spring mvc常用註解的說明

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       最近一段時間學習了springboot,所以熟悉一下mvc中常用的註解，這樣可以方便開發

   

簡介：

@RequestMapping

RequestMapping是一個用來處理請求地址映射的註解，可用於類或方法上。用於類上，表示類中的所有響應請求的方法都是以該地址作為父路徑。

RequestMapping註解有六個屬性，下面我們把她分成三類進行說明。

1、 value， method；

value：     指定請求的實際地址，指定的地址可以是URI Template 模式（後面將會說明）；

method：  指定請求的method類型， GET、POST、PUT、DELETE等；

 

2、 consumes，produces；

consumes： 指定處理請求的提交內容類型（Content-Type），例如application/json, text/html;

produces:    指定返回的內容類型，僅當request要求標頭中的(Accept)類型中包含該指定類型才返回；

 

3、 params，headers；

params： 指定request中必須包含某些參數值是，才讓該方法處理。

headers： 指定request中必須包含某些指定的header值，才能讓該方法處理請求。

樣本：1、value  / method 樣本

預設RequestMapping("....str...")即為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<String, Appointment> get() {14         return appointmentBook.getAppointmentsForToday();15     }16 17     @RequestMapping(value="/{day}", method = RequestMethod.GET)18     public Map<String, Appointment> 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值為以下三類：

A） 可以指定為普通的具體值；

B)  可以指定為含有某變數的一類值(URI Template Patterns with Path Variables)；

C) 可以指定為含Regex的一類值( 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 樣本

cousumes的範例：

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

方法僅處理request Content-Type為“application/json”類型的請求。

produces的範例：

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

方法僅處理request請求中Accept頭中包含了"application/json"的請求，同時暗示了返回的內容類型為application/json;

 

 

3 params、headers 樣本

params的範例：

@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  }}

僅處理請求中包含了名為“myParam”，值為“myValue”的請求；

 

 

headers的範例：

@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) 該註解用於讀取Request請求的body部分資料，使用系統預設配置的HttpMessageConverter進行解析，然後把相應的資料繫結到要返回的對象上；

      ii) 再把HttpMessageConverter返回的對象資料繫結到 controller中方法的參數上。

使用時機：

A) GET、POST方式提時， 根據request header Content-Type的值來判斷:

•     application/x-www-form-urlencoded， 可選（即非必須，因為這種情況的資料@RequestParam, @ModelAttribute也可以處理，當然@RequestBody也能處理）；
•     multipart/form-data, 不能處理（即使用@RequestBody不能處理這種格式的資料）；
•     其他格式， 必須（其他格式包括application/json, application/xml等。這些格式的資料，必須使用@RequestBody來處理）；

 

B) PUT方式提交時， 根據request header Content-Type的值來判斷:

 

•     application/x-www-form-urlencoded， 必須；
•     multipart/form-data, 不能處理；
•     其他格式， 必須；

說明：request的body部分的資料編碼格式由header部分的Content-Type指定；

 

 

@ResponseBody

 

作用： 

      該註解用於將Controller的方法返回的對象，通過適當的HttpMessageConverter轉換為指定格式後，寫入到Response對象的body資料區。

使用時機：

      返回的資料不是html標籤的頁面，而是其他某種格式的資料時（如json、xml等）使用；

 

 

 

HttpMessageConverter

<span style="font-family:Microsoft YaHei;">/** * 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<T> {    /**     * 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<MediaType> 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<? extends T> 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;}</span>

該介面定義了四個方法，分別是讀取資料時的 canRead(), read() 和 寫入資料時的canWrite(), write()方法。

 

在使用 <mvc:annotation-driven />標籤配置時，預設配置了RequestMappingHandlerAdapter（注意是RequestMappingHandlerAdapter不是AnnotationMethodHandlerAdapter,詳情查看Spring 3.1 document “16.14 Configuring Spring MVC”章節），並為他配置了一下預設的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<String, String>.    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: 負責讀取二進位格式的資料和寫出二進位格式的資料；

StringHttpMessageConverter：   負責讀取字串格式的資料和寫出二進位格式的資料；

 

ResourceHttpMessageConverter：負責讀取資源檔和寫出資源檔資料； 

FormHttpMessageConverter：       負責讀取form提交的資料（能讀取的資料格式為 application/x-www-form-urlencoded，不能讀取multipart/form-data格式資料）；負責寫入application/x-www-from-urlencoded和multipart/form-data格式的資料；

 

MappingJacksonHttpMessageConverter:  負責讀取和寫入json格式的資料；

 

SouceHttpMessageConverter：                   負責讀取和寫入 xml 中javax.xml.transform.Source定義的資料；

Jaxb2RootElementHttpMessageConverter:  負責讀取和寫入xml 標籤格式的資料；

 

AtomFeedHttpMessageConverter:              負責讀取和寫入Atom格式的資料；

RssChannelHttpMessageConverter:           負責讀取和寫入RSS格式的資料；

 

當使用@RequestBody和@ResponseBody註解時，RequestMappingHandlerAdapter就使用它們來進行讀取或者寫入相應格式的資料。

 

HttpMessageConverter匹配過程：

@RequestBody註解時： 根據Request對象header部分的Content-Type類型，逐一匹配合適的HttpMessageConverter來讀取資料；

spring 3.1原始碼如下：

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<MediaType> allSupportedMediaTypes = new ArrayList<MediaType>();        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註解時： 根據Request對象header部分的Accept屬性（逗號分隔），逐一按accept中的類型，去遍曆找到能處理的HttpMessageConverter；

原始碼如下：

private void writeWithMessageConverters(Object returnValue,                HttpInputMessage inputMessage, HttpOutputMessage outputMessage)                throws IOException, HttpMediaTypeNotAcceptableException {            List<MediaType> acceptedMediaTypes = inputMessage.getHeaders().getAccept();            if (acceptedMediaTypes.isEmpty()) {                acceptedMediaTypes = Collections.singletonList(MediaType.ALL);            }            MediaType.sortByQualityValue(acceptedMediaTypes);            Class<?> returnValueType = returnValue.getClass();            List<MediaType> allSupportedMediaTypes = new ArrayList<MediaType>();            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);        }

補充：

MappingJacksonHttpMessageConverter 調用了 objectMapper.writeValue(OutputStream stream, Object)方法，使用@ResponseBody註解返回的對象就傳入Object參數內。若返回的對象為已經格式化好的json串時，不使用@RequestBody註解，而應該這樣處理：

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

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

直接輸出到body區，然後的視圖為void。

spring mvc常用註解的說明