Java中，关于资源Resource的定位问题

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通过class的getResource方法，查找与给定类相关的资源。

1、class中getResource在JDK中的定义

public URL getResource(String name)

getResource方法的实现如下

//getResourcepublic 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);}//resolveNameprivate String resolveName(String name) {if (name == null) {return name;}if (!name.startsWith("/")) {Class c = this;while (c.isArray()) {c = c.getComponentType();}String baseName = c.getName();int index = baseName.lastIndexOf('.');if (index != -1) {name = baseName.substring(0, index).replace('.', '/')+"/"+name;}} else {name = name.substring(1);}return name;}

2、classloader中的getResource在JDK中的定义

public URL getResource(String name)

getResource方法的实现如下

    //getResourcepublic 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;}/*** Find resources from the VM's built-in classloader.*/private static URL getBootstrapResource(String name) {try {// If this is a known JRE resource, ensure that its bundle is // downloaded.  If it isn't known, we just ignore the download// failure and check to see if we can find the resource anyway// (which is possible if the boot class path has been modified).sun.jkernel.DownloadManager.getBootClassPathEntryForResource(name);} catch (NoClassDefFoundError e) {// This happens while Java itself is being compiled; DownloadManager// isn't accessible when this code is first invoked.  It isn't an// issue, as if we can't find DownloadManager, we can safely assume// that additional code is not available for download.}URLClassPath ucp = getBootstrapClassPath();Resource res = ucp.getResource(name);return res != null ? res.getURL() : null;}/*** Finds the resource with the given name. Class loader implementations* should override this method to specify where to find resources.  </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** @since  1.2*/protected URL findResource(String name) {return null;}

3、总结

获取资源是，推荐使用class的getResource方法，它实质上是调用的classloader的getResource方法。

class的getResource方法，对name的路径做了一下解析，

所以，自己没有必要调用classloader的getResource方法（因为它的参数name是有规则要求的，但是在API中没有体现。从类路径下搜索，不能以"/"开头）。

例如：

package org.wsr.spring.demo;public class Demo {public static void main(String[] args) throws Exception {String path = new Demo().getClass().getClassLoader().getResource("").getPath();System.out.println(path);path = new Demo().getClass().getResource("").getPath();System.out.println(path);path = Demo.class.getResource("text.txt").getPath();System.out.println(path);}
}//  output
// /D:/WorkSpace/e_my_work/beantest/target/classes/
// /D:/WorkSpace/e_my_work/beantest/target/classes/org/wsr/spring/demo/
// /D:/WorkSpace/e_my_work/beantest/target/classes/org/wsr/spring/demo/text.txt

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