修复X转换Time Zone出错问题

IllegalArgumentException Unknown pattern character 'x', when using SimpleDateFormat

代码如下：

        try {
          new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ssX").parse("2019-05-14T19:00:11+08:00");
        } catch (ParseException e) {
          e.printStackTrace();
        }

在Android 8.0运行没问题，但在5.1及以下会抛“IllegalArgumentException Unknown pattern character 'x', when using SimpleDateFormat”，如此看来基本可以认为是版本兼容问题

首先我们查找文档对于格式化定义，之前文章日期格式化YYYY日期错位中有提到Java中Date and Time Patterns，下面我们再看看Android中java.txt.SimpleDateFormat中的
Date and Time Patterns

Date and Time Patterns

Symbol	Meaning	Kind	Example
D	Day in year	Number	189
E	Day of week	Text	E/EE/EEE:Tue,EEEE:Tuesday,EEEEE:T
F	Day of week in month	Number	2(2nd Wed inJuly)
G	Era designator	Text	AD
H	Hour in day (0-23)	Number	0
K	Hour in am/pm (0-11)	Number	0
L	stand-alone month	Text	L:1 LL:01 LLL:Jan LLLL:January LLLLL:J
M	Month in year	Text	M:1 MM:01 MMM:Jan MMMM:January MMMMM:J
S	fractional seconds	Number	978
W	Week in month	Number	2
Z	time zone (RFC 822)	time zone	Z/ZZ/ZZZ:-0800 ZZZZ:GMT-08:00 ZZZZZ:-08:00
a	Am/pm marker	Text	PM
c	stand-alone day of week	Text	c/cc/ccc:Tue, cccc:Tuesday, ccccc:T
d	Day in month	Number	10
h	Hour in am/pm (1-12)	Number	12
k	Hour in day (1-24)	Number	24
m	Minute in hour	Number	30
s	Second in minute	Number	55
w	Week in year	Number	27
y	Year	Number	yy:10 y/yyy/yyyy:2010
z	time zone	Time Zone	z/zz/zzz:PST zzzz:Pacific Standard Time
'	escape for text	Delimiter	'Date=':Date=
' '	single quote	Literal	'o''clock':o'clock

从中我们看到X和Z都是time zone，改成Z即可。
Android中的SimpleDateFormat也是使用Java的api
Android 5.0开始采用了JDK 7，对应应该已经有X了，见SimpleDateFormat
但是我们从Android 22的源码中可以看到

public class SimpleDateFormat extends DateFormat {

    private static final long serialVersionUID = 4774881970558875024L;

    // 'L' and 'c' are ICU-compatible extensions for stand-alone month and stand-alone weekday.
    static final String PATTERN_CHARS = "GyMdkHmsSEDFwWahKzZLc";

    // The index of 'Z' in the PATTERN_CHARS string. This pattern character is supported by the RI,
    // but has no corresponding public constant.
    private static final int RFC_822_TIMEZONE_FIELD = 18;

    // The index of 'L' (cf. 'M') in the PATTERN_CHARS string. This is an ICU-compatible extension
    // necessary for correct localization in various languages (http://b/2633414).
    private static final int STAND_ALONE_MONTH_FIELD = 19;
    // The index of 'c' (cf. 'E') in the PATTERN_CHARS string. This is an ICU-compatible extension
    // necessary for correct localization in various languages (http://b/2633414).
    private static final int STAND_ALONE_DAY_OF_WEEK_FIELD = 20;

    private String pattern;

    private DateFormatSymbols formatData;

Android 28

public class DateFormatSymbols implements Serializable, Cloneable {
...
    /**
     * Unlocalized date-time pattern characters. For example: 'y', 'd', etc.
     * All locales use the same these unlocalized pattern characters.
     */
    // Android-changed: Add 'c' (standalone day of week), 'b' (day period),
    //   'B' (flexible day period)
    static final String  patternChars = "GyMdkHmsSEDFwWahKzZYuXLcbB";

重点：
static final String PATTERN_CHARS = "GyMdkHmsSEDFwWahKzZLc";
static final String patternChars = "GyMdkHmsSEDFwWahKzZYuXLcbB";

源码里可以看到导致问题原因，但是为何Android 22中的java代码与Java 7中不一致呢？

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