最近一段时间学习了springboot,所以熟悉一下mvc中常用的注解，这样可以方便开发

   

简介：

@RequestMapping

RequestMapping是一个用来处理请求地址映射的注解，可用于类或方法上。用于类上，表示类中的所有响应请求的方法都是以该地址作为父路径。

RequestMapping注解有六个属性，下面我们把她分成三类进行说明。

1、 value， method；

value：     指定请求的实际地址，指定的地址可以是URI Template 模式（后面将会说明）；

method：  指定请求的method类型， GET、POST、PUT、DELETE等；

 

2、 consumes，produces；

consumes： 指定处理请求的提交内容类型（Content-Type），例如application/json, text/html;

produces:    指定返回的内容类型，仅当request请求头中的(Accept)类型中包含该指定类型才返回；

 

3、 params，headers；

params： 指定request中必须包含某些参数值是，才让该方法处理。

headers： 指定request中必须包含某些指定的header值，才能让该方法处理请求。

示例：

1、value  / method 示例

默认RequestMapping("....str...")即为value的值；

1 @Controller 2 @RequestMapping("/appointments") 3 public class AppointmentsController { 4  5     private AppointmentBook appointmentBook; 6      7     @Autowired 8     public AppointmentsController(AppointmentBook appointmentBook) { 9         this.appointmentBook = appointmentBook;10     }11 12     @RequestMapping(method = RequestMethod.GET)13     public Map
     
       get() {14         return appointmentBook.getAppointmentsForToday();15     }16 17     @RequestMapping(value="/{day}", method = RequestMethod.GET)18     public Map
      
        getForDay(@PathVariable @DateTimeFormat(iso=ISO.DATE) Date day, Model model) {19         return appointmentBook.getAppointmentsForDay(day);20     }21 22     @RequestMapping(value="/new", method = RequestMethod.GET)23     public AppointmentForm getNewForm() {24         return new AppointmentForm();25     }26 27     @RequestMapping(method = RequestMethod.POST)28     public String add(@Valid AppointmentForm appointment, BindingResult result) {29         if (result.hasErrors()) {30             return "appointments/new";31         }32         appointmentBook.addAppointment(appointment);33         return "redirect:/appointments";34     }35 }
      
     

value的uri值为以下三类：

A） 可以指定为普通的具体值；

B)  可以指定为含有某变量的一类值(URI Template Patterns with Path Variables)；

C) 可以指定为含正则表达式的一类值( URI Template Patterns with Regular Expressions);

example B)

@RequestMapping(value="/owners/{ownerId}", method=RequestMethod.GET)public String findOwner(@PathVariable String ownerId, Model model) {  Owner owner = ownerService.findOwner(ownerId);    model.addAttribute("owner", owner);    return "displayOwner"; }

example C)

@RequestMapping("/spring-web/{symbolicName:[a-z-]+}-{version:\d\.\d\.\d}.{extension:\.[a-z]}")  public void handle(@PathVariable String version, @PathVariable String extension) {        // ...  }}

2 consumes、produces 示例

cousumes的样例：

@Controller@RequestMapping(value = "/pets", method = RequestMethod.POST, consumes="application/json")public void addPet(@RequestBody Pet pet, Model model) {        // implementation omitted}

方法仅处理request Content-Type为“application/json”类型的请求。

produces的样例：

@Controller@RequestMapping(value = "/pets/{petId}", method = RequestMethod.GET, produces="application/json")@ResponseBodypublic Pet getPet(@PathVariable String petId, Model model) {        // implementation omitted}

方法仅处理request请求中Accept头中包含了"application/json"的请求，同时暗示了返回的内容类型为application/json;

 

 

3 params、headers 示例

params的样例：

@Controller@RequestMapping("/owners/{ownerId}")public class RelativePathUriTemplateController {  @RequestMapping(value = "/pets/{petId}", method = RequestMethod.GET, params="myParam=myValue")  public void findPet(@PathVariable String ownerId, @PathVariable String petId, Model model) {        // implementation omitted  }}

仅处理请求中包含了名为“myParam”，值为“myValue”的请求；

 

 

headers的样例：

@Controller@RequestMapping("/owners/{ownerId}")public class RelativePathUriTemplateController {@RequestMapping(value = "/pets", method = RequestMethod.GET, headers="Referer=http://www.ifeng.com/")  public void findPet(@PathVariable String ownerId, @PathVariable String petId, Model model) {        // implementation omitted  }}

@RequestBody

作用： 

      i) 该注解用于读取Request请求的body部分数据，使用系统默认配置的HttpMessageConverter进行解析，然后把相应的数据绑定到要返回的对象上；

      ii) 再把HttpMessageConverter返回的对象数据绑定到 controller中方法的参数上。

使用时机：

A) GET、POST方式提时， 根据request header Content-Type的值来判断:

•     application/x-www-form-urlencoded， 可选（即非必须，因为这种情况的数据@RequestParam, @ModelAttribute也可以处理，当然@RequestBody也能处理）；
•     multipart/form-data, 不能处理（即使用@RequestBody不能处理这种格式的数据）；
•     其他格式， 必须（其他格式包括application/json, application/xml等。这些格式的数据，必须使用@RequestBody来处理）；

 

B) PUT方式提交时， 根据request header Content-Type的值来判断:

 

•     application/x-www-form-urlencoded， 必须；
•     multipart/form-data, 不能处理；
•     其他格式， 必须；

说明：request的body部分的数据编码格式由header部分的Content-Type指定；

 

 

@ResponseBody

 

作用： 

      该注解用于将Controller的方法返回的对象，通过适当的HttpMessageConverter转换为指定格式后，写入到Response对象的body数据区。

使用时机：

      返回的数据不是html标签的页面，而是其他某种格式的数据时（如json、xml等）使用；

 

 

 

HttpMessageConverter

/** * Strategy interface that specifies a converter that can convert from and to HTTP requests and responses. * * @author Arjen Poutsma * @author Juergen Hoeller * @since 3.0 */public interface HttpMessageConverter
      
        {    /**     * Indicates whether the given class can be read by this converter.     * @param clazz the class to test for readability     * @param mediaType the media type to read, can be {@code null} if not specified.     * Typically the value of a {@code Content-Type} header.     * @return {@code true} if readable; {@code false} otherwise     */    boolean canRead(Class
        clazz, MediaType mediaType);    /**     * Indicates whether the given class can be written by this converter.     * @param clazz the class to test for writability     * @param mediaType the media type to write, can be {@code null} if not specified.     * Typically the value of an {@code Accept} header.     * @return {@code true} if writable; {@code false} otherwise     */    boolean canWrite(Class
        clazz, MediaType mediaType);    /**     * Return the list of {@link MediaType} objects supported by this converter.     * @return the list of supported media types     */    List
       
         getSupportedMediaTypes();    /**     * Read an object of the given type form the given input message, and returns it.     * @param clazz the type of object to return. This type must have previously been passed to the     * {@link #canRead canRead} method of this interface, which must have returned {@code true}.     * @param inputMessage the HTTP input message to read from     * @return the converted object     * @throws IOException in case of I/O errors     * @throws HttpMessageNotReadableException in case of conversion errors     */    T read(Class
         clazz, HttpInputMessage inputMessage)            throws IOException, HttpMessageNotReadableException;    /**     * Write an given object to the given output message.     * @param t the object to write to the output message. The type of this object must have previously been     * passed to the {@link #canWrite canWrite} method of this interface, which must have returned {@code true}.     * @param contentType the content type to use when writing. May be {@code null} to indicate that the     * default content type of the converter must be used. If not {@code null}, this media type must have     * previously been passed to the {@link #canWrite canWrite} method of this interface, which must have     * returned {@code true}.     * @param outputMessage the message to write to     * @throws IOException in case of I/O errors     * @throws HttpMessageNotWritableException in case of conversion errors     */    void write(T t, MediaType contentType, HttpOutputMessage outputMessage)            throws IOException, HttpMessageNotWritableException;}
       
      

该接口定义了四个方法，分别是读取数据时的 canRead(), read() 和 写入数据时的canWrite(), write()方法。

 

在使用 <mvc:annotation-driven />标签配置时，默认配置了RequestMappingHandlerAdapter（注意是RequestMappingHandlerAdapter不是AnnotationMethodHandlerAdapter,详情查看Spring 3.1 document “16.14 Configuring Spring MVC”章节），并为他配置了一下默认的HttpMessageConverter：

ByteArrayHttpMessageConverter converts byte arrays.    StringHttpMessageConverter converts strings.    ResourceHttpMessageConverter converts to/from org.springframework.core.io.Resource for all media types.    SourceHttpMessageConverter converts to/from a javax.xml.transform.Source.    FormHttpMessageConverter converts form data to/from a MultiValueMap
     
      .    Jaxb2RootElementHttpMessageConverter converts Java objects to/from XML — added if JAXB2 is present on the classpath.    MappingJacksonHttpMessageConverter converts to/from JSON — added if Jackson is present on the classpath.    AtomFeedHttpMessageConverter converts Atom feeds — added if Rome is present on the classpath.    RssChannelHttpMessageConverter converts RSS feeds — added if Rome is present on the classpath.
     

ByteArrayHttpMessageConverter: 负责读取二进制格式的数据和写出二进制格式的数据；

StringHttpMessageConverter：   负责读取字符串格式的数据和写出二进制格式的数据；

 

ResourceHttpMessageConverter：负责读取资源文件和写出资源文件数据； 

FormHttpMessageConverter：       负责读取form提交的数据（能读取的数据格式为 application/x-www-form-urlencoded，不能读取multipart/form-data格式数据）；负责写入application/x-www-from-urlencoded和multipart/form-data格式的数据；

 

MappingJacksonHttpMessageConverter:  负责读取和写入json格式的数据；

 

SouceHttpMessageConverter：                   负责读取和写入 xml 中javax.xml.transform.Source定义的数据；

Jaxb2RootElementHttpMessageConverter:  负责读取和写入xml 标签格式的数据；

 

AtomFeedHttpMessageConverter:              负责读取和写入Atom格式的数据；

RssChannelHttpMessageConverter:           负责读取和写入RSS格式的数据；

 

当使用@RequestBody和@ResponseBody注解时，RequestMappingHandlerAdapter就使用它们来进行读取或者写入相应格式的数据。

 

HttpMessageConverter匹配过程：

@RequestBody注解时： 根据Request对象header部分的Content-Type类型，逐一匹配合适的HttpMessageConverter来读取数据；

spring 3.1源代码如下：

private Object readWithMessageConverters(MethodParameter methodParam, HttpInputMessage inputMessage, Class paramType)            throws Exception {        MediaType contentType = inputMessage.getHeaders().getContentType();        if (contentType == null) {            StringBuilder builder = new StringBuilder(ClassUtils.getShortName(methodParam.getParameterType()));            String paramName = methodParam.getParameterName();            if (paramName != null) {                builder.append(' ');                builder.append(paramName);            }            throw new HttpMediaTypeNotSupportedException(                    "Cannot extract parameter (" + builder.toString() + "): no Content-Type found");        }        List
     
       allSupportedMediaTypes = new ArrayList
      
       ();        if (this.messageConverters != null) {            for (HttpMessageConverter
        messageConverter : this.messageConverters) {                allSupportedMediaTypes.addAll(messageConverter.getSupportedMediaTypes());                if (messageConverter.canRead(paramType, contentType)) {                    if (logger.isDebugEnabled()) {                        logger.debug("Reading [" + paramType.getName() + "] as \"" + contentType                                +"\" using [" + messageConverter + "]");                    }                    return messageConverter.read(paramType, inputMessage);                }            }        }        throw new HttpMediaTypeNotSupportedException(contentType, allSupportedMediaTypes);    }
      
     

@ResponseBody注解时： 根据Request对象header部分的Accept属性（逗号分隔），逐一按accept中的类型，去遍历找到能处理的HttpMessageConverter；

源代码如下：

private void writeWithMessageConverters(Object returnValue,                HttpInputMessage inputMessage, HttpOutputMessage outputMessage)                throws IOException, HttpMediaTypeNotAcceptableException {            List
     
       acceptedMediaTypes = inputMessage.getHeaders().getAccept();            if (acceptedMediaTypes.isEmpty()) {                acceptedMediaTypes = Collections.singletonList(MediaType.ALL);            }            MediaType.sortByQualityValue(acceptedMediaTypes);            Class
       returnValueType = returnValue.getClass();            List
      
        allSupportedMediaTypes = new ArrayList
       
        ();            if (getMessageConverters() != null) {                for (MediaType acceptedMediaType : acceptedMediaTypes) {                    for (HttpMessageConverter messageConverter : getMessageConverters()) {                        if (messageConverter.canWrite(returnValueType, acceptedMediaType)) {                            messageConverter.write(returnValue, acceptedMediaType, outputMessage);                            if (logger.isDebugEnabled()) {                                MediaType contentType = outputMessage.getHeaders().getContentType();                                if (contentType == null) {                                    contentType = acceptedMediaType;                                }                                logger.debug("Written [" + returnValue + "] as \"" + contentType +                                        "\" using [" + messageConverter + "]");                            }                            this.responseArgumentUsed = true;                            return;                        }                    }                }                for (HttpMessageConverter messageConverter : messageConverters) {                    allSupportedMediaTypes.addAll(messageConverter.getSupportedMediaTypes());                }            }            throw new HttpMediaTypeNotAcceptableException(allSupportedMediaTypes);        }
       
      
     

补充：

MappingJacksonHttpMessageConverter 调用了 objectMapper.writeValue(OutputStream stream, Object)方法，使用@ResponseBody注解返回的对象就传入Object参数内。若返回的对象为已经格式化好的json串时，不使用@RequestBody注解，而应该这样处理：

1、response.setContentType("application/json; charset=UTF-8");

2、response.getWriter().print(jsonStr);

直接输出到body区，然后的视图为void。