Spring in action 阅读笔记3

5.3接受请求的输入

@RequestParam(value="", defaultValue="") long max
尽管defaultValue是String类型的值，但是绑定到max参数时，会转换成Long类型

"/spittles/12345" vs "/spittles/show?spittle_id=12345"
前者能够识别出要查询的资源，后者描述的是带有参数的一个操作-本质上是通过HTTP发起的RPC

7.1配置的替代方案

添加其他的Servlet与Filter
实现WebApplicationInitializer，注册其他组件

7.2Multipart

1. MultipartResolver
   A. StandardServletMultipartResolver 配置信息在DispatcherServlet之中

@Bean
public MultipartResolver multipartResolver() throws IOException {
return new StandardServletMultipartResolver();
}

// 1.WebApplicationInitializer
DispatcherServlet ds = new DispatcherServlet();
Dynamic registration = context.addServlet("appServlet", ds);
registration.addMapping("/");
registration.setMultipartConfig(
new MultipartConfigElement("/tmp/spittr/uploads"));
//
// 2.AbstractAnnotationConfigDispatcherServletInitializer
@Override
protected void customizeRegistration(Dynamic registration) {
registration.setMultipartConfig(
new MultipartConfigElement("/tmp/spittr/uploads"));
}
//
// 3.web.xml
<servlet>
    <servlet-name>SpringDispatcher</servlet-name>
    <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
    <multipart-config>
        <location>/tmp</location>
        <max-file-size>5242880</max-file-size><!--5MB-->
        <max-request-size>20971520</max-request-size><!--20MB-->
        <file-size-threshold>0</file-size-threshold>
    </multipart-config>
</servlet>

B. CommonsMultipartResolver
只需要配置bean

@Bean
public MultipartResolver multipartResolver() throws IOException {
CommonsMultipartResolver multipartResolver =
new CommonsMultipartResolver();
multipartResolver.setUploadTempDir(
new FileSystemResource("/tmp/spittr/uploads"));
multipartResolver.setMaxUploadSize(2097152);
multipartResolver.setMaxInMemorySize(0);
return multipartResolver;
}

MultipartResolver在DispatcherServlet转发请求之前对request进行处理，如果是Multipart的请求，就分解为MultipartHttpServletRequest

2. 请求
   POST enctype="multipart/form-data"
   <input type="file" name="" accept="" />
3. 处理Multipart请求
   A. @RequestPart("name") byte[] filebyte
   B. @RequestPart("name") MultipartFile/Part file
   [Facepalm][Facepalm]如果使用Part参数接收文件，就不需要配置MultipartResolver了

7.3异常处理

• 使用@ResponseStatus(value=HttpStatus.NOT_FOUND, reason="Not Found")标注异常，将异常映射到状态码
• 使用@ExceptionHandler(Exception.class)标注异常处理方法，处理同一个Controller中handle method（RequestMapping）抛出的此类异常
• 使用@ControllerAdvice进行全局的异常处理，处理所有Controller抛出的此类异常

• Any Spring bean declared in the DispatcherServlet’s application context that implements HandlerExceptionResolver will be used to intercept and process any exception raised in the MVC system and not handled by a Controller. The interface looks like this:

public interface HandlerExceptionResolver {

    /**
     * Try to resolve the given exception that got thrown during on handler execution,
     * returning a ModelAndView that represents a specific error page if appropriate.
     * <p>The returned ModelAndView may be {@linkplain ModelAndView#isEmpty() empty}
     * to indicate that the exception has been resolved successfully but that no view
     * should be rendered, for instance by setting a status code.
     * @param request current HTTP request
     * @param response current HTTP response
     * @param handler the executed handler, or {@code null} if none chosen at the
     * time of the exception (for example, if multipart resolution failed)
     * @param ex the exception that got thrown during handler execution
     * @return a corresponding ModelAndView to forward to,
     * or {@code null} for default processing
     */
    ModelAndView resolveException(
            HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex);

}