JDK 17国际化指南：Java SE 17国际化详解

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本资源名为《JDK17国际化指南》（JavaPlatform, Standard Edition Internationalization Guide, Release 17），发布日期为2023年7月。这份文档是针对Java平台标准版的国际化特性详细介绍，适用于JDK 17版本。它提供了全面的指导，帮助开发者理解和实现多语言支持，确保软件在不同语言环境下的兼容性和用户体验。在JDK 17中，国际化的关注点包括字符串处理、日期和时间格式化、数字格式、货币格式以及字符集管理。文档强调了如何正确地设计和实现代码，以便在国际化环境中保持一致性，并遵循本地化最佳实践。这包括使用`java.text`包中的类，如`MessageFormat`, `DateFormat`, 和 `NumberFormat`，以及`java.util.Locale`类来处理语言和地区特定的文本和数值格式。值得注意的是，该文档明确指出，所有提供的软件和相关文档受到版权保护，用户只能按照许可协议的条款进行使用、复制或分发，禁止未经许可的修改、编译或逆向工程。同时，由于文档可能存在更新和错误，用户应报告发现的问题以便于改进。对于政府或受托人从Oracle或其关联公司获得软件、软件文档或相关资料的情况，文档提醒这些内容可能受联邦采购规定约束，使用时需遵循相关规定。《JDK17国际化指南》是一个实用的工具，对于开发国际化软件的开发者来说，是不可或缺的参考资料，它详尽地阐述了如何在最新的Java平台上实施和优化多语言功能。

Internationalization Overview

Internationalization is the process of designing an application so that it can be adapted to

various languages and regions without engineering changes. Sometimes the term

internationalization is abbreviated as i18n, because there are 18 letters between the first "i"

and the last "n."

An internationalized program has the following characteristics:

• With the addition of localization data, the same executable can run worldwide.

• Textual elements, such as status messages and the GUI component labels, are not

hardcoded in the program. Instead they are stored outside the source code and retrieved

dynamically.

• Support for new languages does not require recompilation.

• Culturally-dependent data, such as dates and currencies, appear in formats that conform

to the end user's region and language.

• It can be localized quickly.

The internet demands global software - that is, software that can be developed independently

of the countries or languages of its users, and then localized for multiple countries or regions.

The Java Platform provides a rich set of APIs for developing global applications. These

internationalization APIs are based on the Unicode standard and include the ability to adapt

text, numbers, dates, currency, and user-defined objects to any country's conventions.

This guide summarizes the internationalization APIs and features of the Java Platform,

Standard Edition. For coding examples and step-by-step instructions, see the

Internationalization Trail in the Java Tutorials.

Text Representation

The Java programming language is based on the Unicode character set, and several libraries

implement the Unicode standard. Unicode is an international character set standard which

supports all of the major scripts of the world, as well as common technical symbols. The

original Unicode specification defined characters as fixed-width 16-bit entities, but the

Unicode standard has since been changed to allow for characters whose representation

requires more than 16 bits. The range of legal code points is now U+0000 to U+10FFFF. An

encoding defined by the standard, UTF-16, allows to represent all Unicode code points using

one or two 16-bit units.

The primitive data type char in the Java programming language is an unsigned 16-bit integer

that can represent a Unicode code point in the range U+0000 to U+FFFF, or the code units of

UTF-16. The various types and classes in the Java platform that represent character

sequences - char[], implementations of java.lang.CharSequence (such as the String

class), and implementations of java.text.CharacterIterator - are UTF-16 sequences.

Most Java source code is written in ASCII, a 7-bit character encoding, or ISO-8859-1, an 8-bit

character encoding, but is translated into UTF-16 before processing.

The Character class is an object wrapper for the char primitive type. The Character

class also contains static methods such as isLowerCase() and isDigit() for

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determining the properties of a character. These methods have overloads that accept

either a char (which allows representation of Unicode code points in the range U+0000

to U+FFFF) or an int (which allows representation of all Unicode code points).

Locale Identification and Localization

A Locale object is an identifier for a particular combination of language and region.

Localization is the process of adapting software for a specific region or language by

adding locale-specific components and translating text.

Locales

On the Java platform, a locale is simply an identifier for a particular combination of

language and region. It is not a collection of locale-specific attributes. Instead, each

locale-sensitive class maintains its own locale-specific information. With this design,

there is no difference in how user and system objects maintain their locale-specific

resources. Both use the standard localization mechanism.

Java programs are not assigned a single global locale. All locale-sensitive operations

may be explicitly given a locale as an argument. This greatly simplifies multilingual

programs. While a global locale is not enforced, a default locale is available for

programs that do not wish to manage locales explicitly. A default locale also makes it

possible to affect the behavior of the entire presentation with a single choice.

Java locales act as requests for certain behavior from another object. For example, a

French Canadian locale passed to a Calendar object asks that the Calendar

behave correctly for the customs of Quebec. It is up to the object accepting the locale

to do the right thing. If the object has not been localized for a particular locale, it will try

to find a "close" match with a locale for which it has been localized. Thus if a

Calendar object was not localized for French Canada, but was localized for the

French language in general, it would use the French localization instead.

Locale Class

A Locale object represents a specific geographical, political, or cultural region. An

operation that requires a locale to perform its task is called locale-sensitive and uses

the

Locale

object to tailor information for the user. For example, displaying a number is

a locale-sensitive operation - the number should be formatted according to the

customs and conventions of the user's native country, region, or culture.

Supported Locales

On the Java platform, there does not have to be a single set of supported locales,

since each class maintains its own localizations. Nevertheless, there is a consistent

set of localizations supported by the classes of the Java Platform. Other

implementations of the Java Platform may support different locales. Locales that are

supported by the JDK are summarized by release. Use the search field on the

Technical Resources from Oracle page and search for "Supported Locales" to see

what is supported.

Chapter 1

Locale Identification and Localization

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