ResponseBodyAdvice是一个接口,接口描述,
- package org.springframework.web.servlet.mvc.method.annotation;
- /**
- * Allows customizing the response after the execution of an {@code @ResponseBody}
- * or an {@code ResponseEntity} controller method but before the body is written
- * with an {@code HttpMessageConverter}.
- *
- * <p>Implementations may be may be registered directly with
- * {@code RequestMappingHandlerAdapter} and {@code ExceptionHandlerExceptionResolver}
- * or more likely annotated with {@code @ControllerAdvice} in which case they
- * will be auto-detected by both.
- *
- * @author Rossen Stoyanchev
- * @since 4.1
- */
- public interface ResponseBodyAdvice<T> {
- /**
- * Whether this component supports the given controller method return type
- * and the selected {@code HttpMessageConverter} type.
- * @param returnType the return type
- * @param converterType the selected converter type
- * @return {@code true} if {@link #beforeBodyWrite} should be invoked, {@code false} otherwise
- */
- boolean supports(MethodParameter returnType, Class<? extends HttpMessageConverter<?>> converterType);
- /**
- * Invoked after an {@code HttpMessageConverter} is selected and just before
- * its write method is invoked.
- * @param body the body to be written
- * @param returnType the return type of the controller method
- * @param selectedContentType the content type selected through content negotiation
- * @param selectedConverterType the converter type selected to write to the response
- * @param request the current request
- * @param response the current response
- * @return the body that was passed in or a modified, possibly new instance
- */
- T beforeBodyWrite(T body, MethodParameter returnType, MediaType selectedContentType,
- Class<? extends HttpMessageConverter<?>> selectedConverterType,
- ServerHttpRequest request, ServerHttpResponse response);
- }
package org.springframework.web.servlet.mvc.method.annotation;/** * Allows customizing the response after the execution of an {@code @ResponseBody} * or an {@code ResponseEntity} controller method but before the body is written * with an {@code HttpMessageConverter}. * * <p>Implementations may be may be registered directly with * {@code RequestMappingHandlerAdapter} and {@code ExceptionHandlerExceptionResolver} * or more likely annotated with {@code @ControllerAdvice} in which case they * will be auto-detected by both. * * @author Rossen Stoyanchev * @since 4.1 */public interface ResponseBodyAdvice<T> { /** * Whether this component supports the given controller method return type * and the selected {@code HttpMessageConverter} type. * @param returnType the return type * @param converterType the selected converter type * @return {@code true} if {@link #beforeBodyWrite} should be invoked, {@code false} otherwise */ boolean supports(MethodParameter returnType, Class<? extends HttpMessageConverter<?>> converterType); /** * Invoked after an {@code HttpMessageConverter} is selected and just before * its write method is invoked. * @param body the body to be written * @param returnType the return type of the controller method * @param selectedContentType the content type selected through content negotiation * @param selectedConverterType the converter type selected to write to the response * @param request the current request * @param response the current response * @return the body that was passed in or a modified, possibly new instance */ T beforeBodyWrite(T body, MethodParameter returnType, MediaType selectedContentType, Class<? extends HttpMessageConverter<?>> selectedConverterType, ServerHttpRequest request, ServerHttpResponse response);}
作用:
Allows customizing the response after the execution of an {@code @ResponseBody} or an {@code ResponseEntity} controller method but before the body is written
with an {@code HttpMessageConverter}.
其中一个方法就是 beforeBodyWrite 在使用相应的HttpMessageConvert 进行write之前会被调用,就是一个切面方法。
和jsonp有关的实现类是AbstractJsonpResponseBodyAdvice,如下是 beforeBodyWrite 方法的实现,
- @Override
- public final Object beforeBodyWrite(Object body, MethodParameter returnType,
- MediaType contentType, Class<? extends HttpMessageConverter<?>> converterType,
- ServerHttpRequest request, ServerHttpResponse response) {
- MappingJacksonValue container = getOrCreateContainer(body);
- beforeBodyWriteInternal(container, contentType, returnType, request, response);
- return container;
- }
@Overridepublic final Object beforeBodyWrite(Object body, MethodParameter returnType, MediaType contentType, Class<? extends HttpMessageConverter<?>> converterType, ServerHttpRequest request, ServerHttpResponse response) { MappingJacksonValue container = getOrCreateContainer(body); beforeBodyWriteInternal(container, contentType, returnType, request, response); return container;}
位于AbstractJsonpResponseBodyAdvice的父类中,而beforeBodyWriteInternal是在AbstractJsonpResponseBodyAdvice中实现的 ,如下,
- @Override
- protected void beforeBodyWriteInternal(MappingJacksonValue bodyContainer, MediaType contentType,
- MethodParameter returnType, ServerHttpRequest request, ServerHttpResponse response) {
- HttpServletRequest servletRequest = ((ServletServerHttpRequest) request).getServletRequest();
- for (String name : this.jsonpQueryParamNames) {
- String value = servletRequest.getParameter(name);
- if (value != null) {
- MediaType contentTypeToUse = getContentType(contentType, request, response);
- response.getHeaders().setContentType(contentTypeToUse);
- bodyContainer.setJsonpFunction(value);
- return;
- }
- }
- }
@Overrideprotected void beforeBodyWriteInternal(MappingJacksonValue bodyContainer, MediaType contentType, MethodParameter returnType, ServerHttpRequest request, ServerHttpResponse response) { HttpServletRequest servletRequest = ((ServletServerHttpRequest) request).getServletRequest(); for (String name : this.jsonpQueryParamNames) { String value = servletRequest.getParameter(name); if (value != null) { MediaType contentTypeToUse = getContentType(contentType, request, response); response.getHeaders().setContentType(contentTypeToUse); bodyContainer.setJsonpFunction(value); return; } }}
就是根据callback 请求参数或配置的其他参数来确定返回jsonp协议的数据。
如何实现jsonp?
首先继承AbstractJsonpResponseBodyAdvice ,如下,
- package com.usoft.web.controller.jsonp;
- import org.springframework.web.bind.annotation.ControllerAdvice;
- import org.springframework.web.servlet.mvc.method.annotation.AbstractJsonpResponseBodyAdvice;
- /**
- *
- */
- @ControllerAdvice(basePackages = "com.usoft.web.controller.jsonp")
- public class JsonpAdvice extends AbstractJsonpResponseBodyAdvice {
- public JsonpAdvice() {
- super("callback", "jsonp");
- }
- }
package com.usoft.web.controller.jsonp;import org.springframework.web.bind.annotation.ControllerAdvice;import org.springframework.web.servlet.mvc.method.annotation.AbstractJsonpResponseBodyAdvice;/** * */@ControllerAdvice(basePackages = "com.usoft.web.controller.jsonp")public class JsonpAdvice extends AbstractJsonpResponseBodyAdvice { public JsonpAdvice() { super("callback", "jsonp"); }}
super("callback", "jsonp");的意思就是当请求参数中包含callback 或 jsonp参数时,就会返回jsonp协议的数据。其value就作为回调函数的名称。
这里必须使用@ControllerAdvice注解标注该类,并且配置对哪些Controller起作用。关于注解@ControllerAdvice 的作用这里不做描述。
Controller实现jsonp,
- package com.usoft.web.controller.jsonp;
- import org.springframework.stereotype.Controller;
- import org.springframework.web.bind.annotation.RequestMapping;
- import org.springframework.web.bind.annotation.ResponseBody;
- import com.usoft.web.controller.JsonMapper;
- import com.usoft.web.controller.Person;
- /**
- * jsonp
- */
- @Controller
- public class JsonpController {
- /**
- * callback({"id":1,"age":12,"name":"lyx"})
- *
- * @param args
- */
- public static void main(String args[]) {
- Person person = new Person(1, "lyx", 12);
- System.out.println(JsonMapper.nonNullMapper().toJsonP("callback",
- person));
- }
- @RequestMapping("/jsonp1")
- public Person jsonp1() {
- return new Person(1, "lyx", 12);
- }
- @RequestMapping("/jsonp2")
- @ResponseBody
- public Person jsonp2() {
- return new Person(1, "lyx", 12);
- }
- @RequestMapping("/jsonp3")
- @ResponseBody
- public String jsonp3() {
- return JsonMapper.nonNullMapper().toJsonP("callback",
- new Person(1, "lyx", 12));
- }
- }
package com.usoft.web.controller.jsonp;import org.springframework.stereotype.Controller;import org.springframework.web.bind.annotation.RequestMapping;import org.springframework.web.bind.annotation.ResponseBody;import com.usoft.web.controller.JsonMapper;import com.usoft.web.controller.Person;/** * jsonp */@Controllerpublic class JsonpController { /** * callback({"id":1,"age":12,"name":"lyx"}) * * @param args */ public static void main(String args[]) { Person person = new Person(1, "lyx", 12); System.out.println(JsonMapper.nonNullMapper().toJsonP("callback", person)); } @RequestMapping("/jsonp1") public Person jsonp1() { return new Person(1, "lyx", 12); } @RequestMapping("/jsonp2") @ResponseBody public Person jsonp2() { return new Person(1, "lyx", 12); } @RequestMapping("/jsonp3") @ResponseBody public String jsonp3() { return JsonMapper.nonNullMapper().toJsonP("callback", new Person(1, "lyx", 12)); }}
jsonp2 方法就是 一个jsonp协议的调用。http://localhost:8081/jsonp2?callback=test可以直接调用这个方法,并且返回jsonp协议的数据。
通过debug代码,我们来看一下他是怎么返回jsonp协议的数据的。
正因为我们前面在 该Controller 上配置了 JsonpAdvice 的 ControllerAdvice,在调用 MappingJackson2HttpMessageConverter的write()方法往回写数据的时候,首先会调用
beforeBodyWrite,具体的代码如下,
- @Override
- protected void beforeBodyWriteInternal(MappingJacksonValue bodyContainer, MediaType contentType,
- MethodParameter returnType, ServerHttpRequest request, ServerHttpResponse response) {
- HttpServletRequest servletRequest = ((ServletServerHttpRequest) request).getServletRequest();
- for (String name : this.jsonpQueryParamNames) {
- String value = servletRequest.getParameter(name);
- if (value != null) {
- MediaType contentTypeToUse = getContentType(contentType, request, response);
- response.getHeaders().setContentType(contentTypeToUse);
- bodyContainer.setJsonpFunction(value);
- return;
- }
- }
- }
@Overrideprotected void beforeBodyWriteInternal(MappingJacksonValue bodyContainer, MediaType contentType, MethodParameter returnType, ServerHttpRequest request, ServerHttpResponse response) { HttpServletRequest servletRequest = ((ServletServerHttpRequest) request).getServletRequest(); for (String name : this.jsonpQueryParamNames) { String value = servletRequest.getParameter(name); if (value != null) { MediaType contentTypeToUse = getContentType(contentType, request, response); response.getHeaders().setContentType(contentTypeToUse); bodyContainer.setJsonpFunction(value); return; } }}
当请求参数中含有配置的相应的回调参数时,就会bodyContainer.setJsonpFunction(value);这就标志着 返回的数据时jsonp格式的数据。
然后接下来就到了 MappingJackson2HttpMessageConverter 的write()方法真正写数据的时候了。看他是怎么写数据的,相关的代码如下,
- @Override
- protected void writeInternal(Object object, HttpOutputMessage outputMessage)
- throws IOException, HttpMessageNotWritableException {
- JsonEncoding encoding = getJsonEncoding(outputMessage.getHeaders().getContentType());
- JsonGenerator generator = this.objectMapper.getFactory().createGenerator(outputMessage.getBody(), encoding);
- try {
- writePrefix(generator, object);
- Class<?> serializationView = null;
- Object value = object;
- if (value instanceof MappingJacksonValue) {
- MappingJacksonValue container = (MappingJacksonValue) object;
- value = container.getValue();
- serializationView = container.getSerializationView();
- }
- if (serializationView != null) {
- this.objectMapper.writerWithView(serializationView).writeValue(generator, value);
- }
- else {
- this.objectMapper.writeValue(generator, value);
- }
- writeSuffix(generator, object);
- generator.flush();
- }
- catch (JsonProcessingException ex) {
- throw new HttpMessageNotWritableException("Could not write content: " + ex.getMessage(), ex);
- }
- }
- @Override
- protected void writePrefix(JsonGenerator generator, Object object) throws IOException {
- if (this.jsonPrefix != null) {
- generator.writeRaw(this.jsonPrefix);
- }
- String jsonpFunction =
- (object instanceof MappingJacksonValue ? ((MappingJacksonValue) object).getJsonpFunction() : null);
- if (jsonpFunction != null) {
- generator.writeRaw(jsonpFunction + "(");
- }
- }
- @Override
- protected void writeSuffix(JsonGenerator generator, Object object) throws IOException {
- String jsonpFunction =
- (object instanceof MappingJacksonValue ? ((MappingJacksonValue) object).getJsonpFunction() : null);
- if (jsonpFunction != null) {
- generator.writeRaw(");");
- }
- }
@Overrideprotected void writeInternal(Object object, HttpOutputMessage outputMessage) throws IOException, HttpMessageNotWritableException { JsonEncoding encoding = getJsonEncoding(outputMessage.getHeaders().getContentType()); JsonGenerator generator = this.objectMapper.getFactory().createGenerator(outputMessage.getBody(), encoding); try { writePrefix(generator, object); Class<?> serializationView = null; Object value = object; if (value instanceof MappingJacksonValue) { MappingJacksonValue container = (MappingJacksonValue) object; value = container.getValue(); serializationView = container.getSerializationView(); } if (serializationView != null) { this.objectMapper.writerWithView(serializationView).writeValue(generator, value); } else { this.objectMapper.writeValue(generator, value); } writeSuffix(generator, object); generator.flush(); } catch (JsonProcessingException ex) { throw new HttpMessageNotWritableException("Could not write content: " + ex.getMessage(), ex); }}@Overrideprotected void writePrefix(JsonGenerator generator, Object object) throws IOException { if (this.jsonPrefix != null) { generator.writeRaw(this.jsonPrefix); } String jsonpFunction = (object instanceof MappingJacksonValue ? ((MappingJacksonValue) object).getJsonpFunction() : null); if (jsonpFunction != null) { generator.writeRaw(jsonpFunction + "("); }}@Overrideprotected void writeSuffix(JsonGenerator generator, Object object) throws IOException { String jsonpFunction = (object instanceof MappingJacksonValue ? ((MappingJacksonValue) object).getJsonpFunction() : null); if (jsonpFunction != null) { generator.writeRaw(");"); }}
代码非常清晰。看我们jsonp调用的结果。
http://localhost:8081/jsonp2?callback=test
响应消息如下,
HTTP/1.1 200 OK
Server: Apache-Coyote/1.1
Content-Type: application/javascript
Transfer-Encoding: chunked
Date: Sun, 19 Jul 2015 13:01:02 GMT
test({"id":1,"age":12,"name":"lyx"});