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Pengalaman pisanan karo Jackson.

Diterbitake ing grup
Halo kabeh! Biyen, ing galaksi sing adoh, adoh, JSON sing dawa banget ditemokake ... Lan aku dadi kesed kanggo nggawe POJO. Lan aku takon dhewe: Mbayangno kahanan sing aku nampa respon ing wangun JSON karo, contone, kurs. Ana akeh lapangan ing JSON dhewe, lan aku butuh 2. Lan saiki aku pengin ngerti - bisa nggawe kelas karo lapangan aku kudu lan nyoba kanggo parse json iki menyang obyek kelas? Apa Jackson bakal ngerti apa sing dakkarepake saka dheweke? Lan, miturut, yen dheweke ngerti lan bisa nindakake kanthi cara iki, kepiye carane bisa nindakake kanthi bener lan apa sing bakal luwih cepet? Dadi, babagan pitakonan sing dakkarepake babagan JSON lan persepsi Jackson babagan: Jackson bakal ngerti kabeh. Dheweke pinter. Dheweke mung butuh bantuan sethithik babagan iki. Kita nggawe POJO - kelas Jawa biasa, sing bakal njlèntrèhaké variabel sing dibutuhake saka JSON. Aku bakal langsung ngomong yen iki pancene dikarepake kanggo sinau JSON dhewe, sing kita nulis kelas (kemungkinan bakal duwe kelas nested sing uga kudu digawe). Sabanjure, nggunakake anotasi @JsonCreator ing ndhuwur konstruktor, kita nuduhake yen kolom kelas iki kudu diisi saka JSON. Ing paramèter konstruktor, kita bisa nemtokake lapangan Json sing bakal ditugasake menyang lapangan kelas nggunakake anotasi @JsonParam("JsonFieldName". Yen ana luwih akeh lapangan ing json tinimbang sing kita butuhake (lan iki asline pitakonanku), kita kudu ngelingake babagan iki lan nerangake yen kita ora butuh lapangan sing isih ana. Kanggo iki, kita nggunakake @JsonIgnoreProperties(ignoreUnknown=true) anotasi. Banjur, nalika nemoni lapangan sing ora dingerteni, program kasebut ora bakal nabrak. Lan, drum roll...! Kita duwe obyek kelas kanthi kolom sing diisi (ya, persis sing dibutuhake) lan kita bisa nggunakake. Kaping pisanan, aku nulis kelas dhewe kanthi cara statis sing njupuk nilai sing dibutuhake lan, yen perlu, nggawa menyang wujud ilahi. Iku tugas. Iku artisanal. Iki minangka kruk. Mangkene kelas dhewe kanthi metode: 
public class Methods {
    public static double findRes(String body, String need){
        int begin = body.indexOf(need);
        int end = body.indexOf(",", begin);
        String res = body.substring(begin, end);
        String res2 = res.substring(res.indexOf(":")+2);
        double finalRes = Double.parseDouble(res2);
        return finalRes;
    }

    public static String findUrl(String body, String need){
        int begin = body.indexOf(need) + need.length();
        int end = body.indexOf(",", begin);
        String res = body.substring(begin, end);
        String res2 = res.substring(res.indexOf(":")+1);
        return res2;
    }
}
Java-университет
Nggunakake Jackson luwih trep lan bisa diwaca (paling ora luwih ayu). Ing obrolan karo para sepuh kita, dheweke ngonfirmasi: nggunakake perpustakaan, ing kasus kita Jackson, luwih disenengi. 
import com.fasterxml.jackson.annotation.JsonCreator;
import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
import com.fasterxml.jackson.annotation.JsonProperty;
import org.springframework.stereotype.Component;

@Component
@JsonIgnoreProperties(ignoreUnknown = true)
public class CurrencyPojo {
    private Rates rates;

    public CurrencyPojo() {
    }

    @JsonCreator
    public CurrencyPojo(@JsonProperty("rates") Rates rates) {
        this.rates = rates;
    }

    public Rates getRates() {
        return rates;
    }

    public void setRates(Rates rates) {
        this.rates = rates;
    }

    @Override
    public String toString() {
        return "CurrencyPojo{" +
                "rates=" + rates +
                '}';
    }

    @Component
    @JsonIgnoreProperties(ignoreUnknown = true)
    public static class Rates {

        private double rub;
        private double inr;
        private double eur;

        public Rates() {
        }

        @JsonCreator
        public Rates(@JsonProperty("RUB") double rub,
                     @JsonProperty("INR") double inr,
                     @JsonProperty("EUR") double eur) {
            this.rub = rub;
            this.inr = inr;
            this.eur = eur;
        }

        public double getRub() {
            return rub;
        }

        public void setRub(double rub) {
            this.rub = rub;
        }

        public double getInr() {
            return inr;
        }

        public void setInr(double inr) {
            this.inr = inr;
        }

        public double getEur() {
            return eur;
        }

        public void setEur(double eur) {
            this.eur = eur;
        }

        @Override
        public String toString() {
            return "Rates{" +
                    "rub=" + rub +
                    ", inr=" + inr +
                    ", eur=" + eur +
                    '}';
        }
    }
}
Aku kaya kanggo tarik manungsa waé kanggo nggunakake kelas nested. Sadurunge tugas iki, aku ora bisa mikir babagan gunane kanggo wong-wong mau =) Lan iki minangka conto JSON sing mlebu: Aku ora ngerti carane nggawe "spoiler", dadi ayo nglatih driji kita)) 
{
    "disclaimer": "Usage subject to terms: https://openexchangerates.org/terms",
    "license": "https://openexchangerates.org/license",
    "timestamp": 1638143999,
    "base": "USD",
    "rates": {
        "AED": 3.672934,
        "AFN": 95.889778,
        "ALL": 107.277494,
        "AMD": 483.27152,
        "ANG": 1.802446,
        "AOA": 585,
        "ARS": 100.99011,
        "AUD": 1.400119,
        "AWG": 1.80025,
        "AZN": 1.700805,
        "BAM": 1.734322,
        "BBD": 2,
        "BDT": 85.804468,
        "BGN": 1.727247,
        "BHD": 0.377164,
        "BIF": 1994.344572,
        "BMD": 1,
        "BND": 1.370223,
        "BOB": 6.905713,
        "BRL": 5.593606,
        "BSD": 1,
        "BTC": 0.000017488138,
        "BTN": 74.895631,
        "BWP": 11.828585,
        "BYN": 2.560653,
        "BZD": 2.015918,
        "CAD": 1.27258,
        "CDF": 2003.492833,
        "CHF": 0.92439,
        "CLF": 0.030154,
        "CLP": 831.315923,
        "CNH": 6.395085,
        "CNY": 6.393,
        "COP": 3975.845415,
        "CRC": 639.731775,
        "CUC": 1,
        "CUP": 25.75,
        "CVE": 97.95,
        "CZK": 22.7447,
        "DJF": 178.031664,
        "DKK": 6.585348,
        "DOP": 56.599119,
        "DZD": 139.135508,
        "EGP": 15.756894,
        "ERN": 15.000155,
        "ETB": 47.819833,
        "EUR": 0.885541,
        "FJD": 2.12473,
        "FKP": 0.749595,
        "GBP": 0.749595,
        "GEL": 3.095,
        "GGP": 0.749595,
        "GHS": 6.142755,
        "GIP": 0.749595,
        "GMD": 52.425,
        "GNF": 9472.013443,
        "GTQ": 7.738789,
        "GYD": 209.235741,
        "HKD": 7.7981,
        "HNL": 24.17051,
        "HRK": 6.661782,
        "HTG": 98.81349,
        "HUF": 327.09539,
        "IDR": 14379.716018,
        "ILS": 3.185445,
        "IMP": 0.749595,
        "INR": 75.050444,
        "IQD": 1458.680982,
        "IRR": 42275,
        "ISK": 130.231848,
        "JEP": 0.749595,
        "JMD": 155.740793,
        "JOD": 0.709,
        "JPY": 113.7185,
        "KES": 112.535405,
        "KGS": 84.774702,
        "KHR": 4069.37439,
        "KMF": 436.000041,
        "KPW": 900,
        "KRW": 1195.716418,
        "KWD": 0.30268,
        "KYD": 0.833396,
        "KZT": 436.292325,
        "LAK": 10839.499888,
        "LBP": 1520.868483,
        "LKR": 202.516227,
        "LRD": 142.25,
        "LSL": 16.236278,
        "LYD": 4.615464,
        "MAD": 9.244198,
        "MDL": 17.763696,
        "MGA": 3988.128848,
        "MKD": 54.637275,
        "MMK": 1790.896161,
        "MNT": 2854.559306,
        "MOP": 8.033255,
        "MRO": 356.999828,
        "MRU": 36.094075,
        "MUR": 43.067396,
        "MVR": 15.45,
        "MWK": 816.475065,
        "MXN": 21.738389,
        "MYR": 4.239,
        "MZN": 63.857001,
        "NAD": 16.26,
        "NGN": 410.875846,
        "NIO": 35.230131,
        "NOK": 9.0605,
        "NPR": 119.833306,
        "NZD": 1.465193,
        "OMR": 0.385109,
        "PAB": 1,
        "PEN": 4.033921,
        "PGK": 3.51889,
        "PHP": 50.480705,
        "PKR": 176.598456,
        "PLN": 4.168379,
        "PYG": 6826.299832,
        "QAR": 3.646364,
        "RON": 4.37388,
        "RSD": 103.877366,
        "RUB": 75.58127,
        "RWF": 1024.40338,
        "SAR": 3.7514,
        "SBD": 8.064563,
        "SCR": 14.654883,
        "SDG": 438,
        "SEK": 9.148279,
        "SGD": 1.370086,
        "SHP": 0.749595,
        "SLL": 11119.30017,
        "SOS": 580.721202,
        "SRD": 21.52,
        "SSP": 130.26,
        "STD": 21187.940504,
        "STN": 22.195,
        "SVC": 8.750748,
        "SYP": 2512.5,
        "SZL": 15.967534,
        "THB": 33.757117,
        "TJS": 11.286041,
        "TMT": 3.51,
        "TND": 2.882,
        "TOP": 2.277258,
        "TRY": 12.378954,
        "TTD": 6.78112,
        "TWD": 27.866934,
        "TZS": 2302.544214,
        "UAH": 27.094403,
        "UGX": 3563.214629,
        "USD": 1,
        "UYU": 44.148288,
        "UZS": 10783.399861,
        "VES": 4.57705,
        "VND": 22678.30849,
        "VUV": 111.998805,
        "WST": 2.563531,
        "XAF": 580.876668,
        "XAG": 0.04289544,
        "XAU": 0.00055691,
        "XCD": 2.70255,
        "XDR": 0.714635,
        "XOF": 580.876668,
        "XPD": 0.00055962,
        "XPF": 105.673123,
        "XPT": 0.00101782,
        "YER": 250.249937,
        "ZAR": 16.1344,
        "ZMW": 17.776133,
        "ZWL": 322
    }
}
Kanggo ngowahi json dadi obyek kelas kita nggunakake mapper: 
ObjectMapper mapper = new ObjectMapper();
currencyPojo(an object нашего класса) = mapper.readValue(jsonResponse(Джсон в стринге), CurrencyPojo.class(класс, который нам нужен));
Kode iki digunakake, narik metu saka hulk iki persis apa aku kudu. Punika output saka obyek kelas sawise parsing: CurrencyPojo{rates=Rates{rub=73,6944, inr=75,621547, eur=0,885436}} Aku remen. Dina kaping pindho aku keplok kabeh rai lan mesem karo tanganku ... Utawa kaya sing. Nilai tarif bisa beda-beda amarga Teks JSON lan obyek dicithak saka tanggal sing beda-beda, nanging umume asile kudu jelas. PS Aku nulis artikel kanggo pisanan, supaya ora ngadili strictly. Lan aku mung hacker pamula =) Aku tresna lan nampa kritik;) PS2 Aku njaluk ngapura kanggo "akeh huruf", nanging aku nyoba kanggo saiki apa aku wis digunakake kanggo dina.
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