byteArr);

5、json字符串转为对象

ObjectClass obj = mapper.readValue(jsonStr, ObjectClass.class);System.out.println("json字符串转为对象：" + obj);

6、byte数组转为对象

ObjectClass obj = mapper.readValue(byteArr,ObjectClass.class);System.out.println("byte数组转为对象：" + obj);

7、集合转为字符串

String jsonStr = mapper.writeValueAsString(userList);System.out.println("集合转为字符串：" + jsonStr);

8、字符串转集合

List list = null;try {    list = mapper.readValue(jsonStr, List.class);} catch (IOException e1) {    e1.printStackTrace();}

9、Map转为字符串

String jsonStr = mapper.writeValueAsString(testMap);System.out.println("Map转为字符串：" + jsonStr);

10、字符串转Map

Map map = null;try {    map = mapper.readValue(jsonStr, Map.class);} catch (IOException e1) {    e1.printStackTrace();}

三、JsonUtils工具类

import com.fasterxml.jackson.core.JsonProcessingException;import com.fasterxml.jackson.databind.DeserializationFeature;import com.fasterxml.jackson.databind.ObjectMapper;import com.fasterxml.jackson.databind.SerializationFeature;import java.io.IOException;import java.text.SimpleDateFormat;import java.util.List;import java.util.Map;/** * @Author Guixing * @Date 2019/1/7 11:10 * @Description */public class JsonUtils {    public static ObjectMapper mapper = new ObjectMapper();    static {        // 转换为格式化的json        mapper.enable(SerializationFeature.INDENT_OUTPUT);        // 如果json中有新增的字段并且是实体类类中不存在的，不报错        mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);        //修改日期格式        mapper.setDateFormat(new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"));    }    /**     * 对象转为字符串     *     * @param obj     * @return     */    public static String Object2Json(Object obj) {        String jsonStr = null;        try {            jsonStr = mapper.writeValueAsString(obj);        } catch (JsonProcessingException e1) {            e1.printStackTrace();        }        return jsonStr;    }    /**     * 对象转为byte数组     *     * @param obj     * @return     */    public static byte[] object2ByteArray(Object obj) {        byte[] byteArr = new byte[0];        try {            byteArr = mapper.writeValueAsBytes(obj);        } catch (JsonProcessingException e1) {            e1.printStackTrace();        }        return byteArr;    }    /**     * json字符串转为对象     *     * @param jsonStr     * @param beanType     * @param 
    
          * @return     */    public static 
     
       T json2Object(String jsonStr, Class
      
        beanType) {        T t = null;        try {            t = mapper.readValue(jsonStr, beanType);        } catch (IOException e1) {            e1.printStackTrace();        }        return t;    }    /**     * byte数组转为对象     *     * @param byteArr     * @param beanType     * @param 
       
             * @return     */    public static 
        
          T byteArr2Object(byte[] byteArr, Class
         
           beanType) { T t = null; try { t = mapper.readValue(byteArr, beanType); } catch (Exception e) { e.printStackTrace(); } return t; } /** * 集合转为字符串 * * @param list * @return */ public static String list2String(List list) { String jsonStr = null; try { jsonStr = mapper.writeValueAsString(list); } catch (JsonProcessingException e1) { e1.printStackTrace(); } return jsonStr; } /** * 字符串转集合 * * @param jsonStr * @return */ public static List json2List(String jsonStr) { List list = null; try { list = mapper.readValue(jsonStr, List.class); } catch (IOException e1) { e1.printStackTrace(); } return list; } /** * Map转为字符串 * * @param map * @return */ public static String map2String(Map map) { String jsonStr = null; try { jsonStr = mapper.writeValueAsString(map); } catch (JsonProcessingException e1) { e1.printStackTrace(); } return jsonStr; } /** * 字符串转Map * * @param jsonStr * @return */ public static Map json2Map(String jsonStr) { Map map = null; try { map = mapper.readValue(jsonStr, Map.class); } catch (IOException e1) { e1.printStackTrace(); } return map; }}