Mybaits源码分析一之加载输入流

1  String resource="mybatis-config.xml";
2  InputStream inputStream=Resources.getResourceAsStream(resource);

 1  /*
 2    * Returns a resource on the classpath as a Stream object
 3    *
 4    * @param resource The resource to find
 5    * @return The resource
 6    * @throws java.io.IOException If the resource cannot be found or read
 7    */
 8   public static InputStream getResourceAsStream(String resource) throws IOException {
 9     return getResourceAsStream(null, resource);
10   }
11 
12   /*
13    * Returns a resource on the classpath as a Stream object
14    *
15    * @param loader   The classloader used to fetch the resource
16    * @param resource The resource to find
17    * @return The resource
18    * @throws java.io.IOException If the resource cannot be found or read
19    */
20   public static InputStream getResourceAsStream(ClassLoader loader, String resource) throws IOException {
21     InputStream in = classLoaderWrapper.getResourceAsStream(resource, loader);
22     if (in == null) {
23       throw new IOException("Could not find resource " + resource);
24     }
25     return in;
26   }

 1   /*
 2    * Get a resource from the classpath, starting with a specific class loader
 3    *
 4    * @param resource    - the resource to find
 5    * @param classLoader - the first class loader to try
 6    * @return the stream or null
 7    */
 8   public InputStream getResourceAsStream(String resource, ClassLoader classLoader) {
 9     return getResourceAsStream(resource, getClassLoaders(classLoader));
10   }

 1 ClassLoader[] getClassLoaders(ClassLoader classLoader) {
 2     return new ClassLoader[]{
 3     //参数指定的类加载器
 4         classLoader,
 5    //系统指定的默认类加载器
 6         defaultClassLoader,
 7     //当前线程绑定的类加载器
 8         Thread.currentThread().getContextClassLoader(),
 9    //当前类使用的类加载器
10         getClass().getClassLoader(),
11    // 系统的类加载器
12         systemClassLoader};
13   }

 1  /*
 2    * Try to get a resource from a group of classloaders
 3    *
 4    * @param resource    - the resource to get
 5    * @param classLoader - the classloaders to examine
 6    * @return the resource or null
 7    */
 8   InputStream getResourceAsStream(String resource, ClassLoader[] classLoader) {
 9 //从指定的资源（resource资源的URL）  按顺序（ClassLoader[]中的顺序）加载，加载到开始返回
10     for (ClassLoader cl : classLoader) {
11       if (null != cl) {
12 
13         // try to find the resource as passed
14         InputStream returnValue = cl.getResourceAsStream(resource);
15 
16         // now, some class loaders want this leading "/", so we‘ll add it and try again if we didn‘t find the resource
17         if (null == returnValue) {
18           returnValue = cl.getResourceAsStream("/" + resource);
19         }
20 
21         if (null != returnValue) {
22           return returnValue;
23         }
24       }
25     }
26     return null;
27   }