在java编程中，json字符串和对象的相互转化十分常用，下面我们就对象如何转化为json字符串以及json字符串如何转化为对象进行简要介绍，以便在代码中能方便使用。

1、依赖

本次介绍的方法依赖jackson，这是非常通用的json工具。

<dependency>

    <groupId>com.fasterxml.jackson.core</groupId>

    <artifactId>jackson-databind</artifactId>

    <version>2.9.8</version>

</dependency>

2、实体

下面我们编写一个稍微复杂的实体，以便进行测试。

package com.yefengyu.utils;

import java.util.Date;

public class Car

{

    private Integer id;

    private String brand;

    private Date date;

    public Car()

    {

    }

    public Car(Integer id, String brand, Date date)

    {

        this.id = id;

        this.brand = brand;

        this.date = date;

    }

    public Integer getId()

    {

        return id;

    }

    public void setId(Integer id)

    {

        this.id = id;

    }

    public String getBrand()

    {

        return brand;

    }

    public void setBrand(String brand)

    {

        this.brand = brand;

    }

    public Date getDate()

    {

        return date;

    }

    public void setDate(Date date)

    {

        this.date = date;

    }

    @Override

    public String toString()

    {

        return "Car{" +

               "id=" + id +

               ", brand='" + brand + '\'' +

               ", date=" + date +

               '}';

    }

}

上面编写了一个Car类，下面再编写一个Person类。

package com.yefengyu.utils;

public class Person

{

    private Integer id;

    private String name;

    private String email;

    private Car car;

    public Person()

    {

    }

    public Person(Integer id, String name, String email, Car car)

    {

        this.id = id;

        this.name = name;

        this.email = email;

        this.car = car;

    }

    public Integer getId()

    {

        return id;

    }

    public void setId(Integer id)

    {

        this.id = id;

    }

    public String getName()

    {

        return name;

    }

    public void setName(String name)

    {

        this.name = name;

    }

    public String getEmail()

    {

        return email;

    }

    public void setEmail(String email)

    {

        this.email = email;

    }

    public Car getCar()

    {

        return car;

    }

    public void setCar(Car car)

    {

        this.car = car;

    }

    @Override

    public String toString()

    {

        return "Person{" +

               "id=" + id +

               ", name='" + name + '\'' +

               ", email='" + email + '\'' +

               ", car=" + car +

               '}';

    }

}

注意的是：必须有无参构造函数。若无则在字符串转为对象的时候：

com.fasterxml.jackson.databind.exc.InvalidDefinitionException: Cannot construct instance of `com.yefengyu.utils.Person` (no Creators, like default construct, exist): cannot deserialize from Object value (no delegate- or property-based Creator)

 at [Source: (String)"{"id":1,"name":"yefengyu","email":"110@qq.com","car":{"id":1,"brand":"Rolls-Royce","date":"2019-06-22 13:25:30"}}"; line: 1, column: 2]

3、工具

下面的代码是一个工具类，实现了Json字符串到对象的相互转化过程。

package com.yefengyu.utils;

import com.fasterxml.jackson.core.JsonProcessingException;

import com.fasterxml.jackson.core.type.TypeReference;

import com.fasterxml.jackson.databind.ObjectMapper;

import java.io.IOException;

import java.text.SimpleDateFormat;

//使用final关键字防止继承

public final class JsonSerializer

{

    private static final ObjectMapper MAPPER;

    static

    {

        MAPPER = new ObjectMapper();

        MAPPER.setDateFormat(new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"));//日期格式化

     }

    private JsonSerializer()

    {

        //防止new对象

     }

    //对象转化为json字符串

     public static String toJson(Object object)

    {

        try

        {

            return MAPPER.writeValueAsString(object);

        }

        catch (JsonProcessingException e)

        {

            e.printStackTrace();

        }

        return null;

    }

    //对象转化为json字符串，并格式化输出

     public static String toPrettyJson(Object object)

    {

        try

        {

            return MAPPER.writerWithDefaultPrettyPrinter().writeValueAsString(object);

        }

        catch (JsonProcessingException e)

        {

            e.printStackTrace();

        }

        return null;

    }

    //字符串转为单个对象

     public static <T> T fromJson(String json, Class<T> clazz)

    {

        if (json == null || json.trim().isEmpty() || clazz == null)

        {

            return null;

        }

        try

        {

            return MAPPER.readValue(json, clazz);

        }

        catch (IOException e)

        {

            e.printStackTrace();

        }

        return null;

    }

    //字符串转为对象，比如对象列表

     public static <T> T fromJson(String json, TypeReference<T> typeReference)

    {

        if (json == null || json.trim().isEmpty() || typeReference == null)

        {

            return null;

        }

        try

        {

            return MAPPER.readValue(json, typeReference);

        }

        catch (IOException e)

        {

            e.printStackTrace();

        }

        return null;

    }

}

4、测试

1、单个对象转化为json字符串

Car car = new Car(1,"Rolls-Royce",new Date());

Person person = new Person(1, "yefengyu", "110@qq.com", car);

System.out.println(JsonSerializer.toJson(person));

System.out.println(JsonSerializer.toPrettyJson(person));

结果为：

{"id":1,"name":"yefengyu","email":"110@qq.com","car":{"id":1,"brand":"Rolls-Royce","date":"2019-06-22 13:25:30"}}

{

  "id" : 1,

  "name" : "yefengyu",

  "email" : "110@qq.com",

  "car" : {

    "id" : 1,

    "brand" : "Rolls-Royce",

    "date" : "2019-06-22 13:25:30"

  }

}

2、集合对象转化为json字符串

Car car = new Car(1,"Rolls-Royce",new Date());

List<Person> personList = new ArrayList<>();

Person p1 = new Person(1, "yefengyu", "1@qq.com",car);

Person p2 = new Person(2, "yefengyu", "2@qq.com",car);

Person p3 = new Person(3, "yefengyu", "3@qq.com",car);

personList.add(p1);

personList.add(p2);

personList.add(p3);

System.out.println(JsonSerializer.toJson(personList));

System.out.println(JsonSerializer.toPrettyJson(personList));

结果为：

[{"id":1,"name":"yefengyu","email":"1@qq.com","car":{"id":1,"brand":"Rolls-Royce","date":"2019-06-22 13:33:10"}},{"id":2,"name":"yefengyu","email":"2@qq.com","car":{"id":1,"brand":"Rolls-Royce","date":"2019-06-22 13:33:10"}},{"id":3,"name":"yefengyu","email":"3@qq.com","car":{"id":1,"brand":"Rolls-Royce","date":"2019-06-22 13:33:10"}}]

[ {

  "id" : 1,

  "name" : "yefengyu",

  "email" : "1@qq.com",

  "car" : {

    "id" : 1,

    "brand" : "Rolls-Royce",

    "date" : "2019-06-22 13:33:10"

  }

}, {

  "id" : 2,

  "name" : "yefengyu",

  "email" : "2@qq.com",

  "car" : {

    "id" : 1,

    "brand" : "Rolls-Royce",

    "date" : "2019-06-22 13:33:10"

  }

}, {

  "id" : 3,

  "name" : "yefengyu",

  "email" : "3@qq.com",

  "car" : {

    "id" : 1,

    "brand" : "Rolls-Royce",

    "date" : "2019-06-22 13:33:10"

  }

} ]

3、字符串转为单个对象

String json = "{\"id\":1,\"name\":\"yefengyu\",\"email\":\"110@qq.com\",\"car\":{\"id\":1,\"brand\":\"Rolls-Royce\",\"date\":\"2019-06-22 13:25:30\"}}";

System.out.println(JsonSerializer.fromJson(json, Person.class));

结果如下：

Person{id=1, name='yefengyu', email='110@qq.com', car=Car{id=1, brand='Rolls-Royce', date=Sat Jun 22 13:25:30 CST 2019}}

4、字符串转为对象集合

String list = "[{\"id\":1,\"name\":\"yefengyu\",\"email\":\"1@qq.com\",\"car\":{\"id\":1,\"brand\":\"Rolls-Royce\",\"date\":\"2019-06-22 13:33:10\"}},{\"id\":2,\"name\":\"yefengyu\",\"email\":\"2@qq.com\",\"car\":{\"id\":1,\"brand\":\"Rolls-Royce\",\"date\":\"2019-06-22 13:33:10\"}},{\"id\":3,\"name\":\"yefengyu\",\"email\":\"3@qq.com\",\"car\":{\"id\":1,\"brand\":\"Rolls-Royce\",\"date\":\"2019-06-22 13:33:10\"}}]";

 
List<Person> persons = JsonSerializer.fromJson(list, new TypeReference<List<Person>>()

{

});

for (Person person : persons)

{

    System.out.println(person);

}

结果如下：

Person{id=1, name='yefengyu', email='1@qq.com', car=Car{id=1, brand='Rolls-Royce', date=Sat Jun 22 13:33:10 CST 2019}}

Person{id=2, name='yefengyu', email='2@qq.com', car=Car{id=1, brand='Rolls-Royce', date=Sat Jun 22 13:33:10 CST 2019}}

Person{id=3, name='yefengyu', email='3@qq.com', car=Car{id=1, brand='Rolls-Royce', date=Sat Jun 22 13:33:10 CST 2019}}

最新文章

  1. HttpPost过程中使用的URLEncoder.encode(something, encode)
  2. 经受时间沉淀的15 个 Android 通用流行框架大全
  3. libnode 0.4.0 发布，C++ 语言版的 Node.js
  4. MySql视图、存储过程、函数、索引
  5. WCF初探-4：WCF消息交换模式之请求与答复模式
  6. SQL：查找被锁的表，以及锁表的SQL语句（重点推荐）
  7. BAT批处理（一）
  8. 监听Android CTS测试项解决方案（二）
  9. 通过gdb跟踪Linux内核装载和启动可执行程序过程
  10. read/write拥塞与非拥塞
  11. rapid-framework脚手架快速搭建springMVC框架项目
  12. 网络1712--c语言嵌套循环作业总结
  13. [NOI2015]软件包管理器
  14. mysql定时任务event——清理过期数据
  15. 开源网站流量统计系统Piwik源码分析——参数统计（一）
  16. python---redis实现自定义session
  17. 海明码 CRC冗余校验码
  18. 恢复Intellij idea删除的文件
  19. black-hole《XSS的原理分析与解剖》阅读笔记
  20. win10企业版永久激活2017怎么用

热门文章

  1. 使用jdbc查询防止出现中文乱码的方法
  2. BZOJ 1683.City skyline 城市地平线
  3. 工作流引擎 springmvc SSM 流程审批 Java Activiti 后台框架源码
  4. 软件工程第六组U-Helpβ版使用说明
  5. Ansible用法playbook
  6. 【串线篇】SQL映射文件select简单查询标签
  7. kaildi讲解
  8. 【学习笔记】整体二分（BZOJ2738矩阵乘法）
  9. Java Web入门二
  10. 安装RabbitMQ服务器及基本配置