springmvc的RequestResponseBodyMethodProcessor解析_晏无心_新浪博客

逃离我推掉我的手 2022-12-20 15:50 279阅读 0赞

前面分析了springmvc对一些基本的请求参数的解析和绑定，接下来会进行分析springmvc对http请求消息体的解析。将会分析json、xml和mutipart（file）。

[![springmvc的RequestResponseBodyMethodProcessor解析][springmvc_RequestResponseBodyMethodProcessor]][springmvc_RequestResponseBodyMethodProcessor_springmvc_RequestResponseBodyMethodProcessor]  
POST请求，contentType为Json，消息体为json数据。

springmvc要解析绑定json数据，必须在handler的接收参数前添加@RequestBody注解，不然没法绑定参数：

[![springmvc的RequestResponseBodyMethodProcessor解析][springmvc_RequestResponseBodyMethodProcessor 1]][springmvc_RequestResponseBodyMethodProcessor_springmvc_RequestResponseBodyMethodProcessor 1]

首先来看supportsParameter()：

[![springmvc的RequestResponseBodyMethodProcessor解析][springmvc_RequestResponseBodyMethodProcessor 2]][springmvc_RequestResponseBodyMethodProcessor_springmvc_RequestResponseBodyMethodProcessor 2]  
supportsParameter()方法比较简单，只支持添加了@RequestBody注解的参数。

再来看resolveArgument()方法：

[![springmvc的RequestResponseBodyMethodProcessor解析][springmvc_RequestResponseBodyMethodProcessor 3]][springmvc_RequestResponseBodyMethodProcessor_springmvc_RequestResponseBodyMethodProcessor 3]  
  
[![springmvc的RequestResponseBodyMethodProcessor解析][springmvc_RequestResponseBodyMethodProcessor 4]][springmvc_RequestResponseBodyMethodProcessor_springmvc_RequestResponseBodyMethodProcessor 4]  
  
[![springmvc的RequestResponseBodyMethodProcessor解析][springmvc_RequestResponseBodyMethodProcessor 5]][springmvc_RequestResponseBodyMethodProcessor_springmvc_RequestResponseBodyMethodProcessor 5]  
可以看出，参数的具体解析是通过MessageConverters进行的。

来看看this.messageConverters是如何初始化的：

在RequestMappingHandlerAdapter里进行初始化：

[![springmvc的RequestResponseBodyMethodProcessor解析][springmvc_RequestResponseBodyMethodProcessor 6]][springmvc_RequestResponseBodyMethodProcessor_springmvc_RequestResponseBodyMethodProcessor 6]  
所以，如果不手动对MessageConverters进行配置，默认是可以支持String类型的参数转换的：

[![springmvc的RequestResponseBodyMethodProcessor解析][springmvc_RequestResponseBodyMethodProcessor 7]][springmvc_RequestResponseBodyMethodProcessor_springmvc_RequestResponseBodyMethodProcessor 7]  
这里接收到的就是json格式字符串。

要想在参数接收的地方将json直接转换成map或者实体类，则需要手动配置其他的MessageConverters，常用的是MappingJackson2HttpMessageConverter。

springmvc虽然提供了MappingJackson2HttpMessageConverter，但具体使用还需要引入第三方jar包：

[![springmvc的RequestResponseBodyMethodProcessor解析][springmvc_RequestResponseBodyMethodProcessor 8]][springmvc_RequestResponseBodyMethodProcessor_springmvc_RequestResponseBodyMethodProcessor 8]  
这三个jar必须都引入，不然会出现异常。

在springmvc.xml里进行配置：

[![springmvc的RequestResponseBodyMethodProcessor解析][springmvc_RequestResponseBodyMethodProcessor 9]][springmvc_RequestResponseBodyMethodProcessor_springmvc_RequestResponseBodyMethodProcessor 9]  
这样，handler的参数类型为map和实体类时，都可以正常对json格式的数据进行解析：

[![springmvc的RequestResponseBodyMethodProcessor解析][springmvc_RequestResponseBodyMethodProcessor 10]][springmvc_RequestResponseBodyMethodProcessor_springmvc_RequestResponseBodyMethodProcessor 10]  
MessageConverters可以配置多个，来简单看下：

[![springmvc的RequestResponseBodyMethodProcessor解析][springmvc_RequestResponseBodyMethodProcessor 11]][springmvc_RequestResponseBodyMethodProcessor_springmvc_RequestResponseBodyMethodProcessor 11]  
MessageConverters都是实现了这个接口。

[![springmvc的RequestResponseBodyMethodProcessor解析][springmvc_RequestResponseBodyMethodProcessor 12]][springmvc_RequestResponseBodyMethodProcessor_springmvc_RequestResponseBodyMethodProcessor 12]  
canRead()方法判断当前MessageConverter是否可以对参数进行转换。 [![springmvc的RequestResponseBodyMethodProcessor解析][springmvc_RequestResponseBodyMethodProcessor 13]][springmvc_RequestResponseBodyMethodProcessor_springmvc_RequestResponseBodyMethodProcessor 13]

read()方法从http消息体里读取数据，转换成具体类型的参数。

**StringHttpMessageConverter：**

[![springmvc的RequestResponseBodyMethodProcessor解析][springmvc_RequestResponseBodyMethodProcessor 14]][springmvc_RequestResponseBodyMethodProcessor_springmvc_RequestResponseBodyMethodProcessor 14]  
[![springmvc的RequestResponseBodyMethodProcessor解析][springmvc_RequestResponseBodyMethodProcessor 15]][springmvc_RequestResponseBodyMethodProcessor_springmvc_RequestResponseBodyMethodProcessor 15]  
StringHttpMessageConverter可以支持参数类型为String的。

**MappingJackson2HttpMessageConverter：**

[![springmvc的RequestResponseBodyMethodProcessor解析][springmvc_RequestResponseBodyMethodProcessor 16]][springmvc_RequestResponseBodyMethodProcessor_springmvc_RequestResponseBodyMethodProcessor 16]  
[![springmvc的RequestResponseBodyMethodProcessor解析][springmvc_RequestResponseBodyMethodProcessor 17]][springmvc_RequestResponseBodyMethodProcessor_springmvc_RequestResponseBodyMethodProcessor 17]  
[![springmvc的RequestResponseBodyMethodProcessor解析][springmvc_RequestResponseBodyMethodProcessor 18]][springmvc_RequestResponseBodyMethodProcessor_springmvc_RequestResponseBodyMethodProcessor 18]  
MappingJackson2HttpMessageConverter可以解析http请求contentType为json的，至于handler的参数类型，则没有限制。

PS：这里应该是存在一个BUG，MappingJackson2HttpMessageConverter并不能转换任意类型的参数，比如如果参数类型为String，解析是会失败的。所以如果需要String类型也可以解析，则需要在springmvc.xml里同时配置StringHttpMessageConverter和MappingJackson2HttpMessageConverter，并且StringHttpMessageConverter要在MappingJackson2HttpMessageConverter前面，先判断StringHttpMessageConverter是否可以转换，如果不可以，再使用MappingJackson2HttpMessageConverter转换。

[![springmvc的RequestResponseBodyMethodProcessor解析][springmvc_RequestResponseBodyMethodProcessor 19]][springmvc_RequestResponseBodyMethodProcessor_springmvc_RequestResponseBodyMethodProcessor 19]

springmvc接收json类型的数据的大致流程就分析完了，主要是通过MessageConverter进行解析转换。

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