Spring MVC 3.x annotated controller的几点心得体会

最近拿Spring MVC 3.x做项目，用了最新的系列相关Annotation来做Controller，有几点心得体会值得分享。


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一、编写一个AbstractController.java，所有的Controller必须扩展

    除了获得Template Design Pattern的好处之外，还能一点，那就是放置全局的@InitBinder：

public class AbstractController {
...
	@InitBinder
	protected void initBinder(WebDataBinder binder) {
		SimpleDateFormat dateFormat = new SimpleDateFormat("MM/dd/yyyy");
		dateFormat.setLenient(false);
		binder.registerCustomEditor(Date.class,new CustomDateEditor(dateFormat, false));
	}
...
}

二、每个域都应该有一个Controller，且做好URI规划

    大家都知道Spring MVC 3.x是完全支持Restful的，我们把URI做好规划，对于诸如ACL的实现会有很大的帮助。建议的URI规划如下：{Domain}[/{SubDomain}]/{BusinessAction}/{ID}。比如：

    hotels/bookings/cancel/{id} ——表示此URI匹配hotels域的bookings子域，将要进行的是取消某项booking的操作。代码如下：

@Controller
@RequestMapping(value = "/hotels")
public class HotelsController extends AbstractController {
...
	@RequestMapping(value = "/bookings/cancel/{id}", method = RequestMethod.POST)
	public String deleteBooking(@PathVariable long id) {
		bookingService.cancelBooking(id);
		//use prefix 'redirect' to avoid duplicate submission
		return "redirect:../../search";
	}
...
}

另外还有几个重要原因：


    1、由于Spring的DefaultAnnotationHandlerMapping.java在做Mapping的时候，先做是否有类匹配，再找方法，把基本的mapping放在类上面，可以加速匹配效率；

    2、后续可以通过更细腻的支持Ant path style的AntPathMatcher来规划URI Template资源，做ACL控制（请参考后面的心得体会）。




三、JSON/XML等ajax的支持很cool，可以尝试

    JSON/XML/RSS等均可支持，当然有些denpendency，比如JSON的默认支持，需要jackson jar出现在lib中，POM的artifact如下：

<dependency>
	<groupId>org.codehaus.jackson</groupId>
	<artifactId>jackson-mapper-asl</artifactId>
	<version>1.5.3</version>
</dependency>

这样，我们其实根本就不需要进行额外的JSON转换了，Spring MVC 3会根据请求的格式自行转换：

	@ResponseBody
	@RequestMapping(value = "/ajax", method = RequestMethod.POST)
	public JsonDataWrapper<Hotel> ajax(WebRequest request, Hotel hotel, Model model) 
		throws Exception {
		JsonDataWrapper<Hotel> jsonDataWrapper = this.getPaginatedGridData(request, hotel, hotelService);
		return jsonDataWrapper;
	}

注 ：我上面的JsonDataWrapper只是我自己做的一个简单的wrapper，目的是为jQuery Flexigrid plugin做数据准备的。还是贴出来吧：

/**
 * A wrapper class for jQuery Flexigrid plugin component.
 * 
 * The format must be like this:
 * <code>
 * 		{"total":2,"page":1,"rows":[
 * 			{"personTitle":"Mr","partyName":"Test8325","personDateOfBirth":"1970-07-12"},
 * 			{"personTitle":"Ms","partyName":"Ms Susan Jones","personDateOfBirth":"1955-11-27"}
 * 		]}
 * </code>
 * 
 * @author bright_zheng
 *
 * @param <T>: the generic type of the specific domain
 */
public class JsonDataWrapper<T> implements Serializable {
	private static final long serialVersionUID = -538629307783721872L;

	public JsonDataWrapper(int total, int page, List<T> rows){
		this.total = total;
		this.page = page;
		this.rows = rows;
	}
	private int total;
	private int page;
	private List<T> rows;
	
	public int getTotal() {
		return total;
	}
	public void setTotal(int total) {
		this.total = total;
	}
	public int getPage() {
		return page;
	}
	public void setPage(int page) {
		this.page = page;
	}
	public List<T> getRows() {
		return rows;
	}
	public void setRows(List<T> rows) {
		this.rows = rows;
	}
}

四、Controller的单元测试变得很可为且简单

    以前的项目从来不做controller层的测试，用了Spring MVC 3这一点就不再难为情，做吧：

public class HotelsControllerTest {
	
	private static HandlerMapping handlerMapping;
	private static HandlerAdapter handlerAdapter;
	
	private static MockServletContext msc;

	@BeforeClass
	public static void setUp() {
		String[] configs = {
				"file:src/main/resources/context-*.xml",
				"file:src/main/webapp/WEB-INF/webapp-servlet.xml" };
		XmlWebApplicationContext context = new XmlWebApplicationContext();  
        context.setConfigLocations(configs);  
        msc = new MockServletContext();  
        context.setServletContext(msc);  
        context.refresh();  
        msc.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, context);
        ApplicationContextManager manager = new ApplicationContextManager();
		manager.setApplicationContext(context);		
		handlerMapping = (HandlerMapping) ApplicationContextManager.getContext().getBean(DefaultAnnotationHandlerMapping.class);
		handlerAdapter = (HandlerAdapter) ApplicationContextManager.getContext().getBean(ApplicationContextManager.getContext().getBeanNamesForType(AnnotationMethodHandlerAdapter.class)[0]);		
	}

	@Test
	public void list() throws Exception {
		MockHttpServletRequest request = new MockHttpServletRequest();
		MockHttpServletResponse response = new MockHttpServletResponse();
		
		request.setRequestURI("/hotels");
		request.addParameter("booking.id", "1002");
		request.addParameter("hotel.name", "");
		request.setMethod("POST");
		
		//HandlerMapping
		HandlerExecutionChain chain = handlerMapping.getHandler(request);
		Assert.assertEquals(true, chain.getHandler() instanceof HotelsController);
		
		//HandlerAdapter
		final ModelAndView mav = handlerAdapter.handle(request, response, chain.getHandler());
		
		//Assert logic
		Assert.assertEquals("hotels/search", mav.getViewName());
	}
}

需要说明一下 ：由于当前最想版本的Spring(Test) 3.0.5还不支持@ContextConfiguration的注解式context file注入，所以还需要写个setUp处理下，否则类似于Tiles的加载过程会有错误，因为没有ServletContext。3.1的版本应该有更好的解决方案，参见：https://jira.springsource.org/browse/SPR-5243 。

    Service等其他layer就没有这类问题，测试的写法将变得更加优雅，贴个出来：

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(locations = {"file:src/main/resources/context-*.xml" })
public class DefaultServiceImplTest {
	/** @Autowired works if we put @ContextConfiguration at junit type */
	@Autowired
	@Qualifier("hotelService")
	private HotelService<Hotel> hotelService;

	@Test
	public void insert() {
		Hotel hotel = new Hotel();
		hotel.setAddress("addr");
		hotel.setCity("Singapore");
		hotel.setCountry("Singapore");
		hotel.setName("Great Hotel");
		hotel.setPrice(new BigDecimal(200));
		hotel.setState("Harbarfront");
		hotel.setZip("010024");
		hotelService.insert(hotel);
	}
}

五、ACL可以写一个HandlerInterceptorAdapter，在“事前”拦截。

    由于Spring是Restful friendly的framework，做ACL就不要用过滤器了，用interceptor吧：

public class AclInterceptor extends HandlerInterceptorAdapter {
	private static final Logger logger = Logger.getLogger(AclInterceptor.class);
	
	/** default servlet prefix */
	private static final String DEFAULT_SERVLET_PREFIX = "/servlet";
	
	/** will be injected from context configuration file */
	private AclService service;
	
	@Override
	public boolean preHandle(HttpServletRequest request,
			HttpServletResponse response, Object handler) throws Exception {
		String currentUri = request.getRequestURI();
		boolean isAccessible = true;
		//only intercept for annotated business controllers
		Controller c = AnnotationUtils.findAnnotation(handler.getClass(), Controller.class);
		if(c!=null){
			String[] grantedResource = getGrantedResource(request);
			if(grantedResource==null || grantedResource.length==0){
				throw new AccessDeniedException("No resource granted");
			}
			isAccessible = service.isAccessible(grantedResource, currentUri);
			if(logger.isDebugEnabled()){
				logger.debug("ACL interceptor excueted. Accessible for Uri[" + currentUri +"] = " + isAccessible);
			}
			//if isAccessible==true, throw custom AccessDeniedException
			if(!isAccessible) throw new AccessDeniedException();
		}
		return isAccessible;
	}
	
	/**
	 * transfer the original Uri to resource Uri
	 * e.g.:
	 * 	original Uri: /servlet/hotels/ajax
	 * 	target Uri  : /hotels/ajax
	 * @param originalUri
	 * @return
	 */
	protected String getUri(String originalUri){
		return originalUri.substring(DEFAULT_SERVLET_PREFIX.length());
	}
	
	/**
	 * Get the granted resource from session
	 * @param request
	 * @return
	 */
	protected String[] getGrantedResource(HttpServletRequest request){
		//get the resources from current session
		//String[] uriResourcePattern = (String[]) request.getSession().getAttribute("uriResourcePattern");		
		//TODO: mock data here
		String[] uriResourcePattern = new String[]{"/**"};
		
		return uriResourcePattern;
	}

	public void setService(AclService service) {
		this.service = service;
	}
}

注 ：上面还有TODO部分，很简单，登录后把当然用户可访问的Ant path style的URI Resources放到session中，作为一个String[]，这里拿来出匹配即可，建议匹配就用org.springframework.util.AntPathMatcher。



六、对于Ajax Form Validation，正在寻求更佳的解禁方案。

    Spring 3已经支持@Valid的注解式validation，又一个JSR，但通过我研究代码发现，默认的org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.java实现还是非常封闭，并不能很好的实现binding后执行业务代码前处理，所以目前的实现办法还不算优雅。

    已经实现，大致的思路是：

    1）发出ajax form post请求（用jQuery）；

    2）正常mapping到controller的方法中处理；

    3）做form validation；

    4）不管怎样，forward到一个解析错误消息的JSP，叫ajaxFormValidatorResult.jsp；

    5）再写一个jquery plugin，叫errorBinder.js，解析错误并自定binding为Tooltip，如果没错误就正常submit

贴个简单的demo效果，欢迎拍砖。

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