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spring mvc常用注解的说明

时间:2017-11-04 19:45:23      阅读:227      评论:0      收藏:0      [点我收藏+]

标签:been   pen   may   资源文件   drive   feed   表达式   ram   void   

       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:

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@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
  }
}
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仅处理请求中包含了名为“myParam”,值为“myValue”的请求;

 

 

headers的样例:

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@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
  }
}
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@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

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<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>
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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:

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    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.
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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:

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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);
    }
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@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:

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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);
        }
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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。

spring mvc常用注解的说明

标签:been   pen   may   资源文件   drive   feed   表达式   ram   void   

原文地址:http://www.cnblogs.com/bingshu/p/7784027.html

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