4.5.4. 注册组件中的 DispatcherServlet
本节将介绍如何将一个应用程序组件中的 servlet 和 filter 配置传递到使用该组件的应用程序。为了避免web.xml文件中的代码重复,需要在组件中使用特殊的 ServletRegistrationManager
bean 注册 servlet 和 filter。
关于 Servlet 注册的最常见情况在示例HTTP servlet 注册中介绍。我们考虑一个更复杂的例子:一个应用程序组件带有一个用于处理 Web 请求的自定义 DispatcherServlet
的实现。
这个 servlet 从 demo-dispatcher-spring.xml
文件加载配置,如果要该 servlet 正常工作,应该在源码根目录(例如 web/src
)先创建一个同名的空文件。
public class WebDispatcherServlet extends DispatcherServlet {
private volatile boolean initialized = false;
@Override
public String getContextConfigLocation() {
String configFile = "demo-dispatcher-spring.xml";
File baseDir = new File(AppContext.getProperty("cuba.confDir"));
String[] tokenArray = new StrTokenizer(configFile).getTokenArray();
StringBuilder locations = new StringBuilder();
for (String token : tokenArray) {
String location;
if (ResourceUtils.isUrl(token)) {
location = token;
} else {
if (token.startsWith("/"))
token = token.substring(1);
File file = new File(baseDir, token);
if (file.exists()) {
location = file.toURI().toString();
} else {
location = "classpath:" + token;
}
}
locations.append(location).append(" ");
}
return locations.toString();
}
@Override
protected WebApplicationContext initWebApplicationContext() {
WebApplicationContext wac = findWebApplicationContext();
if (wac == null) {
ApplicationContext parent = AppContext.getApplicationContext();
wac = createWebApplicationContext(parent);
}
onRefresh(wac);
String attrName = getServletContextAttributeName();
getServletContext().setAttribute(attrName, wac);
if (this.logger.isDebugEnabled()) {
this.logger.debug("Published WebApplicationContext of servlet '" + getServletName() +
"' as ServletContext attribute with name [" + attrName + "]");
}
return wac;
}
@Override
public void init(ServletConfig config) throws ServletException {
if (!initialized) {
super.init(config);
initialized = true;
}
}
@Override
protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
_service(response);
}
@Override
public void service(ServletRequest req, ServletResponse res) throws ServletException, IOException {
_service(res);
}
private void _service(ServletResponse res) throws IOException {
String testMessage = AppContext.getApplicationContext().getBean(Messages.class).getMainMessage("testMessage");
res.getWriter()
.write("WebDispatcherServlet test message: " + testMessage);
}
}
要注册 DispatcherServlet
,必须手动对此类进行加载、实例化、初始化,否则不同的类加载器可能会在 SingleWAR/SingleUberJAR 部署的情况下引发问题。而且,自定义 DispatcherServlet
应该需要进行双重初始化 - 第一次手动初始化,第二次由 servlet 容器初始化。
下面是一个初始化 WebDispatcherServlet
的组件示例:
@Component
public class WebInitializer {
private static final String WEB_DISPATCHER_CLASS = "com.demo.comp.web.WebDispatcherServlet";
private static final String WEB_DISPATCHER_NAME = "web_dispatcher_servlet";
private final Logger log = LoggerFactory.getLogger(WebInitializer.class);
@Inject
private ServletRegistrationManager servletRegistrationManager;
@EventListener
public void initialize(ServletContextInitializedEvent e) {
Servlet webDispatcherServlet = servletRegistrationManager.createServlet(e.getApplicationContext(), WEB_DISPATCHER_CLASS);
ServletContext servletContext = e.getSource();
try {
webDispatcherServlet.init(new AbstractWebAppContextLoader.CubaServletConfig(WEB_DISPATCHER_NAME, servletContext));
} catch (ServletException ex) {
throw new RuntimeException("Failed to init WebDispatcherServlet");
}
servletContext.addServlet(WEB_DISPATCHER_NAME, webDispatcherServlet)
.addMapping("/webd/*");
}
}
注入的 ServletRegistrationManager
bean 的 createServlet()
方法从 ServletContextInitializedEvent
获取应用程序上下文,并获取 WebDispatcherServlet
类的完全限定名。要初始化 servlet,需要传递从 ServletContextInitializedEvent
获得的 ServletContext
实例和 servlet 名称。addMapping()
方法用于定义通过 URL:/webd/
访问 servlet 的 HTTP 映射。