忘记以前有没有问过这个问题,总之我现在有看到几个地方有这个:
Thread.currentThread().getContextClassLoader()
我总是想不出在什么情况下会用这种方式获得一个ClassLoader,因为好像默认情况下,它返回的是和加载应用的ClassLoader是同一个,比如说在一个类Test中写
ClassLoader cl = Thread.currentThread().getContextClassLoader();
为何不直接用Test.class.getClassLoader()
获得当前上下文的类加载器是啥意思?有啥好处?
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http://stackoverflow.com/questions/676250/different-ways-of-loading-a-file-as-an-inputstream
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http://uule.iteye.com/blog/813841
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假设要装载的类，通过当前类的Classloader链装载不了，那就得设ContextClassLoader
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通过当前类的Classloader链装载不了，那就得设ContextClassLoader
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- Java code
public class Test { public static void main(String[] args) { // 此时三个ClassLoader是同一个对象 System.out.println(Thread.currentThread().getContextClassLoader()); // 当前线程的类加载器 System.out.println(Test.class.getClassLoader()); // 当前类的类加载器 System.out.println(ClassLoader.getSystemClassLoader()); // 系统初始的类加载器 }}
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- Java code
final ClassLoader parent = findParentClassLoader(); String libDirString = System.getProperty("openfire.lib.dir"); File libDir; if (libDirString != null) { // If the lib directory property has been specified and it actually // exists use it, else use the default libDir = new File(libDirString); if (!libDir.exists()) { Log.warn("Lib directory " + libDirString + " does not exist. Using default " + DEFAULT_LIB_DIR); libDir = new File(DEFAULT_LIB_DIR); } } else { libDir = new File(DEFAULT_LIB_DIR); } // Unpack any pack files. unpackArchives(libDir, true); String adminLibDirString = System.getProperty("openfireHome"); if (adminLibDirString == null) { adminLibDirString = DEFAULT_ADMIN_LIB_DIR; } else { adminLibDirString = adminLibDirString+"/plugins/admin/webapp/WEB-INF/lib"; } File adminLibDir = new File(adminLibDirString); if (adminLibDir.exists()) { unpackArchives(adminLibDir, false); } else { Log.warn("Admin Lib Directory " + adminLibDirString + " does not exist. Web admin console may not work."); } ClassLoader loader = new JiveClassLoader(parent, libDir); Thread.currentThread().setContextClassLoader(loader); Class containerClass = loader.loadClass( "org.jivesoftware.openfire.XMPPServer"); containerClass.newInstance();