轉載:Spring MVC之@RequestBody, @ResponseBody 詳解

以前練習springboot+mybatis實現Restful服務，給予HTTP/JSON格式傳輸，可是在新增的時候出現一個維妮塔，就是我傳的參數到數據庫爲Null值，我仔細檢查了個個層的代碼，後面發現實在Controller中將@Requestbody寫成了@ResponseBody,由於我這裏只需直接添加數據，使用postman工具進行測試，不須要返回值，因此致使出錯，下面就說下這二者的區別吧。

簡介：

@RequestBody

做用： 

      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，而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，由於這種狀況的數據@RequestParam, @ModelAttribute也能夠處理，固然@RequestBody也能處理）；
•     multipart/form-data, 不能處理（即便用@RequestBody不能處理這種格式的數據）；
•     其餘格式， 必須（其餘格式包括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；
•     其餘格式， 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

做用： 

      該註解用於將Controller的方法返回的對象，經過適當的HttpMessageConverter轉換爲指定格式後，寫入到Response對象的body數據區。

使用時機：

      返回的數據不是html標籤的頁面，而是其餘某種格式的數據時（如json、xml等）使用；

    

 

    HttpMessageConverter

    

 1 * Strategy interface that specifies a converter that can convert from and to HTTP requests and responses. 
 2  * 
 3  * @author Arjen Poutsma 
 4  * @author Juergen Hoeller 
 5  * @since 3.0 
 6  */  
 7 public interface HttpMessageConverter<T> {  
 8   
 9     /** 
10      * Indicates whether the given class can be read by this converter. 
11      * @param clazz the class to test for readability 
12      * @param mediaType the media type to read, can be {@code null} if not specified. 
13      * Typically the value of a {@code Content-Type} header. 
14      * @return {@code true} if readable; {@code false} otherwise 
15      */  
16     boolean canRead(Class<?> clazz, MediaType mediaType);  
17   
18     /** 
19      * Indicates whether the given class can be written by this converter. 
20      * @param clazz the class to test for writability 
21      * @param mediaType the media type to write, can be {@code null} if not specified. 
22      * Typically the value of an {@code Accept} header. 
23      * @return {@code true} if writable; {@code false} otherwise 
24      */  
25     boolean canWrite(Class<?> clazz, MediaType mediaType);  
26   
27     /** 
28      * Return the list of {@link MediaType} objects supported by this converter. 
29      * @return the list of supported media types 
30      */  
31     List<MediaType> getSupportedMediaTypes();  
32   
33     /** 
34      * Read an object of the given type form the given input message, and returns it. 
35      * @param clazz the type of object to return. This type must have previously been passed to the 
36      * {@link #canRead canRead} method of this interface, which must have returned {@code true}. 
37      * @param inputMessage the HTTP input message to read from 
38      * @return the converted object 
39      * @throws IOException in case of I/O errors 
40      * @throws HttpMessageNotReadableException in case of conversion errors 
41      */  
42     T read(Class<? extends T> clazz, HttpInputMessage inputMessage)  
43             throws IOException, HttpMessageNotReadableException;  
44   
45     /** 
46      * Write an given object to the given output message. 
47      * @param t the object to write to the output message. The type of this object must have previously been 
48      * passed to the {@link #canWrite canWrite} method of this interface, which must have returned {@code true}. 
49      * @param contentType the content type to use when writing. May be {@code null} to indicate that the 
50      * default content type of the converter must be used. If not {@code null}, this media type must have 
51      * previously been passed to the {@link #canWrite canWrite} method of this interface, which must have 
52      * returned {@code true}. 
53      * @param outputMessage the message to write to 
54      * @throws IOException in case of I/O errors 
55      * @throws HttpMessageNotWritableException in case of conversion errors 
56      */  
57     void write(T t, MediaType contentType, HttpOutputMessage outputMessage)  
58             throws IOException, HttpMessageNotWritableException;  
59   
60 }  

      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 />標籤配置時，默認配置了RequestMappingHandlerAdapter（注意是RequestMappingHandlerAdapter不是AnnotationMethodHandlerAdapter,詳情查看Spring 

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（能讀取的數據格式爲 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 標籤格式的數據；

 

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。

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。若返回的對象爲已經格式化好的json串時，不使用@RequestBody註解，而應該這樣處理：

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

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

直接輸出到body區，而後的視圖爲void。

本文轉載自:http://blog.csdn.net/kobejayandy/article/details/12690555