ZoneRegion.java

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/*
 * Copyright (c) 2007-2012, Stephen Colebourne & Michael Nascimento Santos
 *
 * All rights reserved.
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package java.time;

import java.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;
import java.io.InvalidObjectException;
import java.io.ObjectInputStream;
import java.io.Serializable;
import java.time.zone.ZoneRules;
import java.time.zone.ZoneRulesException;
import java.time.zone.ZoneRulesProvider;
import java.util.Objects;

/**
 * A geographical region where the same time-zone rules apply.
 * <p>
 * Time-zone information is categorized as a set of rules defining when and
 * how the offset from UTC/Greenwich changes. These rules are accessed using
 * identifiers based on geographical regions, such as countries or states.
 * The most common region classification is the Time Zone Database (TZDB),
 * which defines regions such as 'Europe/Paris' and 'Asia/Tokyo'.
 * <p>
 * The region identifier, modeled by this class, is distinct from the
 * underlying rules, modeled by {@link ZoneRules}.
 * The rules are defined by governments and change frequently.
 * By contrast, the region identifier is well-defined and long-lived.
 * This separation also allows rules to be shared between regions if appropriate.
 *
 * @implSpec
 * This class is immutable and thread-safe.
 *
 * @since 1.8
 */
// 基于地理时区的时区ID，可以处理夏令时
final class ZoneRegion extends ZoneId implements Serializable {
    
    /**
     * The time-zone ID, not null.
     */
    /*
     * 时区ID的字符串表示
     *
     * 此处的ID是基于地理时区的，比如：
     * Asia/Shanghai（并不等同于GMT/UTC+8时区）
     * America/Los_Angeles（有夏令时的时区）
     * GMT0
     * GMT
     * UTC
     * Etc/UTC
     * Etc/GMT0
     * Etc/GMT
     * Etc/GMT+0
     * Etc/GMT-0
     * Etc/GMT-8（相当于GMT/UTC+8）
     * Etc/GMT+8（相当于GMT/UTC-8）
     *
     * 参见：ZoneId#getAvailableZoneIds()
     */
    private final String id;
    
    /**
     * The time-zone rules, null if zone ID was loaded leniently.
     */
    // 时区规则集
    private final transient ZoneRules rules;
    
    
    
    /*▼ 构造器 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    /**
     * Constructor.
     *
     * @param id    the time-zone ID, not null
     * @param rules the rules, null for lazy lookup
     */
    ZoneRegion(String id, ZoneRules rules) {
        this.id = id;
        this.rules = rules;
    }
    
    /*▲ 构造器 ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    
    /*▼ 工厂方法 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    /**
     * Obtains an instance of {@code ZoneId} from an identifier.
     *
     * @param zoneId         the time-zone ID, not null
     * @param checkAvailable whether to check if the zone ID is available
     *
     * @return the zone ID, not null
     *
     * @throws DateTimeException  if the ID format is invalid
     * @throws ZoneRulesException if checking availability and the ID cannot be found
     */
    /*
     * 根据指定的地理时区ID来构造ZoneRegion对象。
     *
     * checkAvailable: 当无法找到zoneId对应的时区规则集时是否抛异常
     */
    static ZoneRegion ofId(String zoneId, boolean checkAvailable) {
        Objects.requireNonNull(zoneId, "zoneId");
        checkName(zoneId);
        
        ZoneRules rules = null;
        try {
            /* always attempt load for better behavior after deserialization */
            // 加载时区规则集
            rules = ZoneRulesProvider.getRules(zoneId, true);
        } catch(ZoneRulesException ex) {
            if(checkAvailable) {
                throw ex;
            }
        }
        
        return new ZoneRegion(zoneId, rules);
    }
    
    /*▲ 工厂方法 ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    /*▼ 部件 ████████████████████████████████████████████████████████████████████████████████┓ */
    // 返回时区ID的字符串表示
    @Override
    public String getId() {
        return id;
    }
    
    // 返回与当前时区ID对应的"时区规则集"
    @Override
    public ZoneRules getRules() {
        /*
         * additional query for group provider when null allows for possibility
         * that the provider was updated after the ZoneId was created
         */
        return (rules != null ? rules : ZoneRulesProvider.getRules(id, false));
    }
    
    /*▲ 部件 ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    /**
     * Checks that the given string is a legal ZondId name.
     *
     * @param zoneId the time-zone ID, not null
     *
     * @throws DateTimeException if the ID format is invalid
     */
    private static void checkName(String zoneId) {
        int n = zoneId.length();
        if(n<2) {
            throw new DateTimeException("Invalid ID for region-based ZoneId, invalid format: " + zoneId);
        }
        for (int i = 0; i < n; i++) {
            char c = zoneId.charAt(i);
            if (c >= 'a' && c <= 'z') continue;
            if (c >= 'A' && c<='Z')
                continue;
            if(c == '/' && i != 0)
                continue;
            if(c >= '0' && c<='9' && i != 0)
                continue;
            if(c == '~' && i != 0)
                continue;
            if(c == '.' && i != 0)
                continue;
            if(c == '_' && i != 0)
                continue;
            if(c == '+' && i != 0)
                continue;
            if(c == '-' && i != 0)
                continue;
            throw new DateTimeException("Invalid ID for region-based ZoneId, invalid format: " + zoneId);
        }
    }
    
    
    
    /*▼ 序列化 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    /**
     * Serialization version.
     */
    private static final long serialVersionUID = 8386373296231747096L;
    
    /**
     * Writes the object using a
     * <a href="../../serialized-form.html#java.time.Ser">dedicated serialized form</a>.
     * @serialData
     * <pre>
     *  out.writeByte(7);  // identifies a ZoneId (not ZoneOffset)
     *  out.writeUTF(zoneId);
     * </pre>
     *
     * @return the instance of {@code Ser}, not null
     */
    private Object writeReplace() {
        return new Ser(Ser.ZONE_REGION_TYPE, this);
    }

    /**
     * Defend against malicious streams.
     *
     * @param s the stream to read
     * @throws InvalidObjectException always
     */
    private void readObject(ObjectInputStream s) throws InvalidObjectException {
        throw new InvalidObjectException("Deserialization via serialization delegate");
    }

    @Override
    void write(DataOutput out) throws IOException {
        out.writeByte(Ser.ZONE_REGION_TYPE);
        writeExternal(out);
    }
    
    void writeExternal(DataOutput out) throws IOException {
        out.writeUTF(id);
    }
    
    static ZoneId readExternal(DataInput in) throws IOException {
        String id = in.readUTF();
        return ZoneId.of(id, false);
    }
    
    /*▲ 序列化 ████████████████████████████████████████████████████████████████████████████████┛ */
    
}