轉：解決 java.util.MissingResourceException: Can’t find bundle for base name com…config, loc

轉：解決 java.util.MissingResourceException: Can't find bundle for base name com...config, locale zh_CN 錯誤

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)

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:

1. These resource properties files are loaded by classloader, similar to java classes.  So you need to include them in your runtime classpath.
2. 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.
3. 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.
4. 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


C:/ws/netbeans5/scrap>
|   build.xml
+---build
|   /---classes
|       /---com
|           /---cheng
|               /---scrap
|                       Scrap.class
|
+---src
|   /---com
|       /---cheng
|           /---scrap
|                   config.properties
|                   Scrap.java



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: 

1. 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.
2. 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.