引言:
接上一篇文章講述處理@RequestMapping的方法參數綁定之後,詳細介紹下@RequestBody、@ResponseBody的具體用法和使用時機;
簡介:
@RequestBody
作用:
i) 該注解用于讀取Request請求的body部分資料,使用系統預設配置的HttpMessageConverter進行解析,然後把相應的資料綁定到要傳回的對象上;
ii) 再把HttpMessageConverter傳回的對象資料綁定到 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,因為這種情況的資料@RequestParam, @ModelAttribute也可以處理,當然@RequestBody也能處理);
- multipart/form-data, 不能處理(即使用@RequestBody不能處理這種格式的資料);
- 其他格式, 必須(其他格式包括application/json, application/xml等。這些格式的資料,必須使用@RequestBody來處理);
B) PUT方式送出時, 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;
- 其他格式, 必須;
說明:request的body部分的資料編碼格式由header部分的Content-Type指定;
@ResponseBody
作用:
該注解用于将Controller的方法傳回的對象,通過适當的HttpMessageConverter轉換為指定格式後,寫入到Response對象的body資料區。
使用時機:
傳回的資料不是html标簽的頁面,而是其他某種格式的資料時(如json、xml等)使用;
HttpMessageConverter
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- <span style="font-family:Microsoft YaHei;">
- 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;
- }
- </span>
該接口定義了四個方法,分别是讀取資料時的 canRead(), read() 和 寫入資料時的canWrite(), write()方法。
在使用 <mvc:annotation-driven />标簽配置時,預設配置了
RequestMappingHandlerAdapter(注意是
RequestMappingHandlerAdapter
不是AnnotationMethodHandlerAdapter,詳情檢視Spring 3.1 document “16.14 Configuring Spring MVC”章節),并為他配置了一下預設的HttpMessageConverter:
[java] view plain copy
- 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資料和寫出二進制格式的資料;
StringHttpMessageConverter: 負責讀取字元串格式的資料和寫出二進制格式的資料;
ResourceHttpMessageConverter:負責讀取資源檔案和寫出資源檔案資料;
FormHttpMessageConverter: 負責讀取form送出的資料(能讀取的資料格式為 application/x-www-form-urlencoded,不能讀取multipart/form-data格式資料);負責寫入application/x-www-from-urlencoded和multipart/form-data格式的資料;
MappingJacksonHttpMessageConverter: 負責讀取和寫入json格式的資料;
SouceHttpMessageConverter: 負責讀取和寫入 xml 中javax.xml.transform.Source定義的資料;
Jaxb2RootElementHttpMessageConverter: 負責讀取和寫入xml 标簽格式的資料;
AtomFeedHttpMessageConverter: 負責讀取和寫入Atom格式的資料;
RssChannelHttpMessageConverter: 負責讀取和寫入RSS格式的資料;
當使用@RequestBody和@ResponseBody注解時,
RequestMappingHandlerAdapter
就使用它們來進行讀取或者寫入相應格式的資料。
HttpMessageConverter比對過程:
@RequestBody注解時: 根據Request對象header部分的Content-Type類型,逐一比對合适的HttpMessageConverter來讀取資料;
spring 3.1源代碼如下:
[java] view plain copy
- <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注解時: 根據Request對象header部分的Accept屬性(逗号分隔),逐一按accept中的類型,去周遊找到能處理的HttpMessageConverter;
源代碼如下:
[java] view plain copy
- <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>
補充:
MappingJacksonHttpMessageConverter 調用了 objectMapper.writeValue(OutputStream stream, Object)方法,使用@ResponseBody注解傳回的對象就傳入Object參數内。若傳回的對象為已經格式化好的json串時,不使用@RequestBody注解,而應該這樣處理:
1、response.setContentType("application/json; charset=UTF-8");
2、response.getWriter().print(jsonStr);
直接輸出到body區,然後的視圖為void。