我的Java开发学习之旅------>JAVA 笔记ClassLoader.getResourceAsStream() 与 Class.getResourceAsStream()的区别

今天，一读者在我的 Android通过调用Webservice实现手机号码归属地查询 文章中给我回复了一个问题，由于没有具体说明我的sop12.xml文件是放在src目录下，不是和具体操作类AddressService.java放在同一目录下，引起了误会。

1. InputStream inputStream = AddressService.class.getClassLoader()  
2.                 .getResourceAsStream("sop12.xml");  

现在在这里总结一下Java中getResourceAsStream的用法。

首先，Java中的getResourceAsStream有以下几种：
1. Class.getResourceAsStream(String path) ： path 不以’/'开头时默认是从此类所在的包下取资源，以’/'开头则是从

ClassPath根下获取。其只是通过path构造一个绝对路径，最终还是由ClassLoader获取资源。

2. Class.getClassLoader.getResourceAsStream(String path) ：默认则是从ClassPath根下获取，path不能以’/'开头，最终是由

ClassLoader获取资源。

3. ServletContext. getResourceAsStream(String path)：默认从WebAPP根目录下取资源，Tomcat下path是否以’/'开头无所谓，

当然这和具体的容器实现有关。

4. Jsp下的application内置对象就是上面的ServletContext的一种实现。

其次，getResourceAsStream 用法大致有以下几种：

第一： 要加载的文件和.class文件在同一目录下，例如：com.x.y 下有类me.class ,同时有资源文件myfile.xml

那么，应该有如下代码：

me.class.getResourceAsStream("myfile.xml");

第二：在me.class目录的子目录下，例如：com.x.y 下有类me.class ,同时在 com.x.y.file 目录下有资源文件myfile.xml

那么，应该有如下代码：

me.class.getResourceAsStream("file/myfile.xml");

第三：不在me.class目录下，也不在子目录下，例如：com.x.y 下有类me.class ,同时在 com.x.file 目录下有资源文件myfile.xml

那么，应该有如下代码：

me.class.getResourceAsStream("/com/x/file/myfile.xml");

总结一下，可能只是两种写法

第一：前面有 “ / ”

“ / ”代表了工程的根目录，例如工程名叫做myproject，“ / ”代表了myproject

me.class.getResourceAsStream("/com/x/file/myfile.xml");

第二：前面没有 “ / ”

代表当前类的目录

me.class.getResourceAsStream("myfile.xml");

me.class.getResourceAsStream("file/myfile.xml"); 

最后，自己的理解： 
getResourceAsStream读取的文件路径只局限与工程的源文件夹中，包括在工程src根目录下，以及类包里面任何位置，但是如果配置文件路径是在除了源文件夹之外的其他文件夹中时，该方法是用不了的。 

附注：java.lang.ClassLoader.gClassLoader()源码

 /**
     * Returns an input stream for reading the specified resource.
     *
     * <p> The search order is described in the documentation for {@link
     * #getResource(String)}.  </p>
     *
     * @param  name
     *         The resource name
     *
     * @return  An input stream for reading the resource, or <tt>null</tt>
     *          if the resource could not be found
     *
     * @since  1.1
     */
    public InputStream getResourceAsStream(String name) {
	URL url = getResource(name);
	try {
	    return url != null ? url.openStream() : null;
	} catch (IOException e) {
	    return null;
	}
    }

/**
     * Finds the resource with the given name.  A resource is some data
     * (images, audio, text, etc) that can be accessed by class code in a way
     * that is independent of the location of the code.
     *
     * <p> The name of a resource is a '<tt>/</tt>'-separated path name that
     * identifies the resource.
     *
     * <p> This method will first search the parent class loader for the
     * resource; if the parent is <tt>null</tt> the path of the class loader
     * built-in to the virtual machine is searched.  That failing, this method
     * will invoke {@link #findResource(String)} to find the resource.  </p>
     *
     * @param  name
     *         The resource name
     *
     * @return  A <tt>URL</tt> object for reading the resource, or
     *          <tt>null</tt> if the resource could not be found or the invoker
     *          doesn't have adequate  privileges to get the resource.
     *
     * @since  1.1
     */
    public URL getResource(String name) {
	URL url;
	if (parent != null) {
	    url = parent.getResource(name);
	} else {
	    url = getBootstrapResource(name);
	}
	if (url == null) {
	    url = findResource(name);
	}
	return url;
    }

/**
     * Finds a resource with a given name.  The rules for searching resources
     * associated with a given class are implemented by the defining
     * {@linkplain ClassLoader class loader} of the class.  This method
     * delegates to this object's class loader.  If this object was loaded by
     * the bootstrap class loader, the method delegates to {@link
     * ClassLoader#getSystemResourceAsStream}.
     *
     * <p> Before delegation, an absolute resource name is constructed from the
     * given resource name using this algorithm:
     *
     * <ul>
     *
     * <li> If the <tt>name</tt> begins with a <tt>'/'</tt>
     * (<tt>'\u002f'</tt>), then the absolute name of the resource is the
     * portion of the <tt>name</tt> following the <tt>'/'</tt>. 
     *
     * <li> Otherwise, the absolute name is of the following form:
     *
     * <blockquote><pre>
     *   <tt>modified_package_name</tt>/<tt>name</tt>
     * </pre></blockquote>
     *
     * <p> Where the <tt>modified_package_name</tt> is the package name of this
     * object with <tt>'/'</tt> substituted for <tt>'.'</tt>
     * (<tt>'\u002e'</tt>).
     *
     * </ul>
     *
     * @param  name name of the desired resource
     * @return      A {@link java.io.InputStream} object or <tt>null</tt> if
     *              no resource with this name is found
     * @throws  NullPointerException If <tt>name</tt> is <tt>null</tt>
     * @since  JDK1.1
     */
     public InputStream getResourceAsStream(String name) {
        name = resolveName(name);
        ClassLoader cl = getClassLoader0();
        if (cl==null) {
            // A system class.
            return ClassLoader.getSystemResourceAsStream(name);
        }
        return cl.getResourceAsStream(name);
    }

java.lang.Class.getResource(String name)源码

/**
     * Finds a resource with a given name.  The rules for searching resources
     * associated with a given class are implemented by the defining
     * {@linkplain ClassLoader class loader} of the class.  This method
     * delegates to this object's class loader.  If this object was loaded by
     * the bootstrap class loader, the method delegates to {@link
     * ClassLoader#getSystemResource}.
     *
     * <p> Before delegation, an absolute resource name is constructed from the
     * given resource name using this algorithm:
     *
     * <ul>
     *
     * <li> If the <tt>name</tt> begins with a <tt>'/'</tt>
     * (<tt>'\u002f'</tt>), then the absolute name of the resource is the
     * portion of the <tt>name</tt> following the <tt>'/'</tt>. 
     *
     * <li> Otherwise, the absolute name is of the following form:
     *
     * <blockquote><pre>
     *   <tt>modified_package_name</tt>/<tt>name</tt>
     * </pre></blockquote>
     *
     * <p> Where the <tt>modified_package_name</tt> is the package name of this
     * object with <tt>'/'</tt> substituted for <tt>'.'</tt>
     * (<tt>'\u002e'</tt>).
     *
     * </ul>
     *
     * @param  name name of the desired resource
     * @return      A  {@link java.net.URL} object or <tt>null</tt> if no
     *              resource with this name is found
     * @since  JDK1.1
     */
    public java.net.URL getResource(String name) {
        name = resolveName(name);
        ClassLoader cl = getClassLoader0();
        if (cl==null) {
            // A system class.
            return ClassLoader.getSystemResource(name);
        }
        return cl.getResource(name);
    }