Spring MVC 实践 – Component

Converter

Spring MVC的数据绑定并非没有任何限制, 有案例表明: Spring在如何正确绑定数据方面是杂乱无章的. 比如: Spring总是试图用默认的语言区域将日期输入绑定到 java.util.Data , 如果想要使用不同的日期格式(format),就需要 Converter 的协助.

Spring提供了 Converter 接口来供开发者自定义 Converter 类:

/**  * @since 3.0  * @param <S> the source type  * @param <T> the target type  */ public interface Converter<S, T> {     T convert(S source); }

• 自定义 Converter :

/**  * @author jifang.  * @since 2016/6/19 7:23.  */ public class StringDateConverter implements Converter<String, Date> {      private String pattern;      public StringDateConverter(String pattern) {         this.pattern = pattern;     }      @Override     public Date convert(String source) {         try {             return new SimpleDateFormat(pattern).parse(source);         } catch (ParseException e) {             throw new RuntimeException(e);         }     } }

• 配置

  为了能够让Spring MVC使用我们自定义的 Converter , 需要在配置文件中配置一个 ConversionServiceFactoryBean :

<bean id="conversionService" class="org.springframework.context.support.ConversionServiceFactoryBean">     <property name="converters">         <set>             <bean class="com.fq.mvc.converter.StringDateConverter">                 <constructor-arg type="java.lang.String" value="yyyy-MM-dd hh:mm:ss"/>             </bean>         </set>     </property> </bean>

然后为 <annotation-driven/> 配置 conversion-service 属性:

<mvc:annotation-driven conversion-service="conversionService"/>

注: 还可以使用 FormattingConversionServiceFactoryBean 来加载 Converter , 由于其配置方法与 ConversionServiceFactoryBean , 故在此就不再赘述.

• Controller

@RequestMapping("/add_user.do") public String addUser(User user, BindingResult binding) {     if (binding.hasErrors()) {         FieldError error = binding.getFieldError();         // log ...     }      service.addUser(user);     return "redirect: users.do"; }

BindingResult 参数中放置了Spring的所有绑定错误.

Interceptor

Spring MVC的拦截器类似于Servlet中的 Filter (关于 Filter ,详细可参考 Servlet – Listener、Filter、Decorator ),用于 Controller 进行预处理和后处理.

Spring提供了 Interceptor 接口来供开发者自定义 Interceptor 类:

public interface HandlerInterceptor {      /**      * 进入Controller方法前执行      * 应用场景: 身份认证、身份授权等      */     boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler)         throws Exception;      /**      * 进入Controller方法后, 返回ModelAndView前执行      * 应用场景: 将公共模型数据填充到ModelAndView、统一指定视图等      */     void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView)             throws Exception;      /**      * 执行完Controller方法后执行      * 应用场景: 统一日志处理、统一异常处理等      */     void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex)             throws Exception;  }

<code>示例: 统计Controller执行耗时. </code>

• 自定义 Interceptor

/**  * @author jifang  * @since 16/7/4 上午10:35.  */ public class HandleTimeInterceptor implements HandlerInterceptor {      private static final String START_TIME = "start_time";      private static final String HANDLE_TIME = "handle_time";      private static final Logger LOGGER = LoggerFactory.getLogger(HandleTimeInterceptor.class);      @Override     public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {         request.setAttribute(START_TIME, System.currentTimeMillis());         return true;     }      @Override     public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {         long start = (long) request.getAttribute(START_TIME);         request.setAttribute(HANDLE_TIME, System.currentTimeMillis() - start);     }      @Override     public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {         String uri = request.getRequestURI();         long consume = (long) request.getAttribute(HANDLE_TIME);         LOGGER.info("uri: {} consume {}s", uri, consume / 1000);     } }

• 配置

<mvc:interceptors>     <mvc:interceptor>         <mvc:mapping path="/**"/>         <bean class="com.fq.mvc.interceptor.HandleTimeInterceptor"/>     </mvc:interceptor> </mvc:interceptors>

Spring MVC提供了对Servlet 3.0文件上传的支持(关于Servlet 3.0文件上传可参考博客 Servlet – Upload、Download、Async、动态注册 ).

Spring MVC提供了 MultipartFile 接口,上传到应用中的文件都被包装在一个 MultipartFile 对象中:

在Servlet 3.0及更高版本的容器中进行文件上传编程,总是围绕着 @MultipartConfig 注解和 Part 接口,处理上传文件的Servlet必须以 @MultipartConfig 注解标注, 但 DispatcherServlet 是Spring jar包已经编译好的类, 无法进行修改,值得庆幸的是Servlet 3.0还可以使用部署描述符web.xml将一个Servlet变为 MultipartConfig Servlet :

<servlet>     <servlet-name>mvc</servlet-name>     <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>     <init-param>         <param-name>contextConfigLocation</param-name>         <param-value>classpath:spring/mvc-servlet.xml</param-value>     </init-param>     <load-on-startup>1</load-on-startup>     <multipart-config>         <max-file-size>20848820</max-file-size>         <file-size-threshold>1048576</file-size-threshold>     </multipart-config> </servlet> <servlet-mapping>     <servlet-name>mvc</servlet-name>     <url-pattern>*.do</url-pattern> </servlet-mapping>

此外, 在mvc-servlet.xml文件中配置一个 MultipartResolver :

<bean id="multipartResolver" class="org.springframework.web.multipart.support.StandardServletMultipartResolver"/>

此时就可以进行文件上传编程了:

@RequestMapping("/upload.do") public String upload(MultipartFile file) throws IOException {     String name = file.getOriginalFilename();     String fileName = String.format("/data/file/%s", name);     file.transferTo(new File(fileName));     return "file_upload"; }

Exception

系统异常包含两类: 预期异常 、 运行时异常 RuntimeException .前者通过捕获异常从而获取异常信息,后者主要通过规范代码开发、测试等手段减少运行时异常的发生.

基于Spring MVC的 DAO 、 Service 、 Controller 的异常都可以通过 throw 向上层抛出,最后统一由 DispatcherServlet 的异常处理器进行处理.

• 自定义异常

  如果 Controller / Service / DAO 抛出此类异常说明是 预期异常 :

/**  * @author jifang.  * @since 2016/6/21 16:28.  */ public class MVCException extends Exception {      private String message;      public MVCException(String message) {         super(message);         this.message = message;     }      @Override     public String getMessage() {         return this.message;     }      public void setMessage(String message) {         this.message = message;     } }

• 异常处理器

/**  * @author jifang.  * @since 2016/6/21 16:33.  */ public class MVCExceptionResolver implements HandlerExceptionResolver {      @Override     public ModelAndView resolveException(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) {          String message;         if (ex instanceof MVCException) {             message = ex.getMessage();         } else {             message = "未知异常";         }          return new ModelAndView("error", "message", message);     } }

• error.vm

<html> <head>     <title>错误信息</title>     <meta http-equiv="content-type" content="text/html; charset=UTF-8"/> </head> <body> ${message} </body> </html>

• 注册异常处理器

<bean class="com.fq.mvc.exception.MVCExceptionResolver"/>

JSON数据格式形式简单, 解析方便, 因此常用在接口调用、HTML页面中.

Spring MVC对其提供了如下支持:在 Controller 方法上添加 @ResponseBody 注解, Spring MVC会自动将Java对象转换成JSON字符串输出; 在方法形参上添加 @RequestBody 注解, Spring MVC会自动将JSON串转换成Java对象:

@ResponseBody @RequestMapping("/user_json.do") public User userJSON(@RequestBody User user) {     return user; }

• fastjson

  Spring MVC默认使用jackson对 request / response 进行JSON转换,而在此我们选用性能更高的fastjson, 因此需要在 <annotation-driven/> 中另做配置.

首先, 使用fastjson需要在pom.xml中添加如下依赖:

<dependency>     <groupId>com.alibaba</groupId>     <artifactId>fastjson</artifactId>     <version>1.2.7</version> </dependency>

然后在mvc-servlet.xml中做如下配置:

<mvc:annotation-driven>     <mvc:message-converters register-defaults="false">         <bean id="fastJsonHttpMessageConverter"               class="com.alibaba.fastjson.support.spring.FastJsonHttpMessageConverter">             <property name="supportedMediaTypes">                 <list>                     <value>text/html;charset=UTF-8</value>                     <value>application/json;charset=UTF-8</value>                 </list>             </property>             <property name="features">                 <array value-type="com.alibaba.fastjson.serializer.SerializerFeature">                     <value>DisableCircularReferenceDetect</value>                 </array>             </property>         </bean>     </mvc:message-converters> </mvc:annotation-driven>

1. POST Encoder

在web.xml配置一个编码 Filter 可以解决POST乱码问题:

<filter>     <filter-name>encodingFilter</filter-name>     <filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class>     <init-param>         <param-name>encoding</param-name>         <param-value>UTF-8</param-value>     </init-param>     <init-param>         <param-name>forceEncoding</param-name>         <param-value>true</param-value>     </init-param> </filter> <filter-mapping>     <filter-name>encodingFilter</filter-name>     <url-pattern>/*</url-pattern> </filter-mapping>

2. GET Encoder

对于GET乱码, 由于Tomcat 8.0之前版本默认使用 ISO-8859-1 编码, 因此有两种解决方案:

• 修改tomcat配置文件

  修改tomcat配置文件server.xml设置编码与工程编码一致:

<Connector URIEncoding="utf-8" connectionTimeout="20000" port="8080" protocol="HTTP/1.1" redirectPort="8443"/>

• 重新编码

  将经Tomcat编码的内容解码后再重新编码为UTF-8:

String name = new String(request.getParamter("name").getBytes("ISO8859-1"),"utf-8");

注: Tomcat 8.0及更高版本的容器不用此配置.

3. Static Resources Mapping

如果将 DispatherServlet 配置成拦截所有请求 <url-pattern>/</url-pattern> , 则必须额外配置 静态资源 的映射规则, 否则Spring MVC会对像js/css之类的文件也做转发.

Spring MVC使用 <mvc:resources/> 元素配置对静态资源的映射:

<mvc:resources location="/js/" mapping="/js/**"/>