使用commons-configuration2读取properties、yaml、xml配置文件，实现配置文件的热更新【享学Java】

The Commons Configuration software library provides a generic configuration interface which enables a Java application to read configuration data from a variety of sources. 
Commons Configuration provides typed access to single, and multi-valued configuration parameters

Commons Configuration软件库提供了一个**通用的**配置接口，它允许Java应用程序从**各种来源**读取配置数据。
Commons Configuration提供对单值和多值配置参数的**类型化**访问（getDouble、getInteger等等）

<!-- https://mvnrepository.com/artifact/commons-beanutils/commons-beanutils -->
<dependency>
    <groupId>commons-beanutils</groupId>
    <artifactId>commons-beanutils</artifactId>
    <version>1.9.3</version>
</dependency>

person.name=fsx
person.age=10

spring.application.name=mydemoshow

## 示范一个中文
country.zh=中国

    public static void main(String[] args) throws ConfigurationException {
        Configurations configs = new Configurations();

        // 每个Configuration代表这一个配置文件~（依赖beanutils这个jar）
        Configuration config = configs.properties("my.properties");

        // 遍历
        Iterator<String> keys = config.getKeys();
        while (keys.hasNext()) {
            String key = keys.next();
            String value = config.getString(key);
            System.out.println(key + " = " + value);
        }
    }

person.name = fsx
person.age = 10
spring.application.name = mydemoshow::fsx
country.zh = 中国

    public static void main(String[] args) throws ConfigurationException {
        Configurations configs = new Configurations();

        // 设置编码，此处的实际是个PropertiesConfiguration，它默认采用的是`ISO-8859-1`所以中文乱码~
        // 注意：这个前提是你的properties文件是utf-8编码的~~~
        FileBasedConfigurationBuilder.setDefaultEncoding(PropertiesConfiguration.class, "UTF-8");
        // 每个Configuration代表这一个配置文件~（依赖beanutils这个jar）
        Configuration config = configs.properties("my.properties");
        ...
     }

...
		// 采用Builder模式处理更为复杂的一些场景   比如把逗号分隔的字符串解析到数组、解析到list、前后拼接字符串等等操作
		// 其实你直接configs.properties(...)它的内部原理也是builder模式~
        FileBasedConfigurationBuilder<PropertiesConfiguration> builder = configs.propertiesBuilder("my.properties");
        //builder.addEventListener();
        //builder.getConfiguration();
        //builder.getFileHandler();
...

    public static void main(String[] args) throws ConfigurationException, IOException {
        // Spring也是支持很友好的编码解决的~~~
        Properties properties = PropertiesLoaderUtils.loadProperties(new EncodedResource(new ClassPathResource("my.properties"), StandardCharsets.UTF_8));
        System.out.println(properties);
    }

user.file = ${sys:user.home}/settings.xml
java.home = ${env:JAVA_HOME}

# 可以理解为直接引用某个类的静态常量~ 还是蛮强大的
action.key = ${const:java.awt.event.KeyEvent.VK_CANCEL}

...
		// 这里单独set，只是保存在了内存了，并还没有持久化的  需要注意~~~~
        Configuration config = configs.properties("my.properties");
        config.setProperty("dev", "dev");
...

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
    <token>
        <device>
            <validate>true</validate>
        </device>
        <person>
            <validate>true</validate>
            <expire description="人员令牌失效时间(分钟) ">60</expire>
        </person>
    </token>
</configuration>

    public static void main(String[] args) throws ConfigurationException {
        Configurations configs = new Configurations();

        XMLConfiguration config = configs.xml("my.xml");

        // 使用默认的符号定义创建一个表达式引擎
        DefaultExpressionEngine engine = new DefaultExpressionEngine(DefaultExpressionEngineSymbols.DEFAULT_SYMBOLS);
        // 指定表达式引擎
        config.setExpressionEngine(engine);
        System.out.println(config.getBoolean("token.device.validate"));
        System.out.println(config.getInt("token.person.expire"));

        // 此处就是它的默认规则 [@xxx]表示取对应attr的值~  更多默认定义请参考DEFAULT_SYMBOLS常量
        System.out.println(config.getString("token.person.expire[@description]"));
    }

true
60
人员令牌失效时间(分钟) 

<!-- https://mvnrepository.com/artifact/commons-jxpath/commons-jxpath -->
<dependency>
    <groupId>commons-jxpath</groupId>
    <artifactId>commons-jxpath</artifactId>
    <version>1.3</version>
</dependency>

    public static void main(String[] args) throws ConfigurationException {
        Configurations configs = new Configurations();


        XMLConfiguration config = configs.xml("my.xml");

        // 使用 XPath表达式引擎
        XPathExpressionEngine xpathEngine = new XPathExpressionEngine();
        config.setExpressionEngine(xpathEngine);
        System.out.println(config.getBoolean("token/device/validate"));
        System.out.println(config.getInt("token/person/expire"));

        // 请注意这里路径分隔符和attribute标签与上面使用DefaultExpressionEngine是不同的
        System.out.println(config.getString("token/person/expire/@description"));
    }

    public static void main(String[] args) throws ConfigurationException {
        Configurations configs = new Configurations();
        DefaultExpressionEngineSymbols symbols = new DefaultExpressionEngineSymbols.Builder(
                DefaultExpressionEngineSymbols.DEFAULT_SYMBOLS)
                // 指定属性分隔符(路径分隔符)
                .setPropertyDelimiter(".")
                .setIndexStart("{")
                .setIndexEnd("}")
                // 指定@开头就是attribute标志
                .setAttributeStart("@")
                // attribute结尾符为null  也就是木有结尾符
                .setAttributeEnd(null)
                // A Backslash is used for escaping property delimiters
                .setEscapedDelimiter("\\/")
                .create();
        // 用自定义的符号DefaultExpressionEngineSymbols对象创建一个表达式引擎
        // 此处还是使用的DefaultExpressionEngine~~~这个对象
        DefaultExpressionEngine engine = new DefaultExpressionEngine(symbols);
        Parameters params = new Parameters();


        FileBasedConfigurationBuilder<XMLConfiguration> builder = new FileBasedConfigurationBuilder<>(XMLConfiguration.class)
                .configure(params.xml()
                        .setFileName("my.xml")
                        // ~~~~~~~~~~~~~~~~~~~~~~~~~~使用自定义的表达式引擎~~~~~~~~~~~~~~~~~~~~~~~~~~
                        .setExpressionEngine(engine));


        // 使用builder生成配置~  而不用使用Configurations帮忙了~
        XMLConfiguration config = builder.getConfiguration();
        System.out.println(config.getBoolean("token.device.validate"));
        System.out.println(config.getInt("token.person.expire"));

        // 看此处 符号换成了我们自定义的~
        System.out.println(config.getProperty("token.person.expire@description"));
    }

spring:
 application:
   name: mydemoshow::${person.name}

person:
 name: fsx
 age: 10

    public static void main(String[] args) throws Exception {
        YAMLConfiguration config = new YAMLConfiguration();
        config.read(new ClassPathResource("my.yaml").getInputStream());

        Iterator<String> keys = config.getKeys();
        while (keys.hasNext()) {
            String key = keys.next();
            String value = config.getString(key);
            System.out.println(key + " = " + value);
        }
    }

spring.application.name = mydemoshow::fsx
person.name = fsx
person.age = 10

// @since 2.0
public interface FileLocationStrategy {
    URL locate(FileSystem fileSystem, FileLocator locator);
}

public class FileHandler {
    public FileLocationStrategy getLocationStrategy() {
        return FileLocatorUtils.obtainLocationStrategy(getFileLocator());
    }
}

... // 最终调用如下
public final class FileLocatorUtils {
	
    private static FileLocationStrategy initDefaultLocationStrategy() {
        final FileLocationStrategy[] subStrategies = new FileLocationStrategy[] {
                        new ProvidedURLLocationStrategy(),
                        new FileSystemLocationStrategy(),
                        new AbsoluteNameLocationStrategy(),
                        new BasePathLocationStrategy(),
                        new HomeDirectoryLocationStrategy(true),
                        new HomeDirectoryLocationStrategy(false),
                        new ClasspathLocationStrategy()
                };
        return new CombinedLocationStrategy(Arrays.asList(subStrategies));
    }
}