java 中的显示动态配置(ResourceBundle)

在java中想要根据不同的环境设置不同的字符,可以使用下面的这种方法：

import java.text.MessageFormat;
import java.util.MissingResourceException;
import java.util.ResourceBundle;

public class Messages {
 private static final String BUNDLE_NAME ="messages"; //$NON-NLS-1$

 private static final ResourceBundleRESOURCE_BUNDLE = ResourceBundle.getBundle(BUNDLE_NAME);

 private Messages() {
 }

 
 public static String getString(String key){
  try {
   returnRESOURCE_BUNDLE.getString(key);
  } catch(MissingResourceException e) {
   return '!' +key + '!';
  }
 }
 
    publicstatic String getText(String key, String argument1)
    {
       return getText(key, argument1, null);
    }

    publicstatic String getText(String key, String argument1, Stringargument2)
    {
       return getText(key, argument1, argument2, null);
    }

    publicstatic String getText(String key, String argument1, Stringargument2, String argument3)
    {
       String as[] = new String[3];
       as[0] = argument1;
       as[1] = argument2;
       as[2] = argument3;
       return getText(key, as);
    }
   
    // Supportany numbers arguments
    publicstatic String getText(String key, String[] arguments)
    {
       if(RESOURCE_BUNDLE == null)
           return null;
       try
       {
           String message = RESOURCE_BUNDLE.getString(key);
           return MessageFormat.format(message, arguments);
       }
       catch(MissingResourceException missingresourceexception)
       {
        return null;
       }
   } 
}

 

编写messages.properties，上面的类会自动读取里面的变量:

如：

toolItemLoadCode      = Load
view                  = View

 

程序中使用：

toolItemLoadCode.setToolTipText(Messages.getString("view"));

 

在这里有一个要注意的问题，那就是messages.properties文件的放置位置，有的时候会出现下面的错误：

java.util.MissingResourceException: Can't find bundle for basename

 

 

解决解释如下：

Solve java.util.MissingResourceException: Can't findbundle for base name com...config, locale zh_CN

atjava.util.ResourceBundle.throwMissingResourceException(ResourceBundle.java:836)
atjava.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 specificlocale.   You may be baffled whyjava keeps complaining it can't find a properties file that isright there.   A few things tokeep in mind when debugging this type of errors:

1. These resource properties files are loaded by classloader,similar to java classes.   So youneed to include them in your runtime classpath.
2. These resources have fully-qualified-resource-name, similar toa fully-qualified-class-name, excerpt you can't import a resourceinto your java source file.  Why? because its name takes the form of a string.
3. ResourceBundle.getBundle("config") tells theclassloader to load a resource named "config" with default package (that is, nopackage).   It does NOT mean aresource in the current package that has the referencingclass.
4. ResourceBundle.getBundle("com.cheng.scrap.config")tells the classloader to load a resource named "config" with package "com.cheng.scrap."  Itsfully-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 willneed to  cp src\com\cheng\scrap\config.propertiesbuild\classes\ such that config.properties is directly underclasses, and at the same levelas com.  Alternatively, you can put config.properties into a config.jar such that config.properties is at the root ofconfig.jar without anysubdirectories, 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 needto  cpsrc\com\cheng\scrap\config.propertiesbuild\classes\com\cheng\scrap\such thatconfig.properties is directlyunder 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, andinclude config.jar in theclasspath.   

You may be wondering why it is made soconfusing?   The benefits aretwo-fold, as I see it:  

1. Location transparency.   Atruntime, config.properties is NOT a file, it's just a a loadableresource.   config.properites maynot exist in your project at all, and the person who wroteScrap.java may have never seen thisresource.   A URLClassLoader canfind it in a network path or URL atruntime.   This is especiallyimportant for server-side components such as EJB, Servlet, JSP,etc, who are normally not allowed to access filesystems.   When you askclassloaders for a resource, its physical location becomesirrelevant.
2. Namespace mechanism.   Havinga package allows multiple packages to have resources with the sameshort name without causing conflicts. This is no different fromjava packages and xml namespaces.