资源国际化

一、使用
属性文件：
config.properties
属性文件内容如下：
name=jack
password=123456

在java文件里面读取属性文件，可以使用ResourceBundle，如下：
ResourceBundle rs = ResourceBundle.getBundle("config");
String name = rs.getString("name");
String passwd = rs.getString("password");
System.out.println("name="+name);
Systme.out.println("password="+passwd);

输出结果如下：
name=jack
password=123456

二、Exception
如果遇到类似如下Exception:
Solve java.util.MissingResourceException: Can't find bundle for base name com...config, locale zh_CN

at java.util.ResourceBundle.throwMissingResourceException(ResourceBundle.java:836)
at java.util.ResourceBundle.getBundleImpl(ResourceBundle.java:805)
at java.util.ResourceBundle.getBundle(ResourceBundle.java:576)

可以参考如下方法：

You know java is looking for a properties file in a specific locale. You may be baffled why java keeps complaining it can't find a properties file that is right there. A few things to keep in mind when debugging this type of errors:

These resource properties files are loaded by classloader, similar to java classes. So you need to include them in your runtime classpath.
These resources have fully-qualified-resource-name, similar to a fully-qualified-class-name, excerpt you can't import a resource into your java source file. Why? because its name takes the form of a string.
ResourceBundle.getBundle("config") tells the classloader to load a resource named "config" with default package (that is, no package). It does NOT mean a resource in the current package that has the referencing class.
ResourceBundle.getBundle("com.cheng.scrap.config") tells the classloader to load a resource named "config" with package "com.cheng.scrap." Its fully-qualified-resource-name is "com.cheng.scrap.config"

For instance, you have a project like

For this statement in Scrap.java: ResourceBundle config = ResourceBundle.getBundle("config"); to work, you will need to cp src/com/cheng/scrap/config.properties build/classes/ such that config.properties is directly under classes, and at the same level as com. Alternatively, you can put config.properties into a config.jar such that config.properties is at the root of config.jar without any subdirectories, and include config.jar in the classpath.

For this statement in Scrap.java: ResourceBundle config = ResourceBundle.getBundle("com.cheng.scrap.config"); to work, you will need to cp src/com/cheng/scrap/config.properties build/classes/com/cheng/scrap/ such that config.properties is directly under classes/com/cheng/scrap/, and at the same level as scrap. Alternatively, you can put com/cheng/scrap/config.properties (along with the long subdirectories) into a config.jar, and include config.jar in the classpath.

You may be wondering why it is made so confusing? The benefits are two-fold, as I see it:

Location transparency. At runtime, config.properties is NOT a file, it's just a a loadable resource. config.properites may not exist in your project at all, and the person who wrote Scrap.java may have never seen this resource. A URLClassLoader can find it in a network path or URL at runtime. This is especially important for server-side components such as EJB, Servlet, JSP, etc, who are normally not allowed to access file systems. When you ask classloaders for a resource, its physical location becomes irrelevant.
Namespace mechanism. Having a package allows multiple packages to have resources with the same short name without causing conflicts. This is no different from java packages and xml namespaces.

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资源国际化

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