改变线程上下文的类加载器ClassLoader

/**
	 * Override the thread context ClassLoader with the environment's bean ClassLoader
	 * if necessary, i.e. if the bean ClassLoader is not equivalent to the thread
	 * context ClassLoader already.
	 * @param classLoaderToUse the actual ClassLoader to use for the thread context
	 * @return the original thread context ClassLoader, or <code>null</code> if not overridden
	 */
	public static ClassLoader overrideThreadContextClassLoader(ClassLoader classLoaderToUse) {
		Thread currentThread = Thread.currentThread();
		ClassLoader threadContextClassLoader = currentThread.getContextClassLoader();
		if (classLoaderToUse != null && !classLoaderToUse.equals(threadContextClassLoader)) {
			currentThread.setContextClassLoader(classLoaderToUse);
			return threadContextClassLoader;
		}
		else {
			return null;
		}
	}