一、使用openjdk作为docker 镜像

• 建议在环境变量中指定时区

apk add tzdata && \
cp /usr/share/zoneinfo/Asia/Shanghai /etc/localtime && \
echo "Asia/Shanghai" > /etc/timezone && \
apk del tzdata && \

• 也可以在java -jar命令行指定时区

java -jar -Duser.timezone=Asia/Shanghai app.jar

二、详解openjdk的获取时区

3.1、java程序中获取默认时间

import java.util.TimeZone;

public class Test {
    public static void main(String[] args) {
        System.out.println(TimeZone.getDefault());
    }
}

>javac Test.java
>java Test
sun.util.calendar.ZoneInfo[id="GMT",offset=0,dstSavings=0,useDaylight=false,transitions=0,lastRule=null]

如果是oracle jdk，打印的时区详情是：sun.util.calendar.ZoneInfo[id="Asia/Shanghai",offset=28800000,dstSavings=0,useDaylight=false,transitions=29,lastRule=null]

3.2、openjdk的源码跟踪

类TimeZone

package java.util;

// defaultTimeZone 使用关键词volatile修饰
private static volatile TimeZone defaultTimeZone;

// 默认的时区就是GMT
static final String         GMT_ID        = "GMT";

   public static TimeZone getDefault() {
        return (TimeZone) getDefaultRef().clone();
    }

static TimeZone getDefaultRef() {
        TimeZone defaultZone = defaultTimeZone;
        if (defaultZone == null) {
            // Need to initialize the default time zone.
            defaultZone = setDefaultZone();
            assert defaultZone != null;
        }
        // Don't clone here.
        return defaultZone;
    }

jar命令行参数-Duser.timezone=GMT+8

private static synchronized TimeZone setDefaultZone() {
        TimeZone tz;
        // get the time zone ID from the system properties
        String zoneID = AccessController.doPrivileged(
                new GetPropertyAction("user.timezone"));

        // if the time zone ID is not set (yet), perform the
        // platform to Java time zone ID mapping.
        if (zoneID == null || zoneID.isEmpty()) {
            String javaHome = AccessController.doPrivileged(
                    new GetPropertyAction("java.home"));
            try {
                zoneID = getSystemTimeZoneID(javaHome);
                if (zoneID == null) {
                    zoneID = GMT_ID;
                }
            } catch (NullPointerException e) {
                zoneID = GMT_ID;
            }
        }

        // Get the time zone for zoneID. But not fall back to
        // "GMT" here.
        tz = getTimeZone(zoneID, false);

        if (tz == null) {
            // If the given zone ID is unknown in Java, try to
            // get the GMT-offset-based time zone ID,
            // a.k.a. custom time zone ID (e.g., "GMT-08:00").
            String gmtOffsetID = getSystemGMTOffsetID();
            if (gmtOffsetID != null) {
                zoneID = gmtOffsetID;
            }
            tz = getTimeZone(zoneID, true);
        }
        assert tz != null;

        final String id = zoneID;
        AccessController.doPrivileged(new PrivilegedAction<Void>() {
            @Override
                public Void run() {
                    System.setProperty("user.timezone", id);
                    return null;
                }
            });

        defaultTimeZone = tz;
        return tz;
    }

public static void setDefault(TimeZone zone)
    {
        SecurityManager sm = System.getSecurityManager();
        if (sm != null) {
            sm.checkPermission(new PropertyPermission
                               ("user.timezone", "write"));
        }
        defaultTimeZone = zone;
    }

3.3、TimeZone.c类中，会读取系统的时区

/*
 * Gets the platform defined TimeZone ID
 */
JNIEXPORT jstring JNICALL
Java_java_util_TimeZone_getSystemTimeZoneID(JNIEnv *env, jclass ign,
                                            jstring java_home, jstring country)
{
    const char *cname;
    const char *java_home_dir;
    char *javaTZ;

    if (java_home == NULL)
        return NULL;

    java_home_dir = JNU_GetStringPlatformChars(env, java_home, 0);
    if (java_home_dir == NULL)
        return NULL;

    if (country != NULL) {
        cname = JNU_GetStringPlatformChars(env, country, 0);
        /* ignore error cases for cname */
    } else {
        cname = NULL;
    }

    /*
     * Invoke platform dependent mapping function
     */
    javaTZ = findJavaTZ_md(java_home_dir, cname);

    free((void *)java_home_dir);
    if (cname != NULL) {
        free((void *)cname);
    }

    if (javaTZ != NULL) {
        jstring jstrJavaTZ = JNU_NewStringPlatform(env, javaTZ);
        free((void *)javaTZ);
        return jstrJavaTZ;
    }
    return NULL;
}

3.4、findJavaTZ_md(java_home_dir, cname);的不同操作系统实现

• unix操作系统

• windows操作系统

  
  solaris系统和windows系统.png