spring mvc常用注解的说明

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<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")
@ResponseBody
public 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

<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>

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<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: 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<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<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);}

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。

posted @ 2017-11-04 17:57 冰叔博客阅读(...) 评论(...) 编辑收藏