Apprendre Properties File Encoding and Internationalization

When working with Java properties files, it's essential to understand how character encoding affects the way text is stored and read. By default, Java properties files use the ISO-8859-1 encoding, also known as Latin-1. This encoding supports only a limited set of characters, mostly those used in Western European languages. If you need to include characters from other languages—such as Chinese, Russian, or Arabic—you must use Unicode escapes or other strategies to ensure those characters are handled correctly.

A Unicode escape represents a character using the format \uXXXX, where XXXX is the character's hexadecimal Unicode code point. For example, the letter "é" is represented as \u00e9. When you load a properties file in Java, the runtime automatically converts these escapes to their corresponding characters.

To support multilingual applications, it's best to:

Use Unicode escapes for all non-ASCII characters in properties files;
Maintain separate properties files for each language or locale, such as messages_en.properties for English and messages_zh.properties for Chinese;
Use tools like the native2ascii utility to convert UTF-8 encoded files into ISO-8859-1 with Unicode escapes;
Always document the encoding and conversion process in your project guidelines.

Following these best practices ensures your application can display messages correctly, regardless of the user's language.

src/com/example/UnicodePropertiesDemo.java

src/com/example/messages.properties


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package com.example;

import java.io.FileInputStream;
import java.io.InputStreamReader;
import java.util.Properties;

public class UnicodePropertiesDemo {
    public static void main(String[] args) throws Exception {
        Properties props = new Properties();
        try (InputStreamReader reader = new InputStreamReader(
                new FileInputStream("src/com/example/messages.properties"), "ISO-8859-1")) {
            props.load(reader);
        }
        System.out.println("English: " + props.getProperty("greeting.en"));
        System.out.println("Chinese: " + props.getProperty("greeting.zh"));
        System.out.println("Russian: " + props.getProperty("greeting.ru"));
    }
}

When you need to include non-ASCII characters directly in properties files, you can't simply type them in as-is because Java expects ISO-8859-1 encoding. Instead, you use Unicode escapes, which Java will interpret at runtime. For example, the Chinese word for "hello" (你好) becomes \u4F60\u597D in the properties file.

To ease the process of converting UTF-8 encoded text (containing non-ASCII characters) to the required Unicode escapes, you can use the native2ascii tool provided in the Java Development Kit. This tool takes a UTF-8 file and outputs a version with all non-ASCII characters replaced by their Unicode escape sequences, making it compatible with Java's properties file requirements.

Some modern IDEs and build tools can also handle properties file encoding automatically, but it's a good practice to be aware of these details and explicitly document how you handle encoding in your project.

src/com/example/MultiLangPropertiesDemo.java

src/com/example/multilang.properties


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package com.example;

import java.io.FileInputStream;
import java.io.InputStreamReader;
import java.util.Properties;

public class MultiLangPropertiesDemo {
    public static void main(String[] args) throws Exception {
        Properties props = new Properties();
        try (InputStreamReader reader = new InputStreamReader(
                new FileInputStream("src/com/example/multilang.properties"), "ISO-8859-1")) {
            props.load(reader);
        }
        String[] languages = {"en", "es", "ja"};
        for (String lang : languages) {
            System.out.println(lang + ": " + props.getProperty("welcome." + lang));
        }
    }
}

1. What is the default character encoding for Java properties files?

2. How can you represent non-ASCII characters in a properties file?

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Section 1. Chapitre 4

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