Spring MVC请求处理流程

发表于 2022-03-05 更新于 2024-03-28 分类于 spring

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环境: 
- org.springframework:spring-webmvc:5.3.10
- org.springframework.boot:spring-boot:2.5.5

web程序启动时的初始化顺序: ServletContext -> listener -> filter -> servlet spring bean的初始化是在listener中声明的, 可以在后面使用.

Filter

Servlet规范规定的，只能用于Web程序中, 由Servlet容器提供支持
作用于Servlet执行前后

@Order(1)
@WebFilter(filterName = "customized", urlPatterns = "/*")
public class CustomizedFilter implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        log.info("CustomizedFilter Init");
    }

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        log.info("CustomizedFilter doFilter before");

        // 执行Servlet
        filterChain.doFilter(servletRequest, servletResponse);

        log.info("CustomizedFilter doFilter after");
    }

    @Override
    public void destroy() {
        log.info("CustomizedFilter destroy");
    }
}

必须要注解ServletComponentScan才能让自定义的Filter其效果.

在filterChain.doFilter调用的前后来执行操作, 作用于Servlet之前的前后.

DispatcherServlet

为Spring框架定制的Servlet, 用来对请求进行处理

获取请求处理链HandlerExecutionChain以及相应的HandlerAdapter
通过HandlerAdapter对请求进行处理
使用Interceptor对request/response进行拦截
对异常进行处理

Spring MVC中的各种相关配置可参考WebMvcAutoConfigurationAdapter. 通过定义一个或者多个WebMvcConfigurer来扩展Spring MVC中的配置

获取Handler

通过@RequestMapping注解定义方法Handler的匹配要求，生成对应的RequestMappingInfo和多个RequestCondition，用于请求匹配, 匹配成功后调用对应的方法Handler。

@RequestMapping(value = "/{ping}", method = RequestMethod.GET)
public String getPingPong( String ping) {
    return ping;
}

@GetMapping(value = "/{ping}", params = "ex=1")
public String getPingPongEx( String ping) {
    return ping + " Ex";
}

DispatcherServlet::getHandler用于获取请求处理链HandlerExecutionChain，通过比较RequestMappingInfo和RequestCondition，查找最匹配的方法Handler。定义的RequestCondition越多，则方法Handler的针对性越强；反之，则方法Handler越通用。

通过HandlerAdapter处理请求

HandlerAdapter.handle主要做以下几件事：

HandlerMethodArgumentResolver对输入参数进行解析
调用handler对请求进行处理
HandlerMethodReturnValueHandler对返回进行处理
ExceptionHandler异常统一处理

基于String输入的参数解析

通过定义Converters中的bean，就可以在启动时通过WebMvcAutoConfigurationAdapter#addFormatters添加进来，用于AbstractNamedValueMethodArgumentResolver的输入类型转换。

// Money.java
@Getter
@Setter
public class Money {
    private String currency = "CNY";
    private String value;

    @Override
    public String toString() {
        return currency + " " + value;
    }
}

// MoneyFormatter.java
@Component
public class MoneyFormatter implements Formatter<Money> {
    @Override
    public Money parse(String text, Locale locale) throws ParseException {
        String[] input = text.split(" ");
        Money money = new Money();
        if (input.length == 1) {
            money.setValue(input[0]);
        } else {
            money.setCurrency(input[0]);
            money.setValue(input[1]);
        }
        return money;
    }

    @Override
    public String print(Money object, Locale locale) {
        return object.getCurrency()
                + " " + object.getValue();
    }
}

// IndexController.java
@GetMapping(value = "/price")
public Money price( Money money) {
    return money;
}

针对Body的输入和输出处理

通过HttpMessageConverter对body进行序列化和反序列化, 其中最常用的就是json的处理模块MappingJackson2HttpMessageConverter.

通过定义HttpMessageConverters的bean，将自定义的HttpMessageConverter添加进来，通过WebMvcAutoConfigurationAdapter#configureMessageConverters进行注册

// StringConverter.java
public StringConverter implements HttpMessageConverter<String> {
  ...
}

// ConverterConfig.java
@Bean
public HttpMessageConverters converters() {
    return new HttpMessageConverters(new StringConverter());
}

JacksonJson序列化的支持

Spring MVC中提供了MappingJackson2HttpMessageConverter对json对象进行序列化处理。通过JsonComponnet相关的bean来注册JSON序列化组件

JsonSerializer
JsonDeserializer

@JsonComponent
public class MoneyJson extends StdSerializer<Money> {

    protected MoneyJson() {
        super(Money.class);
    }

    @Override
    public void serialize(Money money, JsonGenerator jsonGenerator, SerializerProvider serializerProvider) throws IOException {
        jsonGenerator.writeString(money.toString());
    }
}

Interceptor

Interceptor用于对Controller层进行拦截，处理一些和controller没有依赖的业务，比如鉴权，日志等

作用于Controller前后执行
不能修改request
spring中优先使用Interceptor, 而不是filter

public class CustomizedInterceptor extends HandlerInterceptorAdapter {

    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler)
            throws Exception {
        log.info("CustomizedInterceptor prehandle");
        return true;
    }

    @Override
	public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler,
			@Nullable ModelAndView modelAndView) throws Exception {
		log.info("CustomizedInterceptor postHandle");
	}

	@Override
	public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler,
			@Nullable Exception ex) throws Exception {
		log.info("CustomizedInterceptor afterCompletion");
	}

}

// 添加interceptor
@Configuration
public class AppServiceConfig extends WebMvcConfigurationSupport {

    @Autowired
    private CustomizedInterceptor customizedInterceptor;

    @Override
    protected void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(customizedInterceptor).addPathPatterns("/**");
    }
}

Exception处理

对Request Mapping Handler方法抛出的异常进行处理。

ExceptionHandler
- Controller层异常处理
- ControllerAdvice全局异常处理