Spring MVC之@RequestBody, @ResponseBody @PathVariable @SessionAttributes @ModelAttribute详解
来源:互联网 发布:数据nbastat 编辑:程序博客网 时间:2024/06/07 06:16
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;
@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>
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:
- <span style="font-family:Microsoft YaHei;">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);
- }</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:
- <span style="font-family:Microsoft YaHei;">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);
- }</span>
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。
************************************************************************************
接上一篇文章,对@RequestMapping进行地址映射讲解之后,该篇主要讲解request 数据到handler method 参数数据的绑定所用到的注解和什么情形下使用;
简介:
handler method 参数绑定常用的注解,我们根据他们处理的Request的不同内容部分分为四类:(主要讲解常用类型)
A、处理requet uri 部分(这里指uri template中variable,不含queryString部分)的注解: @PathVariable;
B、处理request header部分的注解: @RequestHeader, @CookieValue;
C、处理request body部分的注解:@RequestParam, @RequestBody;
D、处理attribute类型是注解: @SessionAttributes, @ModelAttribute;
1、 @PathVariable
当使用@RequestMapping URI template 样式映射时, 即 someUrl/{paramId}, 这时的paramId可通过 @Pathvariable注解绑定它传过来的值到方法的参数上。
示例代码:
上面代码把URI template 中变量 ownerId的值和petId的值,绑定到方法的参数上。若方法参数名称和需要绑定的uri template中变量名称不一致,需要在@PathVariable("name")指定uri template中的名称。
- @Controller
- @RequestMapping("/owners/{ownerId}")
- public class RelativePathUriTemplateController {
- @RequestMapping("/pets/{petId}")
- public void findPet(@PathVariable String ownerId, @PathVariable String petId, Model model) {
- // implementation omitted
- }
- }
2、 @RequestHeader、@CookieValue
@RequestHeader 注解,可以把Request请求header部分的值绑定到方法的参数上。
示例代码:
这是一个Request 的header部分:
- Host localhost:8080
- Accept text/html,application/xhtml+xml,application/xml;q=0.9
- Accept-Language fr,en-gb;q=0.7,en;q=0.3
- Accept-Encoding gzip,deflate
- Accept-Charset ISO-8859-1,utf-8;q=0.7,*;q=0.7
- Keep-Alive 300
上面的代码,把request header部分的 Accept-Encoding的值,绑定到参数encoding上了, Keep-Alive header的值绑定到参数keepAlive上。
- @RequestMapping("/displayHeaderInfo.do")
- public void displayHeaderInfo(@RequestHeader("Accept-Encoding") String encoding,
- @RequestHeader("Keep-Alive") long keepAlive) {
- //...
- }
@CookieValue 可以把Request header中关于cookie的值绑定到方法的参数上。
例如有如下Cookie值:
参数绑定的代码:
- JSESSIONID=415A4AC178C59DACE0B2C9CA727CDD84
即把JSESSIONID的值绑定到参数cookie上。
- @RequestMapping("/displayHeaderInfo.do")
- public void displayHeaderInfo(@CookieValue("JSESSIONID") String cookie) {
- //...
- }
3、@RequestParam, @RequestBody
@RequestParam
A) 常用来处理简单类型的绑定,通过Request.getParameter() 获取的String可直接转换为简单类型的情况( String--> 简单类型的转换操作由ConversionService配置的转换器来完成);因为使用request.getParameter()方式获取参数,所以可以处理get 方式中queryString的值,也可以处理post方式中 body data的值;
B)用来处理Content-Type: 为
application/x-www-form-urlencoded
编码的内容,提交方式GET、POST;C) 该注解有两个属性: value、required; value用来指定要传入值的id名称,required用来指示参数是否必须绑定;
示例代码:
- @Controller
- @RequestMapping("/pets")
- @SessionAttributes("pet")
- public class EditPetForm {
- // ...
- @RequestMapping(method = RequestMethod.GET)
- public String setupForm(@RequestParam("petId") int petId, ModelMap model) {
- Pet pet = this.clinic.loadPet(petId);
- model.addAttribute("pet", pet);
- return "petForm";
- }
- // ...
@RequestBody
该注解常用来处理Content-Type: 不是
application/x-www-form-urlencoded
编码的内容,例如application/json, application/xml等;它是通过使用HandlerAdapter 配置的
HttpMessageConverters
来解析post data body,然后绑定到相应的bean上的。因为配置有FormHttpMessageConverter,所以也可以用来处理
application/x-www-form-urlencoded
的内容,处理完的结果放在一个MultiValueMap<String, String>里,这种情况在某些特殊需求下使用,详情查看FormHttpMessageConverter api;示例代码:
- @RequestMapping(value = "/something", method = RequestMethod.PUT)
- public void handle(@RequestBody String body, Writer writer) throws IOException {
- writer.write(body);
- }
4、@SessionAttributes, @ModelAttribute
@SessionAttributes:
该注解用来绑定HttpSession中的attribute对象的值,便于在方法中的参数里使用。
该注解有value、types两个属性,可以通过名字和类型指定要使用的attribute 对象;
示例代码:
- @Controller
- @RequestMapping("/editPet.do")
- @SessionAttributes("pet")
- public class EditPetForm {
- // ...
- }
@ModelAttribute
该注解有两个用法,一个是用于方法上,一个是用于参数上;
用于方法上时: 通常用来在处理@RequestMapping之前,为请求绑定需要从后台查询的model;
用于参数上时: 用来通过名称对应,把相应名称的值绑定到注解的参数bean上;要绑定的值来源于:
A) @SessionAttributes 启用的attribute 对象上;
B) @ModelAttribute 用于方法上时指定的model对象;
C) 上述两种情况都没有时,new一个需要绑定的bean对象,然后把request中按名称对应的方式把值绑定到bean中。
用到方法上@ModelAttribute的示例代码:
- // Add one attribute
- // The return value of the method is added to the model under the name "account"
- // You can customize the name via @ModelAttribute("myAccount")
- @ModelAttribute
- public Account addAccount(@RequestParam String number) {
- return accountManager.findAccount(number);
- }
这种方式实际的效果就是在调用@RequestMapping的方法之前,为request对象的model里put(“account”, Account);用在参数上的@ModelAttribute示例代码:
首先查询 @SessionAttributes有无绑定的Pet对象,若没有则查询@ModelAttribute方法层面上是否绑定了Pet对象,若没有则将URI template中的值按对应的名称绑定到Pet对象的各属性上。
- @RequestMapping(value="/owners/{ownerId}/pets/{petId}/edit", method = RequestMethod.POST)
- public String processSubmit(@ModelAttribute Pet pet) {
- }
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