SpringBoot(五)——JSON相关知识

以往以JSON格式返回只需要在控制器方法上加上@RequestMapping就可以了，记录其他3个知识点

1.常规情况下对于属性值为null的转换为空字符

直接手写一个配置类Jackson，套模板，不用加乱七八糟的依赖包

import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.databind.JsonSerializer;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializerProvider;
import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Primary;
import org.springframework.http.converter.json.Jackson2ObjectMapperBuilder;

import java.io.IOException;

@Configuration
public class Jackson {

    @Bean
    @Primary
    @ConditionalOnMissingBean(ObjectMapper.class)
    public ObjectMapper jacksonObjectMapper(Jackson2ObjectMapperBuilder builder) {
        ObjectMapper objectMapper;
        objectMapper = builder.createXmlMapper(false).build();
        objectMapper.getSerializerProvider().setNullValueSerializer(new JsonSerializer<Object>() {
            @Override
            public void serialize(Object o, JsonGenerator jsonGenerator, SerializerProvider serializerProvider) throws IOException {
                jsonGenerator.writeString("");
            }
        });
        return objectMapper;
    }
}

然后对于控制器类中的方法就可以直接显示

2.JSONObject类的使用

(1)导入依赖包

        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>fastjson</artifactId>
            <version>1.2.35</version>
        </dependency>

(2)语法

在返回json格式上没什么用，常规的也可以，主要是用来把toString方法转化为json格式的字符串，以json格式处理null，上面的模板也是够用的。

    @RequestMapping("/json4")
    public JSONObject json4(){
        JSONObject person4=new JSONObject();//原生JSONObject对象,和map差不多，只会显示设置的key
        person4.put("age",22);
        person4.put("hobbies",new String[] {"乒乓","骑行"});
        System.out.println(person4);
        return person4;
    }

    @RequestMapping("/json5")
    public Person json5(){//实体类转为JSONObject
        Person person5=new Person();
        person5.setAge(22);
        person5.setName("霸王别鸡");
        person5.setHobbies(new String[]{"王者荣耀","羽毛球"});
        System.out.println(person5);
        System.out.println(JSONObject.toJSON(person5));
        System.out.println(JSONObject.toJSONString(person5));
        return person5;
    }

    @RequestMapping("/json6")
    public JSONObject json6(){
        HashMap<String,Object> map=new HashMap<>();//通过Map生成JSONObject
        map.put("name","灰太狼");
        map.put("age",21);
        map.put("student",false);
        map.put("hobbies",new String[]{"发明","抓羊"});
        System.out.println(JSONObject.toJSON(map));
        return (JSONObject) JSONObject.toJSON(map);
    }

    @RequestMapping("json7")
    public JSONObject json7(){
        String string="{ "name":"Mike","age":22 }";//通过字符串生成JSONObject
        //String string="{ "name":,,:"Mike","age":22 ,,,}";//乱来的话运行会报错
        JSONObject jsonObject=JSONObject.parseObject(string);
        return jsonObject;

    }
    @RequestMapping("/json8")
    public JSON json8(){
        ArrayList<Person> list=new ArrayList<Person>();//试一下JSON对象，一般都是用JSONObject的
        list.add(person);
        Person person8=new Person();
        person.setName("person8");
        list.add(person8);
        JSON json= (JSON) JSON.toJSON(list);
        System.out.println(json);
        return json;
    }

    @RequestMapping("/json9")
    public JSONArray json9(){
        JSONArray jsonArray = new JSONArray();//测一下JSONArray
        JSONObject jsonObject1 = new JSONObject();
        jsonObject1.put("name","守林鸟");
        JSONObject jsonObject2 = new JSONObject();
        jsonObject2.put("name","灰太狼");
        jsonArray.add(jsonObject1);
        jsonArray.add(jsonObject2);
        System.out.println(jsonArray);
        return jsonArray;
    }

3.自行封装统一返回的数据结构

就是下面这个东西

自定义一个定义一个类JsonResult

import lombok.Data;

@Data
public class JsonResult<T> {
    private T data;
    private String code;
    private String msg;

    public JsonResult() {
        this.code = "10086";
        this.msg = "没有返回的数据";
    }

    public JsonResult(T data) {
        this.data = data;
        this.code = "200";
        this.msg = "有数据返回";
    }
}

测试方法

    @RequestMapping("/json10")
    public JsonResult<Person> json10(){
        return new JsonResult<>();
    }

    @RequestMapping("/json11")
    public JsonResult<Person> json11(){
        return new JsonResult<>(null);
    }

    @RequestMapping("/json12")
    public JsonResult<Person> json12(){
        Person person12 = new Person();
        person12.setName("person12");
        return new JsonResult<>(person12);
    }

这里保留了上述处理null的Jackson类。

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参考&引用

https://blog.csdn.net/taojin12/article/details/88244907