Spring MVC 实践

标签 ： Java与Web

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;

}

示例: 统计Controller执行耗时.

• 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>

Upload

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

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>

Other

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/**"/>