Principle: webmvcconfigurer and webmvcconfigurationsupport pit avoidance Guide

Source code address （ Contains all and springmvc dependent , Static file path settings ,request Request entry acceptance , Return value processing converter Settings, etc ）：

spring-framework/WebMvcConfigurationSupport.java at b595dc1dfad9db534ca7b9e8f46bb9926b88ab5a · spring-projects/spring-framework · GitHubhttps://github.com/spring-projects/spring-framework/blob/b595dc1dfad9db534ca7b9e8f46bb9926b88ab5a/spring-webmvc/src/main/java/org/springframework/web/servlet/config/annotation/WebMvcConfigurationSupport.javaspring-framework/DelegatingWebMvcConfiguration.java at b595dc1dfad9db534ca7b9e8f46bb9926b88ab5a · spring-projects/spring-framework · GitHubhttps://github.com/spring-projects/spring-framework/blob/b595dc1dfad9db534ca7b9e8f46bb9926b88ab5a/spring-webmvc/src/main/java/org/springframework/web/servlet/config/annotation/DelegatingWebMvcConfiguration.java

（1） In this way, we just create a class inheritance  WebMvcConfigurer

We know , stay Spring Boot 2.0 Then use your own configuration class to inherit WebMvcConfigurerAdapter when ,idea Will prompt that this class is out of date .

Generally, we will adopt the following two alternatives ：

• Realization WebMvcConfigurer  
• Inherit WebMvcConfigurationSupport

But inheritance WebMvcConfigurationSupport It will cause some problems

before this , Let's take a look first WebMvc Automatic configuration class WebMvcAutoConfiguration The definition of ：

Notice the red box around this key statement ：

1	@ConditionalOnMissingBean(WebMvcConfigurationSupport.class)

See this line can understand , original SpringBoot Made this restriction , Only when WebMvcConfigurationSupport Class does not exist before it takes effect WebMvc Automatic configuration ,WebMvc The autoconfiguration class not only defines classpath:/META-INF/resources/,classpath:/resources/,classpath:/static/,classpath:/public/ Equal path mapping , Configuration files are also defined spring.mvc Configuration information at the beginning .

When WebMvcAutoConfiguration Failure to take effect will lead to the following problems ：
1.WebMvcProperties and ResourceProperties invalid

Because the properties in both configuration classes are WebMvcAutoConfiguration Use in

When WebMvc Auto configuration failure (WebMvcAutoConfiguration Automatic configuration ) when , This will cause the view parser to fail to parse and return to the corresponding view

Solution ：

1. stay SpringBoot1.X In the version of the , We can inherit from WebMvcConfigurerAdapter, Override the method you want to implement .

2. But in SpringBoot2.X The definition of ,WebMvcConfigurerAdapter Has been defined as @Deprecated, Let's take a look at the source code ：

SpringBoot In fact, I have already told you WebMvcConfigurerAdapter since Spring5.0 It is not recommended to use this version , But you can achieve WebMvcConfigurer And rewrite relevant methods to achieve similar functions .

2. On the classpath HttpMessageConverter invalid

Such as ：StringHttpMessageConverterConfiguration、MappingJackson2HttpMessageConverter , because HttpMessageConverters Holds all HttpMessageConverter Example , stay WebMvcAutoConfigurationAdapter It will inject HttpMessageConverters , So when WebMvcAutoConfigurationAdapter When not loaded , It will fail , Indirectly cause spring.http.encoding.charset And spring.jackson.date-format A false failure .

Such as ：StringHttpMessageConverter Will use spring.http.encoding.charset To configure , The default encoding is ：ISO-8859-1

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@Bean         @ConditionalOnMissingBean         public StringHttpMessageConverter stringHttpMessageConverter() {             StringHttpMessageConverter converter = new StringHttpMessageConverter(                     this.encodingProperties.getCharset());             converter.setWriteAcceptCharset(false);             return converter;         }

Solution ：
Because the known configuration classes have passed @Bean Register in the container , So we can use WebMvcConfigurationSupport when , adopt @Autowired Inject into the configuration class , And replace it WebMvcConfigurationSupport The default configuration is OK , Such as ：

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@Configuration public class WebConfiguration extends WebMvcConfigurationSupport {     @Autowired     private StringHttpMessageConverter stringHttpMessageConverter;     @Autowired     private MappingJackson2HttpMessageConverter httpMessageConverter;     /**      * Add Converter      */     @Override     public void extendMessageConverters(List<HttpMessageConverter<?>> converters) {         for (int i = 0; i < converters.size(); i++) {             if (converters.get(i) instanceof StringHttpMessageConverter){                 converters.set(i, stringHttpMessageConverter);             }             if (converters.get(i) instanceof MappingJackson2HttpMessageConverter) {                 converters.set(i, httpMessageConverter);             }         }     } }

It can also be re implemented according to requirements .

Add _

WebMvcConfigurer Class code analysis ：

from EnableWebMvcConfiguration Configuration class starts , When it injects, the parent class injects Spring Everything in the container WebMvcConfigurer class

  Then inject RequestMappingHandlerAdapter Bean It will call the parent class requestMappingHandlerAdapter Method

 

Get the configuration at this time , For example, the return result is customized Handler, WebMvcConfigurerComposite Will traverse the call WebMvcConfigurer Implementation class

addReturnValueHandlers Method , The custom configuration will be loaded into the default configuration