Java资源加载详解

Java资源加载详解

Java开发中常常要加载各种各样的资源文件，如property文件，xml配置文件，图片文件等等。

Java的资源加载策略选择比较多，很多资源加载方法都是基于不同的项目配置，没有一种资

源加载方法是万能的。首先来看看Java中的几种常见的资源加载方法：



一：通过ResourceBundle类来实现资源加载

这种方式通常被用来加载多语言支持的property文件，Java语言通过ResourceBundle可以非

常好的支持国际化。假设在默认为英文的系统中有语言资源文件mybundle_en.properties，则

调用代码如下：

ResourceBundle myBundle =ResourceBundle.getBundle("mybundle");

资源文件mybundle_en.properties的位置应该在sourcefolder的根目录下，假如资源文件位于

包路径com.mybundle.test下则上述代码应该改写为：

ResourceBundle myBundle =ResourceBundle.getBundle("com.mybundle.test.mybundle");



二：通过Class类的getResourceAsStream()方法来实现资源加载

这种加载方式同时是最常用也是最容易让开发者搞错的方法，getResourceAsStream()方法使用

默认文件名加载资源时，要求资源必须与Class文件同时相同的包路径。加载代码如下：

client.getClass().getResourceAsStream("mybundle.properties");



三：通过ClassLoader的getResourceAsStream()来实现资源文件加载

通过ClassLoader来加载资源文件是一种非常有效和实用的方法，只要资源位于classpath的路

径下面，ClassLoader都可以通过适当的策略来找到你要加载的资源。但是应该注意的是如果你

的资源位于SourceFloder的根目录，如下代码就可以完成：

this.getClass().getClassLoader().getResource("mybundle.properties");

如果你的资源文件位于独立的config文件中，只需要把config配置到classpath的变量中，然后使

用如下代码即可：

this.getClass().getClassLoader().getResource("config/mybundle.properties");



三种资源加载方式比较与总结：

方法


参数


失败时行为


用法示例代码

ClassLoader.

getResourceAsStream()


绝对路径加载时候不需要反斜杠/


Silent (return null)


This.getCalss().

getClassLoader().

getResourceAsStream(“

some/pkg/resource.prpperties

”);

Class.

getResourceAsStream()


有反斜杠/表现为绝对路径


Silent(return null)


This.getClass().

getResourceAsStream(“

resource.properties”);

ResourceBundle.

getBundle()


不需要反斜杠/, .已经暗示绝对路径

.properties为其默认的文件扩展名


Throws unchecked

java.util.MissingResource

Exception


ResourceBundle.getBundle(

“some.pkg.resource”)

资源加载策略说明：

不同的开发者对资源文件的管理千差万别，有的喜欢把它们放在不同的类路径下面，有的喜

欢放在单一的config文件下，没有一种方法是错误的。但是为了能够正确的加载到你需要的

资源文件，永远应该记得把资源文件夹的路径配置做为classpath的一部分，如果资源文件没

有位于你的source folder之内。否则你不得不通过额外的手段来配置与加载你的资源文件。

基于上述的总结，完成了一个资源加载的UtilityClass, 让你从此不再对Java中资源加载怀有好奇

与恐惧之心。

Resource Loading Utility Class源代码如下：

[java] view plaincopy

    import java.io.InputStream; 
    import java.util.Locale; 
    import java.util.Properties; 
    import java.util.ResourceBundle; 
     
    public class CommonResourceLoader { 
     
            /**
             * please use this method if property files located at same package with CommonResourceLoader
             * Java class
             * 
             * @param PropertiesName
             * @return
             */ 
            public static Properties loadPropertyFile(String PropertiesName) { 
     
                  Properties props = new Properties(); 
     
                  try 
                  { 
                      InputStream in = CommonResourceLoader.class.getResourceAsStream(PropertiesName); 
                     if (in != null) 
                     { 
                        props.load(in); 
                     }  
                     else 
                     { 
                        throw new IllegalArgumentException("No file exists for" + PropertiesName); 
                     } 
                  } 
                  catch (Exception e) 
                  { 
                     e.printStackTrace(); 
                  } 
     
                  return props; 
            } 
             
            /**
             * if the properties file is located at obj's package, please use it
             * @param obj
             * @param PropertiesName
             * @return
             */ 
            public static Properties loadPropertyFile(Class obj,  String PropertiesName) { 
     
                  Properties props = new Properties(); 
     
                  try 
                  { 
                      InputStream in = obj.getResourceAsStream(PropertiesName); 
                     if (in != null) 
                     { 
                        props.load(in); 
                     }  
                     else 
                     { 
                        throw new IllegalArgumentException("No file exists for" + PropertiesName); 
                     } 
                  } 
                  catch (Exception e) 
                  { 
                     e.printStackTrace(); 
                  } 
     
                  return props; 
            } 
             
            /**
             * base name is file name if file located at class path root directory
             * base name is directory + file full name if file at some folder inside class path list.
             * eg: myPro.properties
             * project structure
             * pro--src
             *  |    |---com.mytest.pkg
             *  |    |               |-----Hello.java
             *  |    |               |-----test.properties
             *  |---myPro.properties
             *  baseName= com/mytest/pkg/test.properties if load test.properties
             *  baseName= myPro.properties if load myPro.properties
             *
             * @param baseName
             * @return
             */ 
            public static Properties loadCurrentPropertyFile(String baseName) { 
                Properties props = new Properties(); 
     
                try 
                { 
                    InputStream in = CommonResourceLoader.class.getClassLoader().getResourceAsStream(baseName); 
                   if (in != null) 
                   { 
                      props.load(in); 
                   }  
                   else 
                   { 
                      throw new IllegalArgumentException("No file exists for" + baseName); 
                   } 
                } 
                catch (Exception e) 
                { 
                   e.printStackTrace(); 
                } 
     
                return props; 
            } 
             
            public static Properties loadSystemPropertyFile(String name, ClassLoader loader) { 
                Properties props = new Properties(); 
     
                try 
                { 
                    if(loader == null) 
                        loader = ClassLoader.getSystemClassLoader(); 
                    InputStream in = loader.getResourceAsStream(name); 
                   if (in != null) 
                   { 
                      props.load(in); 
                   }  
                   else 
                   { 
                      throw new IllegalArgumentException("No file exists for" + name); 
                   } 
                } 
                catch (Exception e) 
                { 
                   e.printStackTrace(); 
                } 
     
                return props; 
            } 
             
            /**
             * resourceURL is file name if file located at class path root directory
             * resourceURL is directory + file full name if file at some folder inside class path list.
             * eg: myPro.properties
             * project structure
             * pro--src
             *  |    |---com.mytest.pkg
             *  |    |               |-----Hello.java
             *  |    |               |-----test.properties
             *  |---myPro.properties
             *  resourceURL= com.mytest.pkg.test.properties if load test.properties
             *  resourceURL= myPro.properties if load myPro.properties
             *
             * @param baseName
             * @return
             */ 
            public static ResourceBundle loadResourceBundle(String resourceURL) { 
     
                    Locale locale = Locale.ENGLISH; 
                    ResourceBundle bundle = null; 
     
                    try { 
                            bundle = ResourceBundle.getBundle(resourceURL, locale); 
                            if (bundle == null) { 
                                    throw new IllegalArgumentException("No file exists for" + resourceURL); 
                            } 
                    } catch (Exception e) { 
                            e.printStackTrace(); 
                    } 
     
                    return bundle; 
            } 
     
    } 

特别说明：

这里的资源是指配置文件(xml,property等), 图片,Java程序运行需要的一切文本文件等等。