Spring Mobile是如何判断访问设备的类型的

Spring最近换域名了，去转转，发现了一个有意思的项目：spring mobile。

http://projects.spring.io/spring-mobile/

这个项目有很多实用的功能，如识别访问我们网站的设备是什么类型的（手机，平板，PC），据域名或者url来切换不同访问内容，据不同的访问设备转到不同的view中。

识别访问设备类型的核心代码在org.springframework.mobile.device.LiteDeviceResolver 类中，这个类实际上根据http请求头部的User-Agent的内容来判断设备到底是哪种类型的。

可以看到，这个类实际上是很简单的。不过字符串的匹配算法可能可以优化下。

[java]
view plaincopy

public class LiteDeviceResolver implements DeviceResolver {

private final List<String> mobileUserAgentPrefixes = new ArrayList<String>();

private final List<String> mobileUserAgentKeywords = new ArrayList<String>();

private final List<String> tabletUserAgentKeywords = new ArrayList<String>();

private final List<String> normalUserAgentKeywords = new ArrayList<String>();

public LiteDeviceResolver() {
init();
}

public LiteDeviceResolver(List<String> normalUserAgentKeywords) {
init();
this.normalUserAgentKeywords.addAll(normalUserAgentKeywords);
}

public Device resolveDevice(HttpServletRequest request) {
String userAgent = request.getHeader("User-Agent");
// UserAgent keyword detection of Normal devices
if (userAgent != null) {
userAgent = userAgent.toLowerCase();
for (String keyword : normalUserAgentKeywords) {
if (userAgent.contains(keyword)) {
return resolveFallback(request);
}
}
}
// UAProf detection
if (request.getHeader("x-wap-profile") != null || request.getHeader("Profile") != null) {
return LiteDevice.MOBILE_INSTANCE;
}
// User-Agent prefix detection
if (userAgent != null && userAgent.length() >= 4) {
String prefix = userAgent.substring(0, 4).toLowerCase();
if (mobileUserAgentPrefixes.contains(prefix)) {
return LiteDevice.MOBILE_INSTANCE;
}
}
// Accept-header based detection
String accept = request.getHeader("Accept");
if (accept != null && accept.contains("wap")) {
return LiteDevice.MOBILE_INSTANCE;
}
// UserAgent keyword detection for Mobile and Tablet devices
if (userAgent != null) {
userAgent = userAgent.toLowerCase();
// Android special case
if (userAgent.contains("android") && !userAgent.contains("mobile")) {
return LiteDevice.TABLET_INSTANCE;
}
// Kindle Fire special case
if (userAgent.contains("silk") && !userAgent.contains("mobile")) {
return LiteDevice.TABLET_INSTANCE;
}
for (String keyword : tabletUserAgentKeywords) {
if (userAgent.contains(keyword)) {
return LiteDevice.TABLET_INSTANCE;
}
}
for (String keyword : mobileUserAgentKeywords) {
if (userAgent.contains(keyword)) {
return LiteDevice.MOBILE_INSTANCE;
}
}
}
// OperaMini special case
@SuppressWarnings("rawtypes")
Enumeration headers = request.getHeaderNames();
while (headers.hasMoreElements()) {
String header = (String) headers.nextElement();
if (header.contains("OperaMini")) {
return LiteDevice.MOBILE_INSTANCE;
}
}
return resolveFallback(request);
}

// subclassing hooks

/**
* List of user agent prefixes that identify mobile devices.
* Used primarily to match by operator or handset manufacturer.
*/
protected List<String> getMobileUserAgentPrefixes() {
return mobileUserAgentPrefixes;
}

/**
* List of user agent keywords that identify mobile devices.
* Used primarily to match by mobile platform or operating system.
*/
protected List<String> getMobileUserAgentKeywords() {
return mobileUserAgentKeywords;
}

/**
* List of user agent keywords that identify tablet devices.
* Used primarily to match by tablet platform or operating system.
*/
protected List<String> getTabletUserAgentKeywords() {
return tabletUserAgentKeywords;
}

/**
* List of user agent keywords that identify normal devices.
* Any items in this list take precedence over the mobile and
* tablet user agent keywords, effectively overriding those.
*/
protected List<String> getNormalUserAgentKeywords() {
return normalUserAgentKeywords;
}

/**
* Initialize this device resolver implementation.
* Registers the known set of device signature strings.
* Subclasses may override to register additional strings.
*/
protected void init() {
getMobileUserAgentPrefixes().addAll(Arrays.asList(KNOWN_MOBILE_USER_AGENT_PREFIXES));
getMobileUserAgentKeywords().addAll(Arrays.asList(KNOWN_MOBILE_USER_AGENT_KEYWORDS));
getTabletUserAgentKeywords().addAll(Arrays.asList(KNOWN_TABLET_USER_AGENT_KEYWORDS));
}

/**
* Fallback called if no mobile device is matched by this resolver.
* The default implementation of this method returns a "normal" {@link Device} that is neither mobile or a tablet.
* Subclasses may override to try additional mobile or tablet device matching before falling back to a "normal" device.
*/
protected Device resolveFallback(HttpServletRequest request) {
return LiteDevice.NORMAL_INSTANCE;
}

// internal helpers

private static final String[] KNOWN_MOBILE_USER_AGENT_PREFIXES = new String[] { "w3c ", "w3c-", "acs-", "alav",
"alca", "amoi", "audi", "avan", "benq", "bird", "blac", "blaz", "brew", "cell", "cldc", "cmd-", "dang",
"doco", "eric", "hipt", "htc_", "inno", "ipaq", "ipod", "jigs", "kddi", "keji", "leno", "lg-c", "lg-d",
"lg-g", "lge-", "lg/u", "maui", "maxo", "midp", "mits", "mmef", "mobi", "mot-", "moto", "mwbp", "nec-",
"newt", "noki", "palm", "pana", "pant", "phil", "play", "port", "prox", "qwap", "sage", "sams", "sany",
"sch-", "sec-", "send", "seri", "sgh-", "shar", "sie-", "siem", "smal", "smar", "sony", "sph-", "symb",
"t-mo", "teli", "tim-", "tosh", "tsm-", "upg1", "upsi", "vk-v", "voda", "wap-", "wapa", "wapi", "wapp",
"wapr", "webc", "winw", "winw", "xda ", "xda-" };

private static final String[] KNOWN_MOBILE_USER_AGENT_KEYWORDS = new String[] { "blackberry", "webos", "ipod",
"lge vx", "midp", "maemo", "mmp", "mobile", "netfront", "hiptop", "nintendo DS", "novarra", "openweb",
"opera mobi", "opera mini", "palm", "psp", "phone", "smartphone", "symbian", "up.browser", "up.link",
"wap", "windows ce" };

private static final String[] KNOWN_TABLET_USER_AGENT_KEYWORDS = new String[] { "ipad", "playbook", "hp-tablet",
"kindle" };

}