Can't switch context to webview

Issues/Bugs
17

Hi,
Please make sure that the version of selenium-server-standalone, selenium-java, java-client.
I used them as below:
selenium-server-standalone-2.48.2.jar
selenium-java-2.48.2.jar
java-client-3.2.0.jar

My code as below:
protected void switchToWebview() throws Exception {

	// E.G.['NATIVE_APP', 'WEBVIEW_1', ...]
	Set<String> contexts = driver.getContextHandles();

	// make sure we have something other than the native context
	// assertThat(contexts.size(), greaterThan(1));
	for (String context : contexts) {
		// System.out.println(contexts);
		if (!context.equals("NATIVE_APP")) {
			driver.context((String) contexts.toArray()[1]);
			break;
		}
	}
	System.out.println("execute context switch successfully!!!  "
			+ contexts.toArray()[1]);
}