Spring MVC之@RequestBody, @ResponseBody 详解
2015-07-27 17:09
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引言:
接上一篇文章讲述处理@RequestMapping的方法参数绑定之后,详细介绍下@RequestBody、@ResponseBody的具体用法和使用时机;简介:
@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requestheaderContent-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requestheaderContent-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
[java]<spanstyle="font-family:MicrosoftYaHei;">/**
*StrategyinterfacethatspecifiesaconverterthatcanconvertfromandtoHTTPrequestsandresponses.
*
*@authorArjenPoutsma
*@authorJuergenHoeller
*@since3.0
*/
publicinterfaceHttpMessageConverter<T>{
/**
*Indicateswhetherthegivenclasscanbereadbythisconverter.
*@paramclazztheclasstotestforreadability
*@parammediaTypethemediatypetoread,canbe{@codenull}ifnotspecified.
*Typicallythevalueofa{@codeContent-Type}header.
*@return{@codetrue}ifreadable;{@codefalse}otherwise
*/
booleancanRead(Class<?>clazz,MediaTypemediaType);
/**
*Indicateswhetherthegivenclasscanbewrittenbythisconverter.
*@paramclazztheclasstotestforwritability
*@parammediaTypethemediatypetowrite,canbe{@codenull}ifnotspecified.
*Typicallythevalueofan{@codeAccept}header.
*@return{@codetrue}ifwritable;{@codefalse}otherwise
*/
booleancanWrite(Class<?>clazz,MediaTypemediaType);
/**
*Returnthelistof{@linkMediaType}objectssupportedbythisconverter.
*@returnthelistofsupportedmediatypes
*/
List<MediaType>getSupportedMediaTypes();
/**
*Readanobjectofthegiventypeformthegiveninputmessage,andreturnsit.
*@paramclazzthetypeofobjecttoreturn.Thistypemusthavepreviouslybeenpassedtothe
*{@link#canReadcanRead}methodofthisinterface,whichmusthavereturned{@codetrue}.
*@paraminputMessagetheHTTPinputmessagetoreadfrom
*@returntheconvertedobject
*@throwsIOExceptionincaseofI/Oerrors
*@throwsHttpMessageNotReadableExceptionincaseofconversionerrors
*/
Tread(Class<?extendsT>clazz,HttpInputMessageinputMessage)
throwsIOException,HttpMessageNotReadableException;
/**
*Writeangivenobjecttothegivenoutputmessage.
*@paramttheobjecttowritetotheoutputmessage.Thetypeofthisobjectmusthavepreviouslybeen
*passedtothe{@link#canWritecanWrite}methodofthisinterface,whichmusthavereturned{@codetrue}.
*@paramcontentTypethecontenttypetousewhenwriting.Maybe{@codenull}toindicatethatthe
*defaultcontenttypeoftheconvertermustbeused.Ifnot{@codenull},thismediatypemusthave
*previouslybeenpassedtothe{@link#canWritecanWrite}methodofthisinterface,whichmusthave
*returned{@codetrue}.
*@paramoutputMessagethemessagetowriteto
*@throwsIOExceptionincaseofI/Oerrors
*@throwsHttpMessageNotWritableExceptionincaseofconversionerrors
*/
voidwrite(Tt,MediaTypecontentType,HttpOutputMessageoutputMessage)
throwsIOException,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(注意是不是AnnotationMethodHandlerAdapter,详情查看Spring3.1document“16.14ConfiguringSpringMVC”章节),并为他配置了一下默认的HttpMessageConverter:RequestMappingHandlerAdapter
[java]
ByteArrayHttpMessageConverterconvertsbytearrays.
StringHttpMessageConverterconvertsstrings.
ResourceHttpMessageConverterconvertsto/fromorg.springframework.core.io.Resourceforallmediatypes.
SourceHttpMessageConverterconvertsto/fromajavax.xml.transform.Source.
FormHttpMessageConverterconvertsformdatato/fromaMultiValueMap<String,String>.
Jaxb2RootElementHttpMessageConverterconvertsJavaobjectsto/fromXML—addedifJAXB2ispresentontheclasspath.
MappingJacksonHttpMessageConverterconvertsto/fromJSON—addedifJacksonispresentontheclasspath.
AtomFeedHttpMessageConverterconvertsAtomfeeds—addedifRomeispresentontheclasspath.
RssChannelHttpMessageConverterconvertsRSSfeeds—addedifRomeispresentontheclasspath.
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,就使用它们来进行读取或者写入相应格式的数据。RequestMappingHandlerAdapter
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;spring3.1源代码如下:
[java]
<spanstyle="font-family:MicrosoftYaHei;">privateObjectreadWithMessageConverters(MethodParametermethodParam,HttpInputMessageinputMessage,ClassparamType)
throwsException{
MediaTypecontentType=inputMessage.getHeaders().getContentType();
if(contentType==null){
StringBuilderbuilder=newStringBuilder(ClassUtils.getShortName(methodParam.getParameterType()));
StringparamName=methodParam.getParameterName();
if(paramName!=null){
builder.append('');
builder.append(paramName);
}
thrownewHttpMediaTypeNotSupportedException(
"Cannotextractparameter("+builder.toString()+"):noContent-Typefound");
}
List<MediaType>allSupportedMediaTypes=newArrayList<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+"]");
}
returnmessageConverter.read(paramType,inputMessage);
}
}
}
thrownewHttpMediaTypeNotSupportedException(contentType,allSupportedMediaTypes);
}</span>
@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:
[java]
<spanstyle="font-family:MicrosoftYaHei;">privatevoidwriteWithMessageConverters(ObjectreturnValue,
HttpInputMessageinputMessage,HttpOutputMessageoutputMessage)
throwsIOException,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=newArrayList<MediaType>();
if(getMessageConverters()!=null){
for(MediaTypeacceptedMediaType:acceptedMediaTypes){
for(HttpMessageConvertermessageConverter:getMessageConverters()){
if(messageConverter.canWrite(returnValueType,acceptedMediaType)){
messageConverter.write(returnValue,acceptedMediaType,outputMessage);
if(logger.isDebugEnabled()){
MediaTypecontentType=outputMessage.getHeaders().getContentType();
if(contentType==null){
contentType=acceptedMediaType;
}
logger.debug("Written["+returnValue+"]as\""+contentType+
"\"using["+messageConverter+"]");
}
this.responseArgumentUsed=true;
return;
}
}
}
for(HttpMessageConvertermessageConverter:messageConverters){
allSupportedMediaTypes.addAll(messageConverter.getSupportedMediaTypes());
}
}
thrownewHttpMediaTypeNotAcceptableException(allSupportedMediaTypes);
}</span>
补充:
MappingJacksonHttpMessageConverter调用了objectMapper.writeValue(OutputStreamstream,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。
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