spring mvc常用註解的說明
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請求頭中的(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。
示例:
1、value / method 示例
默認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量的一類值(URI Template Patterns with Path Variables);
C) 可以指定為含正則表達式的一類值( 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 示例
cousumes的樣例:
@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的樣例:
@Controller @RequestMapping(value = "/pets/{petId}", method = RequestMethod.GET, produces="application/json") @ResponseBody public 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 示例
params的樣例:
@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的樣例:
@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部分數據,使用系統默認配置的HttpMessageConverter進行解析,然後把相應的數據綁定到要返回的對象上;
ii) 再把HttpMessageConverter返回的對象數據綁定到 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,因為這種情況的數據@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數據);
- 其他格式, 必須(其他格式包括application/json, application/xml等。這些格式的數據,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部分的數據編碼格式由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數據區。
使用時機:
返回的數據不是html標簽的頁面,而是其他某種格式的數據時(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>
該接口定義了四個方法,分別是讀取數據時的 canRead(), read() 和 寫入數據時的canWrite(), write()方法。
在使用 <mvc:annotation-driven />標簽配置時,默認配置了RequestMappingHandlerAdapter(註意是
RequestMappingHandlerAdapter
不是AnnotationMethodHandlerAdapter,詳情查看Spring 3.1 document “16.14 Configuring Spring MVC”章節),並為他配置了一下默認的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: 負責讀取二進制格式的數據和寫出二進制格式的數據;
StringHttpMessageConverter: 負責讀取字符串格式的數據和寫出二進制格式的數據;
ResourceHttpMessageConverter:負責讀取資源文件和寫出資源文件數據;
FormHttpMessageConverter: 負責讀取form提交的數據(能讀取的數據格式為 application/x-www-form-urlencoded,不能讀取multipart/form-data格式數據);負責寫入application/x-www-from-urlencoded和multipart/form-data格式的數據;
MappingJacksonHttpMessageConverter: 負責讀取和寫入json格式的數據;
SouceHttpMessageConverter: 負責讀取和寫入 xml 中javax.xml.transform.Source定義的數據;
Jaxb2RootElementHttpMessageConverter: 負責讀取和寫入xml 標簽格式的數據;
AtomFeedHttpMessageConverter: 負責讀取和寫入Atom格式的數據;
RssChannelHttpMessageConverter: 負責讀取和寫入RSS格式的數據;
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數據。
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來讀取數據;
spring 3.1源代碼如下:
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,去遍歷找到能處理的HttpMessageConverter;
源代碼如下:
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