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Java Record类介绍及使用方法详解

作者:冉成未来

Record是Java新增的库类,在Java 14和Java 15中以预览(preview)形式公布,这篇文章主要介绍了Java Record类介绍及使用方法的相关资料,需要的朋友可以参考下

简介

Java Record类是Java 14引入的预览特性,并在Java 16中正式成为标准功能,主要用于简化不可变数据载体的创建,自动生成构造方法、字段访问器、equals()、hashCode()和toString()等方法。

Java Record类的核心特性‌

例如:

public record Point(int x, int y) {}

等效于包含多个手动编写方法的普通类。‌‌

与普通类的区别‌

使用场景与最佳实践‌

‌数据传输对象(DTO)‌:简化API请求/响应的数据封装。‌‌

‌不可变数据快照‌:如领域事件或配置参数,确保数据一致性。‌‌

‌扩展功能‌:

通过紧凑构造器实现参数校验:

public record User(String name) {
public User { Objects.requireNonNull(name); }
}

添加自定义方法(如计算衍生属性)。‌‌

jackson中的注解解释

  1. @JsonProperty :此注解用于属性上,作用是把该属性的名称序列化为另外一个名称,如把trueName属性序列化为name,@JsonProperty(“name”)。 对属性名称重命名,比如在很多场景下Java对象的属性是按照规范的驼峰书写,但在数据库设计时使用的是下划线连接方式,此处在进行映射的时候 就可以使用该注解。
  2. @JsonIgnore此注解用于属性或者方法上(最好是属性上),用来完全忽略被注解的字段和方法对应的属性,即便这个字段或方法可以被自动检测到或者还有其 他的注解,一般标记在属性或者方法上,返回的json数据即不包含该属性。
  3. @JsonIgnoreProperties此注解是类注解,作用是json序列化时将java bean中的一些属性忽略掉,序列化和反序列化都受影响。
  4. @JsonFormat此注解用于属性或者方法上(最好是属性上),可以方便的把Date类型直接转化为我们想要的模式。 例子:@JsonFormat(pattern=“yyyy-MM-dd hh:mm:ss”) @JsonFormat(pattern=“yyyy-MM-dd HH:mm:ss”) private Date updateTime;
  5. @JsonSerialize此注解用于属性或者getter方法上,用于在序列化时嵌入我们自定义的代码,比如序列化一个double时在其后面限制两位小数点。
  6. @JsonDeserialize此注解用于属性或者setter方法上,用于在反序列化时可以嵌入我们自定义的代码,类似于上面的@JsonSerialize。
  7. @JsonInclude 属性值为null的不参与序列化。例子:@JsonInclude(Include.NON_NULL)

代码示例

@Service
public class WeatherService {

    private static final String BASE_URL = "https://api.weather.gov";

    private final RestClient restClient;

    public WeatherService() {
        this.restClient = RestClient.builder()
                .baseUrl(BASE_URL)
                .defaultHeader("Accept", "application/geo+json")
                .defaultHeader("User-Agent", "WeatherApiClient/1.0 (your@email.com)")
                .build();
    }

    @JsonIgnoreProperties(ignoreUnknown = true)
    public record Points(@JsonProperty("properties") Props properties) {
        @JsonIgnoreProperties(ignoreUnknown = true)
        public record Props(@JsonProperty("forecast") String forecast) {
        }
    }

    @JsonIgnoreProperties(ignoreUnknown = true)
    public record Forecast(@JsonProperty("properties") Props properties) {
        @JsonIgnoreProperties(ignoreUnknown = true)
        public record Props(@JsonProperty("periods") List<Period> periods) {
        }

        @JsonIgnoreProperties(ignoreUnknown = true)
        public record Period(@JsonProperty("number") Integer number, @JsonProperty("name") String name,
                             @JsonProperty("startTime") String startTime, @JsonProperty("endTime") String endTime,
                             @JsonProperty("isDaytime") Boolean isDayTime, @JsonProperty("temperature") Integer temperature,
                             @JsonProperty("temperatureUnit") String temperatureUnit,
                             @JsonProperty("temperatureTrend") String temperatureTrend,
                             @JsonProperty("probabilityOfPrecipitation") Map probabilityOfPrecipitation,
                             @JsonProperty("windSpeed") String windSpeed, @JsonProperty("windDirection") String windDirection,
                             @JsonProperty("icon") String icon, @JsonProperty("shortForecast") String shortForecast,
                             @JsonProperty("detailedForecast") String detailedForecast) {
        }
    }

    @JsonIgnoreProperties(ignoreUnknown = true)
    public record Alert(@JsonProperty("features") List<Feature> features) {

        @JsonIgnoreProperties(ignoreUnknown = true)
        public record Feature(@JsonProperty("properties") Properties properties) {
        }

        @JsonIgnoreProperties(ignoreUnknown = true)
        public record Properties(@JsonProperty("event") String event, @JsonProperty("areaDesc") String areaDesc,
                                 @JsonProperty("severity") String severity, @JsonProperty("description") String description,
                                 @JsonProperty("instruction") String instruction) {
        }
    }

    /**
     * Get forecast for a specific latitude/longitude
     * @param latitude Latitude
     * @param longitude Longitude
     * @return The forecast for the given location
     * @throws RestClientException if the request fails
     */
    @Tool(description = "Get weather forecast for a specific latitude/longitude")
    public String getWeatherForecastByLocation(double latitude, double longitude) {

        var points = restClient.get()
                .uri("/points/{latitude},{longitude}", latitude, longitude)
                .retrieve()
                .body(Points.class);

        var forecast = restClient.get().uri(points.properties().forecast()).retrieve().body(Forecast.class);

        String forecastText = forecast.properties().periods().stream().map(p -> {
            return String.format("""
					%s:
					Temperature: %s %s
					Wind: %s %s
					Forecast: %s
					""", p.name(), p.temperature(), p.temperatureUnit(), p.windSpeed(), p.windDirection(),
                    p.detailedForecast());
        }).collect(Collectors.joining());

        return forecastText;
    }

    /**
     * Get alerts for a specific area
     * @param state Area code. Two-letter US state code (e.g. CA, NY)
     * @return Human readable alert information
     * @throws RestClientException if the request fails
     */
    @Tool(description = "Get weather alerts for a US state. Input is Two-letter US state code (e.g. CA, NY)")
    public String getAlerts(@ToolParam( description =  "Two-letter US state code (e.g. CA, NY") String state) {
        Alert alert = restClient.get().uri("/alerts/active/area/{state}", state).retrieve().body(Alert.class);

        return alert.features()
                .stream()
                .map(f -> String.format("""
					Event: %s
					Area: %s
					Severity: %s
					Description: %s
					Instructions: %s
					""", f.properties().event(), f.properties.areaDesc(), f.properties.severity(),
                        f.properties.description(), f.properties.instruction()))
                .collect(Collectors.joining("\n"));
    }

    public static void main(String[] args) {
        WeatherService client = new WeatherService();
        System.out.println(client.getWeatherForecastByLocation(47.6062, -122.3321));
        System.out.println(client.getAlerts("NY"));
    }

}
@JsonIgnoreProperties(ignoreUnknown = true)
public record Points(@JsonProperty("properties") Props properties) {
    @JsonIgnoreProperties(ignoreUnknown = true)
    public record Props(@JsonProperty("forecast") String forecast) {
    }
}
相当于下面结构
Points:{
  "properties": {
    "forecast": "晴天",
    "extraField": "会被忽略的值"
  },
  "anotherExtra": "也会被忽略"
}


@JsonIgnoreProperties(ignoreUnknown = true)
public record Forecast(@JsonProperty("properties") Props properties) {
    @JsonIgnoreProperties(ignoreUnknown = true)
    public record Props(@JsonProperty("periods") List<Period> periods) {
    }

    @JsonIgnoreProperties(ignoreUnknown = true)
    public record Period(@JsonProperty("number") Integer number, @JsonProperty("name") String name,
                         @JsonProperty("startTime") String startTime, @JsonProperty("endTime") String endTime,
                         @JsonProperty("isDaytime") Boolean isDayTime, @JsonProperty("temperature") Integer temperature,
                         @JsonProperty("temperatureUnit") String temperatureUnit,
                         @JsonProperty("temperatureTrend") String temperatureTrend,
                         @JsonProperty("probabilityOfPrecipitation") Map probabilityOfPrecipitation,
                         @JsonProperty("windSpeed") String windSpeed, @JsonProperty("windDirection") String windDirection,
                         @JsonProperty("icon") String icon, @JsonProperty("shortForecast") String shortForecast,
                         @JsonProperty("detailedForecast") String detailedForecast) {
    }
}

相当于下面的结构:
{
  "properties": {
    "periods": [
      {
        "number": 1,
        "name": "Tonight",
        "startTime": "2023-11-01T18:00:00-05:00",
        "endTime": "2023-11-02T06:00:00-05:00",
        "isDaytime": false,
        "temperature": 45,
        "temperatureUnit": "F",
        "temperatureTrend": "rising",
        "probabilityOfPrecipitation": {
          "value": 20,
          "unit": "percent"
        },
        "windSpeed": "5 to 10 mph",
        "windDirection": "SW",
        "icon": "https://api.weather.gov/icons/land/night/few?size=medium",
        "shortForecast": "Partly Cloudy",
        "detailedForecast": "Partly cloudy, with a low around 45. Southwest wind 5 to 10 mph."
      },
      {
        "number": 2,
        "name": "Wednesday",
        "startTime": "2023-11-02T06:00:00-05:00",
        "endTime": "2023-11-02T18:00:00-05:00",
        "isDaytime": true,
        "temperature": 72,
        "temperatureUnit": "F",
        "temperatureTrend": null,
        "probabilityOfPrecipitation": {
          "value": 0,
          "unit": "percent"
        },
        "windSpeed": "10 mph",
        "windDirection": "W",
        "icon": "https://api.weather.gov/icons/land/day/skc?size=medium",
        "shortForecast": "Sunny",
        "detailedForecast": "Sunny, with a high near 72. West wind around 10 mph."
      }
    ]
  }
}

总结 

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