{"id":1530,"date":"2012-07-29T16:47:53","date_gmt":"2012-07-29T14:47:53","guid":{"rendered":"http:\/\/doanduyhai.wordpress.com\/?p=1530"},"modified":"2015-01-31T13:13:14","modified_gmt":"2015-01-31T13:13:14","slug":"gwt-rpc-integration-with-spring","status":"publish","type":"post","link":"https:\/\/www.doanduyhai.com\/blog\/?p=1530","title":{"rendered":"GWT RPC integration with Spring"},"content":{"rendered":"

Recently I started studying GWT, a new web framework for my curriculum. The main idea of GWT is to let you code the GUI part in Java (with static compilation and type checking) then translate this code into Javascript.<\/p>\n

For the backend, GWT relies on an RPC system using plain old Servlet. Each RPC service is published as a distinct servlet so you end up having as many servlets are there are distinct RPC services.<\/p>\n

Not only this approach is not optimal for resources management server-side wise, it also pollutes your web.xml<\/strong> with many servlet declarations.<\/p>\n

Ideally we should have an unique servlet serving as a router and dispatching RPC calls to appropriate service beans managed by Spring. Spring is an appropriate framework for managing business in the backend due to its industry-wide adoption and its mature extensions portfolio. Needless to say that this design can be easily adapted for JEE containers too.<\/p>\n

Disclaimer<\/strong>: the code presented below has been inspired from projects like spring4GWT<\/a> and gwtrpc-spring<\/a>. I took the same approach and modified the URL mapping part so the original credits go for them.<\/p><\/blockquote>\n

<\/p>\n

I SpringRPCDispatcherServlet<\/h1>\n

RPC processing with GWT not only consist of calling the appropriate service in the backend. It also involves some plumbing tasks like object serialization\/deserialization<\/strong> to pass parameters back and forth. Instead of re-inventing the wheel and re-coding everything from scratch, it is wiser to re-use the existing GWT infrastructure and extends the RemoteServiceServlet<\/strong> class to adapt it to our needs.<\/p>\n

\r\npublic class SpringRPCDispatcherServlet extends RemoteServiceServlet\r\n{\r\n\tprivate static final long serialVersionUID = 1L;\r\n\tprivate static final Log logger = LogFactory.getLog(SpringRPCDispatcherServlet.class);\r\n\tprivate static final String SERVICE_URL_MAPPER = "serviceURLMapper";\r\n\tprivate static final UrlPathHelper pathHelper = new UrlPathHelper();\r\n\r\n\tprivate WebApplicationContext applicationContext;\r\n\tprivate Map<String, RemoteService> springRPCServices = new HashMap<String, RemoteService>();\r\n\r\n\t@Override\r\n\tpublic void init()\r\n\t{\r\n\t\tapplicationContext = WebApplicationContextUtils.getWebApplicationContext(getServletContext());\r\n\t\tif (applicationContext == null)\r\n\t\t{\r\n\t\t\tthrow new IllegalStateException("No Spring web application context found");\r\n\t\t}\r\n\r\n\t\tif (StringUtils.isEmpty(this.getInitParameter(SERVICE_URL_MAPPER)))\r\n\t\t{\r\n\t\t\tthrow new IllegalArgumentException("The servlet SpringRPCDispatcherServlet should have a '" + SERVICE_URL_MAPPER + "' parameter defined");\r\n\t\t}\r\n\t\telse\r\n\t\t{\r\n\t\t\tString beanName = this.getInitParameter(SERVICE_URL_MAPPER);\r\n\t\t\tthis.initServiceURLMapper(beanName);\r\n\t\t}\r\n\t\tlogger.info("SpringRPCDispatcherServlet deployed");\r\n\t}\r\n\r\n\t@SuppressWarnings("unchecked")\r\n\tprivate void initServiceURLMapper(String beanName)\r\n\t{\r\n\r\n\t\tthis.springRPCServices = (Map<String, RemoteService>) applicationContext.getBean(beanName, Map.class);\r\n\t}\r\n\r\n\t@Override\r\n\tpublic String processCall(String payload) throws SerializationException\r\n\t{\r\n\t\ttry\r\n\t\t{\r\n\t\t\tRemoteService handler = retrieveSpringBean(getThreadLocalRequest());\r\n\t\t\tRPCRequest rpcRequest = RPC.decodeRequest(payload, handler.getClass(), this);\r\n\t\t\tonAfterRequestDeserialized(rpcRequest);\r\n\t\t\tif (logger.isDebugEnabled())\r\n\t\t\t{\r\n\t\t\t\tlogger.debug("Invoking " + handler.getClass().getName() + "." + rpcRequest.getMethod().getName());\r\n\t\t\t}\r\n\t\t\treturn RPC.invokeAndEncodeResponse(handler, rpcRequest.getMethod(), rpcRequest.getParameters(), rpcRequest.getSerializationPolicy());\r\n\t\t}\r\n\t\tcatch (IncompatibleRemoteServiceException ex)\r\n\t\t{\r\n\t\t\tlogger.error("An IncompatibleRemoteServiceException was thrown while processing this call.", ex);\r\n\t\t\treturn RPC.encodeResponseForFailure(null, ex);\r\n\t\t}\r\n\t}\r\n\r\n\tprotected RemoteService retrieveSpringBean(HttpServletRequest request)\r\n\t{\r\n\t\tString serviceURL = extractServiceURL(request);\r\n\t\tRemoteService bean = getBeanByServiceURL(serviceURL);\r\n\r\n\t\tif (logger.isDebugEnabled())\r\n\t\t{\r\n\t\t\tlogger.debug("Bean for service " + serviceURL + " is " + bean.getClass());\r\n\t\t}\r\n\t\treturn bean;\r\n\t}\r\n\r\n\tprivate String extractServiceURL(HttpServletRequest request)\r\n\t{\r\n\t\tString service = pathHelper.getPathWithinServletMapping(request);\r\n\t\tif (logger.isDebugEnabled())\r\n\t\t{\r\n\t\t\tlogger.debug("Service for URL " + request.getRequestURI() + " is " + service);\r\n\t\t}\r\n\t\treturn service;\r\n\t}\r\n\r\n\tprivate RemoteService getBeanByServiceURL(String serviceURL)\r\n\t{\r\n\t\tif (!this.springRPCServices.containsKey(serviceURL))\r\n\t\t{\r\n\t\t\t{\r\n\t\t\t\tthrow new IllegalArgumentException("Spring bean not found for service URL: " + serviceURL);\r\n\t\t\t}\r\n\t\t}\r\n\t\treturn this.springRPCServices.get(serviceURL);\r\n\t}\r\n}\r\n<\/pre>\n
Let’s analyze the code step-by-step.<\/p>\n
As private fields, we declare a UrlPathHelper<\/strong> (line 6<\/strong>) to extract paths from URL (necessary to determine which service bean to call) and a map linking a serviceURL<\/strong> to the appropriate Spring bean (line 9<\/strong>).<\/p>\n
First in the init()<\/em> method (line 12<\/strong>) we get a reference on the current Spring Web application context. We check for the presence of the “serviceURLMapper<\/em>” servlet parameter. If it’s set we initialize the map of serviceURL<\/strong> by calling the method initServiceURLMapper()<\/em> (line 27<\/strong>). This method simply retrieve the map from Spring context.<\/p>\n
At runtime, when a request is sent to the servlet, the processCall(String payload)<\/em> method is called. This method is copied from the original RemoteServiceServlet<\/strong> class and I introduced some modifications.<\/p>\n