java笔记二（IO流与json）_io与json

注：导包问题自行解决

模板类

/*
商家，设计商家模型
 */
public class Merchant {
    //商家名称
    private String name;
    //商家地址
    private String address;
    //商家菜品
    private Dishes[] dishes;
    //经度
    private double lon;
    //纬度
    private double lat;
    //距离
    private double distance;

    private String id;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    public Dishes[] getDishes() {
        return dishes;
    }

    public void setDishes(Dishes[] dishes) {
        this.dishes = dishes;
    }

    public double getLon() {
        return lon;
    }

    public void setLon(double lon) {
        this.lon = lon;
    }

    public double getLat() {
        return lat;
    }

    public void setLat(double lat) {
        this.lat = lat;
    }

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public double getDistance() {
        return distance;
    }

    public void setDistance(double distance) {
        this.distance = distance;
    }
}
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转换为 json 数据

//存储 json 数据
public class JsonTest {
    public static void main(String[] args) {
        ObjectMapper objectMapper = new ObjectMapper();
        // 转换数据为 json 数据
        Merchant merchant = new Merchant();
        merchant.setName("麦当劳");

        String jsonContent = null;
        Merchant merchant1 = null;
        File file = new File("./demo.json");
        try{
            jsonContent = objectMapper.writeValueAsString(merchant);
            System.out.println(jsonContent);

            merchant1 = objectMapper.readValue(
                    jsonContent, Merchant.class);
            System.out.println(merchant1.getName());

            objectMapper.writeValue(file, merchant);
        }catch (JsonProcessingException e){
            e.printStackTrace();
        }catch (IOException e){
            e.printStackTrace();
        }
    }
}
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结果

{"name":"麦当劳","address":null,"dishes":null,"lon":0.0,"lat":0.0,"distance":0.0,"id":null}
1

读取 json + 筛选

[
  {
    "id": null,
    "name": "麦当劳",
    "distance": 100
  },
  {
    "id": "2",
    "name": "麦乐基",
    "distance": 200
  },
  {
    "id": "3",
    "name": "肯德基",
    "distance": 150
  },
  {
    "id": "4",
    "name": "必胜客",
    "distance": 10
  },
  {
    "id": "5",
    "name": "必胜客",
    "distance": 103
  }
]
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public class JsonTest {
    public static void main(String[] args) {
        ObjectMapper objectMapper = new ObjectMapper();
        // 读取 json 文件，转化为 list 格式
        List<Merchant> merchantList = null;
        try{
            merchantList = objectMapper.readValue(
                    new File("./demo.json"),
                    new TypeReference<List<Merchant>>(){});
        }catch (IOException e){
            e.printStackTrace();
        }

        // 执行 stream 过滤
        List<Merchant> merchantList1 = merchantList.stream().
                filter(m ->m.getName().indexOf("必胜客") >= 0).collect(Collectors.toList());
        for (Merchant merchant : merchantList1){
            System.out.println(merchant.getId());
            System.out.println(merchant.getName());
            System.out.println(merchant.getDistance());
        }
    }
}
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