SpringMVC the Java API (V)

1. HttpMessageConverter message converter

(1) HttpMessageConverter Interface Source:

public interface HttpMessageConverter<T> {
    boolean canRead(Class<?> clazz, MediaType mediaType);
    boolean canWrite(Class<?> clazz, MediaType mediaType);
    List<MediaType> getSupportedMediaTypes();
    T read(Class<? extends T> clazz, HttpInputMessage inputMessage)
            throws IOException, HttpMessageNotReadableException;
    void write(T t, MediaType contentType, HttpOutputMessage outputMessage)
            throws IOException, HttpMessageNotWritableException;

}

The interface defines four methods are canRead (), canWrite (), write () method when a read () and write data to the read data.

(2) if the label configuration, the default configuration of RequestMappingHandlerAdapter (note the RequestMappingHandlerAdapter not AnnotationMethodHandlerAdapter), and configure the default HttpMessageConverter a bit for him:

• 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: responsible for reading the data in binary format and write data in binary format;
• StringHttpMessageConverter: responsible for reading and writing data string format data in a binary format;
• ResourceHttpMessageConverter: responsible for reading the resource file and write the resource file data;
• FormHttpMessageConverter: submitted form is responsible for reading data (data format readable by application / x-www-form-urlencoded, can not be read multipart / form-data format of the data); responsible for writing application / x-www-from- urlencoded and multipart / form-data format of the data;
• MappingJacksonHttpMessageConverter: responsible for reading and writing data json format;
• SouceHttpMessageConverter: xml is responsible for reading and writing data in javax.xml.transform.Source defined;
• Jaxb2RootElementHttpMessageConverter: responsible for reading and writing data xml label format;
• AtomFeedHttpMessageConverter: responsible for reading and writing data in Atom format;
• RssChannelHttpMessageConverter: responsible for reading and writing data RSS format;

When using @RequestBody @ResponseBody and annotations, RequestMappingHandlerAdapter using them to read or write data to the respective formats.

When @RequestBody Note: The Content-Type header portion Request object type, matching one by one to read the data HttpMessageConverter suitable.
When @ResponseBody Note: The Accept Request object attribute header portion (comma delimited), accept one by one according to the type, to traverse to find HttpMessageConverter can handle.

(3) HttpMessageConverter class diagram

• HttpMessageConverter
  • AbstractHttpMessageConverter
    • AbstractJackson2HttpMessageConverter
    • AbstractWireFeedHttpMessageConverter
    • AbstractXmlHttpMessageConverter
    • ByteArrayHttpMessageConverter
    • GsonHttpMessageConverter
    • ObjectToStringHttpMessageConverter
    • ProtobufHttpMessageConverter
    • ResourceHttpMessageConverter
    • StringHttpMessageConverter
    • SourceHttpMessageConverter

• • BufferedImageHttpMessageConverter
  • FormHttpMessageConverter
    • AllEncompassingFormHttpMessageConverter
  • GenericHttpMessageConverter
    • AbstractJackson2HttpMessageConverter
    • GsonHttpMessageConverter
    • Jaxb2CollectionHttpMessageConverter

2. HandlerMethodArgumentResolver parameter parser

In the beginner springmvc framework, I always had a question, why the controller method was able to put so many parameters, but also can get the desired object, such as HttpServletRequest or HttpServletResponse, various notes @ RequestParam, @ RequestHeader, @ RequestBody , @ PathVariable, @ ModelAttribute and so on.

Of course, the main character is: org.springframework.web.method.support.HandlerMethodArgumentResolver interface.

// interface defines the 
public  interface HandlerMethodArgumentResolver {
     // for determining whether the process parameters decomposition, returns true need, and to call the following method will resolveArgument. 
    Boolean supportsParameter (MethodParameter Parameter);
     // Object real processing parameters for decomposition method, the object parameter is returned in the controller method. 
    ResolveArgument Object (MethodParameter Parameter, ModelAndViewContainer mavContainer, 
            NativeWebRequest WebRequest, WebDataBinderFactory binderFactory) throws Exception; 

}

springmvc comes with some implementations:

• ServletRequestMethodArgumentResolver and ServletResponseMethodArgumentResolver handled automatically bound HttpServletRequest and HttpServletResponse
• RequestParamMapMethodArgumentResolver handled @RequestParam
• RequestHeaderMapMethodArgumentResolver handled @RequestHeader
• PathVariableMapMethodArgumentResolver handled @PathVariable
• ModelAttributeMethodProcessor handled @ModelAttribute
• RequestResponseBodyMethodProcessor handled @RequestBody

3. HandlerMethodReturnValueHandler return value resolver

HandlerMethodReturnValueHandler for the return value of the function execution Controller performs processing operations, springMVC provided a plurality HandlerMethodReturnValueHandler implementation class.

(1) HandlerMethodReturnValueHandler interface definition:

• supportsReturnType support the processing for determining whether the returned value.
• handleReturnValue realize the processing operation of the return value.

springMVC operation flow of the return value: the process is performed in the invokeAndHandle in ServletInvocableHandlerMethod, embodied in HandlerMethodReturnValueHandlerComposite in HandlerMethodReturnValueHandlerComposite return value processor contains all springMVC provided.

(2) HandlerMethodReturnValueHandler class diagram

•  AbstractMessageConverterMethodProcessor
• AsyncTaskMethodReturnValueHandler
• CallableMethodReturnValueHandler
• DeferredResultMethodReturnValueHandler
• HandlerMethodReturnValueHandlerComposite
• HttpHeadersReturnValueHandler
• ListenableFutureReturnValueHandler
• MapMethodProcessor
• ModelAndViewMethodReturnValueHandler
• ModelAndViewResolverMethodReturnValueHandler